The Series of Environmental Radioactivity Measuring Methods
AD-N･E(No.36)

Method for Measurement ofRadioactive Materials in the Air

Published in June 2022
Radiation Monitoring Division
Radiation Protection Department
The Secretariat of
Nuclear Regulation Authority

1Introduction
The measurement of radioactive materials in the air plays an essential role in the early
detection of radioactive materials released from nuclear facilities, confirmation of the spread ofradioactive materials to the environment, and evaluation of exposure doses due to inhalation of theair. The Series of Environmental Radioactivity Measuring Methods No. 36, "Method formeasurement of radioactive materials in the air", is a manual for measuring the "concentration ofradioactive material in the air" stipulated in Nuclear Emergency Response Guidelines (Nuclear
Regulation Authority, partially amended on April 6, 2022) [1].
The measurement of radioactive material in the air uses dust monitors and air monitors forcontinuous measurement of airborne dust containing particulate radioactive materials, dust
samplers for collecting airborne dust, iodine samplers for collecting radioactive iodine (particulate
and gaseous) in the air, and gas monitors for continuous measurement of gaseous radioactive
materials such as radioactive noble gases in the air.
Dust monitor is a name for generic equipment. However, in principle, this report on themeasurement method defines the equipment for use in normal times as dust monitors and theequipment only for use during emergencies as air monitors. The measurement principles arecommon for both. Air monitors are the equipment added for emergencies. Their specifications
include the prompt, short-interval measurement of radioactive material concentrations in the air.
In principle, the dust monitor is a device used in normal times. However, in an emergency, it will
be additionally operated in emergency mode, which has the same functions as the air monitor, tostrengthen the monitoring system.
This measurement method specifies the measurement procedures in normal times andemergencies.
In normal times and emergencies, the basic objective of measuring radioactive material
concentrations in the air and the equipment for use includes common parts. However, there aredifferent parts to the purpose of monitoring and the concept of data evaluation. Thus, this reportconsists of two parts: Part 1 discusses radioactive material measurements in the air in normal times,
and Part 2 discusses radioactive material measurements in the air in emergencies. Each part isdesigned also for use as an independent manual.
Radioactive material measurements in the air in normal times (Part 1) describe measurement
procedures for continuous monitoring with dust monitors, collecting and analyzing air samples
with dust samplers and other equipment, collecting and analyzing air samples with iodine samplers,and continuous monitoring with gas monitors.
Radioactive material measurements in the air in emergencies (Part 2) describe measurement
procedures of continuous measurements with air monitors, analysis of air samples collected with
air monitors, collection and analysis of air samples with iodine samplers, and collection andanalysis of air samples with dust samplers.
The Series of Environmental Radioactivity Measuring Methods presents standard measuringmethods to assist each organization in producing reliable measurement data. These measurement
methods reflect technical levels and knowledge updated at the time of formulation. However, it
does not preclude the possibility of more reliable and adequate measurements by considering newtechniques that are developed daily. We hope the use of these measurement methods assists inselecting optimal methods for adequate implementation of the radioactive material concentration
measurements in the air, considering the aims of The Series of Environmental Radioactivity
Measuring Methods based on their descriptions.

2Configuration
Part 1 Measurement of Radioactive Materials in the Air in Normal Times
Chapter 1 Introduction
Chapter 2 Basics and Scope
Chapter 3 Continuous Measurement using Dust Monitor
Chapter 4 Collection of Air Samples using Dust Sampler, etc.
Chapter 5 Analysis of Air Samples Collected using Dust Sampler, etc.
Chapter 6 From Collection to Analysis of Air Samples using Iodine Sampler
Chapter 7 Continuous Measurements with Gas Monitor
Explanation

Part 2 Measurement of Radioactive Materials in the Air in Emergencies
Chapter 1 Introduction
Chapter 2 Basics and Scope
Chapter 3 Continuous Measurements with Air Monitoring
Chapter 4 Analysis of Air Samples Collected by Air Monitoring
Chapter 5 Collection and Analysis of Air Samples using Iodine Sampler
Chapter 6 Collection and Analysis of Air Samples using Dust Sampler
Explanation
Common to Part 1 and Part 2
Information
Appendix
Reference3

The Series of Environmental Radioactivity Measuring Methods No.36
Method for measurement of radioactive materials in the airPart 1 Measurement of Radioactive Materials in
the Air in Normal Times4

5

Table of Contents

Part 1 Measurement of Radioactive Materials in the Air in Normal Times
Chapter 1 Introduction...................................................................................................................................9
Chapter 2 Basics and Scope of Application ................................................................................................10
2.1 Purpose ........................................................................................................................................11
2.2 Equipment and Flow ...................................................................................................................12
Chapter 3 Continuous Measurement with Dust Monitor ............................................................................19
3.1 Equipment ...................................................................................................................................19
3.2 Air Absorbent ..............................................................................................................................30
3.3 Installation, Calibration, and Inspection .....................................................................................32
3.4 Measurement ...............................................................................................................................40
3.5 Evaluation of Measurement Results............................................................................................44
Chapter 4 Collection of Air Samples by Dust Samplers, etc. .....................................................................57
4.1 Equipment ...................................................................................................................................57
4.2 Air Absorbent ..............................................................................................................................61
4.3 Installation and Inspection ..........................................................................................................62
4.4 Collection ....................................................................................................................................64
Chapter 5 Analysis of Air Samples Collected by Dust Samplers, etc.........................................................66
5.1 Pretreatment ................................................................................................................................68
5.2 Analysis.......................................................................................................................................75
5.3 Evaluation of Analysis Results ...................................................................................................76
5.4 Sample Storage ...........................................................................................................................77
Chapter 6 From Air Samples Collection by Iodine Sampler to Analysis ...................................................78
6.1 From Collection to Analysis .......................................................................................................78
Chapter 7 Continuous Measurement with Gas Monitors ............................................................................80
7.1 Equipment ...................................................................................................................................80
7.2 Installation, Calibration, and Inspection .....................................................................................84
7.3 Measurement ...............................................................................................................................86
7.4 Evaluation of Measurement Results............................................................................................876

Explanation .................................................................................................................................................89
Explanation A Validity of Airborne Radioactive Material Measurements ..........................................91
Explanation B Detection Limit ............................................................................................................95
Explanation C Concept of Dust Monitor Measurement Condition Setting .........................................98
Explanation D Efficiency of Dust Monitor ........................................................................................110
Explanation E Effect of Radon-Thoron Decay Products on Dust Monitor Measured Values ..........116
Explanation F Distinction Methods for Facility-Caused Radioactive Material Contribution in Dust
Monitor Measurements ............................................................................................................1197

8

Chapter 1 Introduction
The “Monitoring in Normal Times (Supplementary Reference Materials for the Nuclear
Emergency Response Guidelines)” (Nuclear Regulation Authority, Radiation Protection
Department, Radiation Monitoring Division, revised on Dec. 21, 2021)[2] defines monitoring innormal times as monitoring for preparing the monitoring in emergencies by grasping the air dose
rates and radioactive material concentrations in the environment of nuclear facilities in normal
times, and for early detection of an abnormality of nuclear facilities and evaluation of its impacts
on nearby residents and environments.
The purpose of the radioactive material concentration measurements in normal time
monitoring is (1) estimation and evaluation of exposure doses to nearby residents, etc., and (2)early detection of unexpected releases of radioactive materials from nuclear facilities andevaluation of environmental impacts.
Part 1 describes the procedures of continuous measurement with dust monitors, collection andanalysis of air samples with dust sampler and other equipment, collection and analysis of air
samples with iodine sampler, and continuous measurement with gas monitor, which are
implemented as normal time monitoring.

9

Chapter 2 Basics and Scope of Application
2.1 Purpose
Normal-time monitoring measures radioactive material concentrations in the air for thefollowing two purposes based on the Normal Time Supplementary Reference Materials.
(1) Estimation and evaluation of exposure doses to nearby residents, etc.
To protect the health and safety of nearby residents and other people of nuclear facilities,
normal-time exposure doses to nearby residents and other people due to radioactive materials in
the environment caused by the nuclear facilities are estimated and evaluated.
(2) Detection of the unexpected release of radioactive materials and evaluation of environmental
impacts in early stage.
Detection of the unexpected release of radioactive materials from nuclear facilities outside thepremises contributes to early detection of the abnormality of nuclear facilities. The results ofnormal-time monitoring are examined to adequately and promptly evaluate the impact in the caseof unexpected releases of radioactive materials from nuclear facilities.

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2.2 Equipment and flow
This section indicates equipment used for normal-time monitoring. Refer to the respective
chapters for details on each piece of equipment.
2.2.1 Dust monitor(1) Outline of equipment
A dust monitor is an equipment for continuously measuring radioactivity concentration in
airborne dust while collecting airborne dust with filter paper as radioactive material concentrationsin the air. Dust monitor is a name for generic equipment. This report on the measurement methods
defines the equipment for use as dust monitors in normal times. However, to strengthen themonitoring system in an emergency, dust monitors will be additionally operated in emergencymode.
The use of dust monitors as dust samplers (refer to 2.2.2) is included in the scope of thismeasurement method.

Figure 2-1. Examples of dust monitors11(2) Flow of use
The flow of use of the dust monitor is shown below. The main Series of Environmental
Radioactivity Measuring Methods for reference are also shown.
(a) Continuous measurement of radioactive material concentration in the air<Measurement targets> Gross α radioactivity, gross β radioactivity, etc.
(Discriminative evaluation of facility
contribution)(Selected according to the nuclear facility)*The purpose of collecting airborne dust is also included if the dust monitor is also used as a dust
sampler.
(b) Analysis of air samples (if necessary)<Analysis and measurement targets> γ-ray emitting nuclides, α-ray emitting
nuclides, β-ray emitting nuclides (Selectedaccording to the nuclear facility)<The Series of Environmental Radioactivity
Measuring Methods for major reference> No. 4, " Radioactive iodine analysis method " No. 7, "γ-ray spectrometry using germanium
semiconductor detector”
 No. 12, "Plutonium analysis method" No. 13, "Sample pretreatment method for
instrumental analysis using germanium
semiconductor detectors, etc.”
 No. 14, "Uranium analysis method"12

2.2.2 Dust samplers(1) Outline of equipment
A dust sampler collects airborne dust on filter paper.
Dust monitors can also be used as dust samplers in terms of equipment that can collect airborne
dust.
High-volume air sampler

Low-volume air sampler

Figure 2-2. Examples of dust samplers

13(2) Flow of use
The flow of use of dust samplers is shown. The main Series of Environmental Radioactivity
Measuring Methods to be referenced are also shown.

・From collection to analysis of air samples in the air<Analysis and measurement targets> γ-ray emitting nuclides, α-ray emitting nuclides, β-ray
emitting nuclides (Selected according to the nuclear
facility)<Major Series of Environmental Radioactivity Measuring
Methods for reference> No. 4, "Radioactive iodine analysis method" No. 7, " γ -ray spectrometry using germanium
semiconductor detector"
 No. 12, "Plutonium analysis method" No. 13, "Sample pretreatment method for instrumental
analysis using germanium semiconductor detectors,
etc." No. 14, "Uranium analysis method" No. 16, "Environmental sampling method"14

2.2.3 Iodine sampler(1) Outline of equipment
Iodine samplers collect radioactive iodine (particulate and gaseous) from the air on filter paper
and activated carbon cartridges.
Transportable typeInstalled typeFigure 2-3. Examples of Iodine Sampler

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(2) Flow of use
The flow of use of iodine samplers is shown.
The Series of Environmental Radioactivity Measuring Methods is also shown for major
reference.
・ From collection to analysis of radioactive iodine<Analysis and measurement targets> Radioactive iodine<The Series of Environmental Radioactivity Measuring
Methods for major reference> No. 4, "Radioactive iodine analysis method" No. 7, " γ -ray spectrometry using germanium
semiconductor detector"
 No. 16, "Environmental sampling method"16

2.2.4 Gas monitor(1) Outline of equipment
Gas monitors continuously measure the gaseous radioactive material concentration ofradioactive noble gases, etc., in the air.

Figure 2-4. Examples of gas monitor(2) Flow of use
The flow of gas monitor use is shown.
・Continuous measurement of the concentration of gaseous radioactive materials in the air<Measurement targets>
・Gaseous radioactive materials

17Chapter 3 Continuous Measurement with Dust Monitor
The principle of the continuous measurement with dust monitors is to measure the count ratesof α-, β-, and γ-rays emitted from airborne dust without energy discrimination* and promptly
evaluate the radioactivity concentrations in the airborne dust as radioactive material concentrationsin the air for the early detection of the unexpected release of radioactive materials from nuclear
facilities.
Refer to Explanation A for the effectiveness of the radioactive material measurement in the
air.
Quantitative determination of the concentrations of radioactive nuclides in airborne dust
involves collecting paper filters from dust monitors and precise analysis with γ-ray spectrometry
or radiochemical analysis. Refer to Chapter 5 for the procedures of precise analysis.
*Excluding cases of spectrum analysis using silicon semiconductor detectors, etc. (all treated thesame from 3.1 onward).
3.1 Equipment
The basic information on dust monitors described in this section is based on JIS Z 4316:2013"Radioactive dust monitors"[4].
3.1.1 Classification of equipment
Dust monitors are classified into (1) – (5), shown in Table 3-1.
Table 3-1. Classification of Dust Monitors
Classification

Definition(1) α-ray dust monitor

Dust monitor to measure α radiation from airborne dust(2) β-ray dust monitor

Dust monitor to measure β radiation from airborne dust(3) γ-ray dust monitor

Dust monitor to measure γ rays from airborne dust(4) α- and β-ray dust monitors

Dust monitor that simultaneously measures α- and β-rays
from airborne dust using a single detector(5) Dust monitor into which (1) Dust monitor in which at least any two detection parts of– (4) are combined(1) – (4) are installed
3.1.2 Scope(a) Gross α radioactivity concentration
α-rays from α-ray emitting nuclides in airborne dust are measured without energy
discrimination and calculated as the radioactivity concentration (Bq/m3) evaluated with one typeof α-ray standard source used in the efficiency calibration of the dust monitor (refer to 3.3.2).

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(b) Gross β radioactivity concentration
β-rays from β-ray emitting nuclides in airborne dust are measured without energy
discrimination and calculated as the radioactivity concentration (Bq/m3) evaluated with one typeof β-ray standard source used in the efficiency calibration of the dust monitor (refer to 3.3.2).
(c) Total count rates of γ rays
Measure the γ-ray gross count rate (s-1) from airborne dust.
Dust monitor measurements include contributions from natural radioactive materials (mainly
radon-thoron decay products), and those fluctuations at normal background levels can greatly
affect the measurements, thus hindering early detection of unexpected radioactive releases from
nuclear facilities. Refer to Explanation E for the effects of radon/thoron decay products.
A combination of (a) – (c) or spectral analysis may evaluate the contribution of radioactive
materials from nuclear facilities that are included in measurements. For an evaluation of themeasurement results, refer to 3.5. For the discrimination method for the facility-induced portion,refer to Explanation F.
Note that continuous measurement with dust monitors can evaluate the contribution fromfacility-induced radioactive materials. However, it isn’t easy to quantify the concentration of eachradionuclide.
3.1.3 Equipment selection
Refer to Table 3-1 and select a dust monitor appropriate for the type of radiation to be measured.
Table 3-2 shows the measurement targets of dust monitors according to the nuclear facilities listed
in the Normal Time Supplementary Reference Materials.
In the Normal Time Supplementary Reference Materials, for all nuclear facilities in Table 32, the contribution of facility-induced radioactive materials in dust monitor measurements is to bediscriminatively evaluated for early detection of unexpected releases of radioactive materials from
nuclear facilities.
Considering this purpose, this measurement method is based on selecting α- and β-ray dust
monitors.

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Table 3-2. Targets of dust monitor measurements according to nuclear facilities
Nuclear facility

Measurement target

Nuclear power reactor facilities(PAZ and UPZ settings required)

Facility-induced artificial radionuclides

Reactor facilities for power generation as specified Facility-induced artificial radionuclides
in the Cooling Notice
Nuclear power reactor facilities(UPZ setting not required)

Facility-induced artificial radionuclides

Nuclear reactor facilities for testing, research, etc.
(UPZ setting required)

Facility-induced artificial radionuclides

Uranium processing facility*(UPZ setting required)

Gross αProcessing facility for handling plutonium*

Gross αReprocessing facility*
Gross α, gross β*The measurement targets are gross α for uranium processing facilities (requiring UPZ setting)and processing facilities that handle plutonium, and gross α and β for reprocessing facilities.
However, it is necessary to discriminate and evaluate facility-induced radioactive materials at
any facility.
3.1.4 Equipment configuration
The dust monitor consists of a sampler, detection unit, indicator, alarm section, and datatransmission unit, as shown in Figure 3-1. The configuration and functions of each part are shownin (1) – (6).
General matters(a) To withstand continuous operation, the equipment shall be robust and easy to operate andmaintain.
(b) The structure shall resist vibration, impact, corrosive gases, etc.
(c) The structure shall not be susceptible to electromagnetic induction, static electricity, etc.
In addition, the structure shall be designed to have little or no electromagnetic induction or othereffects on other devices.
(d) The equipment desirably has a self-diagnostic function in case of any failure.

20Figure 3-1. Example of dust monitor equipment configuration(1) Sampler
The sampler consists of a pump that draws air, a flow meter, and an air sampling unit thatcollects airborne dust with attached filter paper.
Refer to Chapter 4 for pump and flow meter specifications, etc.
(a) Air sampling unit
The air sampling unit shall be airtight and constructed to measure the radiation emitted fromthe collected airborne dust properly.
The relationship between air sampling time and the required lower detection limit determines
the flow rate. Use a pump whose flow rate can be set to 100*-250 L/min for airborne dust only,
approximately 50 L/min for radioactive iodine only, and approximately 50 L/min for both airborne
dust and radioactive iodine. Mass flow meters capable of compensating for pressure fluctuations
are recommended for flow meters. Refer to 3.4(3) for setting measurement conditions.
* It is acceptable to set the flow rate smaller than 100 L/min if it is possible to properly
discriminate facility-induced radioactive materials and ensure the detection limit in the precise
analysis after filter paper collection.

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Examples of specifications for an air sampling unit and points to be considered are shown in Table
3-3.
Table 3-3. Examples of specifications and notes for an air sampling unit
Item
Air sampling
methodExample specifications and notesAir sampling shall be continuous, and the filter paper collection method
shall be used.
The air sampling unit shall start suctioning from the startup moment and,after that, repeatedly measure the integrated flow volume at set intervals.

Flow rateadjustment range

50 to 250 L/min approx.

Flow meter

10 to 300 L/min

Pressure gauge(Vacuum gauge)-101.3 to 0 kPa[gage]

Suction port

The height of the suction port should be about 1 m above the ground tomatch the height at which the radiation dose rate in the air is measured.
However, this does not preclude the installation of a suction port higher
than 1 m above the ground if there is a special reason, such as to prevent
suction due to the uplift of surrounding soil, etc., or to prevent the suction
port from being buried in snow, making it impossible to suction the air.
Install on the side of the wall, etc.

The structure should be designed to prevent intrusion of water, garbage,insects, etc. (e.g., with wire mesh, etc.).



The exhaust shall be vented outside the station through the wall surfaceof the station building, etc.
Exhaust should be expelled as far away from the suction port as possible
to avoid re-suction of exhaust from the suction port.

Exhaust port
Humidity andcondensation
control

To avoid the influence of condensation on filter paper, it is desirable toreduce the relative humidity of the air using a heating tube or insulationmaterials.
The heating control system shall be equipped with a temperature monitor
to prevent high-temperature runaway and with a safety device to stop theheating control system in the event of a high-temperature runaway.

(b) Filter paper
Examples of filter paper specifications are shown below. Refer to 3.2 for the material of filter
paper, etc.
 For fixed filter paper samplers, circular or square filter paper is used, and for mobile filter
paper samplers, rolled (long) filter paper is used.
 The quantity of filter paper should allow continuous measurement for at least one month.
 The filter paper shall be of a structure that can be replaced safely, quickly, and easily.
 Prevent contamination of the filter paper due to surrounding air by covering the filter paperwith a cover, etc., or by making the area airtight.
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(c) Filter paper feeding method
The filter paper of the dust monitor needs to be replaced or moved at regular intervals toprevent clogging.
With mobile filter paper samplers, there are two types: intermittent feeding, in which the filter
paper is moved at regular time intervals, and continuous feeding, in which the filter paper is moved
continuously at a fixed speed. This measurement method employs an intermittent feed method(Refer to 3.4(3)).
An example specification of the filter paper feeding system is shown below.
 The filter paper feeding can be remotely controlled, and it can be set to any time.
 To shorten the blank time of continuous measurement due to filter paper feeding, the timeof filter paper feeding operation should be kept as short as possible.
 The filter paper can be fed automatically when the concentration of radioactive materials
in the air exceeds the set value, when the flow rate falls below the set value, or when thepressure difference between the front and back sides of the filter paper exceeds the set
value.
 It is also desirable to manually feed filter paper (on-site operation and remote control).
(2) Detector unit
The detector unit is the part that detects radiation emitted from airborne dust.
The following are points to be noted in the detector unit.
 The structure shall have a small gap near the detector unit so that the measurement is notaffected by radioactive noble gases in the collected air that remain near the detector unit
during measurement.
 The structure shall be resistant to contamination and easy to decontaminate or replace.
An example of detector specifications is shown below.
 The shape of the effective surface of the detector should be the same as or larger than the
shape of the air sampling surface.
 The surface of the detector (the part in contact with the aspirated air) should be made of amaterial that is difficult to adsorb, etc., to prevent the adsorption of radioactive materials.
 The detector should be shielded by a lead shield that is approximately 3 – 5 cm thick to
reduce background radiation from the outside.
Refer to 3.1.5 for details on the measurement principle of the detector.
(3) Indicator
The indicator is the part that measures signals from the sampler and detector, displays theindicated values, and outputs them to the data transmission section.
The main body of the dust monitor does not necessarily need to have the functions ofcalculating the concentration of radioactive materials in the air in the indicator and issuing an alarmin the alarm section, as long as the telemeter system, etc., has such functions. Table 3-4 shows anexample of specifications for the indicator.

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Table 3-4. Example of indicator specifications
Item

Example specifications
Radioactivity concentration (Bq/m3)*Only the count rate shall be used if the radioactivity concentration cannot
be evaluated.
Measurement item Count rate (s-1), integrated count (count)
Flow rate (L/min), Integrated flow volume (L)Measurement time (sec)Date and time of measurement: XX year, XX month, XX day, XX hour,
XX minute, XX second
Nearest radioactivity concentration (Bq/m3)
Display items

Count rate (s-1), integrated count (count)
Flow rate (L/min), Integrated flow volume (L)Measurement time (sec)Pressure (kPa)
The measurements, etc., and status signals can be stored in a data recorder.

Data storage
function(A) Measurements, etc.
(a) Location name, (b) Device number, (c) Location information, (d) Dateand time of measurement, (e) Radioactivity concentration, (f) Count rate,(g) Integrated count, (h) Integrated flow volume, (i) Measurement time(B) Status signals (including alarms)(a) Under measurement, (b) Under calibration, (c) Under adjustment, (d)Communication error, (e) High radioactivity level, (f) Sampler error, (g)Detector error, (h) HV power failure, (i) LV power failure, (j) Pressure ishigh, (k) Pump flow rate is low, (l) Filter paper is out, (m) Filter paper isbeing fed, (n) Filter paper remaining low(C) Storage capacity(A) must be able to save every hour (or every 10 minutes in case of
emergency),(B) Record the event when it occurs. The number of stored cases should
be secured in the unit for at least one month. In addition, the stored data
shall be outputted by connecting a USB memory stick or PC, etc., to themain unit.

External output

Control input

Timesynchronization

The measurements, etc., and status signals shall be able to be output to atelemeter system, etc., via a data transmission device.
Control signals can be input from telemeter systems via data transmission
devices.
Control signals: start (measurement start), stop (measurement stop), filter
paper feed, changing paper feed interval (switch to emergency mode)
The time server of the telemeter system or other systems shall be accessedat startup to synchronize the time, and the time shall be synchronized atleast once daily regularly.
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(4) Alarm section
The alarm section detects and notices that the indicated value exceeds a certain set value, etc.
Depending on the alarm’s content, the system should be set up to issue a warning to the indicatoror telemeter system, etc.
Examples of specifications for the alarm section are shown below. Examples of alarm events
are shown in Table 3-5.
 When the measurement exceeds the alarm setpoint, an alarm shall be issued using a lamp,
buzzer, etc.
 When an alarm occurs, the alarm contents shall be displayed on the display screen of themain body or telemeter system, etc.
 Alarms shall be maintained until reset or the cause is eliminated, and the alarm shall berecorded.
 The user shall be able to check the alarm setpoints and confirm that the alarms usuallyoperate.
 It is desirable to be able to display failures or abnormalities separately for each cause.
Table 3-5. Examples of alarm events
Item
Alarm
event

Radioactivity concentration is high; the detector is abnormal; thesampler is abnormal; the power supply is abnormal; the pressure ishigh; the pump flow rate is low; the filter paper is out; the filter paper
feed is abnormal.

(5) Data transmission section
This part outputs the data collected in the indicator to the telemeter system and other devices
via communication devices. It controls the dust monitor by receiving control signals from thetelemeter system and other devices.
Refer to 3.4(5) for examples of data transmission items.
For data communication, the communication lines used by the facilities in the monitoring
station building, if any, should be used. Communication lines are desirably multiplexed to prevent
data communication outages.
(6) OtherIf necessary, a heating pipe or water trap should be installed on the intake side to prevent
condensation on the airflow path and filter paper, and a silencer on the exhaust side to prevent
noise generated by the pump.
3.1.5 Detector types and measurement principles
The types of detectors used for dust monitoring are listed in Table 3-6.
However, these apply to any detector with performance equivalent to or greater than the listed
types and are not limited to them. For detector performance, refer to the detection limit in
Explanation B.

25

Table 3-6. Types of Detectors Used in Dust Monitors
Detector typeα-ray detector

ZnS(Ag) scintillation detector
Silicon semiconductor detector

β-ray detector

Plastic scintillation detector
Silicon semiconductor detector

γ-ray detector

NaI(Tl) scintillation detector

α- and β- ray ZnS(Ag) scintillation detector
detector+Plastic scintillation detector
Silicon semiconductor detector(1) α-ray detector(a) ZnS(Ag) scintillation detector
Light generated from the ZnS(Ag) scintillator upon radiation incident is converted tophotoelectrons by a photomultiplier tube, amplified, and output as a pulse signal for measurement.
ZnS (Ag) scintillators are made of ZnS (Ag) particles of about 0.1 mm diameter coated on thesurface of a transparent glass plate, etc. Since ZnS is a white powder, light transmission is low.
However, the emission intensity of short-range α-rays is higher than that of β-rays and γ-rays, so
the α-ray output pulse is discriminated, and detection is easy.
ZnS (Ag) is one of the inorganic crystal scintillators and has the following physical properties.
 It is a white powder sensitive to α-rays.
 The mainly emission wavelength is at 450 nm, close to the maximum sensitivity
wavelength of general photomultiplier tubes.
 The decay time of 200 ns is comparable to that of NaI (Tl) at 230 ns.
 Coating the surface of a plastic scintillator sensitive to β-rays enables simultaneous
measurement of α- and β-rays.
(b) Silicon semiconductor detector
Secondary electrons are generated due to the interaction between the incident radiation and thesilicon crystal.
The ionizing action of these secondary electrons produces electron-hole pairs. Applying a highvoltage allows the anode to collect electrons and the cathode to collect holes, and an electric current
through them. The signal is output as a pulse.
(2) β-ray detector(a) Plastic scintillation detector
The principle of measurement of a plastic scintillation detector as a scintillation detector is thesame as that of the ZnS(Ag) scintillation detector. A plastic scintillation detector measures α- andβ-rays and fast neutrons. However, because of its low luminous efficiency for radiation with highionization density, such as α-rays, it is used in dust monitors for measuring β-rays. Plastic
scintillators are made by dissolving organic scintillators in a solvent and then polymerizing theminto a solid plastic. Base materials include polystyrene, polyvinyl toluene, and polymethyl
methacrylate.
(b) Silicon semiconductor detector
Same as (1) α-ray detector
26

(3) γ-ray detector(a) NaI (Tl) scintillation detector
Excitation luminescence (fluorescence) generated in the NaI(Tl) crystal upon radiation
incident is converted to photoelectrons in a photomultiplier tube, amplified, and output as a pulse
proportional to the intensity of the light. Since the output pulse signal’s magnitude is proportional
to the incident radiation’s energy, analyzing the γ-ray spectrum enables qualitative or quantitative
determination of radionuclides.
The detector is characterized by not directly measuring the absorption reaction of radiation in
the form of ionization or energy but indirectly by light. The low photoelectron conversion
efficiency results in a small number of photoelectrons generated, which does not allow for highenergy resolution. On the other hand, the photomultiplier tube’s extremely high electron
multiplication factor allows the pulse height discriminator to distinguish and separate signal fromnoise even in extremely low-level signals, thus enabling high and stable radiation detection.
For details, refer to the Radioactivity Measurement Methods Series No. 6 "NaI (Tl)scintillation spectrometer instrumental analysis method".
(4) α- and β-ray detectors(a) ZnS (Ag) scintillation detector + plastic scintillation detector
To detect α- and β-rays simultaneously, an integrated detector with a ZnS(Ag) scintillator
coated on a plastic scintillator is used. The measurement principle is the same for each of thedetectors described above. There is also a method to evaluate the contribution from facilityinduced radionuclides using the α and β simultaneous measuring function (refer to Explanation F).
(b) Silicon semiconductor detector
Same as (1) α-ray detector and (2) β-ray detector
3.1.6 Example of equipment specifications
An example of dust monitor equipment specifications is shown in Table 3-7. Refer to 3.2 forair absorbent. Equipment not listed in the example specifications may be used if it meets therequired performance. For the performance of dust monitors, refer to the detection limit in
Explanation B.

27

Table 3-7. Examples of dust monitor equipment specifications
Item

Type A

Type B

Measurementtarget

α-ray

β-ray

ZnS(Ag)scintillator

Plastic
scintillator

Air
Membraneabsorbent filter paper

Cellulose/
Glass fiber
filter paper

Detector

Detectorsize
Flow rate

50 mm ϕ50 mm ϕType CType D

α- and β-rays
ZnS(Ag)Scintillator+
Plastic
scintillator

Siliconsemiconductor

Membrane filter paper, or,
Cellulose/glass fiber filter
paper*1
50 mm ϕ25 mm ϕType E
γ-ray

NaI(Tl)scintillator

Cellulose/
Glass fiber
filter paper
2 inch ϕ× 2 inch

50 to 250 L/min

Filterpaper
Intermittent feed or exchange at a fixed time*2
feed
method*1 Use membrane filter paper, etc., when measuring mainly α-rays, and cellulose/glass fiber
filter paper, etc., when measuring mainly β-rays.
*2 Intermittent feeding for long and fixed filter paper is changed at a fixed interval.

28

3.2 Air absorbent
3.2.1 Selection of air absorbent
Dust monitors are based on using long filter paper because of the need to change the air
absorbent at regular time intervals automatically. If circular or square filter paper is used, the air
absorbent should be changeable automatically at regular intervals.
When α-rays are measured, membrane filter paper or the like should be used to avoid
underestimating measurement results due to airborne dust entering the filter paper. When β- andγ-rays are measured, cellulose/glass fiber filter paper should be used, prioritizing the pressure loss
and strength of the filter paper because the effect of airborne dust entering the filter paper is small,as is the case with α-rays.
In the radiochemical analysis of α-ray emitting radionuclides described in Chapter 5, if it ischallenging to analyze membrane filter paper, use filter paper that can appropriately perform
radiochemical analysis, such as cellulose/glass fiber filter paper. It may also be done by analyzing
cellulose/glass fiber filter paper from dust or iodine samplers collected separately.
Examples of air absorbents to be selected according to the classification of dust monitors areshown in Table 3-8. Refer to 4.2 and Reference A for the characteristics of each air absorbent.
Table 3-8. Examples of air absorbent selection
Classification

Example of selection of air absorbent

α-ray dust monitor

Membrane filter paper

β-ray dust monitor

Cellulose/glass fiber filter paper

γ-ray dust monitor

Cellulose/glass fiber filter paperα- and β-ray dust
monitorMembrane filter paper (when α-rays are measured primarily)
Cellulose/glass fiber filter paper (when measuring mainly βrays)

3.2.2 Examples of specifications for air absorbent
Table 3-9 shows an example of specifications for air absorbents used for dust monitors. If therequired performance is met, using air absorbents not listed in the example specifications is
acceptable.

29

Table 3-9. Examples of air absorbent specifications
Item
Material
Shape

Type A

Type B

Cellulose/glass fiber
Rolled (long)

Circular form

Type C
Membrane
Rolled (long)Hole
diameter—

3.0 μmThickness

0.41 mm0.13 mm

Dimension

75 mm×10 – 90 m

Collection
efficiency

99.7% or more (0.31 μm polystyrene latex

99.7% (> 0.15 μmϕ particles,

particles, ventilation rate 55-135 cm/s)

ventilation speed 878 cm/s)

Pressure loss

0.27 kPa

8 to 15 kPa

Lined with cloth (cold gauze) for strength,
Water repellent

PTFE lined with
polyethylene, etc., forstrength

130 ℃

130 ℃

Physicalproperties
Heatresisting
property

60 mm ϕ30

35 mm×12 m

3.3 Installation, calibration, and inspection
To obtain measurements representative of the installation site, it is essential to install dust
monitors in appropriate locations and to ensure the integrity of the equipment through calibrationand inspection.
3.3.1 Installation(1) Selection of installation site
The following items (a) to (c) should be considered when selecting the installation site.
In principle, dust monitors should be fixedly installed in the monitoring station building
where monitoring posts, etc., are installed. However, the selection conditions are shown
below, considering the case where new dust monitors will be built.
(a) Social environment
Item

Selection criteria

Distance from nuclear
facilities

Locate within a 5 km radius*1.

Direction from nuclear
facilities

The installation site should be centered on the nuclear facility sothat the orientation of the installation site is unbiased.

Population distribution

Priority will be given to areas with large populations.

*1 The Normal Time Supplementary Reference Materials states that “In the application for theestablishment permit of a nuclear facility based on the Reactor Regulation Act, etc., the dose
received by the public around the facility due to radioactive materials released into theenvironment during normal operation is evaluated as follows depending on the facility
characteristics. The effective dose from radioactive rare gases is evaluated where the dose ismaximum. The effective dose from radioactive iodine and particulate radioactive materials is
evaluated where the concentration is maximum. Because the points are set within a 5 km radiusfrom the facility, the normal monitoring necessary for early detection of the unexpected releaseof radioactive materials or radiation from the nuclear facility and for assessing the impact on
the surrounding environment is conducted within a 5 km radius from the nuclear facility, andappropriate points within this radius are selected and implemented”.

31

(b) Natural environment
Selection criteria

Item



Select a location with open surroundings and easy access.
Ideally, the site should be flat and surrounded by at least several tens of metersof open space. Even if dust monitors are located in an existing monitoring
station building, avoid locations where trees, cliffs, or other influences may
interfere with the suction of airborne dust.

To facilitate early detection of the release of radioactive materials from
nuclear facilities, the past wind condition record, such as prevailing winds,
should be investigated, and priority should be given to the location in theconditions
record

downwind direction of nuclear facilities.
In addition to past wind condition records, it would be helpful to understandthe diffusion trends specific to the vicinity of nuclear facilities based on longterm air diffusion calculations using past meteorological data, etc.



Avoid places with high temperatures, high humidity, and different adverse
environments.
In the Great East Japan Earthquake, the damage caused by the tsunami aftera large-scale earthquake was enormous. Therefore, when installing at a pointclose to the sea, it is necessary to consider installing on higher ground where
there will be no tsunami impact.

TerrainPast wind



Other

On the other hand, however, if a community is located along the coast, it must
be installed at a point close to the sea.
Therefore, if the equipment becomes unusable, it is necessary to respond to
the event, including substituting transportable type equipment.
(c) Other and local condition
Item

Selection criteria

Power supply Select a location where a stable power supply is available from the stationbuilding or other facilities.
Communicati

Select a location where multiple means of data communication can beons network

constructed in consideration of a disaster.

Access to theinstallation
location

Avoid locations that are difficult to access, as periodic filter paper changes
and equipment adjustments must be performed.
In addition, since it may be used for emergency monitoring, it is necessary toconsider road disruptions during disasters.

Other

In roadsides with heavy traffic, places close to factories, or other places, selecta location where the dust monitor’s filter paper is less likely to be impacted
since the effects of exhaust gases and dust may clog the filter paper in a shortperiod.
32

(2) Indoor installation condition
For indoor installation, the following items (a) – (i) should be considered before selecting the
installation site.
Item
Installation conditions


Station(a)building







(b)

Suction
port







(c)

Exhaustport

The monitoring station desirably has a wide entrance to allow
equipment delivery.
The space and ceiling height should allow enough space for theequipment to be installed to facilitate maintenance and inspection.
It is desirable to apply a dust-proof coating to the floor.
A piping pit is needed on the floor to accommodate cables and otherwiring.
The height of the suction port should be basically about 1 m above theground, in accordance with the height at which the air dose rate ismeasured. However, this does not preclude the installation of a suction
port higher than 1 m above the ground if there is a particular reason,such as to prevent suction due to the uplift of surrounding soil, etc., or
to prevent the suction port from being buried in snow and making it
impossible to draw in air.
Do not install a suction port on the same side as the air conditioning
blower.
The direction of the fence should be downward or oblique downward
to prevent rain and snow from getting in, and a wire mesh or similar
matter should be provided in order to avoid the entry of insects andother foreign matter.
Minimize obstructions around air suction ports.
In the piping from the suction port to the air sampling unit, considering
the reduction of deposition of particulate matter in the piping, it isdesirable that the piping should be as short as possible, curved pipes(elbows) be avoided, and corrosion-resistant metals such as stainlesssteel being used.
To prevent the exhaust air from being sucked back through the suction
port, the positional relationship to be kept in mind between the suction
port and exhaust port includes avoiding installation on the same wall
surface as the suction port as much as possible.

33

Supply power and other infrastructure may be cut off in a nuclear disaster

(d)

Power
supplyaccompanied by a large-scale natural disaster. In anticipation of such a case,the power supply method is multiplexed using private generators, batteries,
solar power generation equipment, etc. However, for the generator, securing
fuel that can be supplied continuously (light oil, LPG, etc.) is necessary.
 The structure desirably facilitates maintenance.
 The power supply circuit shall have a protective device or protection
circuit.
 Switching sections, connections, etc., shall maintain electricalperformance even after being operated repeatedly.
 Unexpected lightning strikes can cause the instrument’s electricalAir(e) conditioning

system to fail via AC power. It is advisable to install arrestors to avoid
this situation.
Grounding for noise reduction.

Provide air conditioning in the station building for stable operation ofequipment Maintain a range of temperature and humidity within which the
manufacturer guarantees normal operation of the dust monitor.
 To maintain a constant room temperature, it is effective to insulate theinterior walls of the station building.

Condensation
Preven(f) tive
measureTake measures to prevent condensation to avoid the effect of condensationon the filter paper.
 A heating tube with a built-in heater is installed between the suction
port and the air sampling unit to heat the suctioned air and reduce
relative humidity. Heating the room by about 10 °C can reduce therelative humidity from 90% to 35% - 55%.
 Cover the piping and air sampling unit with heat-insulating material.

Earth-

Earthquake countermeasures, including the station building, equipment, and(g)quakepiping, shall be taken to have earthquake resistance at Class S or equivalent
resistance grade to Class S in the earthquake resistance standards of the BuildingStandards Act.

Commu- Assuming that the means of data transmission may be cut off, it is desirable(h) nication to have multiplex communication methods, including the construction ofsatellite communications, etc., which are relatively unaffected by disasters.
(i)

Other

Enclose the area around the installation site with a fence, etc., and takemeasures to prevent intrusion from outside, tampering, etc..

34

3.3.2 Calibration
The calibration of detectors used in dust monitors is described here. Flow meters are desirably
calibrated periodically for proper evaluation of air suction volume.
(1) Standard sources for calibration
Use the standard sources listed in Table 3-10 depending on the type of radiation to be measured.
The standard source should be a plane source, as shown in Figure 3-2, with the same shape as
the air sampling surface. The traceability to national standards shall be clear, and the relative
expanded uncertainty U of the surface emission rate or radioactivity shall be below 10% (k = 2).
Table 3-10. Standard sources for calibration
Radiation type

Standard source

α-ray

Am-241

β-ray

Cl-36 or Tl-204

γ-ray

Cs-137

Figure 3-2. Example of standard source (Cl-36, 2-inch ϕ)(2) Calibration method
To ensure that the geometric relationship between the air absorbent and the detector is thesame, a standard source is installed at the position of the air absorbent, as shown in Figure 3-3;
calibration is performed, and the instrument efficiency is measured according to Equation 3.1.
Instrument efficiency is the ratio of the net count rate of the instrument that is measured under
defined geometric conditions to the surface emission rate of the radiation source (the number ofrays per unit time emitted from the surface of the standard source).
A special jig for source installation should be prepared in advance to ensure that the installation
conditions do not change each time calibration is performed.

35Ε = N/ϕ(Equation 3.1)

ε: Equipment efficiency
N: Net count rate (s-1) (Calculated by subtracting the pre-measured background countrate.)
ϕ: Surface emission rate of radiation source (s-1)
The concentration of radioactive materials in the air measured by the dust monitor is calculated
as the radioactivity concentration evaluated by one standard source used for efficiency calibrationand is the total radioactivity concentration.
Refer to Explanation D for details on the efficiency of dust monitors.

Jig and radiation source

Radiation source
installation position

Radiation source
installed on the jig

Figure 3-3. Example of standard source installation during calibration(3) Calibration frequency
Calibration shall be performed at the installation site at the time of equipment installation.
After that, the equipment efficiency should be checked about once a year during inspections,etc., using a standard source to confirm that there is no change in equipment efficiency.
If the equipment efficiency deviates from the range of ±(10+U)% with respect to theequipment efficiency used in the calculation, recalibration should be performed to change theequipment efficiency, or if there is a possibility of equipment abnormality, an equipment
inspection should be performed, focusing on the detector. U is the relative expanded uncertainty(k = 2) associated with the calibration work.

36

3.3.3 Inspection(1) Daily inspection
Daily inspections include items to be conducted remotely by telemeter systems, etc., and items
at the installation site.
Examples of daily inspection items are shown below.
(a) Examples of items to be conducted remotely by telemeter systems, etc.
Example of daily inspection items
Operation check

Is it operating and communicating normally?
Is there any anomaly in flow rate or integrated flow volume?
Are the pressure values within the normal range?

Abnormal values Is the alarm not triggered?
Is there any anomaly in radioactivity concentration or count rate?
(b) Example of items at the installation site
Example of daily inspection items
Operation check

Is it operating and communicating normally?
Is there any anomaly in flow rate or integrated flow volume?
Is there any abnormality in the operating noise of the pump?
Is the filter paper being fed properly?
Is the suction port clogged?
Whether the pressure values are within the normal range

Abnormal values Is the alarm not triggered?
Is there any anomaly in radioactivity concentration or count rate?
Operatingenvironment

Is the air conditioning in the station building working properly?

Remaining
amount of filter
paper

Is enough filter paper remaining (until the next inspection, etc.)?

37

(2) Periodic inspection
Examples of periodic inspection items by the manufacturer are shown below.
Example of periodic inspection items
Sampler
Detection unit(a) Visual inspection

Indicator
Data transmission unit
Cable and connector(b) Unit operation and performance test
External output signal check
Leak test

Sampler

Power failure countermeasure operation check
Confirmation of filter paper feed operation
Filter paper

Confirmation of control operation
Operation check

Flow meter

Pump

Flow rate indication accuracy
Operation check (heat generation, unusual noise, vibration,
odor, etc.)
Periodic replacement of worn parts

Condensation
prevention unit
Detector

Confirmation of heating control
Temperature indication accuracy
Equipment efficiency check
Operation check
External output signal check
Count rate indication accuracy

Indicator

Flow indication accuracy
Scaler operation check
Recorder indication accuracy

Alarm section

Alarm operation check

Data transmission unit

Data transmission check(3) Inspection frequency
For routine inspections, inspections should be conducted daily by the telemeter system, etc,
and about monthly at the installation site.
Periodic inspections shall be conducted at least once a year.

38

3.4 Measurement(1) Start-up of equipment
The system should be activated at all times to perform continuous measurements from normal
times.
(2) Installation of air absorbent
Install the air absorbent according to the dust monitor’s user manual.
* Avoid mistaking the filter paper’s front and back when installing the air absorbent. Also
note that if the long filter paper is loosely installed, the filter paper feeding may not work
properly, and the equipment may stop.
(3) Setting of measurement conditions
The measurement conditions should be set based on early detection of the effects of
unexpected releases of radioactive materials from nuclear facilities.
Examples of measurement conditions are shown in Table 3-11, and the points to be considered
for each item are described in (a) – (e).
Changes in measurement conditions shall be feasible by remote control using a telemetersystem or other means.
Table 3-11. Primary measurement conditions for continuous measurement with dust monitors
Item

Measurement condition(a) Sampling flow rate

Approximately 50 to 250 L/min.

(b) Filter paper feeding method (longfilter paper case)Intermittent feeding(c) Sampling time (filter paper feedtime)

Six hours(d) Measurement position

Air sampling position(e) Measurement timeContinuous (measurement at least every one hour)(a) Sampling flow rate
The flow rate should be approximately 50 to 250 L/min.
When collecting filter paper from dust monitors for precise analysis of radionuclide
concentrations, the flow rate should be set considering the detection limit shown in Explanation B.
* A flow rate of approximately 230 L/min is required to obtain a sample amount of 10,000 m3 forone month (30 days), described as the detection limit in Table B-2 of Explanation B. A flow rateof approximately 70 L/min is required to obtain a sample of 3,000 m3 in one month (30 days).
When radioactive iodine is sampled simultaneously, the collection rate should be about 50 L/min
to maintain the collection efficiency of iodine.
* Make sure that the flow rate does not drop by more than 10% due to clogging of the filter paper.
Refer to Explanation C for an example of evaluating flow reduction.

(b) Filter paper feeding method39

An intermittent feeding method shall be used when long filter paper is used. The continuous
feed method is not employed in this measurement method.
(c) Sampling time (filter paper feed time)
As a general rule, the sampling time shall be 6 hours long. However, this does not preclude asampling time longer than 6 hours if it does not affect the early detection of facility-induced
radioactive materials released from nuclear facilities. The longer the filter paper feeding time is,the greater the amount of airborne dust collected, and the natural radioactive materials contained
are, which is likely to make it more challenging to detect facility-induced radioactive materials.
The Normal Time Supplementary Reference Materials also describes a method of continuous
sampling for one hour and measurement for about 10 minutes after sample collection. In this case,the filter paper is fed every hour. However, in this method, the filter paper must be replaced more
frequently*, so the remaining filter paper must be carefully monitored. It should also be noted thatas the amount of filter paper required increases further, more time and labor are required to replace
the filter paper.
In an emergency, the filter paper feeding time shall be able to be switched every hour byswitching to the emergency mode, etc., because hourly filter paper feeding is required inaccordance with the air monitor.
* If a 90 m long filter paper is used and the filter paper feeding distance is 20 cm, the filter paper
needs to be replaced at intervals of approximately 112 days for a filter paper feeding every 6hours or 18 days for a filter paper feeding every hour.
(d) Measurement position
While collecting airborne dust, the radiation emitted from the collected airborne dust ismeasured with a detector installed at the air sampling location.
(e) Measurement time
In principle, the measurement shall be consecutive, but measurements shall be taken at least
once per hour. If the filter paper feeding time is set to 6 hours, 6 measurements are taken at least
once per hour during one filter paper feeding interval.
In case of emergency, it shall be possible to switch to the emergency mode, obtaining
measurements every 10 minutes since measurements taken every 10 minutes are required inaccordance with the air monitor.
(4) Start of measurement
Start measurement by pressing the start button, etc.
To facilitate evaluating the measurement data, it may be designed to set the filter paper feedingat times such as 0:00, 6:00, 12:00, and 18:00 and to obtain the hourly measurement values everyhour.
It is desirable to remotely control the start and stop of measurement by the telemeter systemor other means.
(5) Data transmission
Data should be transmitted to the telemeter system at least once per hour. In an emergency,
the system can switch to data transmission at an interval of every 10 minutes. Alarms and othermonitoring information shall be transmitted to the telemeter system rapidly after an abnormality
occurs. An example of data transmission items is shown in Table 3-12.

40

Table 3-12. Example of data transmission items to telemeter system
Classification

Component

Output item
Date and time of measurement
Measurement point
Measurement time

Indicator

Count rate (s-1)
Radioac Integrated count (count)tivityRadioactivity
concentration (Bq/m3)

Measurements

Flow
rate

Sampler

Average flow rate
(L/min)Integrated flow volume(m3)

Detector abnormal
Measurement unit abnormalHigh radioactivity level

Indicator

Low radioactivity level
High count rate
Low count rate
In the process of air sampling
Filter paper is being fed

Status signal

Abnormal pump flow rate
Abnormal pressure
Abnormal filter paper feed

Sampler

Out of filter paper
Abnormal air sampling unit
Pump overload
Sampler power failure
Abnormal heating unit

GeneralControl signal(ReceivedStart or stop
Under adjustment

Indicator

Reset during adjustment

information )Sampler

Filter paper feed41

(6) Calculation of radioactivity concentration(a) Dust monitors that measure α or β radiation
The hourly gross α or β radioactivity concentration (Bq/m3) is calculated as the averageradioactivity concentration up to the elapsed time from the filter paper feeding using Equation 3.2.
If necessary, correction is made, considering factors affecting the measurements, such as collection
efficiency.
Figure 3-4 shows the hourly net count rate and integrated flow volume for calculation in a 6hour filter paper feed.
N

Ct = (ϵ × tV ) (Equation 3.2)t

Ct: Gross α or β radioactivity concentration at t hours after filter paper feeding (Bq/m3)
Nt: Net count rate at time t hours after filter paper feed (s-1)ε: Equipment efficiency
Vt: Integrated flow volume from filter paper feed to t hours later (m3)Supplementary information on how to obtain the net count rate
The net count rate is calculated by subtracting the pre-measured background count rate.
In principle, the net count rate at t hours after filter paper feeding should be evaluated as
precisely as possible.
Since this method is based on measurement during air sampling, a count rate meter is usedfundamentally to obtain the count rate (instantaneous value) of airborne dust collected on filter
paper at the time of t hours after the filter paper is fed.
Note that care should be taken when the count rate is calculated from the integrated counts
measured by the scaler. Refer to Explanation C for the concept.

Figure 3-4. Net count rate and integrated flow volume used in calculations(for 6-hour filter paper feed)42

Dust monitor measurements are calculated as the average concentration from the filter paper
feeding. But for air monitors used in an emergency, the average concentration per 10 minutes
evaluated from the difference in the count rate (count rate from the radioactivity in airborne dust
collected on the filter paper at each 10-minute time starting from the filter paper feeding) is used.
Refer to Explanation C for the difference between the two calculation methods.
If the evaluation of the average concentration per unit time is used in normal times, it isdifficult to properly evaluate the difference due to the short half-life of radon/thoron decay
products. However, if it is feasible to conduct a reliable evaluation, we do not reject the evaluation
based on the average concentration per unit time to evaluate the contribution of the facility-induced
radioactive material.
(b) γ-ray dust monitors
Record all hourly counts. If radionuclide concentrations can be quantified, hourly
concentrations of facility-induced γ-ray emitting radionuclides (Bq/m3) should be calculated.
Refer to the Radioactivity Measurement Method Series No. 6 “NaI(Tl) scintillation
spectrometer instrumental analysis method” for the analysis method.
(7) Collection of filter paper
If the filter paper of the dust monitor is subjected to precise analysis, collect the filter paper
periodically.
Care must be taken to prevent abnormal filter paper feeding caused by the improper installation
when long filter paper is cut off in the middle and reinstalled.
Refer to Section 4.4 for the filter paper collection procedure and Chapter 5 for the subsequent
analysis procedure.
3.5 Evaluation of measurement results
3.5.1 Evaluation flow
The purpose of evaluating dust monitor measurements is to provide early detection of theeffects of unexpected releases of radioactive materials from nuclear facilities. For this purpose, itis necessary to establish an appropriate confirmation start setpoint and initiate a factor investigation
to determine if the facility contribution is present or not when that value is exceeded. An example
flowchart for discriminating facility contributions is shown in Figure 3-5.
The Normal Time Supplementary Reference Materials states that the confirmation start
setpoint should be set considering the variation of individual devices and the maximum value inthe past. In light of the current technical standards, the maximum value should be approximately
5 Bq/m3 (gross β radioactivity concentration or γ-ray emitting radionuclide concentration) or 1
Bq/m3 (gross α radioactivity concentration) for the measurement after facility contribution
discrimination. Measurements also vary with natural factors (refer to 3.5.3). Thus, measurements
can exceed the confirmation start setpoint even without a facility contribution. Since theconfirmation start setpoint triggers the confirmation action, the facility contribution of the above
level must at least be detectable in light of the current technical level. However, a lower value may
be used as the confirmation start setpoint considering equipment performance, natural variations,administrative requirements, and other factors.

43Normal measurement

Indication value increase in dust
monitor*1

Exceeds confirmation start
setpoint *2

No

NNormal measurement

o

Yes Y
Yes Y
es

es
Abnormal measurementinfacility*3
No
Impacts of weather and naturalradioactive nuclides*4

Yes
Normal measurement

No N
oAbnormality in themeasurement instrument

Yes Y After adjustment, proceed toesnormal measurement

No
Judge that there was a facility contribution (including cases
where it is judged that the facility contribution cannot be
ruled out)

Collect the filter paper that collected the radioactive materials
in the air at that time and analyze the radioactive material
concentration (see Chapter 5)*1 Measurement after facility contribution discrimination*2 After evaluating the facility contribution in the dust monitor measurements, the confirmation
start setpoint should be set considering the variation of individual equipment and the past
maximum value. The maximum value for the confirmation start setpoint should be 5 Bq/m3(gross β radioactivity concentration or γ-ray emitting radionuclide concentration) or 1 Bq/m3(gross α radioactivity concentration). Refer to 3.5.2 for setting the confirmation start setpoint.
*3 Abnormal values of area monitoring equipment, etc., in the facility or status of releases(including controlled releases) outside the facility
44

*4 Analysis of β/α ratio (ratio of gross β radioactivity concentration divided by gross α
radioactivity concentration), spectrum, etc. (Weather data such as rainfall, snowfall, andlightning are also considered.)
Figure 3-5. Example of a flowchart for discriminating facility contribution to the results ofcontinuous measurement of airborne radionuclide concentrations(including cases where the possibility that it is a facility contribution cannot be ruled out)
3.5.2 Monitoring for exceeding the confirmation start setpoint(1) Evaluation method
The confirmation start setpoint is for initiating a factor investigation to determine whether there
was a facility contribution to the dust monitor measurements (including cases where the possibilityof a facility contribution cannot be ruled out) when the dust monitor measurements increase after
discriminating the facility contribution.
The Normal Time Supplementary Reference Materials states that the confirmation start setpointshould be set using measurements after facility contribution discrimination, considering individual
device fluctuations and the maximum values in the past. Its maximum value should be set atapproximately 5 Bq/m3 (gross β radioactivity concentration or γ-ray emitting radionuclide
concentration) or 1 Bq/m3 (gross α radioactivity concentration) in light of the current technicalstandards.
Since the confirmation starts setpoint triggers the confirmation action, at least the above level offacility contribution must be detectable in light of current technical standards. However, a lower
value may be used as the confirmation start setpoint considering equipment performance, naturalvariations, administrative requirements, and other factors.
The data used to set the confirmation start setpoint shall be the measurement after facility
contribution discrimination, and the maximum value shall be the confirmation start setpoint. If the
maximum value is greater than 5 Bq/m3 (gross β radioactivity concentration or γ-ray emitting
nuclide concentration) or 1 Bq/m3 (gross α radioactivity concentration), the confirmation start
setpoint shall be set at 5 Bq/m3 (gross β radioactivity concentration or γ-ray emitting nuclide
concentration) or 1 Bq/m3 (gross α radioactivity concentration).
The following are some notes on the data used for the above setup.
 Use the hourly measurements taken over the past 3 to 5 years. If no data is available overthe past three years, use hourly measurements from at least the past year.
 The data should not include abnormal values such as equipment errors.
 The data should not include measurements determined to have been contributed by thefacility.
The confirmation start setpoint should be reviewed periodically in accordance with updates tothe normal time monitoring plan, equipment upgrades, changes in the surrounding environment,
etc.
The alarm level should be set so that the person in charge is notified in real time when ameasurement value exceeds the confirmation start setpoint.
Various methods have been put into practical use to discriminate facility contributions. However,
it is necessary to select an appropriate method according to the characteristics of the facility to bemonitored. It is also essential to fully understand the principles of each method and the meaningof the measurements before evaluation.
In this section, we show how to use the β/α ratio (ratio of gross β radioactivity concentration
divided by gross α radioactivity concentration) when α- and β-ray dust monitors are used. It should
be noted that this method is based on the fact that the β/α ratio is generally constant when there is45

no influence from nuclear facilities and thus can only be used to estimate the facility contribution
to the gross β radioactivity concentration when the major release from nuclear power reactor
facilities, etc., results from β-ray emitting nuclides. There is no influence from α-ray emitting
nuclides.
In cases where facility-induced α-ray emitting radionuclides are released at uranium processing
facilities or plutonium processing facilities, or both α-ray and β-ray emitting radionuclides are
released at reprocessing facilities, it is necessary to discriminate and evaluate the facility
contribution by the method using the αβ coincidence counting or spectral analysis as described in
Explanation F.
Refer to Explanation F for the discrimination evaluation method for the facility-induced portionin the gross α radioactivity concentration and the discrimination evaluation method other than theevaluation method using the β/α ratio in the gross β radioactivity concentration.
(a) Method using β/α ratio
Due to the influence of radon/thoron decay products, the gross α and β radioactivity
concentrations fluctuate to a large extent over time. However, the ratio of the two, the β/α ratio,remains almost constant. Using this property, estimating the total beta radioactivity concentrationfrom natural radioactive materials and subtracting it from measurements allows for evaluating thegross β radioactivity concentration derived from facility-induced radioactive materials.
This method is effective when the gross β radioactivity concentration from facility-induced
radioactive materials is dominant and is not applicable when the ratio of the gross β radioactivity
concentration to the gross α radioactivity concentration from facility-induced radioactive materials
is comparable to the ratio from natural radioactive materials (radon/thoron decay products).
It should be noted that the β/α ratio may be calculated higher for the data immediately after thefilter paper is fed because the gross β radioactivity concentration is apparently higher than the
gross α radioactivity concentration due to airborne dust penetrating the filter paper, and that small
radiation counts may make the β/α ratio vary widely. If this results in a higher frequency of
exceeding the confirmation start setpoint, it is recommended that an evaluation is performed foreach elapsed time since the filter paper was fed (refer to Explanation F.3 for an example ofevaluation).
1) Setting the standard β/α ratio
Calculate the average value of β/α ratio from hourly measurements for the past several
years without influence from nuclear facilities at the target measurement points and set thestandard β/α ratio. The standard β/α ratio may also be determined from the slope of thecorrelation between the gross α and gross β radioactivity concentrations. An example
evaluation is shown in Figure 3-6.
2) Calculating the estimation of facility-induced gross β radioactivity concentration
The natural gross β radioactivity concentration is estimated from the product of the hourly
measurement of the gross α radioactivity concentration and the standard β/α ratio. The
facility-induced gross β radioactivity concentration is estimated by subtracting theestimated natural gross β radioactivity concentration from the hourly measurement of grossβ radioactivity concentration.
Evaluation formula
Measurement of gross α radioactivity concentration × Standard β/α ratio = estimated valueof natural gross β radioactivity concentration

46

Measurement of gross β radioactivity concentration – estimated value of natural gross β
radioactivity concentration＝ estimated value of facility-induced gross β radioactivity
concentration
3) Determination of confirmation start setpoint
The maximum value of the estimated facility-induced gross β radioactivity over the past
several years is set as the discrimination level. The evaluation example of Figure 3-7 shows
0.78 Bq/m3.

47

Figure 3-6. Example of evaluation of standard β/α ratio(Top: Example of evaluation by average value. Bottom: Example of evaluation by the slope ofcorrelation)48

Figure 3-7. Example of evaluation of estimated facility-induced gross β radioactivity
concentration

49

Figure 3-8 shows an example of evaluating the facility-induced contribution of radioactive
materials based on dust monitor measurements in Chiba City, Chiba Prefecture, during the TEPCO’s
Fukushima Daiichi Nuclear Power Plant (hereinafter referred to as “Fukushima Daiichi NPP”)
accident in March 2011. The increase in the gross β radioactivity concentration since March 15 cangenerally be evaluated as an estimate of the facility-induced gross β radioactivity concentration.

Figure 3-8. Example of evaluation of estimated facility-induced gross β radioactivity
concentration at the time of the TEPCO’s Fukushima Daiichi NPP accident*Before 12:00 on March 15, 2011, the measurements are shown for the first hour of every 6 hoursof filter paper feeding, and after that, the measurements are shown hourly for every hour of filter
paper feeding. Only positive values are shown for the estimated values of facility-induced gross β
radioactivity concentration.
(2) Actions to be taken when the confirmation start setpoint is exceeded, etc.
If the hourly measurement exceeds the confirmation start setpoint, check abnormalities or effectsin (a) – (d) below.
(a) Abnormalities in facility measurements, etc.
 Releases outside nuclear facilities (including controlled releases) Abnormal values of area monitoring equipment, etc., in nuclear facilities
 Release and diffusion of artificial radioactive materials into the air due to the effects of nuclear
explosion tests, etc.
(b) Effects of weather, natural radioactive materials, etc.
 Weather factors such as rainfall, snowfall, snow accumulation, etc.
- Washing away of airborne dust from the air by rainfall or snowfall50

- Suppression of resuspension of airborne dust from the ground surface due to rainfall, snowfall,and snow accumulation, and suppression of emission of radon/thoron decay products.
- Increase in airborne dust due to natural phenomena such as soil uplift during high winds andyellow sand- Increase in near-surface radon/thoron decay product concentrations associated withstabilization of the air at dawn
- Noise caused by lightning
 Changes in geography, topography, and other natural conditions due to natural disasters, etc.
 Changes in the surrounding environment due to human factors, such as civil engineering
works in the neighborhood(c) Abnormality of measuring instruments, etc.
 Failure of measuring instrument
 Changes in measurement conditions such as sampling method, the performance of measuring
instruments, measurement method, etc.
- Change in measurements due to contamination around the detector- Fluctuations in measurements due to changes in air sampling flow rate
- Fluctuations in measurements due to improper grounding or unstable voltage- Variation in performance of air absorbents(d) Variation of measurements due to counting uncertainty
3.5.3 Management of dust monitors by normal variation range
Dust monitor measurements before facility contribution discrimination include the contribution
from natural radioactive materials and will vary even in the absence of facility contribution. This isinduced by changes in the concentration of radon/thoron decay products in the air due to natural
factors such as rainfall, snowfall, wind strength, seasonal wind effects, etc. Therefore, it is effectivefrom a management perspective to ascertain the normal fluctuation range and to check for any
abnormalities in the equipment if the measurement exceeds this range. If necessary, investigating thefrequency of exceeding the normal fluctuation range due to natural variations may also be available
to set a confirmation start setpoint. The normal fluctuation range is the certain range within whichmeasurement fluctuations are generally considered to fit under normal operation of nuclear facilities
and when measurement conditions are appropriately managed.
(1) Calculation method of the range of normal fluctuation
The same data used for setting the confirmation start setpoint (refer to 3.5.2(1)) should be used to
calculate the normal fluctuation range. Data including the contribution of natural radioactive materials
without discriminating facility contribution shall be used.
The normal fluctuation range is calculated from the arithmetic mean of hourly measurements ofgross α radioactivity concentration or gross β radioactivity concentration for the past several years +(3 x arithmetic standard deviation), etc.
Fluctuations in dust monitor measurements in normal times are due to changes in theconcentration of radon/thoron decay products and often include seasonal variations, as shown in
Figure 3-9, due to natural factors such as wind strength, seasonal wind effects, rainfall, and snowfall.
The variation in measurements also varies with the time elapsed since air sampling.
51

If the frequency distribution of individual measurements, as shown in Figure 3-9, can be regarded
as a log-normal distribution, as shown in Figure 3-10, it is better to calculate the range of normal
variation using the geometric mean instead of the arithmetic mean, as shown in Figure 3-11*. Using
the geometric mean, the normal fluctuation range is the geometric mean value of hourly measurementsof gross α or β radioactivity concentrations for the past several years × (the cube of the geometricstandard deviation).
*The arithmetic mean is the average value obtained by dividing the sum of all measurements by the
number of measurements and is commonly used.
The geometric mean is the average value obtained by multiplying all the measurements and taking
the radical root of the power of the number of measurements. It is used, for example, to obtain the
average value of the rate of change.

52

数

デ
ー タ

Figure 3-9. Example of change over time in dust monitor measurements (gross β radioactivity
concentration)

Figure 3-10. Frequency distribution of dust monitor measurements (log-normal distribution)

53

Figure 3-11. Setting an example of the normal fluctuation range of dust monitor measurement
values(2) Confirmation of exceeding the normal fluctuation range
If the normal fluctuation range is exceeded, it is effective for management to check whether thecause is due to natural fluctuations or any abnormalities in the equipment.
If the frequency of exceeding the normal fluctuation range increases during periods when the dust
monitor measurements are high due to natural fluctuations, it is recommended to use the maximum
value of gross α or β radioactivity concentration over the past several years or to make an evaluation
by setting the normal fluctuation range for each elapsed time since filter paper feeding or for eachseason.
However, it should be noted that if the maximum value over the past several years is used, it will
be larger as a normal fluctuation range and looser as a criterion for judgment.
3.5.4 What to do when it is determined that there has been a facility contribution
If the confirmation start setpoint was exceeded and a factor investigation determined that there
was a facility contribution (including cases where the possibility of a facility contribution cannot be
ruled out), collect filter paper containing airborne dust collected at the time in question, and conduct
a precise analysis of radionuclide concentration to estimate and evaluate the exposure dose to nearby
residents, etc.
If a dust sampler is installed, collect its filter paper.

54

The measurement targets for precise analysis according to the nuclear facilities listed in theNormal Time Supplementary Reference Materials are shown in Table 3-13. The procedure for precise
analysis is described in Chapter 5.
Table 3-13. Measurement targets for precise analysis when it is determined that there was a facility
contribution
Nuclear facility
Measurement target
Nuclear power reactor facilities(PAZ and UPZ settings required)

γ-ray emitting nuclides,
radioactive iodine

Nuclear power reactor facilities as
specified in the Cooling Notice

γ-ray emitting nuclides,
radioactive iodine

Nuclear power reactor facilities(UPZ setting not required)

γ-ray emitting nuclides,
radioactive iodine

Nuclear reactor facilities for testing and γ-ray emitting nuclides,
research, etc. (UPZ setting required)radioactive iodine
Uranium processing facility(UPZ setting required)

Uranium

Processing facility to handle plutonium Plutonium
Reprocessing plant

γ-ray emitting nuclides andplutonium

55

Chapter 4 Collection of Air Samples by Dust Samplers, etc.
Collecting air samples by dust samplers, etc., and analyzing air samples as described in Chapter 5
should be conducted to estimate and evaluate the exposure doses to nearby residents, etc.
The procedures for collecting air samples are based on the description in The Series ofEnvironmental Radioactivity Measuring Methods No. 16, "Environmental sampling method".
4.1 Equipment
Dust samplers or iodine samplers are used to collect air samples. There are two types of dust
samplers: low-volume air samplers and high-volume air samplers, and the difference between them isbased on suction amount, with no big difference in configuration. The equipment configuration of thedust sampler is shown in (1), and the features of each sampler are shown in (2) and (3). The dust
monitor described in Chapter 3 can also be used as a dust sampler.
The relationship between the air sampling time of filter paper and the required detection limit
concentration, etc., determines the flow rate for collecting air samples. However, a flow rate of 100
to 250 L/min is suitable for airborne dust only, and approximately 50 L/min is suitable for iodine.
(1)

Dust Sampler Equipment Configuration
Figure 4-1 shows that a dust sampler consists of a particle separator, filter medium holder, flow
controller, and suction pump. The functions of each part are shown in (a) through (d).

Figure 4-1. Configuration of a dust sampler(a) Particle separator (particle size sorting unit)
A particle separator separates airborne dust of the required particle size from the collected airborne
dust. There are three types according to screening methods: gravity settling type (multi-stage parallel
plate type particle separator), inertial collision type (inertial collision type particle separator), andcentrifugal sedimentation type (cyclone type particle separator). Particle-size sorting of airborne dust
is not performed when monitoring nuclear facilities. Therefore, as a general rule, using a particle
separator is unnecessary. However, particle separators effectively obtain radioactivity concentrationfor each particle size of airborne dust.
(b) Filter medium holder (mounting unit of absorbents (filter paper))56

The filter medium holder has a structure that facilitates replacing the filter medium (a device suchas a filter paper that filters and collects particulate matter. In this measurement method, it is referred
to as an air absorbent.) and prevents filter medium damage and air leaks.
(c) Flow controller (suction amount adjusting unit)
The flow controller is structured to control the actual flow rate through the particle separator to apredetermined flow rate based on air temperature and air pressure.
The method of controlling the actual flow rate depends on the flow meter used (see JIS Z 8814:2012“Low-volume air samplers” Annex A [6] for the method of correcting the actual flow rate).
Flow meters widely used are area-type, differential pressure-type, volume-type, and mass-type.
(d) Suction pump
A suction pump suctions air at a predetermined flow rate through an air absorbent and includes
linear motor-driven, rotary, and diaphragm types. The rotary type has a high flow rate and low
fluctuation. Diaphragm and piston types have moderate flow rates and fluctuations, while the turbo
type has a high flow rate and fluctuation.
Fluctuations in flow rate due to changes in pressure drop of filter paper, etc., depend on the type ofpump.
(2) Low-volume air sampler
It is designed for continuous air sampling and can withstand approximately several days to a weekof use. The suction amount is approximately from 20 to 100 L/min. Filter paper of approximately 5
cm in diameter is attached to the filter paper holder, and activated carbon cartridges are also attached
for collecting radioactive iodine.
An example of equipment specifications of a low-volume air sampler is shown in Table 4-1. Notethat equipment not listed in the example specifications may be used if it performs well.
For the performance of the dust sampler, refer to the detection limit in Explanation B.

57

Table 4-1. Example of equipment specifications of a low-volume air sampler
itemType A
Type B
Type CType D
Rated suction
120 L/min or
40 L/min or more
50 L/min or more
20 to 120 L/min
amountmore
Variable flow
30 to 50 L/min
50 L/min20 to 120 L/min
range
Cellulose and glass Cellulose and glass
Cellulose and glass
fiber filter paper
fiber filter paper
fiber filter paper
Cellulose and
60 mm ϕ (activated 60 mm jig (activated
60 mm (activatedglass fiber filter
Air absorbent carbon filter paper carbon filter paper or
carbon filter paper
paper (105-110
or activated carbon
activated carbon
or activated carbon
mm ϕ)cartridges can be
cartridges can be
cartridges can be
attached)
attached)
attached)
Measurement
Flow rate, integrated flow volume
Information
Portability
Yes
WeightApprox.* 6 kg
Approx. 15 kg
Approx. 3 kg
Approx. 8 kg
Dimensions
150×205×177
260×260×1000
200×162×262
190×323×285
W×D×H(mm)Battery
AC100 V
AC100 VPower
DC7.4 V 3200
AC100 V
1.5 A
300 VAmA
Continuous
Continuous
Continuous
operation
Other
operation: up to 99
operation:
More than 60
hours
Approx. 1 week
minutes*Approx.=Approximately(3) High-volume air sampler
It is unsuitable for continuous air sampling over a long period because it collects airborne dust bysuctioning a large amount of air in a short time.
The suction amount should be approx. 200-2000 L/min. Attach the large filter paper with approx.
10 cm in diameter or approx. 8 inches (203 mm) x 10 inches (253 mm) square.
There are two types of equipment: transportable type and large installed type equipment.
An example of equipment specifications of a high-volume air sampler is shown in Table 4-2. Notethat equipment not listed in the example specifications may be used if it performs well.
For the performance of the dust sampler, refer to the detection limit in Explanation B.

58

Table 4-2. Example of high-volume air sampler equipment specifications
item
Type A
Type B
Type cRated suction
650 L/min
500 L/min
1000 L/min
amountVariable flow
100 to 800 L/min
100 to 1200 L/min
range
Cellulose and glass fiber
glass fiber filter paper
silica filter paper
Air absorbent filter paper 105 to 110
110 mm ϕ
8 ×10 inchmm ϕMeasurement
Flow rate, integrated flow volume
Information
weightApprox. 4 kg
Approx. 8 kg
Approx. 31 kg
Dimensions
W×D×H
165×169×165
425×200×270
575×575×1420(mm)
AC100 V
AC100 V
AC100 V
Power
580 W
10 A
10 A

59

4.2 Air absorbent
Filter papers for collecting airborne dust include cellulose and glass fiber filter paper, and activatedcarbon filter paper and activated carbon cartridges are used for collecting gaseous radioiodine. Theirintended uses differ.
In JIS Z 4601:2009 “Radioactive dust samplers” [7], the performance of filter paper is describedas “The collection efficiency should be 95% or more for particles of 0.3 µm in diameter”. The filter
paper used has a collection efficiency of approximately 99% for particles of 0.3 µm in diameter.
However, some cellulose and glass fiber filter paper does not necessarily have sufficient collection
efficiency for particles of 0.1 µm or lower in diameter, and caution should be exercised whencollecting samples in an environment dominated by particles of 0.1 µm or lower in diameter*.
* See Reference A Characteristics of air absorbent.
(1) Air absorbent for low-volume air sampler(a) Cellulose and glass fiber filter paper
This filter paper is made of cellulose and fine glass fibers, with a cloth backing and water-repellent
treatment for reinforcement.
It conforms to the filter paper specified in JIS Z 4601: 2009 “Radioactive dust samplers” [7].
(b) Glass fiber filter paper
It is made of ultra-fine borosilicate glass fibers with low hygroscopicity. It is also characterized byhigh collection efficiency.
(2) Air absorbent for high-volume air sampler(a) Cellulose and glass fiber filter paper
Equivalent to (1)(a), circular (105 mm ϕ) and square (8 inches × 10 inches) types are available.
(b) Glass fiber filter paper
Equivalent to (1)(b) and square types (8 inch × 10 inch).
The collection efficiency, etc., of filter paper is shown in Table 4-3.
Table 4-3. Example of filter paper collection efficiency, etc.
Filter paper
Cellulose and glass fiber
Glass fiber
material
Weight (g/m2)
145
120
95
Thickness (mm)
0.41
0. 40
0. 38
Pressure drop
0. 27
0. 32
0. 30
(kPa)
Water repellency
4.9
4.9
(kPa)
Ventilation speed
55
80
135
20
(cm/s)
Collection
99. 7*1 99. 8*1 99. 9*1
99*2
99. 99*3
efficiency (%)

60

Pressure drop: The differential pressure between the upstream side (before passage) and thedownstream side (after passage) of air as the air passes through the filter paper at a ventilation speedof 5 cm/s.
For the measurement method, refer to JIS K 0901: 1991, “Shape, dimensions, and performance test
method of filter medium for collecting dust samples in gas” [8].
Water repellency: pressure required for water to pass through.
Ventilation speed: the speed at which air passes through.
*1 Collection efficiency: measured from particle concentrations upstream and downstream when 0.31
µm polystyrene latex particles were filtered at a ventilation speed of 55 to 135 cm/s.
*2 Collection efficiency: measured from upstream and downstream particle concentrations when 0.3µm polyalphaolefin particles are filtered at a ventilation speed of 20 cm/s.
*3 Collection efficiency: value obtained when 0.3 µm dioctyl phthalate particles are filtered at aventilation speed of 5 cm/s
4.3 Installation and inspection
This section describes the outdoor installation and inspection methods of dust samplers. For indoor
installation, refer to 3.3, as it is common to dust monitors.
4.3.1 Installation
Select an installation location for a dust sampler that is a flat area (e.g., the center of a park or
parking lot) without trees or buildings in the vicinity and where certain facilities do not strongly
influence the dust sampler. In addition, select an installation location, considering the availability ofa power supply and ease of maintenance and inspection. If no suitable location is available, it may beinstalled on a flat rooftop of a building.
The height of the suction port should be approx. 1 m above the ground to match the height at which
the air dose rate is measured. It may be higher than 1 m if there is an effect of updraft from the groundsurface, snow accumulation, etc. Install a rain shelter to prevent rainfall and snowfall from entering it
and take a fall prevention measure.
When multiple dust samplers are used simultaneously, they should be arranged so that their exhaust
does not affect each other. If a transportable type generator is used as a power supply, the suction of
its exhaust is avoided.
4.3.2 Inspection
To maintain the performance of the dust sampler, it must be inspected on a regular daily basis, andthe flow meter must be calibrated about once a year. Inspection and calibration are requested to aprofessional organization or manufacturer for proper maintenance and management.
An Example of daily inspection items is shown below. Refer to the dust sampler’s user manual for
detailed inspection methods.

61

Example of daily inspection items
There is no trace of a strong impact.
(1) Visualinspection

No dirt (dust accumulation, etc.)
No screw or part that is missing or broken
There is no anomaly in the operation panel display and its operation.
No leakages when filter paper is installed(2) Check ofoperation(3) Check oftemperature, airpressure, and flowrate

Flow rate setting and start/stop operation should be standard.
The power anomaly recovery function and its recording should be
expected.
The displayed temperature is within the standard range of an
ordinary thermometer
The displayed air pressure is within the standard range of theatmospheric pressure gauge.
The displayed flow rate (set flow rate) is within the standard range.

An example of the main regular inspection items performed by manufacturers and others is shown
below.
Example of periodic inspection items(1) Visual inspection

Samplers, pumps, recorders, cables, and connectors
Check of control operation
Check of alarm operation
Sampler(2) Stand-alone
operation ⸳
Performance test
Pump
RecorderLeak test of air sampling unit
Flow rate indication accuracy (maximum flow rate
check)
Operation check (heat generation, abnormal noise,
vibration, unusual odor, etc.)
Periodic replacement of worn parts
Indication accuracy

62

4.4 Collection
4.4.1 Collection Method
Procedure
Conduct an operation test of the dust sampler to check its performance, then attach the1
specified filter paper.
Start air sampling and record the time and flow meter reading immediately after the2start.
During air sampling, read the value of the flow meter at appropriate time intervals to
obtain the total suction amount (Vt)* using the following formula.
3
Vt = V1t1 + V2t2 +…......... + Vntn (L)V1 to Vn: flow meter value (L/min)
t1 to tn: time (min) corresponding to the flow rate readings
Read the value of the flow meter immediately before the end of air sampling andrecord the end time.
4
Note that a dust sampler with an integrating flow meter reads the value of theintegrated flow volume.
After the suction, place the filter paper in a designated storage container to prevent the5collected airborne dust from falling out.
* The air suction amount during air sampling varies greatly depending on the amount of airborne dust.
The collection time should be set within the range where the flow rate does not drop below 90% of
the initial suction value due to clogging of the filter paper by collection.
4.4.2 Setting sampling conditions
The air suction amount is determined according to the purpose of γ-ray spectrometry andradiochemical analysis, etc.
Usually, continuous air sampling is conducted for approx. a week at approximately 50 to 100 L/minin case of using a low-volume air sampler fitted with a circular filter paper approx. 5 cm in diameter.
If a high-volume air sampler is equipped with a large circular or rectangular filter paper, the sample
for measurement is prepared by air sampling at 200-1000 L/min from several hours up to 24 hours.

634.4.3 Records of samples
An example of records during sample collection is shown in Table 4-4.
Table 4-4. Example of records during sample collection
Item
Example of records(1) Name of sampling
institution(2) Name of sampler(3) Sample No.
(4) Date and time ofStart time - End timesampling(5) Sampling location
Installation location and surrounding circumstances, suction(latitude, longitude)
port height (latitude and longitude)(6) Sampling situation Weather, etc., during the sampling period
Equipment used, type and size of filter paper, number of(7) Sampling method
sheets, etc.
(8) Flow rate
At the start
L/min At the completion
L/min(9) Suction amountIntegrated flow volume
L Suction timemin(10) Processing
situation(11) Processor name(12) Transportation
Transportation method, sample shape, sample volume, etc.
situation(13) Other reference
items

4.4.4 Sample transport
Filter paper that has collected airborne dust should be placed in a polyethylene bag or other storage
container with the dust collection side folded inward, then sealed with tape, etc., for transportation. A
copy of the sampling record should be attached to the transported sample.

64

Chapter 5 Analysis of Air Samples Collected by Dust Samplers, etc.
Air samples are analyzed either (a) by collecting filter paper from dust samplers, etc., at eachcontinuous sampling for a certain period according to the nuclear facility or (b) by collecting filter
paper from dust samplers urgently when continuous measurement by dust monitors or monitoring
posts detects emitted radioactive materials or radiation (i.e., when the results of continuous
measurement of the concentration of radioactive materials in the air or the air dose rate increaseindicating the facility contribution to the increase (including cases where it is judged that thepossibility of the facility contribution cannot be ruled out)), to estimate and evaluate the exposure
doses to nearby residents, etc.
Analysis methods for filter paper collected from dust samplers, etc., can be broadly classified into
analysis of γ-emitting nuclides by γ-ray spectrometry and analysis of α-emitting nuclides, etc., byradiochemical analysis. This chapter describes the pretreatment and analytical methods for bothanalyses on the collected filter paper.
The Normal Time Supplementary Reference Materials stipulates that at nuclear power reactor
facilities, etc., γ-emitting nuclides in the air are measured by germanium semiconductor detectors
approximate once a month, and at uranium processing facilities and processing facilities handlingplutonium, uranium, or plutonium levels in the air are measured approximately once every threemonths by radiochemical analysis, etc., and further at reprocessing facilities, γ-emitting radionuclides
and plutonium in the air are measured approximately once every three months by germanium
semiconductor detectors or radiochemical analysis (see (a) above). When the contribution of a facility
is recognized by continuous measurements using dust monitors or monitoring posts, samples arecollected from dust samplers, etc., and the following measurements are conducted: the concentrationsof γ-emitting nuclides, etc. are measured by germanium semiconductor detectors, etc. at a nuclear
power reactor facility, etc.; the uranium concentrations are measured by radiochemical analysis, etc.
at a uranium processing facility; at a plutonium processing facility, plutonium concentrations aremeasured by radiochemical analysis, etc.; and at a reprocessing facility, the concentrations of γemitting nuclides, radioactive iodine, and plutonium are measured by germanium semiconductor
detectors or radiochemical analysis (see (b) above).
At a uranium processing facility and processing facility that handles plutonium, uranium or
plutonium in environmental samples should be measured only when facility-derived uranium or
plutonium is detected by the measurement described in (1) above. However, radiochemical analysis
takes time, and there is a high risk that traces will be lost if environmental samples are collected after
the final judgment has been made after the analysis. Therefore, it is necessary to collect and measureenvironmental samples promptly by measuring the gross α radioactivity concentration to determine
early whether or not there is facility contribution and then to conduct a radiochemical analysis ofcollected filter paper.
To determine the presence or absence of facility contribution at an earlier stage than radiochemical
analysis, in (a) and (b), a method should be adopted that can easily measure radiation from airborne
dust on collected filter paper using a survey meter or the like. Measuring γ-rays of U-235 (186 keV)and Am-241 (60 keV) by γ-ray spectrometry is also effective for screening. In (b), it may also be
effective to wait for the decay of natural radioactive materials (radon/thoron decay products) containedin airborne dust before making measurements. Since the apparent half-life of radon decay products is
37 minutes and that of thoron decay products is approximately 12 hours (Figure 5-1), measurement
72 hours (5 hours if radon decay products are predominant) after the stop of air sampling to remove
65their effects may enable to determine the presence of facility contribution earlier than radiochemical
analysis.

Figure 5-1. Radioactive decay of radon/thoron decay products[Series of Environmental Radioactivity Measuring Methods No.1]

66

5.1 Pretreatment
When both γ-ray spectrometry and radiochemical analysis are conducted, the sample should be
divided beforehand for each purpose, or radiochemical analysis should be conducted using the sample
after the measurement by γ-ray spectrometry.
(1) Pretreatment for γ-ray spectrometry
As pretreatment method, filter paper may be filled directly into the measuring container, clipped
and filled, and ashed and filled.
Considering the ease of making a standard radiation source, the highest possible counting
efficiency, and good reproducibility, the filter paper is classified into four types according to shape:small circular, large rectangular, large circular, and extended filter paper, and each type is described
below.
Since some types of filter paper may contain radioactive materials, a blank test using the same lotof filter paper should be conducted and corrected if radioactive materials are contained.
(A) For small circular filter paper(a) Direct filling method
123Procedure
Carefully place the collected airborne dust into a plastic container that is slightly longer
in diameter than the filter paper (measurement container).
Press it with a plastic disk or similar object to reach a specific volume and cover it(Figure 5-2).
Wrap the sample in polyethylene film to make a measurement sample.

Figure 5-2. Example of filling a plastic container with a filter paper sample[Series of Environmental Radioactivity Measuring Methods No.16]

67

(B) For large rectangular filter paper(a) How to fold
1
2

Procedure
Since the air sampling surface is discolored, use scissors to cut off the discolored part,
paying attention to keep the collected airborne dust from falling out.
With the air-sampling surface facing inside, fold the sample to a specific size, and thenwrap it in polyethylene film and seal it, or place it in a plastic container (measuringcontainer) to make a measurement sample.

(b) Circular punching method

12Procedure
Punch out the air sampling surface into several circular shapes (Figure 5-3).
Note: The diameter of the circle to be punched out is determined by considering the size ofthe plastic container (measuring container) and the size of the standard radiation
source. This should be done on a wooden or lead board with a cork borer or stainlesssteel radioactivity measuring dish. When removing the punched filter paper, avoid
dropping a part of the sample. For this reason, cover the surface of the filter paperwith a thin plastic film in advance and punch out the covered film to avoid scattering
the sample.
Pack the punched filter paper in a plastic container (measuring container) as in (A) to makea measurement sample.

Figure 5-3. Example of punching out large rectangular filter paper[Series of Environmental Radioactivity Measuring Methods No.16]68(c) Ashing

1

Procedure
Fold the filter paper (cellulose and glass fiber filter paper, etc.) that has collected airborne
dust with the air sampling surface facing inward or cut it into slices with scissors, etc.,
and place it in a porcelain evaporating dish.

Note: Clean the scissors, etc., thoroughly after use.
Place it in an electric furnace and ash it at 500 ℃* for 4 to 5 hours. If volatilization of2
cesium at 500 ℃ is concerned, ashing at 450 ℃ or lower may be applied.
After open cooling, transfer the ashed sample to a plastic container (measuring container)
3
using a paintbrush or similar tool.
* It is not applicable to some nuclides because they are volatile. It is noted that even applicablenuclides may be volatile when an electric furnace comes to a higher temperature than the set value
due to an abnormal rise in temperature.

69

(C) For large circular filter paper(a) How to fold
1
2

Procedure
Since the air sampling surface is discolored, use scissors to cut off the discolored area,
paying attention to keeping the collected airborne dust from falling out.
With the air sampling surface facing inside, fold the sample to a specific size, and thenwrap it in polyethylene film, seal it, or place it in a plastic container (measuring container)
to make a measurement sample.

(b) Circular punching method

123Procedure
To clearly distinguish the suction part of the filter paper, draw a frame on the sampler
with the filter paper still attached to the sampler using a pencil or other tool, and thenremove the filter paper.
Punch out the filter paper in the suction part to obtain one circular piece with a diameterof 5 cm or less or several smaller circular pieces, as shown in Figure 5-4.
Place the pieces in a plastic container (measuring container) in layers or wrap them inpolyethylene film and seal them to make a measurement sample.

Figure 5-4. Example of punching out large circular filter paper[Series of Environmental Radioactivity Measuring Methods No.16]70(c) Ashing
Procedure
Fold the filter paper (cellulose and glass fiber filter paper, etc.) that has collected airborne
dust with the air sampling surface facing inward or cut it into slices with scissors, etc.,
1
and then place it in a porcelain evaporating dish.
Note: Clean the scissors, etc., thoroughly after use.
Place it in an electric furnace and ash it at 500 ℃* for 4 to 5 hours. If volatilization of2
cesium at 500 ℃ is concerned, ash it at 450 ℃ or lower.
*It is not applicable to some nuclides because they are volatile. It is noted that even applicable nuclides
may be volatile when an electric furnace comes to a higher temperature than the set value due to anabnormal rise in temperature.

71

(D) For extended filter paper(a) How to fold
1
2

ProcedureCut the part not covered with airborne dust at the appropriate size from the collected filter
paper.
With the air sampling surface facing inward, fold the paper to fit the measuring container,
and then wrap it in polyethylene film, seal it, or place it in a plastic container (measuringcontainer) to make a measurement sample.

(b) Punching methods

1

2

Procedure
After collecting the filter paper, cut out the air sampling surface with scissors or othermeans or punch it out with a specific apparatus. When cutting or punching out, matching
the diameter of the surface with that of the measuring container facilitates filling.
Note: Clean the scissors, etc., thoroughly after use.
Place the punched (cut out) filter paper in a plastic container (measuring container) inlayers with the surface with airborne dust facing down, or wrap it in polyethylene film
and seal it to make a measurement sample.

(c) Ashing

1

Procedure
Roll up the filter paper (cellulose and glass fiber filter paper, etc.) that has collected
airborne dust, fold it with the air sampling surface facing inward, or cut it into slices withscissors to place the treated paper in a porcelain evaporating dish.

Note: Clean the scissors, etc., thoroughly after use.
Place it in an electric furnace and ash it at 500 ℃* for 4 to 5 hours if volatilization of2
cesium at 500 ℃ is concerned, ash it at 450 ℃ or lower.
After open cooling, transfer the ashed sample to a plastic container (measuring container)
3
using a paintbrush or similar tool.
*Note that some filter paper, such as membrane filter paper, cannot be ashed.
It is not applicable for some nuclides because they are volatile.
It is noted that even applicable nuclides may be volatile when an electric furnace comes to a higher
temperature than the set value due to an abnormal rise in temperature.

72

(2) Pretreatment for radiochemical analysis
Pretreatment for uranium or plutonium analysis by radiochemical analysis.
(a) Uranium analysis
In principle, the filter paper is ashed and analyzed.
If ashing membrane filter paper, etc., is not possible and uranium contained in airborne dust
collected on the filter paper can be extracted with acid, etc., the extracted solution is used for analysis.
For cellulose and glass fiber filter paper, ash and analyze it.
Some types of filter paper may contain uranium, so unused filter paper from the same lot should
be analyzed to obtain a blank value for correction.
For the pretreatment procedure, refer to The Series of Environmental Radioactivity Measuring
Methods No. 1, "Uranium analysis method".
(b) Plutonium analysis
In principle, the filter paper is ashed and analyzed.
If ashing membrane filter paper, etc., is not possible and plutonium contained in airborne dust
collected on the filter paper can be extracted with acid, etc., the extracted solution is used for analysis.
For cellulose and glass fiber filter paper, ash and analyze it.
For the pretreatment procedure, refer to The Series of Environmental Radioactivity Measuring
Methods No. 2 "Plutonium analysis method".

73

5.2 Analysis(1) γ-ray spectrometry
The measurement sample prepared in 5.1 is measured with a germanium semiconductor detector.
The detection limits are shown in Explanation B.
For detailed measurement procedures, refer to "γ-ray spectrometry using germanium
semiconductor detector" in The Series of Environmental Radioactivity Measuring Methods No.7.
(2) Radiochemical analysis(a) Uranium analysis
Separate and purify uranium in the ashed sample or uranium extract solution by solvent extraction,ion exchange separation, etc. Electrodeposit the uranium in the purified sample on a stainless steel
plate to make a sample for α-ray measurement and quantify it by α-spectrometry with a silicon
semiconductor detector.
Other measurement methods include absorption photometry, Fluorphotometry, and ICP mass
spectrometry.
The detection limits are shown in Explanation B.
For detailed analysis procedures, refer to the "Uranium analysis method" in The Series ofEnvironmental Radioactivity Measuring Methods No. 14.
(b) Plutonium analysis
Separate and purify the plutonium in the ashed sample or plutonium extract by solvent extraction,ion exchange separation, etc. Electrodeposit the plutonium in the purified sample on a stainless steel
plate to make a sample for α-ray measurement and quantify it by α spectrometry with a silicon
semiconductor detector.
Other measurement methods include ICP mass spectrometry and liquid scintillation measurement.
The detection limits are shown in Explanation B.
For detailed analysis procedures, see "Plutonium analysis method" in The Series of Environmental
Radioactivity Measuring Methods No. 12.

74

5.3 Evaluation of analysis results
For the analysis results of airborne dust collected by dust samplers, etc., set the maximum
measurement value for the past several years or since the start of measurement as the upper limit of
the normal fluctuation range.
Figure 5-5 shows an example of a flowchart for discriminating facility contribution (including
cases where the possibility of facility contribution cannot be ruled out).

*1 A maximum value measured over the past several years or since the start of measurement*2 Abnormal values of area monitoring equipment, etc., in the facility or status of releases (including
controlled releases) outside the facility*3 An example of other factors search Contaminated samples may have been mixed in depending on the circumstances of sample
collection.
 Caused by other than the facility subject to the study (including nuclear tests).
 There are no other radioactive materials that are expected to be detected at the same time
due to the effect of the facility.
 Caused by radionuclides related to health.
Figure 5-5. Example of a flowchart for discriminating facility contribution (including cases where
the possibility of facility contribution cannot be ruled out)75

In cases where the measured values exceed the upper limit of the normal fluctuation range, etc., *1
as a result of normal time monitoring, the cause of the excess is first investigated. If it is determinedthat there was a facility contribution (including cases where the possibility of a facility contribution
cannot be denied), the exposure dose due to the facility contribution must be estimated and evaluated.
Estimating the exposure doses to nearby residents, etc., is usually done by separately calculating
the effective dose from external exposure for a year and the committed effective dose from internal
exposure from intake of food and drink, etc., over a year, and then synthesizing the results.
In this case, the former is calculated based on the measurement of air dose rate and the latter basedon the concentration of radioactive materials in the air environmental samples, intake amount, etc.
The exposure doses to nearby residents, etc., are assessed by comparing the dose targets*2 that aredetected in the public in the vicinity of the nuclear power reactor facility and the estimated exposure
doses.
Refer to the Normal Time Supplementary Reference Material for exposure dose evaluation.
*1 If the concentration of radioactive materials in the air exceeds the upper limit of the normal
fluctuation range, etc., the concentration is thought to be caused by fallout from accidents at nuclear
facilities other than those being monitored. Thus, the fallout needs to be verified as one of thecauses.
Fully understanding the nature of fallout from past accidents at nuclear facilities, changes over timein the nuclides contained in the fallout, and continuous radiation measurements allows us toestimate whether the increase is due to facility contributions by comparing those data. So, an effort
to obtain such data is created.
*2 The guidelines on target dose levels around light water reactor facilities for power generation
recommend setting the target effective dose level that is detected in the public around a nuclear
power reactor facility from radioactive materials released to the environment during normal
operation at the effective dose of 50 µSv for a year.
In addition, in the Guidelines for Assessment of Target Dose Values around Light Water Reactor
Facilities for Power Generation, effective doses are to be assessed as effective doses that result
from γ-rays from radioactive noble gases in gaseous waste, from radioactive materials in liquid
waste (effective doses from internal exposure due to ingestion of seafood containing radioactive
materials), and from radioactive iodine in gaseous waste (effective doses from internal exposuredue to inhalation, intake of leafy greens, and intake of milk).
5.4 Sample storage
When storing filter paper before analysis, store it in a desiccator to prevent hygroscopicity.
After analysis, store the filter paper (other than that used for radiochemical analysis) until thestorage period is completed, keeping them ready for reanalysis.

76

Chapter 6 From Air Samples Collection by Iodine Sampler to Analysis
6.1 From collection to analysis
The Normal Time Supplementary Reference Materials stipulates that when a facility contribution
is found in the measured values of dust monitors for a nuclear power reactor facility, etc. (including
cases where it is judged that the possibility of a facility contribution cannot be ruled out), samples
from iodine samplers should be collected. Radioactive iodine (particulate and gaseous) in the air
should be measured.
In addition, radioactive iodine (in particulate and gaseous form) in the air should be collected andmeasured periodically at a reprocessing facility. Cellulose and glass fiber filter paper and activatedcarbon cartridges, etc., removed from the iodine sampler should be subjected to measurement ofradioiodine using a germanium semiconductor detector.
For the measurement procedure, refer to The Series of Environmental Radioactivity Measuring
Methods No. 4, "Radioactive iodine analysis method".
In this report, only an example of equipment specifications for an iodine sampler (Table 6-1) andan outline of air absorbents (Table 6-2) are presented. Note that equipment not listed in the example
specifications may be used if it performs well.
For the performance of the iodine sampler, refer to the detection limit in Explanation B.
Table 6-1. Examples of equipment specifications for iodine samplers
Type A
Type B
Type CType D
Flow rate
40
Max. 30
25 or more
40 or more
(L/min)flow rate range
to be set
5 to 40
0 to 50(L/min)Cellulose and glass fiber filter paper
Filter paper
60 mm ϕtype and size
(Activated carbon filter paper and activated carbon cartridge can be
attached.)
Dimensions
200 × 200 ×
150 × 205 ×
300 × 200 ×
260 × 260 ×
W×D×H
285
117
270
100
(mm)
Weight (kg)Approx. 5 kg
Approx. 5 kg
Approx. 8 kg
Approx. 15 kg
AC100 V, 1 A,
AC100 V, 1 A,
AC100 V, 1 A,
Power supply
AC100 V, 3 A
DC24 V
DC24 V
DC12 V, 6 A
Timer setting:Timer setting:Timer setting
Timer setting:
Function
99 minutes or 99 minutes or
From 1 minute99 hours
99 hours
to 1000 hours

77

Table 6-2. Air absorbents used in iodine samplers
Outline50 mesh activated carbon is packed in a polyvinyl chloride or stainless steel
Activated
container and covered with a non-woven fabric or stainless steel mesh on the
carbonfront and back. Some cartridges have TEDA (triethylenediamine)
cartridge
impregnated* to the activated carbon to increase iodine collection efficiency.
This is filter paper made from highly adsorptive activated carbon (50%) andcellulose fiber, etc., and used to collect radioactive iodine and volatile
Activatedradioactive materials. Protective paper is attached to the front and back to
carbon filter prevent the activated carbon from falling out. Some are also impregnatedpaperwith 5% or 10% TEDA (triethylenediamine).
Equivalent to "filter paper type" specified in JIS Z 4336: 2010 "Radioactive
iodine samplers" [9] Annex A [filter material for iodine collection].
*Impregnating activated carbon with TEDA (triethylenediamine) or potassium iodide, etc., enables
efficient iodine collection. The collection efficiency varies depending on the amount of impregnatedsubstances: above a certain amount, the collection efficiency decreases. Generally, from 1% to 10%
is considered an appropriate amount [12]. However, there are also reports that from 0.1% to 1% isbetter for potassium iodide because it causes a decrease in the ignition point of activated carbon [13].

78Chapter 7 Continuous Measurement with Gas Monitors
7.1 Equipment
A gas monitor continuously measures the concentrations of gaseous radioactive materials such asradioactive noble gases. It is mainly used for monitoring around a reprocessing facility releasing
radioactive noble gases during normal operation. The basic information on gas monitors described inthis section is based on JIS Z 4317:2008 "Radioactive noble gas monitors" [10].
7.1.1 Equipment configuration
The gas monitor consists of a detector unit, an indicator, an alarm section, and a data transmitter,as shown in Figure 7-1. The functions of each part are shown in (1) through (4).
General matters(a) The equipment should be robust to withstand continuous operation and easy to operate andmaintain.
(b) The structure should resist vibration, impact, corrosive gases, etc.
(c) The structure should resist electromagnetic induction, static electricity, etc. In addition, thestructure should be designed to have little electromagnetic induction or other effects on otherequipment.
(d) It desirably has a self-diagnosis function to detect failures.
(e) If the measured value is sensitive to the flow rate, the meter must have functions capable ofmeasuring the flow rate of the sampling gas and controlling or adjusting it. The flow measurement
device should be equipped with a flow rate display device.
(f) If the measured value is sensitive to pressure, as in the case of an ionization chamber, it is desirable
to have a pressure gauge with an alarm and a function to control or adjust the pressure and to output
a warning for excessive pressure fluctuations. In addition, pressure gauges must be calibrated understandard conditions.

79

Figure 7-1. Example of equipment configuration(1) Detector unit
The detector unit circulates the sample air from which particulate matter has been removed throughthe detection tank to detect radiation from gaseous radioactive materials. It is composed of a suction
port, filter, detection tank, detector, flow meter, pump, and attached functional units.
The following are points to be noted in the detector unit.
 The structure should resist contamination and be easy to decontaminate or replace.
 The structure should allow a filter to be attached to the suction side of the sampler to remove
the effects of particulate natural radioactive materials, and the filter should be of a structurethat allows replacing without scattering the collected radioactive materials and does not collector retain noble gases. A monitor that measures ionization current should be structured so that
an ion removal device can be attached to the suction side of the sampler.
 Shielding elements, coincidence mechanisms, anti-coincidence mechanisms, etc., may be
added as necessary to reduce the effects of external γ-rays and noise.
(2) Indicator
The indicator measures signals from the detector unit, displays the indicated values, and outputs
them to the data transmitter.
An example specification of the indicator is shown below.
80






An analog or digital count rate meter, ammeter, or scaler provides an indication.
The units of the measured values are s-1, A, kBq/m3, etc., and the radioactivity concentration is
calculated by multiplying the conversion constant according to the nuclide of interest.
The unit of flow rate should be L/min, etc.
Display with date and time in tabular or graphical format.

(3) Alarm section
The alarm section detects when the device is abnormal or the indicated value exceeds a specific set
value. Examples of specifications for the alarm unit are shown below.
 When the indicated value exceeds the alarm set value, or in the event of equipment failure or
abnormality, a warning is issued by a lamp, buzzer, or other means.
 The notice should be maintained until reset or the cause is eliminated.
 Provide a test function to check alarm operation. If the alarm setting is variable, it must be
possible to set it within the effective measurement range and to check the alarm set value.
(4) Data transmitterThis part sends out the data collected by the indicator to the telemetry system, etc., via
communication equipment and also controls the gas monitor by receiving control signals from thetelemetry system, etc.
An example of data transmission items is shown in Table 7-1.
For data communication, the communication lines used by the facilities in the monitoring stationbuilding, if any, should be used. Communication lines are desirably multiplexed.

(a) Measured value(b) Status signal(c) Control signal(Received
information)

Table 7-1. Examples of data transmission items
Data transmission item
Count rate, radioactivity concentration, flow rate, measurement time,
date and time, and location information
High count rate, low count rate, detector reading anomaly, flow rateanomaly, power anomaly, adjustment in progress, measurement inprogress
Startup and stop

7.1.2 Detector types and measurement principles
The types of detectors used for gas monitoring are listed in Table 7-2.
Table 7-2. Types of detectors used in gas monitors
Detector type
Plastic scintillation detector
β-ray detector
GM counter
Vented ionization chamber81

(1) Plastic scintillation detector
Same as 3.1.5(2)(a)(2) GM counter
This measures the number of output pulses due to electron avalanche caused by electrons generated
by ionization of gas (Q gas, etc.) in the detector due to radiation incidence.
Since the output pulse height is independent of the initial ionization amount due to incident
radiation and remains constant, the output pulse has no energy information.
(3) Vented ionization chamberThis measures the total ionization current generated by radiation emitted from gaseous radioactive
materials released into the ionization chamber.
7.1.3 Example of equipment specifications
An example of gas monitor equipment specifications is shown in Table 7-3. Note that equipment
not listed in the example specifications may be used if it has the required performance.
For the performance of gas monitors, refer to the detection limit in Explanation B.
Table 7-3. Example of gas monitor specifications
Item
Type A
Type B
Measurement target
β-ray
Detector

Plastic scintillator

GM Counter

Type C
Vented ionizationchamber
5 L/min

Flow rate
6.5 L/min
60 L/minDetection tank
Approx. 30 L
Approx. 0.3 L
Approx. 14 L
volumeMeasurement
Continuous measurement
methodElimination of
external radiation
Lead shielding*2 , Pre-filter
effects*1
Power supply
100 V
100 V
100 V
Power consumption
500 VA
150 VA*1 In addition to the functions described here, background reduction functions such as removal of
cosmic ray effects by the anti-coincidence mechanism, noise reduction by the coincidence
mechanism, and ion removal by the ion precipitator (ionization chamber only) are added asnecessary.
*2 Add shielding of 2 to 5 cm thick, if necessary.

82

7.2 Installation, calibration, and inspection
7.2.1 Installation
Gas monitors should be fixed and installed indoors at the monitoring station building, etc.
Installation conditions should be the same as for dust monitors (3.3.1).
7.2.2 Calibration
The calibration of detectors used in gas monitors is described here. The flow meters are also
desirably calibrated periodically for proper evaluation of air suction amount.
(1) Calibration method
When installed, an actual gas calibration test using Kr-85 should be conducted. During
maintenance and inspection, sensitivity tests and plateau characteristic tests should use β and γ-ray
sources (Cl-36, Ba-133, Cs-137).
(2) Standard radiation sources for calibration
The standard radiation sources used for calibration are listed in Table 7-4.
Table 7-4. Standard radiation sources for calibration
Radiation type
Standard radiation source
β-ray
Kr-85 (standard radioactive gas)(3) Calibration frequency
Calibration is conducted at the time of installation.
After that, about once a year, during maintenance and inspection, the detection sensitivity should
be checked with Cl-36, etc., and if it deviates from the true value by ±15% or more, an actual gas
calibration test using Kr-85 should be conducted.
7.2.3 Inspection(1) Daily inspection
Daily inspection is conducted remotely by telemetry systems, etc., and at the installation location,
depending on the items.
(a) Contents are to be implemented remotely by a telemetry system, etc.
Example of daily inspection items
Are operation and communication proper?
Operation check
Is the flow rate normal?
Is a warning being issued?
Abnormal values
Are there any pronounced changes in the count rate and radioactivity
concentration?

83

(b) Contents are to be implemented at the installation location
Example of daily inspection items
Are operation and communication proper?
Operation check
Is the flow rate normal? (Adjust flow rate if necessary)
Is the operating noise of the pump normal?
Is a warning being issued?
Abnormal values
Are the count rate and radioactivity concentration normal?
OperatingIs the air conditioning in the station building working properly?
environment(2) Periodic inspection
An example of periodic inspection items by manufacturers is shown in Table 7-5.
Table 7-5. Example of periodic inspection items
Example of periodic inspection items(a) Visual inspection
Detector unit
Indicator
Cables and connectors(b) Stand-alone operation and performance test
Operation check
Alarm operation check
Count rate indication accuracy
Flow rate indication accuracy
Maximum airflow rate test
Leak test
Detector unit
Sensitivity test
Plateau characteristic test
BG check before and after nitrogen gas
replacement
Check for the lower limit of concentration
for measurement
Periodic replacement of consumables
Indicator
Recorder indication accuracy(3) Inspection frequency
Daily inspections include once-a-day inspections by the telemetry system, monthly inspections at
the installation location, etc.
Periodic inspections should be conducted approximately once a year.

84

7.3 Measurement(1) Startup of equipment
The system should be activated at all times for continuous measurements at normal times.
(2) Setting of measurement conditions
Set the measurement conditions for continuous measurement.
An example of measurement conditions is shown in Table 7-6, and notes on each item are described.
Table 7-6. Example of gas monitor measurement conditions
Item
Measurement conditions(a) Flow rate
This depends on the volume of the detectiontank.
(b) Measurement Continuous (measurements should be madetime
at least every hour)(a) Flow rate
Set the flow rate so that the air suctioned into the detection tank is replaced in approximately 10
minutes, depending on the volume of the detection tank. The rate in a 30 L detection tank should beapprox. 5 L/min.
(b) Measurement time
The measurement should be consecutive, and measurements should be made at least every hour.
To conduct surveys with a higher time resolution when abnormalities, etc., occur, measurements may
be obtained at shorter intervals, allowing us to calculate measured values every hour by using theactual measurements.
(3) Start of measurement
Start measurement.
Desirably, the telemetry system or other means can control the start and stop of measurement
remotely.
(4) Data transmission
Data on measurement information should be transmitted to the telemetry system at least once anhour. Alarms and other monitoring information should be transmitted to the telemetry system as soon
as possible after an abnormality occurs. An example of data transmission items is shown in Table 77.

85

Table 7-7. Example of data transmission items to telemetry system
Category
Component
Output item
Count rate (s-1)
Radioactivity
concentration (kBq/m3)
Measurement
Detector unit
information
Average flow rate (L/min)Integrated flow volume(m3)
Under measurement
Under adjustment
Detector unit
Power anomaly
Monitoring
Flow rate anomaly
information
Power anomaly
Indicator
High count rate
Low count rate(5) Calculation of radioactivity concentration
Calculate the hourly radioactivity concentration (kBq/m3) using Equation 7.1.

C=N×K

(Equation 7.1)

C: Radioactivity concentration (kBq/m3)
N: Net count rate (s-1)(Sample count rate - background count rate)
K: Concentration conversion constant (kBq/m3/s-1)
7.4 Evaluation of measurement results
Like other nuclear facilities, a reprocessing facility should investigate the cause when values
exceeding the upper limit of the normal fluctuation range (e.g., the maximum value measured overthe past several years) are measured. If a facility contribution is found or cannot be ruled out, theexposure dose due to the facility contribution should be evaluated.
However, since facility contributions to measured values may be recognized even when the
reprocessing facility operates normally, and the upper limit of the normal fluctuation range may be
exceeded, caution should be exercised in determining whether an increase in measured values
constitutes an abnormal situation.
Therefore, criteria are required to indicate a situation beyond the normal range of fluctuation,
justify the investigation of the cause, and determine if this is an abnormal situation. For example, one
should set a range of recorded measurements (including measurements where facility contributions
were recognized) obtained when the facility is under normal operating conditions and not underunusual weather conditions and evaluate the measurement results.

86

87

Explanation

88

89

Explanation A Validity of Airborne Radioactive Material Measurements
The Normal Time Supplementary Reference Material stipulates that the concentrations ofradioactive materials in the air should be measured to detect radioactive materials released from
nuclear facilities early.
Examples of actual measurements and calculations on the effectiveness of measuring radioactive
materials in the air are presented.
(1) Observation example during the accident at the TEPCO’s Fukushima Daiichi NPPIn Chiba City, Chiba Prefecture, an increase in gross β radioactivity concentration and β/α ratio
was found by dust monitors in the early morning of March 15, 2011. The increase in the air dose rateoccurred almost simultaneously.

Unit: nGy/h (Radiation dose rate), Bq/m3 (α in dust, β in dust)
Figure A-1. Observation example in Chiba City, Chiba Prefecture [14].
*The data after 6 hours of filter paper feeding until March 15, and data after 1 hour of filter paper
feeding after that.
*The increased air dose rates on March 1 and 7 were attributed to the effects of natural radioactive
materials from rainfall.

90

(2) Example of facility contribution detected after the decay of radon/thoron decay products
Although real-time observations could not be made as in (1), an example of detecting the presenceof a facility contribution after the decay of radon/thoron decay products is shown in (2).
In Niigata Prefecture, no significant increase in the β/α ratio of airborne dust collected on April 18,
2011, from 12:00 to 24:00 was observed in the measurement at the air sampling location (Figure A2(a)). However, a significant increase was observed in the β/α ratio 6 hours after air sampling (FigureA-2(b)). No significant increase was observed in the gross β radioactivity concentration after 6 hoursof air sampling (Figure A-2(c)).
In addition, the air dose rate at monitoring posts only increased due to rainfall, and no increase wasobserved due to the TEPCO's Fukushima Daiichi NPP accident.

91

(a) β/α ratio (10-minute value) at air sampling location (real-time measurement)(b) β/α ratio 6 hours after air sampling (10-minute value)(c) Gross β radioactivity concentration 6 hours after air sampling (10-minute value)*The horizontal axes in Figures (a), (b), and (c) are all measurement times. The data in the arrows
indicate the measurement results at the same air sampling time, but the arrow locations of (b) and (c)are different from the arrow locations of (a) because they were the results of measurements 6 hours
after air sampling.
Figure A-2. Observation examples in Niigata Prefecture [15].

92(3) Effectiveness evaluation by calculation
IAEA-TECDOC-1162 [16] provides conversion factors for every radionuclide from radioactive
material concentrations in the air-to-air dose rates (Table A-1).
Calculation using this conversion factor shows that an increase of 5 Bq/m3 in the concentration of
Cs-134 in the air would increase by 1.7 nSv/h in the air dose rate. However, the increase would be
difficult to detect at monitoring posts that measure air dose rates because the background fluctuations
would hide the increase.
Therefore, the dust monitors can discriminate and evaluate facility-derived radioactive materialsof 5 Bq/m3, thus enabling earlier detection than that of the monitoring post.
Table A-1. Conversion factors from radioactive material concentrations in the air to
air dose rates [16].
(Only conversion factors for radioactive Cs are excerpted.)
Conversion factor
Radionuclide(mSv/h)/(kBq/m3)
Cs-134
3.4E-04
Cs-136
4.8E-04
Cs-137/Ba-137m
1.3E-04
Cs-1385.2E-04

93Explanation B Detection Limit
Detection limits for measuring radioactive material concentrations in the air are shown in (1)through (3).
The detection limits listed here are values that can be reasonably achieved in light of current
technical standards and should be used as a guide for introducing equipment and setting measurement
conditions when measuring the concentration of radioactive materials in the air.
(1) Continuous measurement of radioactive material concentrations in the air using dust monitors
Table B-1. The detection limit of continuous measurement by dust monitor
Reference (measurement
Detection limit
conditions)
SampleGross αGross βMeasurement
radioactivity
radioactivity
Sample amounttime
concentration
concentration
Airborne dust
0.05 Bq/m3
0.10 Bq/m3
9 m3
1 hourMethod of calculating the detection limit
The detection limit is the value overestimated from the maximum detection sensitivity specified in
JIS Z 4316:2016 "Radioactive dust monitors" [5]. It is not a discrimination level for facility-derived
radioactive materials. The assumptions are the following: Detectors: α-ray ZnS(Ag) scintillator, β-ray plastic scintillator Detector size: 50 mm ϕ
 Equipment efficiency approx. 49% (gross α approx. 35% (gross β) Background count rate: α-ray 2 cpm, β-ray 15 cpm
 Flow rate: 150 L/min, test volume: 1 hour of integrated flow volume, collection efficiency:
100%.
(2) Precise analysis table of radioactive material concentrations in airborne dust collected by dust
samplers
Table B-2. The detection limit of γ-ray spectrometry
Reference (measurement
Detection limit
conditions)
SampleSample Measure Relative
Co-60
I-131
Cs-134
Cs-137amount ment time efficiency
Approx.
0.00740.00370.00740.0074
Approx.
4
3
10
m
80,000mBq/m3mBq/m3mBq/m3mBq/m320 %sec.
Airborne
dust, etc.
Approx.
0.037
0. 027*
0. 0350.030
Approx.
Approx.
70,000
3
3
3
3
3
mBq/m
mBq/m
mBq/m
mBq/m
3000 m40 %sec.
 Measurements of samples that were pretreated in U-8 containers for nuclides except for I-131
 I-131 was measured in raw samples in 2 L Marinelli containers
94

*Measurement using a detector with a relative efficiency approx. 30%.
Method of calculating detection limit (Table B-2, lower part)· The average value of the lower detection limit was obtained from the historical actual
measurement data of a representative sample using a detector with a relative efficiency of approx.
40 % (2L Marinelli with a relative efficiency approx. 30%).
· In actual measurements, background and other conditions vary depending on the shielding
material and installation environment, even when the same detector is used. Thus, the detection limit
was calculated by tripling the above-average value, assuming measurement under high backgrounddata conditions, and calculating an overestimated value in the aspect of "the detection limit even incomplicated conditions".
[The Series of Environmental Radioactivity Measuring Methods No.7]

SampleAirborne dust

Table B-3. The detection limit of uranium analysis
Reference (measurement
conditions)
Measurement
Detection limit
methodMeasurement
Sample amount
time
3
3
3
α spectrometry
1 µBq/m
10 m
20 hours.
ICP mass
0.001 µBq/m3
103 m3
10 sec.
spectrometry

Calculation method of detection limit(a) α spectrometry:
The detection limit was set to be three times the counting error associated with the net count rate
when the collection efficiency was 80%, the counting efficiency was 20%, and the background countrate was 1 count/20 hours.
(b) ICP mass spectrometry:
The detection limit was defined as three times the standard deviation of the background counts
when the background count rate was set to 5 s-1.
[The Series of Environmental Radioactivity Measuring Methods No.14]

SampleAirborne dust

Table B-4. Detection limit of plutonium analysis
Reference (measurement
conditions)
Measurement
Detection limit
methodMeasurement
Sample amount
time
3
4
3
α spectrometry
0.2 µBq/m
10 m
24 hours

Method of calculating the detection limit
Three times the counting error associated with a counting efficiency of 20% and a total count valueof α-rays from the nuclides was set as the detection limit.
[The Series of Environmental Radioactivity Measuring Methods No.12]95(3) Continuous measurement of gaseous radioactive material concentrations by gas monitors
Table B-5. The detection limit for continuous measurement by gas monitors
Reference (measurement
Detection limit
conditions)
SampleGross β radioactivity
Measurement time
concentration
Air
1 kBq/m3
1 hourCalculation method of detection limit
The value overestimated from the maximum detection sensitivity of the gas monitor using a plastic
scintillation detector (detection tank approx. 1 L, conversion constant (Kr) 2.8×10-3 Bq/cm3/s-1,
background count rate 14 s-1) was used as the detection limit.

96

Explanation C Concept of Dust Monitor Measurement Condition Setting
The effects of differences in measurement conditions on measurement results are described to assist
in setting up measurement conditions for dust monitors.
See Explanation E for the effects of radon/thoron decay products.
(1) Effects on measurement results due to differences in calculation methods for radioactive material
concentrations in the air
If the concentration of radioactive materials in the air is constant at 10 Bq/m3, the radioactivity on
the filter paper changes, as shown in Figure C-1 for a radionuclide with a long half-life (no physicaldecay during air sampling time) and a radionuclide with a short half-life (assuming radon decay
products, half-life: 30 minutes).
When collecting radionuclides with long half life, the radioactivity on the filter paper increases
linearly if the concentration in the air is constant.
On the other hand, for radionuclides with a short half-life (half-life: 30 min), the radioactivity
supplied on the filter paper increases linearly. However, the radioactivity on the filter paper becomesalmost constant over time because the radioactivity decreases on the filter paper due to physical decay
simultaneously. As a convenient assumption for interpreting Figure C-1, the radioactivity on the filter
paper is calculated on a 10-minute basis, and the increase in radioactivity every 10 minutes does notconsider the physical decay during the capture (during the relevant 10 minutes). For example, theradioactivity that is increased between 10 and 20 minutes after filter paper feeding is not corrected for
decay at 20 minutes after filter paper feeding. However, at 30 minutes after filter paper feeding, thephysical decay during 10 minutes between 20 and 30 minutes is considered.

Figure C-1. Change in radioactivity on filter paper97Dust monitors and air monitors measure radioactivity in collected airborne dust in two ways: (a)measuring as the average concentration starting from the filter paper feeding and (b) measuring as theaverage concentration per unit time based on the difference in count rates per elapsed time. If themethod described in (b) is used in normal times, it may be difficult to properly evaluate the difference
due to the short half-life of radon/thoron decay products, but we do not deny its use if it can be used
to evaluate the contribution of facility-derived radioactive materials.
As the basis of this measurement method, the dust monitor uses (a) the average concentration
starting from the filter paper feeding, and the air monitor uses (b) the average concentration per unittime.
The calculation method for each is shown below.
(a) Method of calculating average concentration starting from filter paper feeding(b) Calculation method of average concentration per unit time (formula below is for 10 minutes)

For cases where the radioactivity on the filter paper changes, as shown in Figure C-1, the resultsof calculating the average concentration starting from the filter paper feeding and the average
concentration per unit time of radioactivity in the collected airborne dust are shown in Figure C-2 andFigure C-3, respectively.
In the case of a radionuclide with a long half-life, the average concentration starting from the filter
paper feeding is not different from the average concentration per unit of time.
On the other hand, in the case of a radionuclide with a short half-life (half-life: 30 minutes), theaverage concentration starting from the filter paper feeding decreases over time because theradioactivity on the filter paper which is almost constant over time, is divided by the integrated flow
volume which increases linearly.
The average concentration for each unit time approaches zero over time because it is calculated by
dividing the difference in the count rates for each unit time by the integrated flow volume (constantvalue) for each unit time.
It should be noted that for radionuclides with short half life, this calculation method underestimates
the actual concentration of radioactive materials in the air (10 Bq/m3 in this case) in terms of both theaverage concentration starting from filter paper feeding and the average concentration per unit time.

98

Figure C-2. Radioactivity concentration in collected airborne dust (average concentration from filter
paper feeding)Figure C-3. Radioactivity concentration in collected airborne dust (average concentration per unit
time)
99

(2) Notes on the evaluation of the count rate
In dust or air monitor measurements, air sampling collects particulate radioactive materials in a
specific air volume on filter paper. The radioactivity concentration in the air (Bq/m3) can be calculated
by measuring the radioactivity of the radioactive materials on the filter paper (Bq) and the volume ofcollected air (m3). The radioactivity on the filter paper is determined by dividing the count ratemeasured by the detector by the equipment efficiency.
JIS Z 4316:2013 "Radioactive dust monitors" [4] state that dust monitor indication should be madeby a count rate meter or scaler.
Since this method is based on measurement during air sampling, a count rate meter isfundamentally used to obtain the count rate (instantaneous value) of airborne dust collected on filter
paper at the time of t hours after the filter paper feeding.
When calculating the count rate from the integrated counts measured by the scaler, care should betaken when measuring during air sampling, so the points to be noted are shown separately for the
calculation methods (1) (a) and (b).

100

(a) When measuring the average concentration starting from the filter paper feeding using a scaler
The measurement method of the concentration of radioactive materials in the air by dust monitors
or air monitors does not describe the measurement after air sampling. However, it describes therelationship between measurement time and count rate for the measurement after air sampling, asshown in a) in contrast with b).

a) When the integrated counts are obtained by measurement after air sampling
When measuring the concentration of radioactive materials in the air after air sampling, the countrate is constant, as shown in Fig. C-4 top right, since changes in the radioactivity on filter paper during
air sampling are irrelevant to subsequent measurements, and the radioactivity on filter paper during
measurement is constant for radionuclides with long half life. The count rate na can be calculated by
dividing the integrated counts by the measurement time ta.
Even if the concentration of the target radioactive material in the air is the same, for a radionuclide
with a short half-life relative to the measurement time, the count rate evaluated by dividing the
integrated counts by the measurement time is underestimated because the radioactivity physicallydecays with time even during measurement. The count rate decreases, as shown in the lower rightpanel of Figure C-4.

Figure C-4. Evaluation of integrated counts by measurement after air sampling
101b) When the integrated counts are obtained by measurement during air sampling
When obtaining the integrated counts by measurement during air sampling, even if the total
radioactivity collected is the same as in a), caution should be exercised when calculating the countrate because the radioactivity collected at a specific time does not contribute to the counts integrated
over the measurement time up to the specific time, and the integrated counts may differ, depending
on changes in the concentration of radioactive materials in the air during air sampling.
Assuming that the concentration of radioactive materials in the air is the same and constant as ina), when measuring during air sampling, the radioactivity on the filter paper during measurement
increases linearly for radionuclides with long half life, and the count rate increases with measurement
time, but the integrated counts are approx. a half of that of a), as shown in Figure C-5. Therefore,
simply dividing the integrated counts by the measurement time underestimates the count rate na thatshould be obtained.
Radionuclides with short half life also cause underestimation of the integrated counts for the same
reason as above, but on the other hand, the underestimation effect due to physical decay ofradioactivity is smaller than that of a). The reason is that the measurement is performed during air
sampling while the measurement of a) is performed after air sampling.
In actual measurements, changes in the concentration of radioactive materials in the air during air
sampling affect the measurement of integrated counts, as shown in Figure C-6. Thus, it is necessary
to note the trend of changes in the concentration of radioactive materials in the air when evaluating
data. Figure C-6 left figure shows the case where the concentration of radioactive materials in the air
tends to increase, and Figure ’-6's right figure shows the case where the concentration of radioactive
materials in the air tends to decrease. The magnitude of the slope of the count rate is proportional tothe concentration of radioactive materials in the air. The tendency to increase the concentration ofradioactive materials in the air is likely to lead to underestimation, while the tendency to decrease islikely to lead to overestimation.

Figure C-5. Evaluation of integrated counts by measurement during air sampling102

*The slope of the count rate represents the concentration of radioactive materials in the air.
Figure C-6. Effect of changes in the concentration of radioactive materials in the air on the
integrated counts(b) When the scaler measures the average concentration per unit time
The difference in count rates is based on the change in the count rate for each unit time, which ismeasured by the count rate meter from the previous time.
When the count rate is obtained by calculation from the integrated counts measured by the scaler,
dividing the difference in the integrated counts (S1-S3) every 10 minutes by the measurement time
(10 minutes) does not result in the count rate at the time of the tens of minutes, but in the count rate
at that intermediate time as shown in Figure C-7, leading to an underestimate of the count rate.

Figure C-7. Evaluation example of the difference in count rate calculated
from the integrated counts-1
103

The following is a method for obtaining a count rate as close as possible to the actual count rate at
tens of minutes from the integrated counts.
a. Method of estimating the count rate from the integrated counts for the relevant10-minute period
If the concentration of radioactive materials (nuclides with long half life) in the air during therelevant 10 minutes is constant, the count rate increases linearly. Thus, the count rate exactly at ten
minutes can be estimated by considering the integrated counts as the area of the triangle (from 0 to 10
minutes) or trapezoid (from 10 to 20 minutes) shown in Figure C-8. However, in an emergency, theconcentration of radioactive materials in the air is expected to change rapidly, as shown in Figure C8, from 20 to 30 minutes. In this case, the change in concentration during this period cannot be known,so the count rate must be estimated by assuming a constant concentration. Therefore, the count rate
exactly at 10 minutes can be calculated by considering the integrated counts for a 10-20 minutes period
as the area of a trapezoid while retaining the integrated counts (equivalent to the area of the filled-inarea for each period) for 20-30 or 30-40 minute periods. Therefore, it should be noted that when the
count rate at exactly 10 minutes is calculated, the deviation from the actual count rate at exactly 10
minutes may be large, depending on the circumstances of concentration changes during the process.

Figure C-8. Example of evaluation of difference in count rate calculated
from the integrated counts-2
b. Method to evaluate the count rate by shortening the divided time of the measurement of theintegrated counts
The shorter the time to measure the integrated counts, the closer the count rate at the end of theintegrated counts can be to the count rate measured by the count rate meter, even when the integrated
counts are simply divided by the measurement time. For example, the count rate obtained by dividing
the integrated counts from 9 to 10 minutes by 1 minute (60 seconds) is close to the count rate obtainedby the count rate meter at 10 minutes in Figure C-9. Another method uses the count rate calculated104

from the 10 integrated counts for every minute for 10 minutes to obtain the count rate at 10 minutes
exactly. It should be noted, however, that the uncertainty in the calculated count rate increases as theintegrated counts become smaller.

Figure C-9. Example of evaluation of difference in count rate calculated
from the integrated counts-3(3) Relationship between air sampling time and lower detection limit
Table C-1 shows an example of evaluating lower detection limits for α- and β-ray dust monitors.
The maximum detection sensitivity (scalar method) described in JIS Z 4316:2006 "Radioactive
dust monitors" [5] was calculated as the lower detection limit. This is not a discrimination level for
facility-derived radioactive materials.







Table C-1 Example of evaluation of detection limits for α- and β-ray dust monitors
The lower limit of detection (Bq/m3)
Air
SampleGross αGross βsampling
amountradioactivity
radioactivity
time
concentration
concentration
3
10 min.
1.5 m
0.07
0.4
3
1 hour9m
0.01
0.06
Flow rate: 150 L/min
Equipment efficiency: α-ray approx. 49%, β-ray approx. 35%
Detectors: α-ray ZnS(Ag) scintillator, β-ray plastic scintillator
Detector size: 50 mmϕ
Background count rate: α-ray 2 cpm, β-ray 15 cpm

105

Figure C-10. depicts the relation between air sampling times and lower detection limits at a flowrate of 150 L/min.

<Calculation conditions> Equipment efficiency: α-ray approx. 49%, β-ray approx. 35%
 Collection efficiency: 100%
 Detectors: α-ray ZnS(Ag) scintillator, β-ray plastic scintillator Detector size: 50 mmϕ
 Counting time: 2 min.
106

Background count value during 2 minutes: 2 counts for α-rays, 30 counts for β-rays
Figure C-10. Relationship between air sampling time and lower detection limit(above Gross α radioactivity concentration, below Gross β radioactivity concentration)(4) Relationship between flow rate and lower detection limit
Figure C-11 depicts the relation between flow rates and lower detection limits during one hour of
air sampling time.

107

<Calculation conditions> Equipment efficiency: α-ray approx. 49%, β-ray approx. 35%
 Collection efficiency: 100%
 Detectors: α-ray ZnS(Ag) scintillator, β-ray plastic scintillator Detector size: 50 mmϕ
 Counting time: 2 min.
 Background counts during 2 minutes: 2 counts for α-rays, 30 counts for β-rays
Figure C-11. Relationship between flow rate and lower detection limit(above Gross α radioactivity concentration, below Gross β radioactivity concentration)(5) Relationship between air sampling time and flow rate drop
The longer the air sampling time is, the larger the amount of airborne dust collected on the filter
paper is, and thus the lower the flow rate is.
Figure C-12 shows an example of evaluating the rate of decrease in flow rate using cellulose andglass fiber filter paper when the flow rate at the start of air sampling was approximately 200 L/min
and suction continued for approximately 10 days. The flow rate decreased by approx. 5% for 3 daysand 35% for 10 days.
It should be noted that the amount of airborne dust varies depending on the installation location of
the dust monitor and the season.

*If the rate of decrease in flow rate is negative, zero is displayed
Figure C-12. Example of evaluation of the rate of decrease in flow rate

108

Explanation D Efficiency of Dust Monitor
The concentration of radioactive materials in the air measured by dust monitors is calculated as theradioactivity concentration evaluated by a single standard radiation source used for efficiency
calibration, which does not consider the energy dependence of the α and β-ray detectors.
Since changing the standard radiation source used for efficiency calibration will also change themeasurement results, this method uses the standard radiation sources listed in Table 3-10 in the text
as a general rule.
(1) Standard radiation source
JIS Z 4316:2013 "Radioactive dust monitors" [4] states that the radiation sources used in the tests
shall be Cl-36 and Tl-204 as β radiation sources, Am-241 as α radiation source, Cs-137 as γ-radiation
source, etc. Other radiation sources may be used by agreement between the delivering and receiving
parties. Currently, Am-241 and Cl-36 are widely used for efficiency calibration of dust monitors forα- and β-ray measurement. For reference, Table D-1 lists examples of suitable radionuclides as βradiation sources as described in JIS Z 4316:2013.
In addition, traceability to national standards is ensured for the surface-emission rate of the standard
radiation sources for α- and β-ray dust monitors and for the radioactivity of the standard radiation
sources for γ-ray dust monitors.
Table D-1. Examples of radionuclides suitable as β radiation sources [4][5]β-ray maximum energy
NuclideHalf-life
(keV)
Ni-63
100.1 years
67
C-14
5700 years157
Hg-203 *1
46.61 days
213
Pm-1472.62 years
225
Ca-45
163 days
257
Co-60 *1
5.27 years318*1
Cs-13730.17 years
514 (94.4%), 1176 (5.6%)
W-185
75.1 days
433
Tl-204
3.78 years
764 (97.1%)
Cl-36
3.01×105 years
709 (98.1%)*1
Au-1982.695 days
961 (99.0%)
Sr-89
50.53 days
1495
P-32
14.26 days
1711
2
9
Natural uranium*
4.46 × 10 years
2269
Sr-90 + Y-90 *3
28.79 years
546, 2280*1 These nuclides also emit γ-rays. Cs-137 and Au-198 also emit internal conversion electrons, so
their effects should be considered.
*2 The half-life is the value for the main component, U-238, and the β-ray maximum energy is thevalue for the series nuclide, Pa-234. In addition, α- and γ-rays are emitted, so their effects should
be considered when using the product.
*3 Based on JIS Z 4329:2004 "Radioactive Surface Contamination Survey Meter" [11], 2280 keV is
used.
109

(2) Effects of changing the standard radiation source
Figure D-1 shows an example evaluation of a plastic scintillation detector for energy characteristics(dependence of efficiency on β energy)

Detector size: 50 mm
Distance between the detector and standard radiation source: approx. 3.5 mm
Figure D-1. Example evaluation of energy characterization of a plastic scintillation detector [17].
Dust monitors introduced in the past underwent efficiency calibrations using U3O8 (α and βradiation) sources*. There may be cases where those efficiencies continue to be used. However, inprinciple, the standard radiation sources in Table 3-10 should be used, and their use for efficiency
calibrations is not recommended.
Note that if the standard radiation source used for efficiency calibration changes, the efficiency andthe measured value calculated by the efficiency will also change.
*The Japan Radioisotope Association stopped selling uranium (U3O8) radiation sources, which
are internationally controlled materials, in 1997.
An example of the evaluation of the difference in counting efficiency between the U3O8 (α and β)radiation sources used in the past and the Am-241 (α) and Cl-36 (β) radiation sources listed in JIS isshown in Table D-2.

110

Table D-2. Evaluation example of the difference in counting efficiencyof U3O8 (α and β) radiation sources with Am-241 and Cl-36 sources
α-ray efficiency
β-ray efficiency
U3O8 (4.2 MeV)
Am-241 (5.5 MeV)
U3O8 (2.3 MeV)
Cl-36 (0.7 MeV)
18%
24%
30%
22%
Detector: α-ray ZnS(Ag) scintillation detector
β-ray Plastic scintillation detector
Both detectors have an effective area of approximately 50 mm and lead shielding ofapproximately 1.5 cm thick.
(3) Effect of different distances between the standard radiation source and detector in the efficiency
calibration
Figure D-2 shows an example of an evaluation of the change in detection efficiency when the
distance between the standard radiation source and the detector is changed. The detection efficiency
decreases as the distance increases, and the amount of change is larger for α-rays with a shorter range.
For this reason, it is essential to perform efficiency calibration under precisely the same conditions
as the geometrical arrangement of the filter paper and detector.

Detection efficiency (%)

-ray (Am-241)
-ray (Cl-36)

Distance between standard radiation source and detector (mm)*Evaluation by Monte Carlo simulation (simulation conditions are the same as in (4))
Figure D-2. Evaluation example of changes in detection efficiency when the distance
between the standard radiation source and the detector is varied111

(4) Calculation of detection efficiency using Monte Carlo simulation
The Monte Carlo method can calculate the interaction between charged particles and detectors tosimulate the detection efficiency for radiation sources of various energies.
Detection efficiencies were calculated from Monte Carlo simulations with Geant4 using thegeometries shown in Table D-3 and Figure D-3 (Mylar membrane + ZnS(Ag) scintillator + plastic
scintillator).
As shown in Figure D-4, the detection efficiency varied greatly depending on the energy of thenuclide, and both ZnS(Ag) scintillators and plastic scintillators tended to have low detection efficiency
for low-energy nuclides.

Detector
Myla film
ZnS(Ag)scintillator
Plastic
scintillator

Table D-3. Geometry parameters used in the simulation
ChemicalDensity
Diameter (cm)formula(g/cm3)C6H8O4
1.4
5

Thickness
4.5 μm

ZnS

4.09

5

7.2 μm

C9H10

1.032

5

0.5 cmFigure D-3. Geometry used for Monte Carlo simulation

112

Figure D-4. Example of detection efficiency evaluation using Monte Carlo simulation

113

<Detection efficiency calculation method>· Simulation of the energy (energy spectrum) given to each detector (ZnS(Ag) scintillator or plastic
scintillator) using Geant4.10.06.
· Number of decays of each radionuclide: 1,000,000· The detection efficiency is calculated by dividing the total counts of energy spectra by the numberof emissions.
· The detection efficiency includes the effects of radiation outside the measurement target, such as
γ-rays.
· Radiation source efficiencies and radiation source surface emission rates are not considered.

114

Explanation E Effect of Radon-Thoron Decay Products on Dust Monitor Measured Values
The measured value of the dust monitor is calculated as the radioactivity concentration in the
airborne dust collected on the filter paper. In the natural environment, the main radioactive materials
in airborne dust that emit α- or β-rays are radon/thoron decay products.
Radon is Rn-222 in the uranium series, and thoron is Rn-220 in the thorium series. Even if theradioactivity concentration of radon and thoron decay products in the air is constant, the radioactivity
concentration of radon and thoron decay products in airborne dust collected on filter paper varies dueto the effects of increase and decay by collection and sequential decay. Figure E-1 shows the decay
diagram of radon/thoron.

Figure E-1. Major decay diagram of radon/thoron(1) Evaluation by actual measurement
For Company A dust monitors, which can measure the approximate radioactivity concentration ofradon/thoron by spectral analysis, and Company B dust monitors, which can measure the gross α andgross β count rates, measurements were continued with the pump stopped after 6 hours of air sampling.
The relationship between the standing time after air sampling and the decay of radon/thoron was
evaluated (Figure E-2).

115

Figure E-2. Evaluation of radon-thoron impact based on actual dust monitor measurements(Top: gross α, bottom: gross β)
The decay patterns of the gross β count rate and radon were almost identical, with a half-life ofabout 30 minutes. The gross β count rate decreased to a BG count rate approximately 2 hours after
stopping the air sampling.
*The actual measurement value of BG count rate (measured with uncollected filter paper after thepump stops) for α was 0.02 s-1 and for β approximately 0.3 s-1.
(2) Evaluation by calculation
Assuming that each of the radon decay products Po-218, Pb-214, Bi-214, and Po-214 is present in
the air at a constant concentration of 5 Bq/m3, Figure E-3 shows the change in radioactivity on filter
paper when sampling the air at a flow rate of 100 L/min and collection efficiency of 100%. The
radioactivity on the filter paper is calculated on a minute-by-minute basis.
The air sampling increases radioactivity on the filter paper. On the other hand, the radioactivity
decreases due to radioactive decay and becomes constant over time.

116

Figure E-3. Change in radioactivity (uranium series) on filter paper
Figure E-4 shows the change in radioactivity on filter paper when each of Po-216, Pb-212, and Bi212, which are thoron decay products, are present in the air at a constant concentration of 0.1 Bq/m3.
The air is collected at a flow rate of 100 L/min and a collection efficiency of 100%. The radioactivity
on the filter paper was calculated on a minute-by-minute basis.
The radioactivity on the filter paper increases almost linearly with air sampling. The radioactivity
is not constant, as in the uranium series shown in Figure E-3, and that reflects the effect of Pb-212,
which has a long half-life of about 11 hours.

Figure E-4. Change in radioactivity (thorium series) on filter paper

117

Explanation F Distinction Methods for Facility-Caused Radioactive Material Contribution in
Dust Monitor Measurements
Table F-1 shows the methods for distinguishing the radioactive materials caused by nuclear
facilities contributing to dust monitor measurements. Since the measurement target in dust monitors
differs depending on the nuclear facility, the appropriate distinction method should be selectedconcerning Table F-1.
Table F-1. Distinction method and distinction target for facility-caused radioactive material
contribution
Distinction methods
Distinction targets
Reference
Method using β/α ratio
Gross β radioactivity concentration
Body text
Methods using α-βGross α radioactivity concentration,
F.1
coincidence counting
gross β radioactivity concentration
Methods using spectral
Gross α radioactivity concentration,
F.2
analysisgross β radioactivity concentration
Methods using normalized
Gross α radioactivity concentration,
F.3
countsgross β radioactivity concentration
Methods using unfolding
γ-emitting nuclide concentration
F.4

118

F.1 Method using α-β coincidence counting
Since β decay of Bi-214 (half-life: approximately 20 minutes), a decay product of radon, and α
decay of Po-214 (half-life: approximately 160 µs), a decay product of Bi-214, occur almost
simultaneously, α- and β-rays are emitted almost simultaneously (Figure F-1).
In the absence of facility-caused radioactive material effects, the regression equation can be used
to evaluate the estimated natural α-ray count rate by taking advantage of the strong positive correlation
between the measured α-β coincidence count rate due to natural radioactive material and the measured
α-ray count rate (Figure F-2).
Obtaining the measured α radioactivity concentration from the measured α count rate andsubtracting the estimated natural α radioactivity concentration from the measured α radioactivity
concentration allows estimating facility-caused radioactivity concentration and distinguishing thefacility-caused radioactive material contribution. However, large contributions from thorium-series
nuclides could slightly reduce the distinction ability because the increased proportion of thoriumseries nuclides is not counted simultaneously.
According to the evaluation by Togawa et al. [18], the level at which the effects of facility-caused
radioactive materials (α-emitting nuclides) could be determined was 1.3 Bq/m3 (Figure F-3).
There is also a strong positive correlation between the measured α-β coincidence count rate andthe measured β-ray count rate that makes this method effective for estimating the facility-caused β
radioactivity concentration as well as the facility-caused α radioactivity concentration (Figure F-4 andFigure F-5).
Evaluation method
Estimated natural α count rate (s-1) = a × Measured α-β coincidence count rate (s-1) + b
a, b: constants obtained by the regression equation
Estimated natural α radioactivity concentration (Bq/m3) calculated from estimated natural α countrate (s-1)
Estimated facility-caused α radioactivity concentration (Bq/m3)＝ Measured α radioactivity concentration (Bq/m3) – Estimated natural α radioactivity
concentration (Bq/m3)

119

Figure F-1. Radon decay diagram

Figure F-2. Evaluation example of correlation plot between α-β coincidence count rate and gross α
count rate [18].

120Estimated  radioactivity Measured  radioactivity
concentration (Bq/m3)
concentration (Bq/m3)

Max. 7.3 Bq/m3

Apr. May

Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar.

Max. 1.3 Bq/m3

Apr. May

Jun. Jul. Aug. Sep. Oct. Nov. Dec. Jan. Feb. Mar.

Figure F-3. Evaluation example of estimated facility-caused α radioactivity concentration [18].
(Top: Change over time of measured α radioactivity concentration(differential evaluation per unit time),
Below: Change over time of estimated facility-caused (estimated artificial in
the figure) α radioactivity concentration)<Measurement conditions (Figure F-2 and Figure F-3)>· Measurement items: α count rate, β count rate, α-β coincidence count rate (coin gate: 100 to 400
μs)· Detector: ZnS (Ag) + plastic scintillation detector· Air absorbent: cellulose/glass fiber long filter paper· Air sampling flow rate: 180 L/min· Suction port heigh: approx. 3.1 m above ground· Air sampling cycle: 24 hours

121

Estimated artificial  radioactivity
concentration (Bq/m3)

Measured  radioactivity
concentration (Bq/m3)

Figure F-4. Evaluation example of correlation plot between α-β coincidence count rates
and gross β count rates [18].

Jun.

Jul.

Aug.

Sep.

Jun.

Jul.

Aug.

Sep.

Figure F-5. Evaluation example of estimated facility-caused β radioactivity concentration [18].
(Top: Change over time of measured β radioactivity concentration (differential evaluation per unittime), Below: Change over time of estimated facility-caused (estimated artificial in the figure) β
radioactivity concentration)<Measurement conditions (Figure F-4 and Figure F-5)>
Same as Figures F-2 and F-3

122F.2 Methods using spectral analysis
Analyzing the spectrum measured by the silicon semiconductor detector enables measuring thegross α and β radioactivity concentrations due to facility-caused radioactive materials by correcting
for the effects of radon/thoron decay products (natural radioactive materials).
Regarding the evaluation of gross α radioactivity concentration, as shown in Figure F-6, the αenergy emitted by uranium and plutonium differs from that of the radon/thoron decay products thatcan be distinguished as different peaks in the spectrum. Figure F-7 shows an example of the results
obtained after correcting for the amount by the influence of radon/thoron decay products by spectral
analysis. The facility-caused gross α radioactivity concentration is calculated from the obtained α-ray
net count rate.
For the evaluation of the gross β radioactivity concentration, since β- and γ-rays are counted in thesame range as shown in Figure F-6, the facility-caused gross β radioactivity concentration is calculated
from the obtained β-ray net count rate by subtracting the γ-ray contribution contained therein and the
α-ray contribution due to the effect of radon-thoron decay products using the following formula. Notethat a separate detector to correct for the γ-ray background is required to evaluate the γ-ray
contribution.
The formula for evaluation of β-ray net count rate
β-ray net count rate = (count rate in β + γ range) - (count rate in α range × contribution factor
to the β range)- (count rate in the γ range of the detector for γ-ray background correction
× correction factor)
Table F-2 shows evaluation examples of decision thresholds. Some products can set the distinctionlevel of gross α and β radioactivity concentrations due to facility-caused radioactive materials to 1
Bq/m3 or less.

123

Figure F-6. Example of spectrum measured with a silicon semiconductor detector [19].

RaA: Po-218 (6.0 MeV), RaC': Po-214 (7.7 MeV),
ThC: Bi-212 (6.1 MeV), ThC': Po-212 (8.8 MeV)
Figure F-7. Evaluation of facility-caused radioactive material contribution by spectral analysis [19].

124Table F-2. Evaluation examples of decision thresholds [19].
α concentration (DT: 1 hour, flow rate: 40 L/min)
222
Rn
α concentration
Radioactivity
CTStandard
Decision thresholdconcentration (min.)deviation (Sb)
(Bq/m3)3
3(Bq/m )
(Bq/m )
5
0.127
0.295
10
20
0.071
0.165
60
0.041
0.095
5
0.184
0.427
20
20
0.099
0.230
60
0.057
0.132
5
0.226
0.524
30
20
0.113
0.262
60
0.065
0.151
5
0.255
0.592
40
20
0.127
0.295
60
0.073
0.169

β concentration (CT: 5 min, DT: 1 hour, flow rate: 40 L/min)
β concentration
γ air dose rate
Standard
Decision threshold(μSv/h)deviation (Sb)
(Bq/m3)(Bq/m3)
0.1
0.09
0.21
1
0.27
0.63
10
0.86
2.00
100
2.73
6.33
Detection sensitivity: α-ray: 24% min (up to 5.7 MeV), β-ray: 24% min (Cl-36 or Sr-90)
Sb: Standard deviation of background
CT: Counting time
DT: Time to find the average value of concentration*Standard deviation is inversely proportional to √CT⸱DT

125

F.3 Methods using normalized counts
The normalized count is an index value designed to monitor in real-time the contamination of
artificial β radioactivity with long half life, such as I-131 and Cs-137, based on the assumption thatnatural radioactivity, such as radon decay products with short half life, is always present in airborne
dust radioactivity [20].
The normalized counts are prepared by dividing the gross α and gross β counts obtained from dust
monitors by their respective historical averages and normalizing them. In this monitoring, thepossibility of contamination with artificial β radioactivity and the concentration of artificial gross β
radioactivity are estimated based on the fact that if airborne dust radioactivity comes only from natural
sources, the ratio will be approximately 1.
This section describes the method using normalized counts, with a case study of its introduction in
Fukui Prefecture.
1. Dust monitor specifications used in Fukui Prefecture· Measuring method: simultaneous measurement of suction and measurement (intermittent
filter paper feed for 3 hours)· Detector: ZnS (Ag) + plastic scintillator· Collection filter paper: Cellulose glass fiber filter paper (HE-40T)· Suction air flow rate: 100 L/min (with flow control)· Measurement items: integrated count value from filter paper feed (gross α, gross β, α-βcoincidence), integrated flow volume from filter paper feed
· Data collection interval: every 10 minutes· Analysis processing: implemented by collection and analysis server
2. Basic flow of data analysis process
Figure F-8 shows a schematic representation of the change in radioactivity on filter paper fromfilter paper feeding in dust monitor measurements, where (1) is assumed to be artificial radioactivity(I-131) with a half-life of 8 days and (2) is assumed to be radon decay products with a half-life of 30
minutes.
Monitoring airborne dust radioactivity with dust monitors requires considering the difference
between (1) and (2). In this monitoring method, the level of airborne dust radioactivity is first
determined based on (2) as the natural part and used to calculate the excess β count. Then, the grossβ count of the artificial part is estimated using a conversion formula based on (1).

126

Figure F-8. Radioactivity on filter paper when suctioning 1 Bq/m3

127

3. Procedures for preparing normalized counts
The airborne dust radioactivity concentration of natural origin varies depending on the topography,
geology, etc., around the station where the dust monitor is installed. Accordingly, all of the following
procedures should be conducted for each station.
Procedure

(a)

(b)

(c)

(d)

Operation details
In the past period without artificial radioactivity effects, for every elapsed
time since the filter paper feeding (in this case, every 10 minutes of the datacollection interval), the integrated count values of gross α and gross β are
taken as a specimen for variables X and Y, and the mean value and firstorder regression equation (Y = A × X + B) are obtained.
* The integrated count value, in this case, shall be the integrated countvalue, including the background count value when airborne dust is not
sampled.
For the specimen for every elapsed time in step (1), subtract the intercept
B from the variable Y to make a variable Y' as a new specimen of gross β
integrated count value and obtain the average value of Y'.
* Intercept B in Table F-3 dominantly includes background counts of βcounts (approximately 20 cpm for dust monitors in use) and may also
include contamination effects during filter paper standby and is determinedby subtracting the total of these backgrounds and effects from intercept B.
This operation does not change the slope A of the first-order regression
equation in Table F-3. However, the intercept B becomes "0" and presents
the relationship between variables X an Y' as a regression line passing
through the origin.
The mean Xm and intercept B in Table F-3 and the mean Y'm in Table F4 are used as the basic statistical values of the past data necessary fornormalization and are databased in the collection and analysis server bystation and by elapsed time since filter paper feeding.
Assuming that the specimen of past measurements belongs to the same
population as the specimen of subsequent measurements, data undermeasurement are processed according to 1) to 3) using the basic statisticalvalues in step (c) for every elapsed time since filter paper feeding.
1) The gross α integrated count values at the current time are divided by
the past average value Xm to calculate the normalized counts (base Cα)that are used as the level of gross α radioactivity concentration in the air
at the current time.
2) The normalized counts (base Cβ) are calculated by subtracting the pastintercept B from the gross β integrated counts at the current time andthen dividing the value by the past average value Y'm and used as thelevel of gross β radioactivity concentration in the air at the current time.
3) The normalized count ratio at the current time (base Cβ/α ratio) is
calculated by dividing the base Cβ by the base Cα to be used as the rating
scale of artificial β radioactivity contamination.
* From Explanation a, if the airborne dust radioactivity at present is onlyof natural origin, the base Cβ/α ratio can be expected to be approximately
128

Reference

Table F-3.

Table F-4.

Explanationa

Explanationb
Explanationc
ExplanationdExplanation
e

(e)

(f)

1. If there is significant contamination with artificial β radioactivity, thebase Cβ/α ratio is expected to be higher than the fluctuation range of thenormal time.
Assuming that the base Cα is only of natural origin and that the expectedvalue of the base Cβ/α ratio is "1" in normal times, the estimated surplus β
integrated count value ZCβ estimated is obtained by the following formulawith contamination of artificial β radioactivity simulated.
ZCβ = (base Cβ/α ratio -1) × base Cα ×Y'm
Y'm: Y'm in Table F-4 at the relevant elapsed time from filter paper
feeding.
Based on ZCβ, the estimated artificial gross β radioactivity concentration
Aβ (Bq/m3) at the current time is calculated using the following formula.
Aβ = 2 × ZCβ ÷ EF ÷ ECl ÷ Eβ ÷ (t × 60) ÷ (DF /1000)
×2: Weight constants for integrated counts in the case ofsimultaneous measurement of suction and measurement
EF: Collection efficiency of dust monitor (≈0.77)
ECl: Counting efficiency of the detector with calibration source Cl36 (≈ 0.21)
Eβ: β-ray expression efficiency of filter paper (= 1.0)
t: Elapsed time from filter paper feeding (min)DF: Integrated flow volume from filter paper feeding (L)Supplement 1: EF = Collection efficiency of HE-40T for airborne dust(≈0.85)× Loss for monitoring airtight mechanism leakage (≈0.9)[21].
Supplement 2: Since the β energy (0.709 MeV) of the calibration
radiation source Cl-36 is close to the β energy (0.606 MeV)of I-131, Aβ can be regarded as the concentrationconsidered as I-131.

129

Table F-3. Example of correlation (Y = A × X + B) between gross α integrated counts (X)and gross β integrated counts (Y)Elapsed time from180
10 min. 20 min.
30 min.
...
60 minutes...
the filter paper feedmin.
Gross α integrated
count average value
217.6
708
1460.3...
5024... 28918.6(Xm)
Gross β integrated
count average value
748
2313.94679.3...
15459.8... 83465.8(Ym)
The slope of a firstorder regression
2.43042 2.64910
2.76874...
2.83175... 2.74468
equation (A)The intercept of afirst-order regression
219.1
438.2
634.7
...
1233.2...
4093.5equation (B)Correlation
0.99230.99580.9968...
0.9973...
0.9973coefficient (r)*Calculated from approximately 2900 samples from the Urasoko observation station in 2019.
Table F-4. Example of correlation (Y' = A × X + B') between gross α integrated counts (X)and gross β integrated counts (Y') after subtracting the intercept
Elapsed time from the60
10 min. 20 min. 30 min.
...
...
180 min.
filter paper feedingminutes
Gross α integrated count
217.6
708.0
1460.3...
5024...
28918.6
average value (Xm)
Gross β integrated countaverage value after
528.9
1875.74044.6...
14226.6...
79372.3
intercept subtraction(Y'm)
The slope of a first-order2.43042 2.64910 2.76874...
2.83175...
2.74468
regression equation (A)The intercept of the firstorder regression equation
0.0
0.0
0.0
...
0.0
...
0.0
(B')
Correlation coefficient
0.99230.99580.9968...
0.9973...
0.9973(r)*Calculated from approximately 2900 samples of Urasoko station observations in FY 2019.

130

Explanation a. Sample space by normalization
For the variables X and Y's, for every elapsed time since the filter paper feeding, divide the variable
X by its average value Xm to make a new variable X" and divide the variable Y' by its average value
Y'm to create a new variable".
When the average values of these variable X" and Y" are obtained, the values of both are exactly"1".
∵ According to a theorem of statistics, if each variable that makes up that specimen is divided
by its average value, each variable will always be a specimen with an average "1". (Definitionof normalization here)
Therefore, these new specimens of variables X" and Y" are replaced by the relation Y" = 1 × X"
+ 0 at any elapsed time since the regression line passes through the point (1, 1). Thus, the intercept of
the first-order regression equation is "0".
∵ According to a statistical theorem, the regression line between variables U and V always
passes through the intersection of the averages of variables U and V.
Therefore, since the average value of normalized gross α and gross β integrated counts is "1"
independent of the time elapsed since the filter paper feeding, and since they maintain a very highcorrelation (0.98 or higher of correlation coefficient in the example in Table F-4), it is expected that
their ratio will always remain approximately "1".
Explanation b Meaning of normalized count = 1
In normal times, it is presumed that the identity of the airborne radioactivity is mainly radon decay
products, but their concentration is unknown.
The long-term time-series variations in the radioactivity concentration of airborne dust in normal
times are divided into short-time samples, such as 3 hours (corresponding to the filter paper feeding
interval of the dust monitor). These samples are then grouped into groups every 10 minutes(corresponding to the data collection interval of the same monitor) from the starting time(corresponding to the filter paper feeding time of the same monitor). If the original time series period
is sufficiently long, short-term variations in concentration, daily periodic changes due to nighttime
calm weather, and seasonal differences in concentration will be canceled out, and the average value
will be homogenized to the average value for the entire period.
Furthermore, when considering the correspondence with the dust monitor measurement, thevariation of the integrated count average Xm and Y'm of gross α and β with the filter paper feedingtime corresponds to the change of the area between the graph (2) and the suction time axis in Figure
F-8, because the target measured in normal times is mainly radon decay products. The values of Xm
and Y'm for which the data collection period is sufficiently long can be viewed as the integrated counts
per filter paper feeding elapsed time corresponding to the average radioactivity concentration of
airborne dust at the observation point in question, for the reason of homogenization mentioned above.
Therefore, the gross α and β integrated counts at a certain time divided by Xm and Y'm can betreated as a multiple (relative concentration) of the past average radioactivity concentration of airborne
dust at the observation point, independent of the time elapsed since the filter paper feeding.
Therefore, "1" in the normalized count corresponds to the average value of the past airborne dust
radioactivity concentration at the observation point. The normalized count can be an index value
representing the airborne dust radioactivity concentration level.

131Explanation c Concentration conversion of radon decay products
Procedures (1) through (3) and Explanations a and b have assumed that natural radioactivity mainly
originates from radon decay products, but the conversion of radon decay products to airborne
concentrations is difficult because of the following points.
· No standard radiation source matches the energy of α- and β-rays emitted by each radon decay
product, and it is difficult to obtain the counting efficiency of the detector for each energy.
· Dust monitors that measure gross radioactivity do not provide information on the energy of α andβ radiation, making it difficult to determine the ratio of each radon decay product.
Explanation d Correction by integrated flow volume
If the integrated flow volume variation is large, steps (1) through (4) should be corrected by the
integrated flow volume.
Explanation e Monitoring of gross α radioactivity by α-β coincidence counting
Regarding the integrated counts of α-β coincidence counting for the radon decay product Po-214,
the normalized counts can be obtained by operating steps (1) to (4) to be used as supplementary
information for the radioactivity concentration level of natural origin.
The α-β simultaneous normalized counts agree well with the gross α and gross β normalized counts
in the confirmation results in normal times (see Figure F-9), and the α-β simultaneous normalizedcounts can be given as an index value of the radioactivity concentration level of natural origin in thecase of monitoring based on the assumption that artificial components contaminate the gross α counts.
In the dust monitor in use, the background count values of gross α counts and α-β coincidence
counting are sufficiently smaller than the count values based on the collected airborne dust
radioactivity so that omitting the operation of subtracting the intercept as in the case of gross β counts
will not make any effect in the relationship between the two.

132

4. Monitoring status by normalized counting
The following is an example of the monitoring results when the basic statistical values are obtained
from the 2019 measurements and applied to the normalization of the 2020 measurements.
(1) Example of time-series analysis results in normal times
Figure F-9 shows a 10-minute time series graph at a time when the normalized counts reached thehighest value for the year in the Urasoko station, which has a large diurnal variation,
The normalized counts for gross α (green), gross β (red), and α-β coincidence (black) exceeded 12near dawn on July 18 when air conditions were stable and fell below 1 in the afternoon of the same
day when concentration levels dropped. However, the changes were in good agreement with eachother. While the normalized counts changed largely, the β/α ratio of the normalized counts expressed
as a percentage (blue) remained stable within the range of 100 ± 20 %, and the estimated artificial
gross β radioactivity concentration (indicated as "dust iodine equivalent concentration") (purple) was
almost within the range of 0 ± 5 Bq/m3.

Figure F-9. Example of 10-minute time series monitoring data
(Urasoko Station, July 17 – July 18, 2020)(2) Example of monitoring result statistical values
Table F-5 summarizes the annual statistics of one-hour values (60, 120, and 180 minutes after filter
paper feeding) for the results monitored at 11 observation stations in Fukui Prefecture. The range ofdata in the table indicates the degree of variation among stations.
Since the integrated count values are low immediately after the filter paper feeding and theevaluation values are scattered, the statistics for only the one-hour values after filter paper feeding(values at 60 minutes after filter paper feeding) are shown in parentheses.
Based on these statistical results, if the normal fluctuation ranges in normal times of the normalizedcount β/α ratio and the estimated artificial gross β radioactivity concentration, which are the rating133

scales of artificial β radioactivity contamination, are set to "average value ± 3 × standard deviation",
the fluctuation range of the normalized count β/α ratio is about 100 ± 20% and that of the estimatedartificial gross β radioactivity concentration is about 0 ± 2 Bq/m3.
Examining the individual data showed that above 2 Bq/m3 of the estimated artificial gross β
radioactivity concentration occurred when the concentrations were relatively high, with the gross α
normalized count exceeding 2. However, the normalized count β/α ratio at the same time wasconfirmed to be within approximately 120%.
Table F-5. Example of annual monitoring result statistical values
based on normalized counts (FY2020)
Maximum
Minimum
AverageStandard
value
value
value
deviation
Gross α normalized
3.87 to 18.39
0.03 to 0.07
0.89 to 0.93
0.51 to 0.86
countsGross β normalized
3.81 to 18.48
0.02 to 0.05
0.91 to 0.94
0.52 to 0.89
countsα-β coincidence
3.83 to 19.88
0.03 to 0.05
0.89 to 0.93
0.51 to 0.84
normalized counts
Normalized counts
β/α ratio (%) (1121.3 to99.2 to 103.0
5.2 to 6.7
56.4 to 82.7
hour value after
133.3(99.2 to103.2)(5.5 to 6.9)
filter paper feeding)
Estimated artificial
gross βconcentration-0.0 to 0.1
0.3 to 0.5
2.1 to 6.4-1.2 to -4.6
3
(Bq/m ) (1-hour(-0.0 to 0.2)
(0.4 to 0.6)
value after filter
paper feeding)134F.4 Methods of unfolding
Unfolding the pulse-height spectrum of γ-rays measured by a radiation detector (NaI(Tl)scintillation detector) using the response function of the detector enables evaluation of theradioactivity concentration of artificial radionuclides in the air.
Unfolding is a technique for deriving energy spectra from pulse-height spectra using the response
function of a detector and can improve the accuracy of the qualitative and quantitative determinationsof radionuclides.
The response function of the detector used for unfolding differs from the conventional response
function for measuring the air dose rate (see The Series of Environmental Radioactivity Measuring
Methods No.17, "Environmental gamma ray measurement method using continuous monitoring"). It
must be derived from the Monte Carlo simulation, taking into account the geometric relationshipbetween the detector and the dust collecting area on the filter paper that serves as the radiation source
and material properties, as shown in Figure F-10.
An example of unfolding results from this method is shown in Figure F-11, and an evaluation
example of decision thresholds for artificial radionuclides is shown in Table F-6.

Figure F-10. Image diagram of unfolding [22].

135Figure F-11. Example of unfolding results [22].
Table F-6. Example of decision threshold evaluation [22].
Decision
Operation cycle
Nuclide3
threshold (Bq/m )(Minute)
Co-60
0.3
60
Cs-1340.9
30
Cs-1370.8
30Measurement conditions: flow rate 100 L/min, air dose rate β approx. 0.05 μSv/h136

The Series of Environmental Radioactivity Measuring Methods No.36
Method for measurement of radioactive materials in the airPart 2: Measurement of Radioactive Materials in the
Air in Emergency Situations

137

138

Table of Contents
Part 2: Measurement of Radioactive Materials in the Air in Emergency Situations
Chapter 1 Introduction...............................................................................................................................142
Chapter 2 Basics and Scope of Application ..............................................................................................143
2.1 Puropse of Measurement ...........................................................................................................144
2.2 Equipment Used and Flow of Use ............................................................................................145
Chapter 3 Continuous Measurement by Air Monitor................................................................................150
3.1 Equipment .................................................................................................................................151
3.2 Air Absorbent ............................................................................................................................153
3.3 Installation, Calibration, and Inspection ...................................................................................153
3.4 Measurement .............................................................................................................................154
3.5 Evaluation of Measurement Results..........................................................................................156
Chapter 4 Analysis of Air Samples Collected by Air Monitor .................................................................156
4.1 Collection of Filter Paper ..........................................................................................................157
4.2 Pretreatment ..............................................................................................................................161
4.3 Analysis.....................................................................................................................................164
4.4 Evaluation of Analysis Results .................................................................................................166
4.5 Sample Storage .........................................................................................................................167
Chapter 5 Sampling to Analysis of Air Sample via Iodine Sampler .........................................................167
5.1 From Sampling to Analysis.......................................................................................................168
Chapter 6 Sampling to Analysis of Air Sample via Dust Sampler ...........................................................169
6.1 Equipment and Air Absorbent .................................................................................................170
6.2 Installation and Inspection ........................................................................................................170
6.3 Sampling ...................................................................................................................................170
6.4 Pretreatment ..............................................................................................................................174
6.5 Analysis.....................................................................................................................................178
6.6 Evaluation of Analysis Results .................................................................................................178
6.7 Sample Storage .........................................................................................................................178

139

Explanation ...............................................................................................................................................178
Explanation A Measurement Range of Air Monitor ..........................................................................180
Explanation B Example of Impact Assessment of the Accident
at TEPCO's Fukushima Daiichi NPP.........................................................................181

140

141

Chapter 1 Introduction
Emergency monitoring is described in the Nuclear Emergency Response Guidelines (Nuclear
Regulation Authority, partially revised on July 21, 2021)[1] as “Environmental radiation monitoring
to be conducted when there is an abnormal or threatened release of radioactive materials or radiation”.
Specific details of emergency monitoring are outlined in “Emergency Monitoring (Supplementary
Reference Materials for Nuclear Emergency Response Guidelines)” (Nuclear Regulation Authority,
Radiation Monitoring Division, partially revised on December 21, 2021) [3] (hereinafter referred to
as “Supplementary Reference Materials for Emergency Monitoring”). The purpose of measuring theconcentration of radioactive materials in the air is (1) to collect information on the status ofenvironmental radiation due to a nuclear disaster and (2) to provide materials for evaluating theradiological impact of a nuclear disaster on residents and the environment.
Part 2 describes the measurement procedures to be conducted as emergency monitoring: continuous
measurement by air monitors, collection to analysis of air samples collected by air monitors, collection
to analysis of air samples by iodine samplers (only an overview is given), and collection to analysis
of air samples by dust samplers.

142

Chapter 2 Basics and Scope of Application
2.1 Purpose of measurement
Emergency monitoring involves measuring the concentration of radioactive materials in the air for
the following purposes, based on the Emergency Supplemental Reference Materials.
(a) Information collection on the environmental radiation situation due to the nuclear disaster(b) Providing materials for evaluating the radiological impact of nuclear disasters on residents andthe environment
For this purpose, we will confirm the spread of radioactive materials and utilize them for exposure
assessment by establishing a measurement system that uses an air monitor that can continuously
monitor changes in the concentration of radioactive materials in the air over time and an iodine
sampler with an automatic sample changer that continuously samples gaseous and particulate iodine,and changes filter paper and activated carbon cartridges at regular intervals. The measuring system
confirms the spread of radioactive materials and is utilized for exposure evaluation.
In addition, in order to respond to accidents at nuclear fuel facilities (excluding criticality accidents
and accidents at spent fuel storage systems in reprocessing facilities), a system will be established to
be able to monitor changes in the concentration of radioactive materials in the air continuously overtime, mainly for α-emitting nuclides, utilizing air monitors and dust samplers.
Table 2-1 shows the emergency monitoring response according to the emergency category.
Table 2-1. Emergency monitoring response
Classification of
Monitoring situation
emergencies
Informationcollection
Normal time monitoring
situation
Alert state

Emergency
preparation

Equipment support

Confirmation of equipment
abnormality, etc.
Confirmation of equipment
monitoring
abnormality, etc.
Startup preparation

Facility site emergency
Emergency monitoring
Startup*
Total emergency* Startup based on the emergency monitoring plan, depending on the facility’s situation.

1432.2 Equipment used and flow of use
This section shows the equipment used in emergency monitoring. Refer to the respective chaptersfor details on each piece of equipment. These devices should be inspected on a daily and periodic
basis. They should be ready for prompt use in an emergency. In addition, personnel who handle thisequipment must learn how to operate and check in advance through education and training.
2.2.1 Air monitor(1) Equipment overview
An air monitor is an equipment that continuously measures the radioactivity concentration in
airborne dust as the concentration of radioactive materials in the air while collecting airborne dust on
filter paper. In addition, dust monitors are continuously used as emergency equipment to strengthen
the monitoring system in an emergency.

Figure 2-1. Example of air monitor

144

(2) Flow of use
The flowchart of the use of air monitors is shown. It also shows the major “The Series ofEnvironmental Radioactivity Measuring Methods” to be referred to.
(a) Continuous measurement of the concentration of radioactive materials in the air and analysis of
air samples<Analysis and measurement targets>· Gross α radioactivity, gross β radioactivity(continuous measurement)· γ-emitting nuclides, α-emitting nuclides, β-emitting
nuclides (Analysis and measurement of filter paper)(Selected according to the nuclear facility)<The Series of Environmental Radioactivity Measuring
Methods for major reference> No. 2, “Radioactive strontium analysis method”
 No. 7, “γ-ray spectrometry using germanium
semiconductor detector”
 No. 12, “Plutonium analysis method”
 No. 14, “Uranium analysis method”
 No. 24, “Sample preparation method for gamma-ray
spectrometry in emergency situations”
 No. 29, “Gamma-ray spectrum analysis method
using germanium semiconductor detector
in emergency situations”
 No. 35, “Environmental sampling methods inemergencies”

145

2.2.2 Iodine sampler(1) Equipment overview
An iodine sampler collects radioactive iodine (particulate and gaseous) from the air on filter paper
and activated carbon cartridges. An iodine sampler with an auto sample changer is used in an
emergency.

Figure 2-2. Example of iodine sampler (with auto sample changer)146

(2) Flow of use
The flow chart below shows the process of using the iodine sampler. It also shows the major
reference documents of “The Series of Environmental Radioactivity Measuring Methods”.
Radioactive iodine collection to analysis<Analysis and measurement target>·
Radioactive iodine<The Series of Environmental Radioactivity Measuring
Methods for major reference>· No. 7, “γ-ray spectrometry using germanium
semiconductor detector”· No. 15, “Radioactive iodine measurement method in
emergencies”· No. 24, “Sample preparation method for gamma-ray
spectrometry in emergency situations”· No. 29, “Gamma-ray spectrum analysis method using
germanium semiconductor detector in emergency
situations”· No. 35, “Environmental sampling methods in emergencies”

147

2.2.3 Dust sampler(1) Equipment overview
A dust sampler collects airborne dust on filter paper.

Figure 2-3. Example of dust sampler148

(2) Flow of use
This section shows the flow of use of the dust sampler. The main series of radioactivity
measurement methods to be referred to are also shown.
Analysis of air samples<Analysis and measurement target>· γ-emitting nuclides, α-emitting nuclides, and β-emitting
nuclides (Selected according to the nuclear facility)<The Series of Environmental Radioactivity Measuring
Methods for major reference>· No. 2, “Radioactive strontium analysis method”· No. 7, “γ-ray spectrometry using germanium
semiconductor detector”· No. 12, “Plutonium analysis method”· No. 14, “Uranium analysis method”· No. 24, “Sample preparation method for gamma-ray
spectrometry in emergency situations”· No. 29, “Gamma-ray spectrum analysis method using
germanium semiconductor detector in
emergency situations”· No. 35, “Environmental sampling methods inemergencies”

149

Chapter 3 Continuous Measurement by Air Monitor
This chapter describes continuous measurement by air monitors in emergencies.
The procedures, etc., in this chapter also apply when using the dust monitor in the emergency mode.
3.1 Equipment
3.1.1 Classification of equipment
Table 3-1 shows the classification of air monitors.
Table 3-1. Classification of air monitors
Classification
Definition(1) α-ray air monitor
Air monitor to measure α radiation from airborne dust(2) β-ray air monitor
Air monitor to measure β radiation from airborne dust
3.1.2 Measurement targets
These monitors measure either gross α radioactivity concentration or gross β radioactivity
concentration. Air monitors cannot quantify individual radionuclide concentrations such as α-emittingor β-emitting nuclide concentrations.
3.1.3 Equipment selection
Table 3-2 shows the air monitors selected according to the nuclear facility and accident type listed
in the Emergency Supplemental Reference Material.
Table 3-2. Air monitors are selected according to the nuclear facility and type of accident
Nuclear facility
Accident typeAir monitors to be selected
Nuclear power reactor
β-ray air monitors
facilities (requiring PAZ and UPZ settings)
Nuclear reactor facilities fortesting and research, etc. β-ray air monitors(requiring UPZ setting)
Uranium processing facility Criticality accident
β-ray air monitors(requiring UPZ setting)*
UF6 Releaseα-ray air monitors
Processing facility to handle Criticality accident
β-ray air monitors
plutonium
Large fire or explosion
α-ray air monitors
Criticality accident
β-ray air monitors
β-ray air monitors
Reprocessing facility
Large fire or explosion
α-ray air monitors
Evaporation dry
β-ray air monitors*Same for nuclear fuel facilities (not requiring UPZ setting)
3.1.4 Equipment configuration
The equipment configuration of the air monitor is the same as that of the dust monitor (Part 1,
3.1.4).
150

3.1.5 Detector types and measurement principles
The types of detectors are listed in Table 3-3. The measurement principle is the same as that ofdust monitors (Part 1, 3.1.5), but to accommodate high-concentration measurements, detectors withsmaller instrument efficiency than those used in dust monitors used in normal times are used.
Table 3-3. Detectors for air monitors
Measurement target
Detector
ZnS(Ag) scintillation detector
α-raySilicon semiconductor detector
Plastic scintillation detector
β-ray
Silicon semiconductor detector
3.1.6 Example of equipment specifications
Table 3-4 shows an example of equipment specifications for an air monitor. Compared to dust
monitors used in normal times, the filter paper feed interval is short, which is used as a material forevaluating exposure doses. In addition, the flow rate is low in order to accommodate highconcentration measurements.
Note that equipment, etc., not listed in the example specifications may be used if it has the required
performance.
Table 3-4. Examples of equipment specifications for air monitor
Item
Type A
Type B
Type C
Measurement target
α-ray
β-ray
α- and β-rays
Silicon
Detector
ZnS(Ag) scintillator
Plastic scintillator
semiconductor
α radiation: 10
Measurement
100 to 100,000
Bq/m3 or higher
concentration
10 Bq/m³ or more
Bq/m³
β radiation: 100 torange*¹
100,000 Bq/m³
Cellulose/glass
Air absorbent
Membrane
Membrane
fiber
Flow rate
Approx. 50 L/min
Filter paper feeding
Intermittent feeding
methodExternal radiation
Lead shielding*²
impact elimination*1 Even if the concentration exceeds the measurement range, it must be possible to confirm thepresence of a radioactive plume above the concentration.
*2 The detector should be shielded with approximately 3 to 5 cm thick lead to reduce backgroundradiation and accommodate measurement under high radiation dose conditions. For performance
evaluation on the effect of external radiation, it is recommended to refer to the determinationthresholds described in JIS Z 4316: 2013, “Radioactive dust monitors” [4].

151

3.2 Air absorbent
Dust monitors are based on using long filter paper, the membrane filter for capturing α-ray
substances, and the cellulose or glass fiber filter is often used for capturing β-ray substances.
(see Part 1, 3.2)
3.3 Installation, calibration, and inspection(1) Installation
The basic installation requirements are the same as those for dust monitors in normal times (Part 1,
3.3.1). However, the following are some ideas for installation specific to air monitors.
(a)Distance and orientation from nuclear facility
The Emergency Supplementary Reference Material stipulates that an air monitor should be locatedat each of the 5-10 km, 10-20 km, and 20-30 km radii in each of the 16 azimuths centered on the target
nuclear facility in principle (Figure 3-1).
If there is a fixed observation station in the region concerned, it shall be installed in the stationbuilding concerned.
Note that for each orientation, air monitors in the same orientation should not be installed on thesame straight line.
Iodine sampler(with auto sample changer)
Air monitor

Nuclear power station
Figure 3-1. Example of an air monitor and iodine sampler arrangement with auto sample changer [3].
(b)Power supply
Assuming a commercial power failure, the system shall have a backup power source, such as an
emergency generator or battery. It shall be able to operate continuously without refueling or othermeasures for at least 3 days after the startup of the air monitor.
(2)Calibration
The calibration method is the same as that for dust monitors in normal times (Part 1, 3.3.2).
The standard radiation source is the α or β radiation source shown in Table 3-5.

152

Table 3-5. Standard radiation sources for calibration
Radiation type
Standard radiation source
α-ray
Am-241
β-ray
Cl-36 or Tl-204(3)Inspection
Although air monitors are not operating normally, daily inspections should be conducted about
once a month. Periodic inspections should be implemented at least once a year to ensure they can beused promptly in an emergency. During daily inspections, it is desirable to implement an operation
verification test, including the acquisition of background data.
Inspection items are the same as those for dust monitors in normal times (Section 1, 3.3.3).
3.4 Measurement(1)Startup
All installed air monitors are activated by remote control using a telemetering system or othermeans. Subsequent operations are also remotely operated using a telemeter system, etc.
(2)Measurement condition setting
Set the measurement conditions of the air monitor as shown in Table 3-6. The measurement
conditions should be set in advance in normal times.
Table 3-6. Measurement conditions for air monitors
Item
Measuring conditions
Flow rate*
Approx. 50 L/min
Filter paper
Intermittent feeding
feeding method
Collection time*(Filter paper
1 hourfeeding time)
Measurement
Air sampling position
position
Measurement
Continuous (measurements takentimeevery 10 minutes)*If the measurement cannot be taken properly due to counting loss or other factors, it is necessary tochange the measurement conditions, including decreasing the flow rate or shortening the samplingtime. It is also desirable to be able to automate the filter paper feeding when the set threshold value
is exceeded.
(3)Start of measurement
Start measurement.
From the viewpoint of data evaluation, it is desirable to be able to set the start time of measurement
every hour on the hour (e.g., 10:00 am, 3:00 pm, etc.).
(4)Items to be checked at the start of measurement
153Check that the integrated flow volume is increasing at a constant pace, that the count rate isincreasing, that the filter paper is being fed every hour, and other items to determine the normal
operation.
(5) Data transmission
Transmit data to the telemetry system at least once every 10 minutes.
Data transmission items are the same as in Section 3. 4(5) of Part 1.
(6) Calculation of radioactivity concentration
The detection unit measures the α- or β-rays from airborne dust collected on filter paper to calculate
the radioactivity concentration. The radioactivity concentration in the air (average concentration overthe last 10 minutes) is calculated by subtracting the count rate at the previous 10s of minutes from thecount rate at the current 10s of minutes or by other methods.
The following formula calculates the radioactivity concentration.
Radioactivity concentration at every 10 minutes
Radioactivity concentration（Bq/m3）＝ ((Count rate at the current 10s of minutes (s-1)-(Count rate at the previous 10s of minutes (s1)))/(equipment efficiency) × Integrated flow volume for 10 minutes(m3))
However, when evaluating the radioactivity concentration at the beginning of the measurement or
the first 10s of minutes after the filter paper feeding, the count rate for the previous 10s of minutes
shall be 0 (s-1).
Supplementary information on how to obtain the count rate
This method is based on measurement during air sampling, and the count rate is basically measured
by a count rate meter.
Note that care should be taken when calculating the count rate from the integrated counts measured
by the scaler in the measurement during air sampling and refer to Explanation C in Part 1 for theconcept.
In emergency monitoring, the effect of background (radon/thoron decay products) in the air
monitor measurement is ignored, and no subtraction or correction is made.

154

3.5 Evaluation of measurement results
The measurement results of air monitors should be evaluated by the methods described in (1) and(2) to confirm the increase or decrease of radioactivity concentration in the air every 10 minutes. To
evaluate the measurement results in an emergency, obtaining background data at the air monitoring
location in normal times is desirable.
(1)Gross α radioactivity concentration
The concentration of gross α radioactivity in the air at the relevant time is determined by theevaluation method described in 3.4(6) to determine whether or not α emitting nuclides caused by anuclear facility are present in the vicinity of the installation site.
(2)Gross β radioactivity concentration
The evaluation method described in 3.4(6) is used to determine the gross β radioactivity
concentration in the air at the relevant time and to determine when the radioactive plume arrived in
the vicinity of the point where the air monitor is installed and how long it existed and passed over thesite. An example of the evaluation is shown in Figure 3-2.
Figure 3-2 uses the data during plume arrival (MS-4) in Figure B-1 in Explanation B. When the
average concentration from the filter paper feeding (blue plot) increases, the increase in the average
concentration (orange plot) every 10 minutes is represented as a peak, helping clearly confirm when
the radioactive plume arrived and passed.

Figure 3-2. Evaluation example of the presence/absence of radioactive plume around an air monitor
installation point

155

Chapter 4 Analysis of Air Samples Collected by Air Monitor
Analyzing filter paper of air monitors with a germanium semiconductor detector, etc., enables
determining the concentration of radionuclides in the air and detailed changes in the composition of
the radionuclides and using them as data for exposure dose assessment, etc.
If the dust monitor is used in an emergency mode, the procedures in this chapter also apply toanalyzing its filter paper.
4.1 Collection of filter paper
Filter paper of air monitors that worked for several days is collected at a time in consideration ofcontamination prevention. Since radionuclides with short half life are included in the analysis, theyshould be collected as soon as possible while considering the reduction of exposure of monitoring
personnel.
The collection procedures (excluding the description of the iodine sampler) described in The Seriesof Environmental Radioactivity Measuring Methods No. 35, "Environmental sampling methods inemergencies" are transcribed below. However, as a rule, air samples should be collected based on the
instructions for emergency monitoring prepared by the EMC (Emergency Radiological Monitoring
Center).
(1)Pre-departure preparations
1

2

3

Procedure
Identify the point (measuring station) where the absorbent
will be collected and exchanged.
Prepare necessary equipment.
Note 1) Replacement absorbents may be kept on hand at themeasuring station where the air monitor is installed.
The method of keeping the absorbent on hand should
be in accordance with the user manual for theabsorbent to be used.
Note 2) In order to prevent contamination of the measuring
station, the absorbent should be replaced quickly.
The method of replacing the absorbent should be
confirmed in advance in the device's instruction
manual.
Check the operation of equipment (especiallycommunication equipment).

Reference/Records*

3.1 Prevention of equipment
contamination

4

Cure the equipment, if necessary.

5

Check the operation of electronic personal dosimeters.
Wear appropriate protective equipment (protective clothing,protective masks, etc.) in accordance with the instructions
for use.
3.2 Protection of monitoring
Also, if indicated, take stable iodine tablets.
personnel

6Note: A dedicated air sampling team should perform thereplacement of absorbents, or, if it is difficult to156

organize a dedicated team, it should be done first
before collecting other environmental samples.
*Reference and record of The Series of Environmental Radioactivity Measuring Methods No. 35“Environmental sampling methods in emergencies”(2) Collection procedure (collection of absorbents)
Procedure
Reference/Records*
Move to the point (measuring station) to collect and install1
absorbents.
Collect the absorbents and record the collection date and time, thelot number of the absorbents, and other information. If theabsorbent is long filter paper, there are two methods: collecting theentire roll of filter paper and cutting off and collecting the used
Collection record sheet
portion.
2
B1-d
After issuing the instructions, collect within the period indicated in
the instructions.
Note: The collection and exchang methods of absorbents should bein accordance with the instruction manual of the equipmentused.
3Place the collected absorbent in a polyethylene bag.
Fold the mouth of the bag, seal it with plastic tape, and affix (or Collection record sheet
4
clearly write) a label with the identification code.
B1
5
Pack the used absorbent by adding another bagging (i.e., outer bag).
Set a new absorbent and verify that the equipment is operating
6
properly.
Collection record sheet
7
Verify packaging, records, and photographs.
B1-e* Reference and record of The Series of Environmental Radioactivity Measuring Methods No. 35“Environmental sampling methods in emergencies”
Note: If monitoring posts are not installed at the collection point, it is necessary to measure the air
dose rate around the collection point using a survey meter, etc., before Step 2.

157

Sampling record form

Air

B1
Date:
/
/
Weather (day of):Team leader:Start time:hour
Weather (day before):
Member:min

Sampling point information
Sampling
location(Location name, address,
etc.)
b GPS
a

b

Snow accumulation

N (latitude)
☐ Yes
☐ No

E (longitude)
Snow
depth

Approx.

cm

Air dose rate at the sampling point

c

c
c
c

Type of equipment
Device name (device
number)Time constant
Detector directionC☐ NaI (Tl) scintillation survey meter☐ Ionization chamber survey meter☐ Neutron radiation survey meter☐ Other:*Elapsed time to measurement:

Air dose rate (☐ μSv / h
☐ μGy / h)
1 m above ground surface (at waist position)

1
2
3
4
5
Average158

Hot (sampling) person in charge:
Cold (no sampling) person in charge:

d

d
d
d
d
d
d

Sampling
equipmentTypeabsorbentofSampling starttime
Flow rate at thestart
Sampling
end
time
Flow rate at theendSuction timedAverage flowratedIntegrated flow
volumedRemarks☐ High-volume air sampler☐ Low-volume air sampler☐ Other:☐ Filter paper:☐ Activated carbon cartridge:☐ Other:[L/min][L/min][min][L/min]*For equipment that does not indicate the total flow rate, the average flow
rates at the start and the end are used as the average flow rate.
[m3]*For equipment that does not display an integrated flow volume, theintegrated flow volume is obtained by “Integrated flow volume = Average
flow rate [L/min] x Suction time [min]/1000”.

Confirmation of collected samples and recordseee

Samplepackaging
OmissionrecordPictures☐ Inner bag OK ☐ Outer bag OK ☐ Sealing OK
of☐ None☐ Landscape ☐ Sampling point ☐ Situation of sampling, close-range view

Recorder:Sample identification code
Sample classification
Receipt

End time:hour☐ Treat as a high-concentration sample
Date and time: //Recipient signature:

159

min.

4.2 Pretreatment
Collected filter paper is pretreated according to the nuclides to be analyzed and measured.
(1) When performing γ-ray spectrometry
In order to measure γ-emitting nuclides with a germanium semiconductor detector, etc., filter paper
must be filled into the measurement container. During the measurement of air monitors, crosscontamination from the air sampling surface occurs due to the winding of the long filter paper. Since
the effect on the analysis results cannot be corrected by calculation or other means, this shall not be
considered. However, it is desirable to be able to take measures to prevent cross-contamination, suchas automatically covering the air sampling surface with polyethylene film, etc., after air sampling.
This section describes the case where filter paper used for 6 hours*¹ is collected together and filled
into a measurement container (select a small container or Marinelli container according to the capacityof the filter paper). In this case, from the viewpoint of preventing contamination of instruments used
for pretreatment, cutting along the shape of the air sampling surface is not performed in principle. The
boundary between the air sampling surfaces is cut, as shown in Figure 4-1*². Since the cut filter paper
may be cut into pieces for detailed measurement for each hour at a later date, it should be wrapped inpolyethylene film or the like, as shown in Figure 4-3, filling into the measurement container to preventcross-contamination among the six air sampling surfaces.
When filling, the air sampling surface should be as close to the bottom of the measuring container
as possible, and the filter paper should be folded or cut into pieces and filled for each hour. Figure 44 shows an example of folding and filling the filter paper. For the pretreatment procedure, anappropriate method should be selected by also referring to section 6.4 and "Sample preparation
method for gamma-ray spectrometry in emergency situations" in The Series of Environmental
Radioactivity Measuring Methods No. 24.
*1 The setting of 6 hours is determined in accordance with the sampling cycle of the iodine sampler
assumed in the Emergency Supplementary Reference Materials. This setting does not exclude thepossibility of further subdividing the period into one hour or other periods in order to grasp detailed
temporal changes in the concentration of radioactive materials in the air.
*2 Depending on the amount of airborne dust, the air sampling surface may not be visible, as shownin Figure 4-2. If, for this reason, it is not possible to separate the air sampling surfaces into 6-hour
portions, collect the air sampling surfaces for several days from the startup of the air monitor to thecollection of filter paper and use them as a measurement sample. To prevent cross-contamination
between the air sampling surfaces, they should be covered with polyethylene film or the like andfilled into the measurement container. It is desirable to be able to record the air sampling start
position and the date and time of air sampling on a long filter paper by time stamping or othermeans so that the filter paper can be subdivided at arbitrary time intervals.

160

Figure 4-1. Example of cutting long filter paper

Figure 4-2. Air sampling surface of long filter paper for air monitor (example of air sampling at
approx. 50 L/min for 1 hour)

Figure 4-3. Example of long filter paper wrapped with polyethylene film, etc.
(Top - before wrapping, bottom - after wrapping)161

Figure 4-4. Example of filling long filter paper (78 mm x 700 mm) used for 6 hours(Top: An example of filling a U-8 container with filter paper folded long and narrow so that the air
sampling surface is close to the bottom.
Bottom: Example of filling a V-9 container by overlapping and folding it for each hour so that the
air sampling surface is centered)(2) When performing radiochemical analysis
If the measurement of γ-emitting nuclides is necessary, the radiochemical analysis should be
performed for α-emitting nuclides and β-emitting nuclides after the measurement is completed.
If necessary, such as when multiple nuclides must be measured, dividing the sample or conductinga systematic analysis is needed. Therefore, the analysis method should be carefully considered anddetermined before conducting the analysis.
Although clipping the air-sampling surface is not precluded when conducting radiochemical
analysis, clipping should be avoided after γ-ray spectrometry since cross-contamination also occurs
in the measurement container of the germanium semiconductor detector.

162

4.3 Analysis
γ-ray spectrometry with a germanium semiconductor detector is performed for γ-emitting nuclides,
and radiochemical analysis is performed for α-ray and β-emitting nuclides.
Table 4-1 shows the nuclides to be measured according to the nuclear facilities and accident types
listed in the Emergency Supplementary Reference Material.
Table 4-1. Examples of nuclides to be analyzed in filter paper collected by air monitors [3].
Accident
Facility
Nuclides for analysis
type
α-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
Nuclearetc.)
reactorβ-emitting nuclides (Sr-89, Sr-90, etc.)
facility for
γ-emitting nuclides (Co-58, Fe-59, Co-60, Zr-95, Nb-95, Mo-99, Tcpower
99m, Ru-103, Te-129, Te-129m, I-131, Te-132, Igeneration*¹
132, I-133, Cs-134, Cs-137, etc.)
Nuclearα-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
reactoretc.)
facility for
β-emitting nuclides (Sr-89, Sr-90, etc.)
test
γ-emitting nuclides (Co-58, Fe-59, Co-60, Zr-95, Nb-95, Mo-99, Tcresearch,
99m, Ru-103, Te-129, Te-129m, I-131, Te-132, Ietc.*²
132, I-133, Cs-134, Cs-137, etc.)
α-emitting nuclides (U-235, U-238, etc.)
Criticality
β-emitting nuclides (Sr-89, Sr-90, etc.)
Uranium
accident
γ-emitting nuclides (I-131, I-133, Cs-134, Cs-137, etc.)
processing
facility*²*³
UF6 release
α-emitting nuclides (U-235, U-238, etc.)(Dispersal)
α-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
Criticality
etc.)
Plutonium
accident
β-emitting nuclides (Sr-89, Sr-90, etc.)(Pu)
γ-emitting nuclides (I-131, I-133, Cs-134, Cs-137, etc.)
processing
Large-scale
facility
α-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
fire oretc.)
explosion
α-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
etc.)
Criticality
β-emitting nuclides (Sr-89, Sr-90, etc.)
accident
γ-emitting nuclides (Co-58, Fe-59, Co-60, Nb-95, Tc-99m, Te-129,
Te-129m, I-131, I-133, Cs-134, Cs-137, etc.)
ReLarge-scale α-emitting nuclides (U-235, U-238, Pu-238, Pu-239+240, Am-241,
processing
fire oretc.)
facility
explosion β-emitting nuclides (Sr-90, Y-90, Tc-99, Pm-147, etc.)
γ-emitting nuclides (Rh-106(Ru-106), Cs-134, Cs-137, Ce-144, etc.)
α-emitting nuclides (Pu-238, Pu-239+240, Am-241, Cm-244, etc.)
Evaporation
β-emitting nuclides (Sr-90, Y-90, Tc-99, Pm-147, etc.)dry
γ-emitting nuclides (Rh-106(Ru-106), Cs-134, Cs-137, Ce-144, etc.)*¹ PAZ and UPZ settings are required.
*² UPZ setting is required.
*³ The same applies to nuclear fuel facilities (not requiring UPZ).
163

(1) γ-ray spectrometry
Table 4-2 shows the approximate measurement time for the germanium semiconductor detector.
The sample amount from sampling per 6 hours of air monitoring is about 18 m3 (50 L/min x 360
min).
Table 4-2. Relationship between measurement time and quantifiable level when measuring
samples at the time of the early stage of the accident (when multinuclear species were detected)using a small container (50 mm × 50 mm) [3]I-131 quantifiable levelCs-137 quantifiable level
SampleMeasurement time
Measurement timeunit
amount1030
1
10 hours
1030
1
10 hoursmin.
min.
hour (Reference) min.
min.
hour
(Reference)
1 m³
6
4
3
0.8
6
3
2
0.7
Bq/m³
*If the sample amount is not 1 m3, the value obtained by dividing the quantifiable level by the sample
amount is used.
For details, see The Series of Environmental Radioactivity Measuring Methods No. 29, "Gammaray spectrum analysis method using germanium semiconductor detector in emergency situations", andThe Series of Environmental Radioactivity Measuring Methods No. 15, "Radioactive iodine
measurement method in emergencies".
Uneven distribution of radionuclide concentrations in airborne dust occurs in the measurement
container. For an example of the evaluation of the effect of uneven distribution, refer to "Document
2: Effect of inhomogeneous distribution of samples in measurement container (example of U-8
container)" in The Series of Environmental Radioactivity Measuring Methods No. 7 "γ-ray
spectrometry using germanium semiconductor detector".
(2) Radiochemical analysis
After measuring γ-emitting nuclides, radiochemical analysis of α-emitting nuclides and β-emitting
nuclides is conducted.
Since the radionuclides released differ depending on the nuclear facility, the nuclides to beanalyzed should be selected with reference to Table 4-1.
The Series of Environmental Radioactivity Measuring Methods referred to for the nuclides to beanalyzed are listed in Table 4-3. In the radiochemical analysis of α-emitting nuclides, if it is difficult
to analyze the membrane filter paper used in the α-ray air monitor, a filter paper that can appropriately
accommodate radiochemical analysis, such as cellulose/glass fiber filter paper, should be used.
Analyzing the cellulose/glass fiber filter paper of dust samplers or iodine samplers collected separately
is also acceptable.
For Tc-99 and Pm-147, which do not have a reference in The Series of Environmental Radioactivity
Measuring Methods, β-ray measurement with a liquid scintillation counter or ICP mass spectrometry
can be applied.

164

Table 4-3. The Series of Environmental Radioactivity Measuring Methods referred to concerning
the nuclides to be analyzed and measured
The Series of Environmental Radioactivity Measuring Methods
Nuclides for analysis
for reference
U-235, U-238 No. 14 "Uranium analysis method"
No. 12 "Plutonium analysis method"
Pu-238, PuNo. 28 "Rapid analysis method for plutonium in environmental
239+240
samples"α-emitting
No. 21 "Americium analysis method"
nuclidesAm-241, Cm- No. 22 "Plutonium and americium sequential analysis method"244
No. 30 "Americium-241 in environmental samples, curium rapid
analysis method "No. 31 "Rapid analysis method for total alpha radioactivity inenvironmental samples"
No. 2 "Radioactive strontium analysis method"
Sr-89, Sr-90,
No. 23 "Radionuclide analysis method using liquid scintillation
Y-90
-emitting
counter"
nuclidesTc-99, PmN/A
147, etc.
4.4 Evaluation of analysis results
The analysis results will be used for the following evaluations for emergency monitoring: (1)collecting information on the environmental radiation situation caused by a nuclear disaster and (2)providing materials for evaluating the radiological impact of a nuclear disaster on residents, etc., andthe environment.
(1) Determination of the concentration of radioactive materials in the air and their nuclide composition
in detailObtaining detailed information on changes over time in the concentration of radioactive materials
in the air and their nuclide composition contributes to evaluating the effects of accidents at nuclear
facilities.
Explanation B describes an example of an impact evaluation of the TEPCO's Fukushima Daiichi
NPP accident.
(2) Provision of materials for evaluating exposure doses
The concentration of radioactive materials in the air evaluated in (1) is used as material forevaluating internal exposure doses due to inhalation and ingestion of airborne dust.
Refer to the Normal Time Supplementary Reference Material for the evaluation method of
exposure doses.
When calculating the concentration of gross radioactive iodine (particulate and gaseous) from theanalytical evaluation of the filter paper of the air monitor, the following procedure is used with themeasurement results of air samples collected from the iodine sampler.
(a) Calculate the ratio of particulate radioactive iodine to gaseous radioactive iodine from the resultsof measurements with a germanium semiconductor detector of air samples collected with an iodine
sampler.
165

(b) Calculate the gross radioactive iodine concentration at the location where the air monitor isinstalled from the concentration of particulate radioactive iodine evaluated from the analysis resultsof the filter paper of the air monitor and the ratio calculated in (1) above.
4.5 Sample storage
When storing filter paper before analysis, samples for γ-ray spectrometry measurement, and filter
paper after analysis that has not been used for radiochemical analysis, store them in a desiccator, etc.,
to prevent moisture absorption.

166

Chapter 5 Sampling to Analysis of Air Sample via Iodine Sampler
Radioactive iodine sampling and analysis using an iodine sampler with an auto sample exchanger
that continuously samples gaseous and particulate iodine and changes filter paper and activated carbon
cartridges at regular intervals confirm the spread of radioactive materials and evaluate exposure. The
Emergency Supplementary Reference Materials stipulates that monitoring shall be conducted for
actual nuclear power reactor facilities and nuclear reactor facilities for test research.
For details, refer to The Series of Environmental Radioactivity Measuring Methods No. 15,"Radioactive iodine measurement method in emergencies".
5.1 From sampling to analysis(1) Equipment specifications
The following are the requirements for an iodine sampler.
····Filter paper samples particulate radioiodine and activated carbon cartridges collect gaseousradioiodine, so a combination of both is used.
The collection time per set of absorbents (a set of filter paper and activated carbon cartridges)
can be approximately 6 hours.
The auto sample changer shall be capable of automatically changing 20 or more absorbents (aset of filter paper and activated carbon cartridges) and continuously operating for at least 5 days.
With an assumption of a power outage from the commercial power supply, the iodine sampler
shall have a backup power supply, such as an emergency generator or battery. It shall be able tooperate continuously without refueling, etc., for at least 3 days after startup.

(2) Installation
When installing an iodine sampler, the location of an iodine sampler should be considered in light of
the actual situation of the region, including population distribution, past wind condition records, andother social and natural environment.
Iodine samplers shall be basically located at one site in a radius of 5 to 30 km in every one or two of
the 16 azimuths centered on the target nuclear facility (see Figure 3-1). As with air monitors, if there
is a fixed observation station site in the area, it is desirable to install the air sampler in that stationbuilding.
(3) Sampling
Sampling is conducted by sampling air for a certain period (approx. 6 hours) and adsorbing
radioactive iodine on filter paper and an activated carbon cartridge. Continuous sampling is carriedout by automatically replacing the filter paper and an activated carbon cartridge after a certain period.
After sampling, filter paper and an activated carbon cartridge shall be collected carefully to prevent
contamination. In order to analyze radionuclides, including those with short half life, filter paper andan activated carbon cartridge shall be collected as soon as possible while considering the radiation
exposure reduction to monitoring personnel.

167

(4) Analysis
A germanium semiconductor detector measures each filter paper and activated carbon cartridge.
The sample amount from the iodine sampler sampling per 6 hours is approximately 18 m 3 (50 L/min
x 360 min).
Table 5-1. Relationship between measurement time andquantifiable level [3] in the case of measurement using a small
container (50 mm ϕ × 50 m)

Sampleamount1 m3

I-131 Quantifiable level
Measurement time
1030
1
10 hours
min.
min. hour (Reference)
6
4
3
0.8

Unit
Bq/m3

* If the sample amount is not 1 m3, the value obtained by dividing the quantifiable level by the sample
amount is used.
(5) Evaluation of result
Evaluating both particulate radioiodine concentration from the measurement result of filter paperand gaseous radioiodine concentration from the measurement result of activated carbon cartridges,
gross radioiodine concentration is calculated by adding up these concentrations to be used for
exposure evaluation.

168

Chapter 6 Sampling to Analysis of Air Sample via Dust Sampler
The purpose of collecting air samples is to obtain information on the environmental radiation
situation caused by nuclear disasters and to obtain information for evaluating the effect of radiation
due to nuclear disasters.
The analysis result of radioactive material concentration in air is not only used to estimate internal
exposure caused by inhalation of radioactive materials but is also useful for estimating the amount of
fallout on the ground surface.
In this section, as the sampling procedure using a transportable type dust sampler, The Series ofEnvironmental Radioactivity Measuring Methods No. 35, "Environmental sampling methods inemergencies" (excluding the description on the iodine sampler), is transcribed. No. 35 names the dust
sampler as a "transportable sampler" to distinguish it from a installed type sampler. It describes
sampling procedures using a low-volume air sampler and a high-volume air sampler.
In principle, air sampling shall be implemented in accordance with the emergency monitoring
instructions prepared by the EMC.
6.1 Equipment and air absorbent
A transportable type dust sampler and an air absorbent used in emergencies are the same as thoseused in normal times (Part 1, Chapter 4).
6.2 Installation and inspection
Installation concepts and inspection methods for a transportable type dust sampler are the same as
those for normal time (Part 1, Chapter 4). If equipment for emergencies is maintained, operational
checks should be conducted periodically at normal times to keep the equipment in good condition.
6.3 Sampling
6.3.1 Preparation
Procedure
1
2
3
4
5
6
7

Receive a written instruction.
Prepare necessary materials and equipment according to the checklist, etc.
Check the operation of equipment (especially communication equipment and GPS).
Check sampling points on the map.
Cure materials and equipment to prevent contamination.
Check the operation of an electronic personal dosimeter.
Wear appropriate protective equipment (protective clothing, protective masks, etc.) in
accordance with the instructions for use. Also, if so instructed, take a stable iodine drug.

1696.3.2 Identifying the sampling point

1
2
3

Procedure
Move to the sampling point indicated in the instructions.
Record the information about the sampling point, address, etc., including photography.
If GPS is available, record the latitude and longitude of the sampling point. If GPS isunavailable, identify the location, mark it on the map, and record it.

6.3.3 Sampling procedure using a low-volume air sampler

1

2

3

Procedure
The air dose rate around the sampling points is measured and recorded using a NaI (Tl)scintillation survey meter or an ionization chamber survey meter.
Install the sampler so that it does not interfere with the airflow.
Note 1) To evaluate internal exposure doses, the suction port of the sampler should beinstalled approximately 1 m above the ground.
Note 2) As sucking in raindrops degrades the collection performance of the filter paper, an
air sampler is installed at a roofed place, etc., during rain to prevent raindrops fromentering the sampler. If there is no coverage, such as a roof around the measuring
point, use an umbrella or other means to avoid the suction of raindrops.
Note 3) If a generator is used as a power source, avoid suction of its exhaust.
Note 4) Avoid getting a power supply from a vehicle used for transportation, if possible,
because the exhaust gas may affect an air sampler (except for the case of a vehiclemounted air sampler).
Note 5) When multiple samplers are used together, their exhaust air should not affect eachother.
Set the filter paper in the suction holder.
The surface of the filter paper without the lattice structure is on the front side, collecting dust.
Note) Use tweezers to handle the filter paper.
Start sampling and record the time and the volume (flow rate) collected.

4

5

6
7
8
9

Note) The flow rate of the air sampler should be set at approximately 50 L/min (set to theflow rate indicated in the instruction).
Sample air until the integrated flow volume indicated in the instruction is reached.
Note 1) If the flow rate is 50 L/min, the integrated flow volume is 1000 L (= 1 m3) after 20
minutes of sampling.
Note 2) If it starts raining while sampling air, stop the suction and use the integrated flow
volume obtained from a sample collected before the rain starts. Alternatively, thesampling may be continued while holding an umbrella or other object to avoid thesuction of raindrops.
Read and record the sampled volume (flow rate) just before the end of sampling.
Stop the air sampler and record the time.
Remove the filter paper from the sampler.
Note: Handle with care as the adhered radioactive materials may make the radiation dosehigh.
Place the filter paper in a polyethylene bag (i.e., inner bag).

170

10
11
12
13

Fold the mouth of the bag, seal it with plastic tape, and affix (or clearly write) a label with an
identification code.
Pack the sample in a second layer of bag (i.e., outer bag).
Check packaging, records, and photographs.
Remove the air sampler and load it into the car.
Note 1) Decontaminate the used equipment by wiping, etc.
Note 2) Decontaminate power cords and extension cords by wiping them while coiling them.

6.3.4 Sampling procedure with a high-volume air sampler

1

2

3
4

5
6
7
8

9

10

Procedure
Measure and record the air dose rate around the sampling points using a NaI (Tl) scintillation
survey meter or an ionization chamber survey meter.
Install air samplers without interfering with airflow.
Note 1) The sampler’s suction port is installed approximately 1 m above the ground toevaluate internal exposure doses.
Note 2) Since the suction of raindrops reduces the collection performance of the filter paper,
the air sampler is installed in a roofed place, etc., when it is raining to prevent
raindrops from entering the sampler. If there is no roof around measuring points, anumbrella or other means are used to avoid the suction of raindrops.
Note 3) If a generator is used as a power source, avoid suction of its exhaust.
Note 4) Avoid power supply from a vehicle used for transportation, if possible (except in thecase of vehicle-mounted air samplers), to prevent the effects of exhaust gas.
Note 5) When multiple samplers are used together, their exhaust air should not affect eachother.
Set the filter paper in the suction holder.
Start sampling and record the time and the sampled volume (flow rate).
Note) The time required to collect an air sample depends on the radioactivity concentrationin the air.
Sample air until the integrated flow volume indicated in the instructions is reached.
Note) If the flow rate is 1000 L/min, the integrated flow volume is 1000 L (= 1 m3) whencollected for 1 minute.
Read and record the sampled volume (flow rate) just before the end of sampling.
Stop the sampler and record the time.
While keeping the sampler placed vertically, remove the holder fixing the filter paper.
Note) For holders secured with screws, remove all screws.
Remove the filter paper from the sampler.
Note 1) Since adhered radioactive materials may make the radiation levels high, handle themwith care.
Note 2) After removal, promptly set a new filter paper to prevent foreign matters fromentering the air sampling unit. After the filter paper is removed, the suction surface
often appears to be mesh-like. Work quickly since small dust and other particles may
pass through the net and enter the air sampling unit.
Place the filter paper measured with the α-ray spectrometer in a Tupperware or box, etc.,
without folding it, with the suction side up, and with care not to touch the wall or lid of thecontainer.
171

11
12
13
14

Fold the filter paper used for other measurements in two with the suction side facing inward
and place it in an inner polyethylene bag.
Attach a label (or clearly write) with an identification code to the container or inner bag withthe mouth folded over and sealed with plastic tape. Seal the lid of the container with plastic
tape, etc., and place it in a polyethylene bag (i.e., inner bag).
Pack the sample in a second layer of bagging (i.e., outer bag).
Check the packaging, records, and photographs.
Remove the air sampler and load it into the vehicle.
Note 1) Decontaminate the used equipment by wiping, etc.
Note 2) Decontaminate power cords and extension cords by wiping them while coiling them.

6.3.5 Notes
Consider and understand the following when collecting samples.
· The types of radioactive materials released into the air during an emergency include (a) particulatematter, (b) noble gases, and (c) volatile halogens (especially radioactive iodine).
· This section describes the collection of air samples using two types of transportable type samplers(low-volume air sampler: flow rate of 10 to 100 L/min, high-volume air sampler: flow rate of 500
L/min or more). Select the sampler to ensure the necessary detection level.
· A sampler may be installed in a monitoring vehicle.
· If an air sample is collected to determine the radioactivity concentration in the air relative to theradioactivity concentration in the soil, the soil sample should be collected at the same time and in
the same location as the air sample.
· The filter paper is usually cellulose-glass fiber filter paper.
· The electrical outlets to be used as the power supply for the sampler during emergency monitoringshould be determined in advance and clearly indicated in a drawing and a photograph. Also,
investigate measurements involved in power supply during power outage in advance, and plan tomake prompt response possible on site.

172

6.4 Pretreatment
This section presents the pretreatment and storage methods for preparing cellulose-glass fiber filter
paper as a measurement sample for radioactive materials in the air. This section also shows the methodof using a Marinelli container or small container as the measuring container.
The pretreatment procedures are transcribed from "Sample preparation method for gamma-ray
spectrometry in emergency situations" The Series of Environmental Radioactivity Measuring
Methods No. 24.
6.4.1 Considerations for sample pretreatment

1
2

3

Procedure
Determine the order of pretreated samples in advance to prevent cross-contamination, referringto the results of measurements by the survey meter at the time of sample delivery.
When handling a sample with a high radiation level, confirm the work procedure or other planamong workers in advance to shorten the sample handling time as much as possible.
Cure the room (floor, workbench, etc.) before the work.
Note) For curing methods, refer to Chapter 2 of "Sample preparation method for gamma-ray
spectrometry in emergency situations".
Spread a plastic sheet over a cured worktable, place a large filter paper on it, and work on eachsample.

45Note) Replacing the covers of the workbench and floor requires much work. Applying a simple,
disposable curing to each sample can reduce the frequency of replacement.
In order to avoid spreading contamination from the sample, it is advisable to distinguishbetween a hot operation of directly touching the sample and a cold operation of not directly
touching the sample and to separate workers and workbenches for them whenever possible.

1736.4.2 Filling the measuring container(1) When using small containers
1

2

3
4
5
6

Procedure
After writing or attaching a number or other data identifying the sample to the small container,
weigh and record the tare weight of the small container.
While paying attention to homogeneity, pack the filter paper that has been pre-folded orotherwise processed into the small container prepared in procedure 1, leaving as small gaps as
possible. (Photo 6.1)
Pack small filter paper and punch filter paper with the surface with airborne dust facing thebottom. (Photo 6.2)
Note) If there are multiple sheets of filter paper, stack them.
Cover the small container and measure and record the height of the sample.
Wipe the outside of the container well with a paper towel moistened with deionized water,
ethanol, etc.
Weigh the small container and subtract the earlier tare weight to obtain and record the weightof the measurement sample.
To prevent contamination of the analyzer, cover a small container with a polyethylene bag andremove air. Seal the bag by tying the mouth so as to avoid wrinkles at the bottom of thecontainer, and use it as the measurement sample. (Photo 6.3)

Photo 6.1. Example of filling a sample
into a small container (glass fiber filter
paper)

Photo 6.2. Example of filling with theadhering surface facing the bottom(glass fiber filter paper)

174

[The Series of Environmental Radioactivity
Measuring Methods No.24]

Photo 6.3. Example of a small
container (glass fiber filter
paper)
coveredwithapolyethylene bag(2) When using Marinelli containers
This method is intended to measure a large amount of filter paper quickly. As a method to measure
only the air sampling portion, fill a small container, as shown in (1).
Procedure
Attach the inner bag for the Marinelli container inside the Marinelli container without a gap
1 (use a disposable inner bag to avoid contamination of the measuring container wall as muchas possible).
After writing or attaching a number or other data identifying the sample to the Marinelli2
container, weigh and record the tare weight of the Marinelli container, a lid, and an inner bag.
Pack the filter paper that has been pre-folded, clipped, or otherwise processed into the Marinelli
container up to the marked line with as little gap as possible, ensuring homogeneity. (Photo
6.4)
3
After filling the container with the sample, weigh the Marinelli container and lid together withthe sample and subtract the tare weight to obtain and record the weight of the measurement
sample.
Seal the mouth of the Marinelli container inner bag with plastic tape. (Photo 6.5)
4Note) Rubber bands, cable ties, etc., may be used in place of plastic tape.
Cover the Marinelli container and seal it by wrapping plastic tape around the lid joint. (Photo5
6.6 and Photo 6.7)
Wipe the outside of the Marinelli container well with a paper towel moistened with deionizedwater, ethanol, etc.
6 To prevent contaminating the measuring instrument, place the Marinelli container in apolyethylene bag, seal it by tying the mouth while sufficiently removing air, and use it as themeasurement sample. (Photo 6.8)

175

Photo 6.4. Filling a sample into a Marinelli
container (long filter paper)Photo 6.5. Closing the inner bag withplastic tape (long filter paper)Photo 6.6. Fixing the lid with plastic tape(long filter paper)Photo 6.7. Fixing the lid with plastic tape(long filter paper)[The Series of Environmental Radioactivity
Measuring Methods No.24]

Photo 6.8. Marinelli container (long filter
paper) covered with a polyethylene bag

176

6.4.3 Sample storage method(1) Relatively short-term storage
1
2

Procedure
Place the measurement sample contained in the small container into another polyethylene bagor container while leaving it in the measurement container and storing it.
Place the measurement sample in the Marinelli container into a separate polyethylene bag orcontainer while leaving it in the inner bag and storing it.

(2) Long-term storage

1
2

3

Procedure
Place the measurement sample contained in the small container into a separate polyethylene
bag or container while leaving it in the measurement container and storing it.
Place the measurement sample contained in the Marinelli container into a separate
polyethylene bag or container while leaving it in the inner bag and storing it.
The sample may be incinerated according to the methods described in The Series ofEnvironmental Radioactivity Measuring Methods No. 13, "Sample pretreatment method for
instrumental analysis using germanium semiconductor detectors, etc." and The Series ofEnvironmental Radioactivity Measuring Methods No. 16, "Environmental sampling method",
but take due care to avoid contaminating other samples by washing and cleaning the apparatus
and equipment after use.
Store an incinerated sample in a low-humidity environment, such as in a desiccator, or in sucha way that it is not exposed to air as much as possible.

6.5 Analysis
Conduct γ-ray spectrometry with a germanium semiconductor detector for γ-emitting nuclides andradiochemical analysis for α- and β-emitting nuclides.
The content is the same as the procedure (4.3) for an air monitor.
6.6 Evaluation of analysis result
The content is the same as procedure (4.4) for an air monitor.
6.7 Sample storage
The content is the same as the procedure (4.5) for air monitor.

177

Explanation

178

179

Explanation A Measurement Range of Air Monitor
The Emergency Supplementary Reference Material requires that the measurement range of the air
monitor shall be 10 Bq/m3 or higher for gross alpha radioactivity concentration and 100 to 100,000
Bq/m3 for gross beta radioactivity concentration. Even if the concentration exceeds 100,000 Bq/m3, it
must be possible to confirm the presence of a radioactive plume above that concentration.
There is concern that when a highly concentrated radioactive plume flows during an emergency, thenumber of radiative particles from collected airborne dust entering the detector of the air monitor
increases, and the increase causes the detector to get saturated and counting loss.
Figure A-1 shows an example of evaluating the ratio of counting loss assuming an air monitor using
a 1-inch ϕ plastic scintillation detector and a decomposition time of the detector of 10 μsec. The ratioof counting loss in the gross β radioactivity concentration at the upper limit of 100,000 Bq/m3 isapproximately 11%. It should be noted, however, that Figure A-1 is an evaluation example assuming
air sampling for 10 minutes and that the ratio of counting loss would be larger for air sampling for 1
hour.
Figure A-1. Example of evaluation of the ratio of counting loss in an air monitor(1 inch ϕ plastic scintillation detector)<Measurement conditions>
Counting efficiency: 0.23, collection efficiency: 0.99, average flow rate: 50 L/min,
Air sampling time: 10 min, measurement time: 10 min

180Explanation B Example of Impact Assessment of the Accident at TEPCO's Fukushima Daiichi
NPP
The release of radioactive materials due to the accident at the TEPCO's Fukushima Daiichi NPP
following the Great East Japan Earthquake on 11 March 2011 caused an increase in the concentrationof radioactive materials in the air. Here are some examples of observations and impact assessments.
It also includes some measurement methods that differ from those described in the text.
(1) Example of continuous measurement with a dust monitor
Although the dust monitors continuously taking measurements in Fukushima Prefecture were unable
to obtain measurement data for March 2011 due to the power outage caused by the earthquake, thedust monitors continuously taking measurements in Tokai-mura, Ibaraki Prefecture, approximately
120 km away from the Fukushima Daiichi NPP, observed increase in the concentration of radioactive
materials in the air caused by the accident (Figure B-1).
Early on 15 March, the radioactive plume largely increased the gross β radioactivity concentration.
Although measurements were not taken immediately after the earthquake on 11 March due to a power
outage, measurements at MS-3 and MS-4 were restored before the radioactive plume arrived on 15
March. That at MS-2 was restored on 22 March.
Subsequently, the gross β radioactivity concentration gradually declined to a level where fluctuations
due to natural radioactive materials could be observed around the end of April. Generally, it was
confirmed to return to the original level around September by referring to annual fluctuations.

181

Figure B-1. Change over time in gross β radioactivity concentration in Ibaraki
Prefecture during the accident at the TEPCO Fukushima Daiichi NPP (MarchApril, 2011) [23].
(MS-2, MS-3, and MS-4 are the names of the station buildings, and the distance between them isapproximately 2 to 3 km. Airborne dust was collected continuously on cellulose filter paper for one
week and measured with a plastic scintillation detector.)
Dust monitor measurement in Fukushima prefecture resumed around April 2011. Figure B-2 shows
the correlation between the gross α and β radioactivity concentrations in dust monitors at Narahatown, Fukushima Prefecture, from April 2011 to March 2012.
Over time, it was observed that the slope was getting closer to the pre-accident slope, and thecorrelation was getting better. In October 2011, the observations were almost the same as before theaccident.

182

(a) April to June, 2011
(3 Bq/m3 or less expanded)(b) July to September, 2011(c) October-December, 2011(d) January-March, 2012Black (plots and approximate straight lines): data for each period(a) 14 Apr. -30 Jun., 2011(b) 1 Jul. - 30 Sep., 2011(c) 1 Oct.– - 31 Dec., 2011(d) 1 Jan. - 31 Mar., 2012

Red (plots and approximate straight lines): Data from January to 10 March, 2011
Figure B-2. Trends in the correlation between gross α and gross β radioactivity concentrations inFukushima Prefecture after the accident at the TEPCO Fukushima Daiichi NPP [24].

183

(2) Example of measurement of airborne dust sampled by a dust sampler
Figure B-3 shows a time-course change in the concentration of artificial radionuclides in airborne
dust collected in Fukushima City, Fukushima Prefecture.
In March 2011, Cs-134, Cs-137, I-131, I-132, Cs-136, and Te-132 were detected. In late May, only
Cs-137 was detected, and its radionuclide concentration decreased to 0.1 Bq/m3 or less.

* Measurements were taken daily, and only the detected data were plotted. All were ND(Not detected)
from 24 April to 7 May.
Collection method: Dust samplers were placed at a height of approximately 1 meter above the groundand sampled once a day.
Air absorbent: cellulose-glass fiber filter paper (HE-40T) + activated carbon cartridge (CHC-50-A10)
Suction amount: 1 m3 (19 March to 8 May), approx. 13 m3 (from 8 May)
Figure B-3. Change over time in the concentration of artificial radionuclides in airborne dust
collected in Fukushima Prefecture [25].
Figure B-4 shows the change over time in concentrations of radioactive cesium and radioactive
iodine (particulate form) among the concentrations of artificial radionuclides in airborne dust
collected in Tokai-mura, Ibaraki Prefecture.
In March 2011, Cs-134, Cs-136, Cs-137, I-131, I-132, I-133, Te-132, Te-129m, Te-129, Tc-99m,
and Xe-133 were detected.

184

Radionuclide concentrations of Cs-134 and Cs-137 were observed at a maximum of 426 Bq/m3 forboth nuclides but decreased to 0.1 Bq/m3 or less in late April. The radionuclide concentration of I131 was observed at a maximum value of 1430 Bq/m3, but by late April, it was almost ND (Not
Detect).

* Only the detected data are plotted.
* The air dose rate at the monitoring post (MP-11) is plotted at the same time.
Collection method: Dust sampler (approximately 1 meter above the ground) maintained in themonitoring car and monitoring post
Air absorbent: cellulose-glass fiber filter paper (HE-40TA)
Suction amount: 1 m3 (15 to 21 March), approx. 35 m3 (21 March to 7 April), approx. 70 m3 (7 to25 April), approx. 500 m3 (25 April to 6 June)
Figure B-4. Change over time in concentrations of artificial radionuclides inairborne dust sampled in Ibaraki Prefecture.
(Upper figure: radioactive cesium, lower figure: radioactive iodine(particulate form)) [26].
185

Figure B-5 shows an example of the evaluation of Cs-137 radioactivity concentration in the air insideand outside the area under evacuation order in Fukushima Prefecture. The data for 12% detected areshown since 88% of the data was ND (Not Detect) up to 2 years after the accident in the area underevacuation order (due to short measurement time and small sample volume).
The radioactivity concentration of Cs-137 in the air was in the range of 10-1 to 100 Bq/m3 up to two
years after the accident in the area under evacuation order and in the range of 10-4 to 10-1 Bq/m3 after
two years.
Outside the area under evacuation order, a decrease in Cs-137 radioactivity concentration in the air
was observed five years after the accident, probably due to decontamination work in the surrounding
areas.

186

Figure B-5. Change over time of Cs-137 radioactivity concentration in

airborne dust (partially edited figure [27])Top: within the hazard area for evacuation, Bottom: outside the hazard areafor evacuation(0: urban area, △: forest, □: grassland, ◇: paddy field)

187

Common to Part 1 and Part 2

188

189

Table of Contents
Common to Part 1 and Part 2
Information ................................................................................................................................................193
Information A Characteristics of Air Absorbents ..............................................................................195
Information B Comparative Measurement of Dust Monitors ............................................................198
Information C Evaluation Methods for Radioactive Material Concentration in the Air by γ-ray Pulse Height
Spectra .....................................................................................................................................201
Appendix ...................................................................................................................................................214
Appendix A Definition of Terms .......................................................................................................216
Reference ..................................................................................................................................................219

190

191

Information

192

193

Information A Characteristics of Air Absorbent
For the collection of an air sample, an appropriate method must be selected to measure theconcentration of radioactive materials in the air, taking into consideration the type of radioactive
materials, their physical and chemical properties, the measurement method, and other factors.
The relationship between the properties of radioactive materials and sampling methods, etc., isshown in Table Information A-1, which classifies radioactive materials into particulate and gaseous(volatile) forms.
Table Information A-1. Relationship between properties of radioactive materials and sampling
methods, etc.
Property ofradioactive
material

Sampling
methodParticulate

Filteringandcollection· Cellulose, glass fiber filter
paper· Membrane filter paper

Cs-137,
U, Pu

Solid
collection· Activated carbon-impregnatedfilter paper· Activated carbon cartridge· Activated carbon fiber filter
paper

I-131,
I-132,
I-133

Gaseous(volatile
matter)

Absorbent

MainnuclideMeasurement method· Gross α, β, and γ
measurements· α-, β-, and γ-ray
spectrum analyses· Gross  and γ
measurements· γ-rayspectrum
analysis

In collecting an air sample, it is necessary to select appropriate air absorbent in consideration of theproperties of radioactive materials in Table Information A-1.
Airborne dust is a particulate matter and is generally collected by a filtration collection method, withcellulose-glass fiber filter papers being widely used. They can be round, square, and rolled.
(1) Filter paper for airborne dust collection
Types of filter paper for airborne dust collection include cellulose-glass fiber filter paper andmembrane filter paper. Factors in selecting filter paper include collection efficiency, pressure drop,
physical strength, etc. In particular, collection efficiency is greatly affected by the particle size of thesample and ventilation speed.
Cellulose-glass fiber filter paper is widely used as filter paper for collecting airborne dust. For thecatalog values of the most commonly used cellulose-glass fiber filter paper, collection efficiency is
99.5% or higher at a ventilation speed of 57 to 141 cm/s, and pressure drop is 0.27 kPa at a ventilation
speed of 5 cm/s. It is commercially available in round and roll shapes and in many sizes.
However, it has been reported [28] that some types of cellulose-glass fiber filter paper do notnecessarily have sufficient collection efficiency for particles 0.1 μm or smaller in diameter. Caution
should be exercised when collecting them in environments where particles with 0.1 μm or smaller indiameter dominate. Cellulose-glass fiber filter paper with improved collection efficiency in thesubmicron range has also been developed, although the pressure drop is larger.
Table Information A-2 shows an example of the properties of cellulose-glass fiber filter paper.

194

Table Information A-2. Example of cellulose-glass fiber filter paper properties
Item

Product (a)Product (b)Weight (g/m2)

145

120

Paper thickness (m/m)

0.41

0.40

Air permeability (sec/cm ϕ)12

19

Tensile strength (kg/15 mm width)

4.5

3.0

80 : 2070 : 30

20 to 25/0.8

20 to 25/0.6

43 to 57

87 to 92

70

93

1.0

1.2

Fiber composition (%)

Cellulose: glass

Fiber diameter (μm)

Cellulose-glass
DOP* 0.07 μm
Minimum collection Surface velocity 20 to 130 cm/s
efficiency (%)
NaCl 0.075 μm
Surface velocity 40 to 60 cm/s
Relative pressure dropSurface velocity 30 to 130 cm/s

* Dioctyl phthalate
Cellulose-glass fiber filter paper is considered to have sufficient performance for practical use whenmeasuring the concentration of radioactive materials in the air and monitoring to contribute toevaluating internal exposure.
However, when collecting and measuring α-emitting nuclides as targets, there is a possibility thatparticles may enter the filter materials and cannot be counted, etc., and thus, correction should beconsidered as needed. It should be noted that moisture adhering to or contained in the filter paper
reduces the α-ray count as well.
(2) Filter paper for α particle collection

The surface collection rate* of filter paper is an important factor in the direct measurement of αemitting radionuclides.
Comparisons of surface collection performance and pressure drop have been reported for many typesof filter paper available in Japan [29]. An example of the report is shown in Table Information A-3.
Among membrane filter paper types, the PTFE (polytetrafluoroethylene resin) type, with areinforced back side of the filter paper, includes products with a high surface collection rate and lowpressure drop that are suitable for use in α-ray dust monitors.
* Percentage occupied by particles captured near the surface of the filter paper, of the particles
collected on the filter paper.

195

Table Information A-3. Example of characteristics of filter paper for α-particle collection
Types of filter paper

Surface collection
efficiency (%)*1

Cellulose-glass fiber
Product (a) (glass 20%, cellulose 80%)
Product (b) (glass 30%, cellulose 70%)
Glass fiber
Product (a)Product (b)Product (c)Silica fiber
Product (a)Membrane (cellulose mixed ester)
Product (a) (0.8 μm pore size)
Product (b) (0.8 μm pore size)
Product (c) (1.0 μm pore size)
Product (d) (5.0 μm pore size)
Membrane (PTFE type)
Product (a) (0.8 μm pore size)
Product (b) (1.0 μm pore size)
Product (c) (3.0 μm pore size)
Membrane (PTFE type with back side reinforced)
Product (a) (1.0 μm pore size)
Product (b) (3.0 μm pore size)
Product (c) (3.0 μm pore size)
Pre-filter
Product (a)Product (b)Product (c)Product (d)Relative pressure
drop*245±0.956
65±1.556±0.3
94

0.26
0.11
1.4

76±1.60.48

94±0.7
95
90
79

1
1.2
0.76
0.42

97±1.9
98
87

2.1
1.5
0.5

99
99
95

0.63
0.31
0.28

98
82
69
91

1.8
0.83
0.27
0.54

*1 Value evaluated from the spread of α-ray spectra of thoron decay products.
*2 Value obtained based on membrane (cellulose mixed ester) product (a).
（Surface velocity 50 cm/sec)

196

0.17
0.20

Information B Comparative Measurement of Dust Monitors(1) Comparative measurement methods
Comparative measurements were made at the same location and time using two or more dust
monitors with different specifications. The specifications of the two dust monitors are shown in Table
Information B-1.
Table Information B-1. Specifications of dust monitor used for comparative measurement
Item

Dust Monitor (a)Air absorbent

Membrane filter paper

Flow rate

Approx. 35 L/min (2 m3/h)

Detector

Removal of the effect ofexternal radiation

Nuclide discrimination
Data interval

Recorded Information

Dust Monitor (b)Cellulose-glass fiber filter
paper
Approx. 200 L/min (12 m3/h)

Double silicon semiconductor ZnS (Ag) + plastic scintillation
detector (PIPS)
detectorShielding by α/β absorber (Cuplate), correction by γ-ray
Lead shielding (approx. 3 cm)
background compensation
detector(γ-ray from outside
and filter paper)
Analyzing the spectrum
attributed to radon and thoron
Noneand correcting the effect level.
2 minutes
Flow rate (m3/h), integrated
flow volume (m3), Gross α andβ radioactivity concentrations(Bq/m3) and count rates (s-1)(Radon-thoron correctingdata), Radon radioactivity
concentration (Bq/m3), Thoron
radioactivity concentration(Bq/m3), etc.

197

2 minutes
Flow rate (m3/h), integrated
flow volume (m3),Integration time (s),Gross α radioactivity
concentration (Bq/m3),
Gross β radioactivity
concentration (Bq/m3),
Count rate (s-1), etc.

Figure Information B-1. Dust monitor used for comparative
measurement(Left: dust monitor (a), Right: dust monitor (b))(2) Comparison measurement result
Since dust monitor (a) can only output the gross α and β radioactivity concentrations after subtracting
the contribution from natural radioactive materials (radon/thoron), the measured radon and thoron
radioactivity concentrations were used for comparison. For dust monitor (b), gross α and gross β
radioactivity concentrations were used for comparison.
The results of comparative measurement are shown in Figure Information B-2. The change trendsof radon radioactivity concentration in dust monitor (a) and gross α and β radioactivity concentrations
in dust monitor (b) showed good agreement. The maximum thoron radioactivity concentration in dust
monitor (a) was approximately one-tenth of the maximum radon radioactivity concentration. It wasconsidered that thoron contributed little to the gross α and β radioactivity concentrations in dust
monitor (b).

198

Figure Information B-2. Comparative measurement result of dust monitor

199

Information C Evaluation Methods for Radioactive Material Concentration in the Airby γ-ray Pulse Height Spectra
This section describes methods and examples of evaluating the concentration of radioactive
materials in the air using γ-ray pulse height spectra obtained from monitoring posts that measure air
dose rate, transportable type germanium semiconductor detectors, dust monitors, etc.
The method described here also allows for the estimation of the radioactivity concentration in the
air of short half-life nuclides such as radioactive iodine and noble gases, which are difficult to measure
in practice.
In addition, measurements for radiation sources in the air are characterized by the ability to evaluate
the average concentrations of radionuclides around the measurement points to measure γ-ray fromradiation sources distributed over a wide space.
(1) Evaluation using pulse height spectra of monitoring post
Terasaka et al. and Moriizumi et al. used pulse height spectra observed at monitoring post using NaI(Tl) scintillation detectors in Ibaraki Prefecture during the Fukushima Daiichi NPP accident (Figure
Information C-1) to establish peak regions for analysis for each radionuclide (Table Information C1). The radioactivity concentration of each radionuclide in the air was estimated using a Monte Carlosimulation. Examples of evaluation are shown in Figures Information C-2 through C-4.
The radioactivity concentrations of several radionuclides in the air have been evaluated. They agree
well with the actually measured values of radioactive iodine and other radionuclides, as shown in
Figure Information C-2.
However, the application of this method assumes that the pulse height spectrum of the NaI (Tl)scintillation detector can be properly acquired. Counting loss, etc., may prevent evaluation in case ofhigh radiation dose rates in the air during an emergency.

200

Figure Information C-1. Pulse height spectra were observed at a monitoring
post in Ibaraki Prefecture [30].

Table Information C-1. Radionuclides and energy ranges were used in the analysis [30].

201

[31]

[30]

Figure Information C-2. Time-series chart of radionuclide concentrations in
the air evaluated by simulation [31].

202Figure Information C-3. The Distribution of radionuclide concentrations in
the air was evaluated by simulation [31].

203

Figure Information C-4. Pulse height spectra reconstructed bysimulation [30].
(Top: with passing plume, Bottom: without the effect of plume)204

(2) Evaluation of a transportable type germanium semiconductor detector using pulse height spectra
The radioactivity concentration in the air for each radionuclide can be evaluated from the γ -ray pulse
height spectrum measured in situ using a transportable type germanium semiconductor detector.
For the measurement method using a transportable type germanium semiconductor detector and thedescription of each parameter, refer to The Series of Environmental Radioactivity Measuring Methods
No. 33, "In-situ measurement method using germanium semiconductor detector".
Assuming that radionuclides are uniformly present in the air, the radioactivity concentration A(Bq/m3) of the radionuclide in the air is calculated by the following formula.
A = Nf /Nf
A

A: Radioactivity concentration in the air (Bq/cm3)
Nf: Peak count rate at a certain energy E in in-situ measurement (s-1)
Nf /A: Efficiency in in-situ measurements
Nf N0 Nf ϕ=∙∙A
ϕ N0 A
N0: Peak count rate due to γ rays with energy E incident from the detector axis direction (0°) (s-1)
ϕ: fluence rate (cm-2s-1)
N0/ϕ and Nf/N0 are detector-specific values. ϕ/A uses the parameters in the Table Information
C-2 corresponds to the radionuclide and photon energy.
Figure Information C-5 shows an example of evaluating changes over time in Xe-133 radioactivity
concentration in the air using this method from the pulse height spectrum of a transportable typegermanium semiconductor detector that was continuously measuring outdoors in Chiba City, Chiba
Prefecture, during the TEPCO Fukushima Daiichi NPP accident in March 2011.
The air dose rate measured at the monitoring post on 15 March showed the same trend of change as
the Xe-133 radioactivity concentration, and it was confirmed that the Xe-133 contained in theradioactive plume contributed largely to the increase in the air dose rate.
The increase in the air dose rate on 21 March was attributed to the deposition of radioactive materials
from the air on the ground surface due to rainfall. The Xe-133 radioactivity concentration at that time
was not as high as on 15 March.
When evaluating the air radioactivity concentration of radionuclides present in particulate form, it isnecessary to subtract the effect of radionuclides deposited on the ground surface. The air dose rate in
Figure Information C-5 includes the contribution of radioactive cesium, radioactive iodine, and otherradionuclides released during the accident. However, the radioactivity concentration in the air is notshown because it was difficult to evaluate it properly.

205

* Xe-133 is shown by a 1-hour value. The period with no plot is non-detectable.
* Germanium semiconductor detector: installed approximately 1 m above the ground with a relative
efficiency of approximately 25%.
Figure Information C-5. Example of evaluation of Xe-133 radioactivity concentration in
the air in Chiba City, Chiba Prefecture (March 2011)206

Table Information C-2 Concentration of radionuclides in the air vs. γ-ray fluence rate at 1 m above the ground [32].
Cont. (a)Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

14.8

Cm-248

0.058

0.2

258.3

Xe-138

0.315

12.4

27.8

Te-129

0.156

2.1

277.6

Np-239

0.144

5.8

28.6

Xe-125

0.539

7.7

278.0

Te-134

0.209

8.5

30.6

Xe-133

0.083

1.3

295.2

Pb-214

0.192

7.9

31.0

Xe-133

0.155

2.5

304.9

Kr-85m

0.140

5.8

32.0

Ba-137m

0.059

1.0

312.1

Te-133

0.624

26.2

74.8

Pb-212

0.104

3.0

340.5

Cs-136

0.422

18.4

77.1

Pb-212

0.176

5.0

344.3

Eu-152

0.266

11.6

81.0

Xe-133

0.371

10.6

345.9

Hf-181

0.120

5.2

99.6

Np-239

0.157

4.7

351.9

Pb-214

0.369

16.2

103.8

Np-239

0.251

7.7

364.5

I-131

0.812

36.1

106.1

Np-239

0.272

8.3

375.0

Xe-127

0.172

7.7

122.1

Co-57

0.855

27.1

402.6

Kr-87

0.496

22.9

133.0

Hf-181

0.419

13.6

407.6

Te-133

0.271

12.6

136.5

Co-57

0.106

3.5

414.5

Sb-126m

0.857

40.0

140.5

Tc-99m

0.890

29.2

414.8

Sb-126

0.833

38.9

143.8

U-235

0.110

3.6

418.0

I-130

0.341

16.0

145.4

Ce-141

0.484

16.1

427.9

Sb-125

0.294

13.9

148.9

Xe-123

0.490

16.4

434.5

Xe-138

0.203

9.7

149.7

Te-131

0.689

23.1

435.1

Te-134

0.186

8.9

151.2

Kr-85m

0.755

25.3

452.3

Te-131

0.182

8.8

172.1

Xe-127

0.255

8.9

459.6

Te-129

0.074

3.6

185.7

U-235

0.572

20.3

461.0

Te-134

0.099

4.8

188.4

Xe-125

0.549

19.7

462.8

Cs-138

0.307

15.0

202.5

Y-90m

0.958

35.1

463.4

Sb-125

0.105

5.1

202.9

Xe-127

0.683

25.0

469.4

Ru-105

0.175

8.6

205.3

U-235

0.050

1.8

473.0

Sb-127

0.247

12.2

210.5

Te-134

0.223

8.2

477.6

Be-7

0.103

5.1

228.2

Np-239

0.113

4.3

479.5

W-187

0.253

12.5

228.2

Te-132

0.882

33.4

479.5

Y-90m

0.900

44.5

234.7

Nb-95m

0.261

10.0

482.0

Hf-181

0.830

41.1

238.6

Pb-212

0.434

16.7

487.0

La-140

0.459

22.8

241.9

Pb-214

0.075

2.9

497.1

Ru-103

0.889

44.6

243.4

Xe-125

0.288

11.2

507.7

Zr-97

0.053

2.7

249.8

Xe-135

0.901

35.2

511.0

Co-58

the 0.301

15.3

207

Table Information C-2 Cont. (b)Cont. (c)Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

511.0

Na-22

the 1.810

91.8

666.3

Sb-126

0.997

56.5

511.0

Xe-123

0.450

22.8

667.7

T-132

0.987

56.0

511.9

Rh-106

0.207

10.5

668.5

I-130

0.961

54.5

514.0

Kr-85

0.004

0.2

676.4

Ru-105

0.157

8.9

526.6

Xe-135m

0.812

41.7

685.7

Sb-127

0.353

20.2

529.9

I-133

0.863

44.4

685.8

W-187

0.316

18.1

536.1

I-130

0.990

51.2

694.8

Sb-126m

0.823

47.4

537.3

Ba-140

0.244

12.6

695.0

Sb-126

0.997

57.5

544.7

Sb-129

0.179

9.3

697.0

Sb-126

0.289

16.7

550.3

Pm-148

0.220

11.5

710.4

Sr-93

0.213

12.4

550.3

Pm-148m

0.944

49.4

719.7

Te-133

0.089

5.2

551.5

W-187

0.059

3.1

720.5

Sb-126

0.538

31.5

555.6

Y-91m

0.949

49.8

723.3

Eu-154

0.197

11.6

569.3

Cs-134

0.150

8.0

724.2

Zr-95

0.444

26.1

583.2

Tl-208

0.851

45.6

724.3

Ru-105

0.473

27.8

590.3

Sr-93

0.328

17.6

725.7

Pm-148m

0.327

19.2

590.9

Mo-101

0.164

8.8

727.2

Bi-212

0.068

4.0

600.6

Sb-125

0.178

9.6

739.5

Mo-99

0.112

7.2

602.7

Sb-124

0.979

53.2

739.5

I-130

0.823

48.7

604.6

Cs-134

0.975

53.0

742.6

Te-134

0.151

9.0

606.6

Sb-125

0.050

2.7

749.8

Sr-91

0.236

14.1

609.3

Bi-214

0.469

25.6

756.7

Zr-95

0.549

32.9

610.3

Ru-103

0.056

3.1

763.9

Ag-110m

0.224

13.5

618.4

W-187

0.073

4.0

765.8

Nb-95

1.000

60.2

621.8

Rh-106

0.098

5.4

767.2

Te-134

0.290

17.5

630.0

Pm-148m

0.866

49.0

772.6

I-132

0.762

46.0

635.9

Sb-125

0.113

6.3

773.7

Te-131m

0.382

23.1

637.0

I-131

0.073

4.1

778.9

Eu-152

0.130

7.9

641.3

La-142

0.474

26.4

783.7

Sb-127

0.145

8.8

642.3

Sb-131

0.220

12.3

793.8

Te-131m

0.139

8.5

647.5

Te-133m

0.194

10.9

795.8

Cs-134

0.851

52.1

652.9

Sr-91

0.080

4.5

810.8

Co-58

0.994

61.4

657.7

Ag-110m

0.947

53.4

811.8

Eu-156

0.103

6.4

657.9

Nb-97

0.983

55.4

812.8

Sb-129

0.430

26.6

661.6

Ba-137m

0.899

50.8

815.8

La-140

0.236

14.6

664.5

Ce-143

0.053

3.0

818.5

Cs-136

0.997

61.8

666.1

Sb-126m

0.857

48.5

834.8

Mn-54

1.000

62.6

208

Table Information C-2 Cont. (d)Cont. (e)Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

834.8

Kr-88

0.130

8.1

1025.9

Np-238

0.096

6.6

845.4

Kr-87

0.073

4.6

1028.5

Np-238

0.203

14.0

846.8

Mn-56

0.989

62.3

1030.1

Sb-129

0.126

8.7

846.8

Co-56

0.999

62.9

1031.9

Rb-89

0.580

40.0

847.0

I-134

0.954

60.1

1038.8

I-135

0.080

5.5

852.2

Te-131m

0.206

13.0

1048.1

Cs-136

0.798

55.5

856.7

Sb-126

0.176

11.1

1072.6

I-134

0.150

10.5

864.0

Te-133m

0.156

9.9

1085.9Eu-152

0.099

7.0

873.2

Eu-1540.115

7.3

1099.2

Fe-59

0.565

40.2

875.7

Sr-93

0.239

15.3

1112.1

Eu-152

0.136

9.7

881.6

Br-84

0.420

26.9

1115.5

Ni-65

0.148

10.6

884.1

I-134

0.649

41.7

1115.5

Zn-56

0.507

36.3

884.7

Ag-110m

0.729

46.8

1120.3

Bi-214

0.155

11.1

888.1

Sr-93

0.216

13.9

1120.5

Sc-46

1.000

71.8

889.3

Sc-46

1.000

64.4

1121.3

Ta-182

0.349

25.1

898.0

Rb-88

0.140

9.1

1123.6

Sb-131

0.083

6.0

911.3

Ac-228

0.290

19.0

1125.5

Te-131m

0.114

8.2

912.7

Te-133m

0.550

35.8

1131.5

I-135

0.228

16.4

914.6

Sb-129

0.200

13.1

1153.5

Eu-156

0.071

5.2

914.8

Te-133m

0.109

7.1

1157.5

I-130

0.113

8.2

914.8

Pm-1480.115

7.5

1173.2

Co-60

0.999

73.4

915.3

Pm-148m

0.171

11.2

1189.0

Ta-182

0.164

12.1

933.1

Sb-131

0.246

16.2

1206.6

Te-131m

0.098

7.3

937.5

Ag-110m

0.343

22.7

1221.4

Ta-182

0.273

20.5

943.4

Sb-131

0.440

29.1

1230.7

Eu-156

0.089

6.7

954.5

I-132

0.181

12.1

1231.0

Ta-182

0.116

8.7

964.1

Eu-1520.145

9.7

1235.4

Cs-136

0.200

15.1

964.8

Ac-2280.055

3.7

1238.3

Co-56

0.670

50.5

966.4

Sb-1290.077

5.2

1242.4Eu-156

0.067

5.1

969.2

Ac-228

0.175

11.7

1248.1

Rb-89

0.423

32.0

984.5

Np-238

0.278

18.8

1260.4

I-135

0.289

22.0

996.3

Eu-1540.103

7.01274.4Eu-154

0.355

27.1

1004.8

Eu-154

0.174

11.9

1274.5

Na-22

0.999

76.4

1009.8

Cs-138

0.298

20.4

1291.6

Fe-59

0.432

33.3

1012.5

Mo-1010.128

8.8

1332.5

Co-60

1.000

78.2

1013.8

Pm-148m

0.202

13.8

1333.2

Te-1330.107

8.4

1024.3

Sr-91

0.334

23.0

1368.6

Na-24

1.000

79.3

209

Table Information C-2 Cont. (f)Cont. (g)Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

Energy[keV]

NuclideRelease ratio[s-1 Bq-1]

ϕ/Av[m s-1 Bq-1]

1383.9

Sr-92

0.900

71.8

2570.2

Rb-89

0.099

10.9

1384.3Ag-110m

0.243

19.4

2598.6

Co-56

0.167

18.5

1408.0Eu-152

0.209

16.8

2614.5Tl-208

0.999

110.7

1435.9

Cs-138

0.763

62.0

2639.6

Cs-1380.076

8.5

1457.6

I-135

0.087

7.1

2754.0

Na-24

0.999

113.5

1460.8

K-40

0.107

8.8

3253.5

Co-56

0.074

9.2

1465.1

Pm-148

0.222

18.2

3927.5

Br-84

0.068

9.3

1481.8

Ni-65

0.235

19.4

1505.0Ag-110m

0.131

10.9

1529.8

Kr-88

0.109

9.1

1532.5

Mo-1010.060

5.0

1596.2

La-140

0.954

81.7

1678.0

I-135

0.096

8.4

1691.0

Sb-124

0.488

43.1

1736.5

Sb-1290.060

5.4

1764.5

Bi-214

0.162

14.6

1768.3

Xe-138

0.167

15.1

1771.4

Co-56

0.155

14.0

1791.2

I-135

0.078

7.1

1810.7

Mn-56

0.272

24.8

1836.0

Rb-88

0.214

19.7

1897.6

Br-84

0.147

13.8

1901.3

La-142

0.072

6.7

2004.8

Xe-1380.054

5.2

2015.8

Xe-138

0.123

11.9

2032.1

Mo-1010.069

6.7

2091.0

Sb-1240.056

5.5

2113.0

Mn-56

0.143

14.2

2195.8

Kr-88

0.132

13.4

2195.9

Rb-89

0.133

13.5

2204.1

Bi-2140.052

5.3

2218.0Cs-138

0.152

15.5

2392.1

Kr-88

0.346

36.6

2397.8

La-142

0.133

14.1

2484.1

Br-84

0.067

7.2

2542.7

La-142

0.100

10.9

2554.8

Kr-87

0.092

10.1

210

(3) Evaluation using pulse height spectra of a dust monitor
Using a germanium semiconductor detector as the detector for the dust monitor enables
quantifying radionuclides and evaluating the concentration of radionuclides in the air due to theexcellent energy resolution of the germanium semiconductor detector.
Dust monitors are used for early detection of radioactive releases from nuclear facilities, and the
NaI (Tl) scintillation detector is superior in terms of sensitivity for this purpose.
It should also be noted that a germanium semiconductor detector is expensive and requires
cooling, which places a heavy administrative burden on the detector when it is used as a continuous
monitor.
For the quantitative measurement method of radionuclides using a germanium semiconductor
detector, refer to The Series of Environmental Radioactivity Measuring Methods No. 7 " γ-ray
spectrometry using germanium semiconductor detector".

Figure Information C-6. Example of dust monitor using a germanium semiconductor detector

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Figure Information C-7 Example of a pulse height spectrum of a germanium
semiconductor detector [33].

212Appendix

213

214

Appendix A Definition of Terms
Definitions of terms used in this measurement method are given below.
Term
Description
Dust monitor An instrument for continuous measurement of radioactivity concentration in
airborne dust and for use at normal times.
Although “dust monitor” is a generic instrument name, this measurement
method defines a dust monitor as an instrument used at normal times inprinciple.
In case of emergency, a dust monitor is operated additionally in emergency
mode to strengthen the monitoring system.
In this measurement method, the use of a dust monitor as a dust sampler is
included in the scope.
Air monitor
An instrument for continuous measurement of radioactivity concentration in
airborne dust and use in an emergency.
The measurement principle is the same as that of a dust monitor. However, an
air monitor is an additional instrument for emergency use. It is designed toquickly measure the concentration of radioactive materials in the air at shorttime intervals.
Dust sampler An instrument for collecting airborne dust on filter paper.
IodineAn instrument for collecting radioactive iodine (particulate and gaseous) in thesampler
air on filter paper and an activated carbon cartridge.
Gas monitor Instrument for continuous measurement of gaseous radioactive material
concentration in the air.
Air absorbent Material for collecting air samples. This measurement method means filter
paper and an activated carbon cartridge.
PAZ
Precautionary Action Zone
The area where preventive, protective measures are prepared.
· The area where preventive, protective measures are prepared from the stage
before the release of radioactive materials, such as immediate evacuationaccording to the EAL, in order to avoid or minimize a serious deterministic
effect due to radiation exposure.
· The specific routine range of a PAZ for a nuclear power reactor facility is"within approximately 5 km radius from the nuclear facility".
UPZ
Urgent Protective action planning Zone
Area where an emergency protective measure is prepared.
· Area where an emergency protective measure is prepared in accordancewith EAL and OIL to reduce the risk of stochastic effect.
· The specific routine range of the UPZ for a nuclear power reactor facility is"within approximately 30 km radius from the nuclear facility".
Normal time Environmental radiation monitoring that should be conducted after the start ofmonitoring
the operation of the nuclear facility (excluding emergencies).
Term
Description
Emergency
Environmental radiation monitoring that should be conducted in an alert statemonitoring
based on the Nuclear Emergency Response Guidelines.
preparation
Emergency
monitoring

Environmental radiation monitoring should be conducted during facility site
emergency and total emergency based on the Nuclear Emergency Response
Guidelines.

215

Informationcollection
situation
Classificationofemergencies
Alert stateStage to confirm whether or not radioactive materials have been released, etc.

Classified into "alert state", "facility site emergency", and "total emergency"
based on the Nuclear Emergency Response Guidelines.

The stage where the occurrence or threat of an abnormal event at a nuclear
facility requires the start of information collection, preparation for emergency
monitoring, or preparation for protective measures such as the evacuation of
those who need to be evacuated in a facility site emergency.
Facility site
The stage in which an event potentially causing radiological consequences toemergency
the public has occurred at a nuclear facility, and it is necessary to start preparing
for major protective measures, such as evacuation, in the vicinity of the nuclear
facility in case of emergency.
Total
The stage in which an event has occurred at a nuclear facility with a highemergency
probability of causing radiological consequences to the public and prompt
protective actions need to be taken to avoid (minimize) severe deterministic
effects and to reduce the risk of stochastic effects.
Airborne dust Airborne particulate matter.
Air
Gase covering the earth's surface.
In this measurement method, in some cases, the air is treated as gaseous matterand is distinguished from particulate matter (airborne dust).
Air moisture Moisture existing in the air.
Radioactive
A group of air containing radioactive gaseous or particulate matter.
plume
External
Receiving radiation from a radiation source outside the body.
exposureInternal
Ingesting radioactive materials into the body by inhalation, oral intake, etc., andexposure
receiving radiation from radiation sources in the body.
Lower limit
The minimum value at which the measurement target can be detected when theof detection
measurement sample and the measurement conditions (measuring instrument,
measurement time, etc.) are determined.
Maximum
Detection sensitivity is required for a dust monitor to measure radioactivity
detection
concentration as specified in JIS Z 4316:2006
sensitivity
Decision
The threshold value of dust monitor measurement where the difference from thethresholdbackground is significant, as specified in JIS Z 4316:2013
Confirmation The value that triggers the initiation of the causal investigation to determine if
start setpoint there is a contribution from a nuclear facility. Confirmation start setpoint is set
considering the variation of an individual equipment and past maximum values,
with the maximum dust monitor measurement value after facility contribution
discrimination set at approximately 5 Bq/m3 (gross β radioactivity

Term
Normalfluctuation
range
Counting
Count rate

concentration or γ-ray emitting nuclide concentration) or 1 Bq/m3 (gross α
radioactivity concentration).
Description
The range of fluctuation of measured values that is generally considered to fallwithin a certain range at the time of normal operation of a nuclear facility andwhen measurement conditions, etc., are properly controlled.
One response (count) of the counting instrument.
Count value per unit time.
Usually indicated in cpm (m-1) or cps (s-1).
216

Count rate
meter
ScalerGross αradioactivity
concentration
Gross βradioactivity
concentration
γ-ray countrate
β/α ratio

An instrument that continuously indicates the average count rate.
Also called the rate meter.
A part of a counting instrument that integrates and displays the number of input
pulses.
Radioactivity concentration (Bq/m3) of α-ray from α-emitting nuclides
contained in airborne dust that is measured without energy discrimination(except when spectrum analysis is performed) and evaluated by one type of α
standard source used in the efficiency calibration of the dust monitor.
Radioactivity concentration (Bq/m3) of β-ray from β-emitting nuclides
contained in airborne dust that is measured without energy discrimination(except when spectrum analysis is performed) and evaluated by one type of βray standard source used in the efficiency calibration of the dust monitor.
Count rate of γ-ray emitted from airborne dust (s-1)

The ratio of gross β radioactivity concentration measured by a dust monitor
divided by gross α radioactivity concentration
Counting loss When counting radioactive particles or pulses, decrease in the measured countvalue due to detector dead time, decomposition time, pile-up, etc., or the amountof decrease.
Facility
Effects of radioactive materials released from a nuclear facility
contribution
StationA facility that concentrates radiation measuring equipment to measure outdoor
building
air dose rate, concentration of radioactive materials in the air, etc., around a
nuclear facility or radiation facility.

217

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