Calibration of Survey Mete

and

Measurements of Contamina

1/18/2011
Types of Calibration
Types of Calibration

A calibration determines the relationship between tinstrument response/reading and a quantity of inter

Instrument Response 

↔ Quantity of Inte

The three common types of calibration:

• Electronic Calibration• Energy Calibration• Radiological (Primary) Calibration

- Exposure Rate Measurements- Counting Efficiency for Activity Measure
Electronic Calibration
General

Count Rate ↔ Pulse Rate

• An electronic calibration determines the relationsh

between the pulse rate and the count rate. If nece

instrument is adjusted so that the count rate exac

Electronic Calibration

j 

matches the pulse rate. In general, electronic caliare only performed on instruments that read out icps). 

• In the early days, it was common to set the instru

usually a scaler, into the test mode whereby it wothe cycles in the AC line current. Since the latter's frequency is 60 cycles per second, 3600 counts sregistered over a one-minute count. 
General

• Electronic calibrations usually involve connecting 

rate meter to a pulse generator (pulser). 

• The generator's pulse rate is variable.

• The amplitude of the pulses can also be adjusted Electronic Calibration

The amplitude of the pulses can also be adjusted

pulse amplitude must exceed the meter’s threshoand should be similar to the size of the pulses prothe detector. 

• If necessary, the meter’s threshold setting can be 

determined by lowering the amplitude of the pulsepoint at which no counts are registered. 
Pulser

Electronic Calibration
General

• Electronic calibrations are generally performed in 

of each scale. 

• For example, if the x1 scale is from 0 to 500 cpm

pulser would be set to 250 pulses per minute.

Electronic Calibration• If the meter being calibrated does not register 250 

would be adjusted to do so.

• The meter would then be switched to the x10 sca

pulse rate from the pulser would be set at 2500 pminute, etc, etc.
Electronic Calibration
Energy Calibration
General

Measured Pulse Size ↔ Energy of Rad

• In an energy calibration, we determine the relatio

between the measured height of the pulses and tof the radiation (gamma rays, alpha particles or b

Energy Calibration

(g y , p p

particles). 

• The measured height of a pulse is the channel nu

which that pulse is sorted. 

• The calibration is accomplished by counting a sou

emits radiation at known energies and assigning numbers to the corresponding "peaks" on the speEach peak consists of many pulses of similar heig
Factors That Affect the Energy Calibratio

• The calibration only applies at a specific high volt

and amplifier gain. 

• Other factors can affect the calibration, e.g., the e

deposition rate in the detector (sodium iodide dete

)

Energy Calibration

particularly prone to this problem . 

• The relationship between radiation energy and th

assigned to the corresponding peak on the spectrusually very close to linear.
Example Energy Calibration Curve

Energy Calibration

E) in keV 1000 1500 Intercept (E

0) in keV

Channel Number (X)

0 500 1000 1500 2000 2

Energy (E 500 E = m X + E

0
Energy Calibration Equation

• Since the relationship between channel number a

is essentially linear, the following equation is oftedescribe the relationship:

E = m X + E

0

Energy CalibrationE is the radiation energy (e.g. keV) responsible for X is the channel assigned to the peakm is the slope (e.g. keV/channel)E

0 is the energy corresponding to channel zero (e.g

• Since the relationship between energy and chann

might not be completely linear, a quadratic equatbe used instead.
Radiological Calibration –

Exposure Rate MeasuremeExposure Rate Measureme
General

Indicated Exposure Rate ↔ Actual Expo

• The relationship between an instrument’s indicate

exposure rate and the actual exposure rate is det

• In other words we determine the accuracy of the

Radiological Calibration – Exposure 

In other words, we determine the accuracy of the

measurements made with the instrument.

• As used here, the term “exposure rate” (e.g., mR/

includes dose rate (e.g., mGy/hr) and dose equiva(e.g., mrem/hr, uSv/hr).

• Instruments that might be calibrated this way inclu

sidewall or side window GMs, uR or uSv meters, chambers, etc.
General

• Survey instrument calibrations for NRC or Agreem

licensees will be performed according to the regulicense requirements. At DOE facilities, the calibrausually performed according to ANSI N323. 

I ith th i d t i d t i 

Radiological Calibration – Exposure • In either case, the accuracy is determined at a mi

two points on each scale (usually 20% and 80% oreading) if the instrument has an analog linear readigital readout with separate scales. 

• If the instrument has a logarithmic readout or dig

readout without scales and in the middle of each (5 mR/hr, 50 mR/hr, 500 mR/hr etc). 
Radiological Calibration – Exposure 

20% of

full scale

80% 

full sc
Determining the Actual Exposure Rate

The actual exposure rates are:

• Calculated theoretically at various distances fro

standard source (usually Cs-137) of known actis the preferred approach. This source must be 

t bl

Radiological Calibration – Exposure 

traceable.

• Measured by a "transfer" instrument, the accur

which has been determined by NIST or a secoNIST laboratory. The transfer instrument shouused for calibration of other instruments. It is no“field” use. One concern is that the response otransfer instrument might change.
Ways to Vary the Calibration Exposure R

Three methods can be employed to produce the vaexposure rates required for calibration:

• Use sources of different activities

Radiological Calibration – Exposure 

• Vary the distance between the detector and so• Employ attenuators between the source and d

Attenuators, usually made of lead, are shieldreduce the intensity of the radiation by a specamount. Unfortunately, attenuators change the spectrum.
Ways to Vary the Calibration Exposure R

• The distance required to achieve a desired expos

involves the use of the following equation:

Radiological Calibration – Exposure d is the distance between the source and detector (A is the activity of the standard source (e.g. mCi)Γ is the specific gamma constant (e.g. mR/hr at 1 cX is the required exposure rate (e.g. mR/hr)F is the attenuator factor (1 if no attenuator is used)
Ways to Vary the Calibration Exposure R

Radiological Calibration – Exposure 

lead 

attenu
Common Calibration Set-ups

• Free in-air source of known activity• Collimated source of known activity• Well calibrato

r

Radiological Calibration – Exposure 

• Box calibrator
Radiological Calibration – Exposure 

F I i St d d S

Standard Source of Known Activity

Free In-air Stan

dar

d

Source

m

Collimated Standard Source
Free In-air Source of Known Activity

• The standard source is not collimated• The beam is omnidirectional• Sometimes performed outdoors

Radiological Calibration – Exposure Collimated Source of Known Activity

• The most common calibration arrangement• The beam is collimated, usually in the form of a • Scatter is reduced• Helps minimize worker exposures
Radiological Calibration – Exposure 

Well Calibrator meter

Standard Source 

(position movable)
Well Calibrator

• The detector is in a fixed position at the top of th• The source is moved up and down in the well to 

the desired exposure rate

• The source does not need to be removed from t

Radiological Calibration – Exposure 

The source does not need to be removed from tcalibration well

• The actual exposure rates are typically measure

transfer instrument rather than calculated
Radiological Calibration – Exposure 

meter

Box Calibrator window
Radiological Calibration – Exposure 

Box Calibrator
Box Calibrator

• The calibration is performed with the sources an

inside a shielded box. The box is usually on whe

• A lead glass window is on the top of the box so 

instrument can be read

Radiological Calibration – Exposure 

• Box calibrators are very convenient when space • The actual exposure rates are measured with a 

instrument because of the potential for scatter in 

• The source to detector distance is not very adju• The primary ways to adjust the exposure rates a

multiple sources and collimators
Reading the Meter During Calibration

To minimize exposures to the calibration personnelmight be read remotely. This might be accomplishe

• Viewing the meter on a remote monitor - a vide

is aimed at the meter dis

pla

y

Radiological Calibration – Exposure 

p y

• Viewing the meter reading (or its reflection in a 

through a telescopic lens or a pair of binoculars

• Coupling the meter to a computer so that the ins

response is indicated on the computer monitor. be a hard-wired or blue tooth connection
Reading the Meter During Calibration

Radiological Calibration – Exposure 
Example Calibration

Prior to the calibration, the instrument was adjusted accurate as possible at the midpoint on each scaleCalibration source nuclide: Cs-137Radiological Calibration – Exposure Specific gamma ray constant: 0.32 R m2 h-1 Ci-1Decay corrected activity of calibration source 1: 25 Decay corrected activity of calibration source 2: 10Attenuator factor: 8.56
Radiological Calibration – Exposure 

Source Activity

(A)

Source to 

Detector 

Distance 

(d)

Attenuator 

Factor

(F)

Actual 

Exposure 

Rate Meter Scale

Indicate

exposur

Rate

25 Ci 2.16 m 8.56 0.2 R/hr 0 – 1 R/hr 0.18 25 Ci 3.16 m 1 0.8 R/hr 0 – 1 R/hr 0.74 

( ) Xt

& ( ) Xi

& 

Example Calibration

25 Ci 2.0 m 1 2.0 R/hr 0 – 10 R/hr 1.97 

100 Ci 2.0 m 1 8.0 R/hr 0 – 10 R/hr 8.10 100 Ci 1.26 m 1 20 R/hr 0 – 100 R/hr 17.6 100 Ci 0.63 m 1 80 R/hr 0 – 100 R/hr 76.0 

Average Calibration 

Factor

Depending on the regulatory/license requirements, no adjustmusing a calibration factor) are necessary if the indicated exposwithin 10 to 20% of the actual exposure rate.
Traceability of the Standard Source

• The standard source should be traceable to the N

Institute of Standards and Technology (NIST). Th

means that the source activity was determined wiinstrument whose efficiency was determined with that came from NIST or a secondar

y laborator

y. 

Radiological Calibration – Exposure 

y y

• National standard: the primary standard source m

by NIST to which other standard sources should b

• Secondary standard: a source whose activity has 

determined by direct comparison with the nationa

• Tertiary standard: a source whose activity was de

comparison with a secondary standard. 
Traceability of the Standard Source

• The standard used by a given laboratory might be 

secondary or tertiary standard. 

• A standard produced at NIST for the purpose of s

another laboratory might be referred to as a trans

Radiological Calibration – Exposure 

standard. 

• See ANSI N42.22-1995 Traceability of Radioactiv

to the National Institute of Standards and Technoand Associated Instrument Quality Control.

• As a rule of thumb, a source should be recertified 

to three half-lives or 8 to ten years, whichever comThis is particularly important for unsealed plated s
Energy Dependence

• Calibrations demonstrate that the measurement a

acceptable at the calibration energy (usually 662 Nevertheless, measurements of exposure rates aphoton energies might not be so accurate. 

Radiological Calibration – Exposure • Fortunately, this effect is rarely an issue above 3

so. Almost any instrument calibrated at 662 keV cexpected to make accurate measurements above 

• However, below 300 keV, many detectors over re

Such instruments, if calibrated at 662 keV, would an exposure rate higher than actually existed due keV photons. 
Energy Dependence

• Characteristics of instruments that over-respond a

energies:- they operate in the pulse mode- the photon interactions in the detector are with a 

Radiological Calibration – Exposure 

the photon interactions in the detector are with a 

whose atomic number is greater than 7 to 8 (the number of air, water, human tissue)

• Instruments that over-respond at low energies: m

NaI detectors (e.g., uR meter), CaF2, CaSO4

• Energy independent instruments: energy compen

ion chambers, plastic scintillators (micro rem mete
Energy Dependence

Radiological Calibration – Exposure 

Indicated 

E Rt

10 Relative 

Response 

Curve

Photon Energy (keV)

0 500 1

Exposure Rate

Actual 

Exposure Rate

1

0.1

Calibratio

Energy
Effective Detector Chamber Center

The exposure rate (radiation intensity) sometimes vthroughout the detector volume, e.g., it might be higside of the detector chamber closest to the source.Radiological Calibration – Exposure 

d d

standard

• In practice, the distance (d) between the source a

detector that we use is the distance from the centsource to the physical center of the detector.

• Sometimes, the required distance is specified from 

center of the source to the “effective” center of the 

d

d

standard

source
Effective Detector Chamber Center

• The effective chamber center is the point at which 

average overall exposure rate within the chamber found.

• At large source to detector distances, the exposu

doesn’t change very much across the chamber an

Radiological Calibration – Exposure 

doesn t change very much across the chamber an

effective chamber center is close to the physical cthe chamber. No problem here.

• However, at small source to detector distances, th

exposure rate can decrease very quickly as we mthe side of the chamber closest to the source to thof the chamber. In this case, the effective chambis shifted forward. Not good.
Effective Detector Chamber Center

Large source to detector distance. Good.Radiological Calibration – Exposure 

1.1 mR/hr

1.0 m

Physical and Effective 

Chamber Center

source
Effective Detector Chamber Center

Small source to detector distance. Bad.Radiological Calibration – Exposure 

1 R/hr

3 R/hr

Physical Cham

source

6 R/hr

20 R/hr

Effective Cham
Effective Detector Chamber Center

• The goal is to calibrate (and make measurements

enough away from a source so that the intensity oradiation is as uniform throughout the detector chpossible.

• A rule of thumb used in ANSI N323 is to keep the Radiological Calibration – Exposure 

A rule of thumb used in ANSI N323 is to keep the 

detector distance at least five times the maximum dimension.

• The source to detector distance is particularly imp

when using ion chambers which tend to have largvolumes (e.g., 7 – 8 cm across).
Effective Detector Chamber Center

• If the detector is elongate (e.g., a side window GM

axis of the detector should be at right angles to thThis helps ensure a uniform radiation intensity witdetector chamber.

Radiological Calibration – Exposure 

Detector a

angle to 

source
Scatter

• During calibration, we must know the actual expo

that the instrument is responding to.

• The following equation, used during calibration to 

the actual exposure rate at a specific distance fro

Radiological Calibration – Exposure 

source, calculates the exposure rate from the dire
Scatter

• However, the actual exposure rate that the instrum

responds to is due to:

- the direct beam from the source- background

scatter

Radiological Calibration – Exposure 

-

• The contribution from the direct beam can be calc• The contribution from background can be measur

absence of the source.

• Determining the contribution from scattered radiat

problem.
Scatter

Radiological Calibration – Exposure 

Exposure rate 

direct beam 

source

scatter

direct beam

ba
Scatter

How the problem of scatter might be handled:1. Scatter is sometimes ignored. This leads to an e

calibration so that a perfectly accurate instrumeappear to over-respond.

Radiological Calibration – Exposure 2. The calibration is performed in a scatter free fac3. A shadow shield is employed to account for sca

background.
Scatter

Use of a shadow shield:• The instrument response (R1) to the direct beam, 

background and scatter is recorded.

• A lead shadow shield is placed between the sour

Radiological Calibration – Exposure 

detector (e.g., midway). It must not be so close to source or detector that it blocks scatter, and it muenough to completely stop the direct beam.

• The instrument response (R2) to background and 

recorded.

• The difference between the two readings (R1 – R2

represents the instrument response to the direct b
Scatter

Radiological Calibration – Exposure 

source

scatter

direct beam

scatter

shadow 

shield

ba

source
Radiological Calibration –

Determining the 

Counting Efficiency forCounting Efficiency for

Activity Measurements

11/26/2009
General

Count Rate ↔ Activity

• This involves determining the relationship betwee

instrument’s count rate and activity.

• In other words, we determine the detector efficien

Radiological Calibration – Counting Effic

, 

particular source. 

• In this discussion we only consider the measurem

alpha and beta activity. The activity is usually expdpm or Bq.

• Instruments that might be calibrated this way inclu

pancake GMs, proportional counters, beta scintillascintillators.
General

• The detector is placed above a plated standard so

known activity and the gross count rate (Rg) is rec

• The ambient background count rate (Rb) is subtra

calculate the net count rate. 

Radiological Calibration – Counting Effic• The detector efficiency is calculated:E is the detector efficiency (e.g., cpm/dpm, cps/Bq)Rn is the net count rate (e.g., cpm, cps)A is the standard source activity (e.g., dpm, Bq)
Two Types of Activity

• There are two types of activities:

- 2π activity (aka. the surface emission rate)

- 4π activity (aka. the total activity)

Si ith ti it b d t l l t th 

Radiological Calibration – Counting Effic• Since either activity can be used to calculate the 

efficiency, there are two types of detector efficien

2π efficie4π efficie
2π Activity (surface emission rate)

• This refers to the number of alpha or beta particle

the surface of the source per unit time.

• The 2π activity of the standard source is usually t

activity that is NIST traceable. In most cases, the 

t t l NIST t bl i it i l l t d

Radiological Calibration – Counting Effic

not truly NIST traceable since it is calculated.

• The manufacturer typically measures the 2π activ

windowless gas flow proportional counter. With thinstrument, any charged particle that leaves the sproduces a count.

• The manufacturer often specifies the 2π activity a

cpm rather than Bq or dpm.
4π Activity (total activity)

• This refers to the number of decays per unit time. 

cases this is the same as the number of alpha or particles emitted by the source per unit time.

• To calculate the reported 4π activity, the manufac

usually multiplies the measured 2π activity by a fa

Radiological Calibration – Counting Effic

usually multiplies the measured 2π activity by a fa

accounts for backscatter in the source.

• For alpha sources which experience very little ba

the 2π activity might be multiplied by a number lik

calculate the 4π activity.

• For beta sources which experience considerable 

backscatter, the 2π activity might be multiplied by similar to 1.60
2π and 4π Activity

Beta Source Alpha Sou

Radiological Calibration – Counting Effic

Source Support

2π Activity = 6 cpm4π Activity = 10 dpm

Source Sup

2π Activity = 4π Activity = 1
Standard Sources

• The standard source consists of a very thin depos

alpha or beta emitter on a smooth supporting surf

• The radioactive material might, or might not, have 

type of thin protective covering.

Radiological Calibration – Counting Effic• The radioactive deposit is usually circular and sm

the detector area. In some cases, “extended” sowhose areas are larger than the detector are used

• The radioactive material should be a pure alpha o

emitter (i.e., no gammas).

• Preferably, the source is a long-lived radionuclide 

decay corrections are unnecessary.
Standard Sources

• The source support is typically a smooth metal su

(e.g., stainless steel, nickel).

• Some supports are flexible in order to mimic curv

surfaces such as pipes.

Radiological Calibration – Counting Effic
Factors Affecting Efficiency - Distance

• Because it has a significant affect on detector effi

source to detector distance during calibration shoidentical to that employed when measurements oare performed.

• At facilities where there is a potential for removabRadiological Calibration – Counting Effic

At facilities where there is

a potential for removab

contamination, the standard counting distance mior 1.0 cm above the surface.

• At facilities where there is little to no removable a

measurements and calibration might be performecontact.”
Factors Affecting Efficiency - Energy

Alpha Emitters: 

• The counting efficiency for alpha emitters is gen

assumed to be independent of the alpha particle This assumption might not be true, but given the uncertainties associated with measuring alpha a

Radiological Calibration – Counting Effic

uncertainties associated with measuring alpha a

(e.g., self-absorption), it is a reasonable approa

Beta Emitters: 

• The counting efficiency for beta particles is defin

affected by the beta particle energy. The higher energy, the higher the counting efficiency.

• How this is dealt with is situation dependent.
Factors Affecting Efficiency - Energy

Beta Emitters cont: 

• Ideally, the energy of the betas emitted by the s

the same as the energy of the betas that will be measured.

Radiological Calibration – Counting Effic

• If that is not possible, it is better to calibrate with 

energy beta particles than will be measured. Thmeasurements of activity are performed, the effbe low (i.e., conservative).

• If the gross activity of multiple nuclides will be m

and an acceptable ratio between these nuclides established, a weighted efficiency might be used
Factors Affecting Efficiency - Energy

f1 is the fraction of the total activity expected to b

contributed by radionuclide 1

Radiological Calibration – Counting Effic

E1 is the detector efficiency for radionuclide 1

f2 is the fraction of the total activity expected to b

contributed by radionuclide 2

E2 is the detector efficiency for radionuclide 2
Radiological Calibration – Counting Effic

Example Calibration

Source 

Number

2

π

Activity

(cpm)

4

π

Activity

(dpm)

Meter 

Scale

Net 

Count Rate 

(cpm)

2

π

Efficien

(c/d)

8410 155 258 x 1 52.5 0.34 

8411 2,210 3,540 x 10 672 0.30 

Detector type: Pancake GMProbe window physical area: 20 cm

2

Source: Tc-99 beta source (294 keV max). Circular 

in diameter, nickel source support

8411 2,210 3,540

x 10 672 0.30 

8412 22,730 36,370 x 100 7,075 0.31 

Average 

Efficiency 0.32 
Measuring Alpha and Beta Ac
General

• Once the detector efficiency has been determined 

the calibration, it becomes possible to measure th

of radioactive material.

• Either of the following might be measured:

Measuring Alpha and Beta Activity

g g

- Activity under the detector (e.g., dpm, Bq)- Activity per unit area (e.g., dpm/100 cm2, Bq/cm

• Activity per unit area (concentration) is usually mo

important because contamination limits specified regulations or facility license are typically in dpm/
Activity Measurements

• The detector is positioned on the source (e.g., be

and the gross count rate is recorded. 

• An appropriate background count rate (see App. 

subtracted to calculate the net count rate. 

Measuring Alpha and Beta Activity• The source activity under the detector is calculateA is the measured source activity (e.g., dpm, Bq)R

n is the net count rate (e.g., cpm, cps)

E is the detector efficiency (e.g., cpm/dpm, cps/Bq)
Activity Measurements

• If we use a 4

π efficiency in the equation, we calcu

activity:

generally what 

Measuring Alpha and Beta Activity• If we use a 2

π efficiency in the equation, we calcu

activity:

rarely of intere
Activity per Unit Area Measurements 

• The concentration of the radioactive material (act

area) is of more importance than the activity undedetector. It is calculated as follows:

Measuring Alpha and Beta ActivityC is the measured 4

π concentration (e.g., dpm/10

R

n is the net count rate (e.g., cpm)

E

4

π is the detector 4

π efficiency (e.g., cpm/dpm)

Ap is the detector probe area (e.g., cm

2

)
Activity per Unit Area Measurements

• While the probe area (A

p) used in the calculation 

the area of the surface that the detector respondpractice we use the physical area of the probe wiprobe’s “effective area” should not be used.

Measuring Alpha and Beta Activity• There are two other approaches that are used to 

the activity per unit area:- use of an extended source during calibration (se- use of ISO-7503-1 methodology (see App. B)
Example Calculation of Activity

A pancake GM is used to measure a spot of Tc-99 keV maximum energy) contamination on a Formica top. Calculate the total 4

π activity in dpm.

Measuring Alpha and Beta ActivityGross count rate: 75 cpm Detector background for Formica (and linoleum): 40 2

π counting efficiency: 32 % (0.32 c/beta)

4

π counting efficiency: 19 % (0.19 c/d)
Example Calculation of Concentration

Assume that the area of the contamination extends area larger than the detector and calculate the concin dpm/100 cm

2.

Measuring Alpha and Beta Activity
Regulations Pertaining to 

Survey Instrument CalibratiSurvey Instrument Calibrati
NRC: Part 20--Standards for Protection Against 

Subpart F--Surveys and Monitoring Sec. 20.1501 G“(a) Each licensee shall make or cause to be madethat–(1) May be necessary for the licensee to comply wi

reg lations in this part and

Regulations

regulations in this part; and

(2) Are reasonable under the circumstances to eva

The magnitude and extent of radiation levels; anConcentrations or quantities of radioactive mate(iii) The potential radiological hazards. 

(b) The licensee shall ensure that instruments and used for quantitative radiation measurements (e.g., and effluent monitoring) are calibrated periodically fradiation measured.”
NRC: Part 34 - Industrial Radiography

Subpart C: 34.25 Radiation survey instruments(a) The licensee shall keep sufficient calibrated and radiation survey instruments at each location where radioactive material is present to make the radiation required by this part and by 10 CFR part 20 of this Regulationsrequired by this part and by 10 CFR part 20 of this 

Instrumentation required by this section must be cameasuring a range from 0.02 millisieverts (2 milliremhour through 0.01 sievert (1 rem) per hour.
NRC: Part 34 - Industrial Radiography

Subpart C: 34.25 Radiation survey instruments(b) The licensee shall have each radiation survey inrequired under paragraph (a) of this section calibra(1) At intervals not to exceed 6 months and after ins

ii f b h

Regulations

servicing, except 

for 

battery c

hanges; 

(2) For linear scale instruments, at two points locate

approximately one third and two-thirds of full-sceach scale; for logarithmic scale instruments, at range of each decade, and at two points of at ledecade; and for digital instruments, at 3 points b0.02 and 10 millisieverts (2 and 1000 millirems) and
NRC: Part 34 - Industrial Radiography

Subpart C: 34.25 Radiation survey instruments(3) So that an accuracy within plus or minus 20 per

calibration source can be demonstrated at each checked.

Regulations(c) The licensee shall maintain records of the resultinstrument calibrations in accordance with § 34.65.
NRC: Part 35 - Medical

Subpart C: 35.61 Calibration of Survey Instrument(a) A licensee shall calibrate the survey instruments show compliance with this part and 10 CFR Part 20 first use, annually, and following a repair that affectcalibration A licensee shall–Regulationscalibration. A licensee shall–(1) Calibrate all scales with readings up to 10 mSv 

mrem) per hour with a radiation source;

(2) Calibrate two separated readings on each scale 

that will be used to show compliance; and 

(3) Conspicuously note on the instrument the date o

calibration. 
NRC: Part 35 - Medical

Subpart C: 35.61 Calibration of survey instruments(b) A licensee may not use survey instrumentsif the difference between the indicated exposure ratcalculated exposure rate is more than 20 percent.Regulations(c) A licensee shall retain a record of each survey icalibration in accordance with § 35.2061.
NRC: Part 36 - Irradiators

Subpart D: 36.57 Radiation Surveys(c) Portable radiation survey meters must be calibraleast annually to an accuracy of +/- 20 percent for tgamma energy of the sources in use. The calibratiodone at two points on each scale or for digital instrRegulationsdone at two points on each scale or, for digital instr

at one point per decade over the range that will be Portable radiation survey meters must be of a type not saturate and read zero at high radiation dose ra
NRC: Part 39 – Well Logging

Subpart C: 39.33 Radiation detection Instruments(c) The licensee shall have each radiation survey inrequired under paragraph (a) of this section calibra(1) At intervals not to exceed 6 months and after ins

servicing;

Regulations(2) For linear scale instruments, at two points locate

approximately 1⁄3 and 2⁄3 of full-scale on each slogarithmic scale instruments, at midrange of eadecade, and at two points of at least one decaddigital instruments, at appropriate points; and

(3) So that an accuracy within plus or minus 20 per

calibration standard can be demonstrated on ea
NRC: Part 39 – Well Logging

Subpart C: 39.33 Radiation detection Instruments(d) The licensee shall retain calibration records for 3 years after the date of calibration for inspection bCommission.Regulations
DOE: Part 835 – Occupational Radiation Protect

Subpart E: 835.401 General Requirements(b) Instruments and equipment used for monitoring (1) Periodically maintained and calibrated on an es

frequency;

Regulations(2) Appropriate for the type(s), levels, and energies 

radiation(s) encountered;

(3) Appropriate for existing environmental

conditions; and

(4) Routinely tested for operability.
Calibration Frequency
NRC 10 CFR

10 CFR 20.1501. General Requirements. “periodicaradiation measured.”10 CFR 34.25 . Industrial radiography. “At intervals exceed 6 months and after instrument servicing, exbattery changes”Calibration Frequencybattery changes10 CFR 35.61. Medical. “before first use, annually, following a repair that affects the calibration.” 10 CFR 36.57. Irradiators. “at least annually”10 CFR 39.33. Well Logging. “At intervals not to exmonths and after instrument servicing”
Regulatory Guide 8.21 Health Physics Surveys f

Byproduct Material at NRC-Licensed Processing Manufacturing Plants (1979) and Regulatory GuHealth Physics Surveys During Enriched UraniuProcessing and Fuel Fabrication (1979)“Portable survey instruments should be placed on a Calibration Frequency

y p

maintenance and calibration program that will ensuproperly calibrated and operable survey instrumentavailable at all times for use by the health physics s
Regulatory Guide 8.23 Radiation Safety Surveys 

Medical Institutions (1981)“at least every 12 months . . . after repair or maintemay affect the calibration of the instrument.”Regulatory Guide 8 30 Health Physics Surveys Calibration FrequencyRegulatory Guide 8.30. Health Physics Surveys 

Uranium Recovery Facilities (2002)“calibrations at 12-month intervals or at the manufasuggested interval, whichever is shorter”
NUREG-1556, Vol. 9. Consolidated Guidance Ab

Materials Licenses: Program-Specific Guidance Medical Use Licenses. “Survey meters must be calibrated at least annuallyfirst use, and after servicing. (Battery changes are nconsidered "servicing.")”Calibration Frequency

g )

DOE 10 CFR10 CFR 835.401. General Requirements. “Periodically maintained and calibrated on an estabfrequency”
RADIATION PROTECTION PROGRAMS GUIDE

for Use with Title 10, Code of Federal Regulation835, Occupational Radiation Protection. DOE G “ANSI N323A establishes an annual calibration freqportable monitoring instruments. The calibration freshould be determined and the calibration should be performed according to the details presented in the Calibration Frequencyperformed according to the details presented in the 

referenced consensus standards. If routine checks routine operability tests and as-found tests) indicate response of an instrument (or type of instrument) restable over a long period of time, then the calibratiofrequency may be extended. Conversely, if routine indicate that an instrument (or type of instrument) faprovide a stable response over the prescribed calibinterval, then the calibration interval should be shor
ANSI N323 (1997)

Each instrument shall be calibrated at least annuallfrequent calibration is recommended if the instrumein extreme environmental conditions, or is subject tparticularly heavy usage (e.g., industrial radiographlogging). Calibration Frequency

gg g)

The calibration frequency should also be increased than 10% of “as-found” readings indicate out-of-calinstruments.Calibration is also required by the standard after anmaintenance or adjustment is performed that might instrument response. This would not normally inclubattery change out (see ANSI N323-1978).
Calibration Points and 

Accuracy 

NRC Requirements
NRC: Part 34 - Industrial Radiography

Subpart C: 34.25 Radiation survey instruments(2) For linear scale instruments, at two points locate

approximately one third and two-thirds of full-sceach scale; for logarithmic scale instruments at 

Calibration Points and Accuracy- NRC Requirements

each scale; for logarithmic scale instruments, at 

of each decade, and at two points of at least onand for digital instruments, at 3 points between 10 millisieverts (2 and 1000 millirems) per hour; 

(3) So that an accuracy within plus or minus 20 per

calibration source can be demonstrated at each checked.
NRC: Part 35 - Medical

Subpart C: 35.61 Calibration of Survey Instrument(1) Calibrate all scales with readings up to 10 mSv 

mrem) per hour with a radiation source;

(2) Calibrate two separated readings on each scale Calibration Points and Accuracy- NRC Requirements(2) Calibrate two separated readings on each scale 

that will be used to show compliance; and 

(3) Conspicuously note on the instrument the date o

calibration. 

(b) A licensee may not use survey instruments if the difference between the indicated exposure rate and calculated exposure rate is more than 20 percent.
NRC: Part 36 - Irradiators

Subpart D: 36.57 Radiation Surveys(c) Portable radiation survey meters must be calibraleast annually to an accuracy of +/- 20 percent for tgamma energy of the sources in use. The calibratioCalibration Points and Accuracy- NRC Requirementsg gydone at two points on each scale or, for digital instrat one point per decade over the range that will be 
NRC: Part 39 – Well Logging

Subpart C: 39.33 Radiation detection Instruments(2) For linear scale instruments, at two points locate

approximately 1⁄3 and 2⁄3 of full-scale on each slo

garithmic scale instruments, at midran

ge of ea

Calibration Points and Accuracy- NRC Requirements

g g

decade, and at two points of at least one decaddigital instruments, at appropriate points; and

(3) So that an accuracy within plus or minus 20 per

calibration standard can be demonstrated on ea
Regulatory Guide 8.30. Health Physics Surveys 

Uranium Recovery Facilities.“Each instrument should be calibrated at two points one-third and two-thirds of each linear scale routinewith a calibration at one point near the midpoint of edecade on logarithmic scales that are routinely useCalibration Points and Accuracy- NRC Requirementsdecade on logarithmic scales that are routinely use

readout instruments with either manual or automatiswitching should be calibrated in the same manner meter-dial instruments. Digital readout instruments scale switching should be calibrated in the same mare logarithmic readout instruments. 

. . . A survey instrument may be considered propercalibrated when the instrument readings are within the calculated or known values for each point chec
NUREG-SR1556, Vol. 2. Consolidated Guidance 

Materials Licenses: Program-Specific Guidance Industrial Radiography Licenses“A single point on a survey meter scale can be conssatisfactorily calibrated if the indicated exposure ratfrom the calculated exposure rate by less than 10% Calibration Points and Accuracy- NRC Requirementsfrom the calculated exposure rate by less than 10%

“Linear Scale: Meters on which the user selects a limust be calibrated at no less that two points on eacat approximately 1/3 and 2/3 of the decade.”“Multidecade Logarithmic Scale: a multidecade logscale must be calibrated at no less that one point odecade and no less than two points on one of the d. approximately 1/3 and 2/3 of the decade.” 
NUREG-SR1556, Vol. 2 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Industrial Radiography Licenses“Automatically Ranging Digital Display: Meters . . .irates must be calibrated at no less than one point oCalibration Points and Accuracy- NRC Requirementsrates must be calibrated at no less than one point o

decade and at no less than two points on one of the . . at approximately 1/3 and 2/3 of the decade.”“Scales in excess of 10 mSv/hr (1,000 mrem/hr) necalibrated. However, such scales should be checkeoperation and approximately correct response.”
NUREG-SR1556, Vol. 7 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Academic, Research and Development, and OthLicenses of Limited Scope “Linear readout instruments with a single calibration f ll l h ll b dj t d t th i t Calibration Points and Accuracy- NRC Requirementsfor all scales shall be adjusted at the point recomm

the manufacturer or at a point within the normal ran

Instruments with calibration controls for each scale adjusted on each scale. After adjustment, the respoinstrument shall be checked at approximately 20% of full scale. The instrument's readings shall be withof the conventionally true values for the lower point 10% for the upper point.” This follows the recommeof ANSI N323A-1997.
NUREG-SR1556, Vol. 7 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Academic, Research and Development, and OthLicenses of Limited Scope “Logarithmic readout instruments, which commonly 

i l d t l i l d d 

Calibration Points and Accuracy- NRC Requirementssingle readout scale spanning several decades, no

have two or more adjustments. The instrument shaadjusted for each scale according to site specificatimanufacturer's specifications. After adjustment, calshall be checked at a minimum of one point on eacInstrument readings shall have a maximum deviatioconventionally true value of no more than 10% of thdecade value.”
NUREG-SR1556, Vol. 7 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Academic, Research and Development, and OthLicenses of Limited Scope “Meters with a digital display device shall be calibraCalibration Points and Accuracy- NRC Requirementssame as meters with a linear scale.”"Readings above 2.58 X 10-4 coulomb/kilogram/hou

need not be calibrated, but such scales should be cfor operation and response to radiation.”
NUREG-SR1556, Vol. 7 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Academic, Research and Development, and OthLicenses of Limited Scope “Surface Contamination Measurement InstrumentsCalibration Points and Accuracy- NRC RequirementsIf each scale has a calibration potentiometer, the reshall be adjusted to read the conventionally true vaapproximately 80% of full scale, and the reading at approximately 20% of full scale shall be observed. calibration potentiometer is available, the reading sadjusted at mid-scale on one of the scales, and reathe other scales shall be observed. Readings shall 20% of the conventionally true value.”
NUREG-SR1556, Vol. 9 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Medical Use Licenses “Instrument readings should be within ± 10% of knoradiation values at calibration points; however, readwithin ± 20% are acceptable if a calibration chart or 

Calibration Points and Accuracy- NRC Requirements

prepared and made available with the instrument.”“Calibrate Linear-Readout Instruments at no fewer points on each scale. . . (at approximately 20% and “Calibrate Logarithmic-Readout Instruments at two each decade.”“Readings above 1000 mR/hr . . . need not be calibhowever, such scales may be checked for operatioapproximately correct response.”
NUREG-SR1556, Vol. 9 Consolidated Guidance A

Materials Licenses: Program-Specific Guidance Medical Use Licenses “Calibrate Digital-Readout Instruments with either mautomatic scale switching for indicating exposure rafewer than two points on each scale Check calibraCalibration Points and Accuracy- NRC Requirementsfewer than two points on each scale. Check calibra

the ends of each scale (at approximately 20% and each scale).”“Calibrate Digital-Readout Instruments without scalswitching for indicating exposure rates at two points decade.”“Calibrate Integrating instruments at two dose rates approximately 20% and 80% of the dose rate range
Calibration Points and 

Accuracy 

ANSI N323 Requirements
Calibration Points and Accuracy 

– ANSI N323 RequirementsGeneralDOE Implementation Guide DOE G 441.1-7 (1999) Monitoring Instrument Calibration Guide states that calibration should be performed according the detapresented in ANSI N323

A-1997.

The ANSI standard considers two categories of ins

1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

2. Instruments for Measuring Surface Contamin
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

e.g., ion chamber, uR meter, urem meter, side wind4.2.1.1 Linear readout instruments“Linear readout instruments with a single calibration for all scales shall be adjusted either at the point recommended by the manufacturer or at a point witnormal range of use. Instruments with calibration ceach scale shall be adjusted on each scale.”“After adjustment, the response of the instrument schecked near the end points of each scale (approx20% and 80% of full scale).”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.1 Linear readout instruments“Note - For microprocessor-based instruments that 

li th h t t ti d/ t 

proven linear throug

h

type 

testing and/or accep

tanc

only one point on each scale or decade is required.“Instrument readings shall be within ±15% of convetrue values (CTV) for the lower point and ±10% of the upper point. Readings within ±20% shall be aca calibration chart or graph is prepared and provideinstrument.”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.2 Logarithmic readout instruments“Logarithmic readout instruments, which commonly 

i l d t l i l d d 

single rea

dou

t scale spanning several deca

des, no

have two or more adjustments. The instrument shaadjusted for each scale according to the site specifthe manufacturer’s specifications. Alternatively, it shpermissible to calibrate at points of particular importhe user if the reasons for the change and impact oaccuracy are documented and justified.”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.2 Logarithmic readout instruments“After adjustment, calibration shall be checked at a 

f i t h d d I t t di 

o

f one poin

t on eac

h

deca

de. Ins

trumen

t readings s

a maximum deviation from the CTV of no more thathe full decade value. If the display is not marked acorresponding to ±10% of the point (i.e., a calibratiomark frequently does not have graduations to ±10% next decade), it is permissible to use the spacing oside of the calibration point to estimate the calibratithe high side of the calibration point.”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.3 Digital readout instruments“Digital instruments shall be calibrated as in 4.2.1.1“Note - For microprocessor-based instruments that proven linear through type testing and/or acceptanconly one point on each scale or decade is required.“If the instrument is designed to auto scale, the calipoint should be selected far enough from the autospoint that auto scaling will not affect the reading. Inshould be cycled through a complete test of all dispsegments or indicators, either electronically or radio
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.4 Integrating instruments“Instruments that integrate dose shall be checked a

i i f t d t t i t l 20% 

minimum o

f

two 

dose ra

tes a

t approxima

t

ely 20% a

the stated dose rate range or as recommended by manufacturer.”“NOTE - If the full instrument dose rate range is not for use, then the range acceptable for use shall be the instrument.”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.4 Integrating instruments“The integrations shall continue to a value sufficien

t ti ti ll lid di th t h ll b ithi 15% 

a s

t

ati

stically valid reading th

a

t s

h

all

be within 15% 

CTV. For digital instrumentation, integration should checked to the maximum reading obtainable on the it is not practical to accomplish the full-scale radiolointegration, the electronics and display may be cheelectronically at the maximum integration point, with radiological integration being performed at a lower is achievable.”
Calibration Points and Accuracy 

– ANSI N323 Requirements1. Instruments for Measuring Exposure Rate, D

or Dose Equivalent Rate

4.2.1.5 Neutron dose equivalent instrumentsCorrections to mistakes in the standard are noted in “shall be calibrated as in 4.2.1.1 through 4.2.1.4; exthe calibration accuracy for ranges from 0-100 Sv/h should read 0-100 microSv/hr] or 0-100 Sv [this sho0-100 microSv] (0-10 mrem/h or 0-10 mrem) shall band the calibration accuracy for ranges from 100 Svshould read 100 microSv/hr] or 100 Sv [this should microSv] (10 mrem/h or 10 mrem) and above shall ±20%.”
Calibration Points and Accuracy 

– ANSI N323 Requirements2. Instruments for Measuring Surface Contamin4.2.2 Surface contamination measurement instrume“Where the instrument is calibrated as an integral uminimum of one point on each scale shall be calibra10

3 B /100

2 ( 6 10

4 d /100

2) If h 

10

3

B

q/100 cm

2

(

~

6 x 10

4

dpm/100 cm

2

). If eac

h s

calibration potentiometer, the reading shall be adjusread the CTV at approximately 80% of full scale, anreading at approximately 20% of full scale shall be If only one calibration potentiometer is available, thshall be adjusted at mid-scale on one of the scalesreadings on the other scales shall be observed. Reshall be within 20% of the CTV.”
Calibration Points and Accuracy 

– ANSI N323 Requirements2. Instruments for Measuring Surface Contamin4.2.2.1 Beta-gamma contamination measurement i“Counting efficiencies should be determined for the activity expected to be measured. Where mixed or contamination is to be measured a number of diffecontamination is to be measured, 

a number of diffe

radionuclides with different energies, including low photons, should be utilized.. The distance from the the face of the detector shall be included with the recounting efficiencies.”
Calibration Points and Accuracy 

– ANSI N323 Requirements2. Instruments for Measuring Surface Contamin4.2.2.1 Beta-gamma contamination measurement i“Where GM tubes are used as detectors, the unit shtested to ensure that saturation does not occur unlemaximum indicated value of the instrument is exceemaximum indicated value of the instrument is excee

least a factor of two. The instrument shall continue a full-scale reading until the radiation field is reducethan the maximum display value. Digital readouts sthat the radiation level present exceeds the upper 

measurement level of the instrument in a manner dby the instrument manufacturer.”
Calibration Points and Accuracy 

– ANSI N323 Requirements2. Instruments for Measuring Surface Contamin4.2.2.2 Alpha contamination measurement instrume“All scintillation and air or gas proportional detectorchecked for light leaks or holes in the window matecalibration is initiated A maximum acceptable backcalibration is initiated. 

A maximum acceptable back

count rate shall be determined, documented, and uinstruments prior to calibration.”“Counting efficiencies shall be determined with the radionuclide to be detected, if possible, or with a rawith similar energy.”
Electronic Calibrations as 

Substitute for a Radiologica

Calibration
Substituting an Electronic Calibratio

GeneralIn some cases, an electronic calibration can be perall the scales of an instrument (e.g., x1, x10, x100, while the primary radiological calibration can only bperformed on selected scales (e.g., x1, x10, x100).The electronic calibration ties the readings on the sThe electronic calibration ties the readings on the s

were not calibrated in a radiation field (e.g., x1000) readings on the scales that were calibrated in a radfield.ANSI N323A-1997: “Electronic calibration shall be afor some instrument ranges where calibration with a impractical, provided the electronic calibration is reactual exposure data at one or more points.”
Substituting an Electronic Calibratio

GeneralRegulatory Guide 8.21 Health Physics Surveys for Material at NRC-Licensed Processing and ManufacPlants (1979): “An adequate calibration of survey incannot be performed solely with built-in check sourElectronic calibrations that do not involve a source radiation also do not determine the proper functioniradiation also do not determine the proper functioni

response of all components of an instrument. Howeinitial calibration with a radiation source and periodusing electronic input signals may be considered adfor high ranges that are not used routinely.” RegulaGuide 8.30 Health Physics Surveys in Uranium ReFacilities and Regulatory Guide 8.24 Health PhysicDuring Enriched Uranium-235 Processing and Fuel Fabrication use almost identical wording.
Substituting an Electronic Calibratio

GeneralNUREG CR-6062 Performance of Portable RadiatioInstruments noted that many NRC licensees calibra

survey instruments at a single point and relied on ecalibrations for the other scales or decades. This, thcommented, was a completely unacceptable practic
Substituting an Electronic Calibratio

Difficulty Calibrating on all Scales• It is always desirable to perform a radiological cal

each scale by exposing the detector to a radiation known intensity.

• However, it might be impossible or inappropriate t

certain scales (usually the highest or lowest scalecertain scales (usually the highest or lowest scale
Substituting an Electronic Calibratio

Difficulty Calibrating the Highest Scales• Calibrating the highest scale of an ion chamber (e

exposing it to over 100 R/hr) might not be consist

keeping worker exposures ALARA. 

• It might also be difficult to obtain a source of suffic

strength to calibrate the highest scalestrength to calibrate the highest scale. 

• Moving the detector very close to the source to in

exposure rate might be inappropriate : according N323A-1997: “A separation between the calibratioand the detector should exceed five times the madimensions of the larger of the source or the dete
Substituting an Electronic Calibratio

Difficulty Calibrating the Lowest Scales• The lowest scales on some instruments such as N

detectors can measure small fractions of backgro0 – 3 uR/hr). 

• Moving the detector very far enough away from th

to 

produce the necessar

y low ex

posure rate can l

p yp

problems because the scattered radiation from thwhich is hard to quantify, will become a major conthe radiation field (NRC Health Physics Position SHPPOS-279 Technical Assistance Request RegaElectronic Calibration of Survey Instruments

)

• It can be difficult to obtain NIST traceable sources 

sufficiently low activity. 
Cable Changeouts
Cable Changeouts

General• The probe, meter, and cable are sometimes calib

package. Replacing a bad cable requires that the 

combination of probe, meter and cable be calibra

• Some facilities do not require recalibration follow

changeouts if the system passes the constancy techangeouts if the system passes the constancy te

• Replacement cables should be identical to the ca

replaced in terms of cable length, cable type and type.

• It is best, at the time of calibration, to document th

replacement cables do not affect the instrument r
Cable Changeouts

General• ANSI N323A-1997:

“It shall be permissible for the probe and count rat

to be calibrated separately. The exchange of probbe permitted if the variations between combinatio

provided to a 

given location has been documente

p gwithin 20% of the CTV [conventionally true value]be documented for all combinations of probe and meter models and ranges. The range of acceptabrates for a specific check source shall be documeexchange of probes is permitted, the new detectorespond within the same range of acceptable couthe previous probe using the same check source with the original probe.”
Instrument Labeling
Instrument Labeling

ANSI N323A-1997.Each survey instrument should be labeled with the 

• Most recent calibration date• Initials or name of calibration personnel• Date for next calibration

Date for next calibration

• Serial number or equipment identifier e.g., barc• If the instrument is for special use, or if the cali

limited in some way (e.g., the instrument is not on the high or low scale), a special label should employed.
Instrument Labeling

NUREG-SR1556, Vol. 2. “The following information should be attached to the instrument as a calibration sticker or tag:”

• Source that was used to calibrate the instrume• A calibration chart or graph for each scale or de

survey meter that is greater than +/ 20% of the survey meter that is greater than +/ 20% of the 

values identifying the average correction factorindicating that scale was checked only for funcinoperative.

• Date of calibration • Date survey instrument is due calibration • Name or initials of individual calibrating instrum
Instrument Labeling

NUREG-SR1556, Vol. 7 and Vol. 11. 

• “For exposure rate meters, the source isotope u

calibrate the instrument (with correction factorsscale

• The efficiency of the instrument, for each isotop

instrument will be used to measure 

(if efficienc

y 

( y

calculated before each use)

• For each scale or decade not calibrated, an indi

the scale or decade was checked only for functicalibrated

• The date of calibration and the next calibration d• The apparent exposure rate or count rate from t

source, if used”
Functional (Operability) Te
Functional (Operability) Test 

General • Each day prior to use, every survey instrument sh

tested to identify any changes in its response that occurred since its last calibration. This test might performed in the middle and/or end of the day.

The results of this test check should be documen

• The results of this test check should be documen

with the detector and probe serial numbers.

• Unless a failure of the QC check is known to be d

specific incident, all the data collected since the pcheck will be of questionable validity. A documentdecision is then made as to whether this data will or discarded.
Functional (Operability) Test 

Typical Components of a Functional TestWhen applicable, the following items should be incl• Battery condition• High voltage setting.• Threshold, discriminator and/or window settin

gs.

, g

• Zero adjustment• The background. Whenever possible, this should 

performed in the same area. 

• Light leaks for scintillators with thin windows.• Instrument response to a check source (constanc
Functional (Operability) Test 

Instrument Response to Check Source (constan• The check source activity does not have to be kno• The check source must emit radiation that the ins

designed to detect. 

• There should be a specific and reproducible geom

b t th d d t t A ji i ht d b

e

tween the source an

d

d

e

tec

tor. 

A jig might use

d

reproducible positioning of the source and detecto

• If the check source is placed directly against the d

small variations in the source position can have bon the count rate. e.g., the readings of a plastic csource can differ by 10% or more depending on wthe two sides of the source is against the detecto
Functional (Operability) Test 

Instrument Response to Check Source (constan• Ideally, a response check is done on each meter 

normally used - therefore several check sources 

activities might be required. 

• Backup check sources are a good idea. If a check 

lost or unavailable and there is no backup, the ins

should not be used.

• The instrument response to the check source(s) s

determined at, or immediately after, the instrumencalibration.
Functional (Operability) Test 

NRC 10 CFR 35.80 Mobile Medical Service“(2) Check instruments used to measure the activity unsealed byproduct material for proper function befmedical use at each client’s address or on each dawhichever is more frequent. At a minimum, the cheproper function required by this paragraph must incconstancy check;constancy check;(3) Check survey instruments for proper operation wdedicated check source before use at each client’s 
Functional (Operability) Test 

Regulatory Guide 8.23 Radiation Safety Surveys Medical Institutions (1981)“Daily constancy checks of survey instruments shomade before and after each use."; Regulatory Guide 8.30. Health Physics Surveys Uranium Recovery FacilitiesUranium Recovery Facilities.

“Survey instruments should be checked for constanoperation with a radiation check source prior to eacthe instrument response to the radiation check soufrom the reference reading by more than 20%, the should be repaired if necessary and recalibrated (Rparagraph 4.6). This constancy check should be supplemented by calibrations at 12-month intervals manufacturer’s suggested interval, whichever is sh
Functional (Operability) Test 

RADIATION PROTECTION PROGRAMS GUIDEfor Use with Title 10, Code of Federal Regulation835, Occupational Radiation Protection. DOE G “Functional tests should be performed prior to initiainstrument in the field. Functional tests should be dthe instrument-use procedures and should include, minimum: general condition; battery condition; verifminimum: general condition; battery condition; verif

current calibration (i.e., check to see that the date dcalibration has not passed); background readings; atests (high voltage, zero setting, alarm functions, etapplicable to the instrument. Functional tests shoulinclude a source response check (i.e., observing thinstrument response to a check source) before initiaoperation.”
Functional (Operability) Test 

RADIATION PROTECTION PROGRAMS GUIDEfor Use with Title 10, Code of Federal Regulation835, Occupational Radiation Protection. DOE G “During use in the field, instruments should be testecheck source to ensure that the readings remain wprescribed limits. This should be done as prescribeN323A The performance of functional tests during N323A. The performance of functional tests during 

field should be appropriately documented. This may simple as a check-list on the survey sheet.”
Functional (Operability) Test 

ANSI N323 (1997)"If at any time the instrument response to the sourcfrom the reference reading by ±20% (for any photoinstrument the reading should be at least ten times background), the instrument shall be returned to the calibration facility for calibration or for maintenanceand recalibration as required Reference readings and recalibration as required. Reference readings 

obtained for each instrument when exposed to a soconstant and reproducible manner, either at the timinstrument is received in the field or before its first u
Functional (Operability) Test 

ANSI N323 (1997)"Check sources should provide radiation of the samtypes as provided by those sources used in instrumcalibration (as described in 5.1). However, check soprovide radiation different than that used for calibraa) The source/instrument geometry is well understoeasily reproducedb) The instrument response to this radiation is well and is not critically dependent on instrument adjustthe use of a beta source to check instruments sensphoton radiation may be acceptable while the use osource to check a detector utilizing a BF3 tube is noacceptable). A reproducible source/detector geomeestablished and used for all source response check
Functional (Operability) Test 

ANSI N323 (1997)"a source response check may not be practicable foinstruments, such as high range instruments and neexposure rate instruments. In these cases, the facdevelop compensatory methods to demonstrate thainstrument is operable before use."
Appendix A

Glossary
Acceptance Testing: Evaluation or measurement of perform

characteristics to verify that certain stated specifications and crequirements are met.Accuracy: The degree of agreement between the observed vreading) and the actual value of the quantity being measured exposure rate or activity).Calibrate: To adjust or determine the instrument response to Glossary

To adjust or determine the instrument response to 

values of the quantity being measured.Check Source: A radioactive source, not necessarily calibratused to confirm the continuing satisfactory operation of an insCoefficient of Variation: The standard deviation expressed a

percentage of the mean (average).Correction (calibration) Factor: A factor that the instrument multiplied to obtain the actual value of the quantity being mea
Energy Dependence: Variation in the instrument response a

of radiation energy for a constant radiation type and intensity, effect of radiation energy on the instrument accuracy.Extracameral: Components of the instrument other than the dproper. Exposure of extracameral components in a radiation affect the instrument reading. Functional Tests: Tests (aka operability or performance testGlossaryFunctional Tests: Tests (aka operability or performance test

determine that an instrument is operational and capable of peintended function. Such tests may include, for example, battezero setting, or source response checks. Geotropism: A change in an instrument's reading as its orienchanges, due to gravitational effects.National (primary) Standard: An instrument or source maintpromulgated by the National Institute of Standards and Techn
Overload Response: The response of an instrument to radia

intensities greater than the upper measurement level.Reference Orientation: The orientation in which the instrumenormally intended to be operated, as stated by the manufactuReference Point: Markings on the instrument used to identify 

of the detector.

GlossaryReproducibility (precision): The degree of agreement betwmeasurements of the same radiation field intensity. Expressestandard deviation computed from a series of measurementsResponse Time: The time it takes for the instrument reading from 10% to 90% of the final reading.Secondary Standard: A source or instrument that has been directly with the national standard.
Source Response Check: A functional test that includes the 

of the response of an instrument to a check source.Tertiary Standard: A source or instrument that has been comdirectly with a secondary standard - often used as the laboratTransfer Standard: A source or instrument compared directly with a National Standard that is designed for transport to a labGlossaryserve as a laboratory standard. Usually a detector.Traceability: The ability to show, through documentation, thainstrument or radiation source has been calibrated using eithenational standard or a transfer standard in a chain or echelon calibrations, ultimately leading to a comparison with the natio
Appendix B

Detector Efficiency DeterminaDetector Efficiency Determina

with Extended Sources
General

• There is a trend towards using calibration sources 

larger than the areas of the detectors being calibr

• Such sources are often referred to as extended s

Counting Efficiency for Extended Source• The manufacturer typically reports the source act

unit area (e.g. dpm/cm2) as well as its total activity 
Advantages

• Extended sources closely mimic large areas of 

contamination.

• The efficiencies determined using large area sou

account for the detector window area. The latter 

have to be determined separately

Counting Efficiency for Extended Source

have to be determined separately. 

Disadvantages

• Extended sources are considerably more expens

small area sources.

• The range of activities is more limited. 
Example Calibration

Detector type: Pancake GM with 20 cm2 window ar

Source: Tc-99 extended NIST traceable source

Counting Efficiency for Extended Source

Source 

Number

2π

Concentration

(cpm/100 cm2)

4π

Concentration

(dpm/100 cm2)

Meter 

Scale

Net 

Count Rate 

(cpm)

2π

Efficiency

(c/d/100 cm2

Note the units for efficiency!

(cpm/100 cm ) (dpm/100 cm ) (cpm) (c/d/100 cm 

8410x 1,550 2,580 x 1 87.9 0.057 

8411x 20,160 33,556 x 10 1,220 0.061 

8412x 202,083 336,370 x 100 11,860 0.059 

Average 

Efficiency 0.060 
Example Calculation of Concentration

A pancake GM is used to measure Tc-99 beta (294 maximum energy) contamination on a Formica benCalculate the total 4

π activity in dpm/100 cm

2.

Gross count rate: 75 cpm

Counting Efficiency for Extended Source

Gross count rate: 75 cpm

Detector background for Formica (and linoleum): 2

π counting efficiency: (0.060 c/beta/100 cm

2

)

4

π counting efficiency: (0.035 c/d/100 cm

2

)
Appendix C

Concentration CalculationConcentration Calculation

Using ISO 7503-1
General

• The conditions under which alpha or beta countin

efficiencies are determined are ideal: - The source is an uncovered very thin deposit. T

eliminates attenuation of the emitted alphas or b

particles in the source

Concentration Calculations Using ISO 75

particles in the source.

- The source support is a very smooth high Z ma

maximizes backscatter of beta particles.

• As such, the efficiencies determined in the calibra

are higher than will be experienced in the “real wothe emitted particles are often attenuated in the sbackscatter is at a minimum.
General

• ISO-7503-1 Evaluation of Surface Contamination 

Beta Emitters and Alpha Emitters attempts to partcorrect this overestimation of the detector efficien

• Within the United States, the ISO methodology ha

it t t t i d i i i Th 

Concentration Calculations Using ISO 75

its greatest acceptance in decommissioning. The 

approach is recommended by MARSSIM (NUREG which provides guidance for Final Status Surveys undergoing decommissioning. NUREG 1507, MinDetectable Concentrations with Typical Radiation Instruments for Various Contaminants and Field Cprovides considerable information relevant to the application of this international standard.
The ISO-7503-1 Equation

• The ISO equation used to calculate the concentra

alpha and beta surface contamination:

Concentration Calculations Using ISO 75C is the measured concentration (e.g., dpm/100 c

R

n is the net count rate (e.g., cpm)

εi is the instrument efficiency (e.g., c/beta)ε

s is the source efficiency

Ap is the detector probe area (e.g., cm

2

)
Instrument Efficiency (εi) 

• Better known as the 2π efficiency, this is the fract

particles leaving the surface that produce a count

Source Efficiency (εs) 

• The fraction of decays that result in a particle leavConcentration Calculations Using ISO 75

The fraction of decays that result in a particle leav

surface. ISO 7503-1 recommends the following d

Beta Emitters 

maximum energy above 0.4 MeV εs = 

maximum energy from 150 – 400 keV εs = 

Alpha Emitters 

all energies εs = 0.25
Example Calculation

A pancake GM is used to measure Tc-99 beta (294 maximum energy) contamination on a Formica benCalculate the concentration in dpm/100 cm2.

D t t i d 20 2

Concentration Calculations Using ISO 75

Detector window area: 20 cm2

Gross count rate: 75 cpm Detector background for Formica (and linoleum): 2π counting efficiency: 32 % (0.32 c/beta)4π counting efficiency: 19 % (0.19 c/d)
Example Calculation

Since the beta maximum energy is between 150 anwe will use a source efficiency of 0.25.Concentration Calculations Using ISO 75
Appendix D

Assessing the Survey InstrumAssessing the Survey Instrum

Background Count Rate
Introduction

• With one minor exception, ZnS alpha scintillators 

proportional counters (operated in the alpha only are unresponsive to anything but alpha particles, background count rate should be close to 0 to 1 c

• Higher backgrounds typically mean that the detec

Background Count Rate

Higher backgrounds typically mean that the detec

contaminated, or in the case of a ZnS alpha scintthe detector has a light leak. ZnS detectors can refast neutrons, but neutrons are rarely a significancontributor to background.

• Detectors that respond to beta particles (e.g., GM 

detectors, beta scintillators, proportional countersrespond to photons and cosmic rays. The larger tdetector, the greater the background count rate.
Assessing Background Count Rate for Beta Det

• Different approaches can and are employed for 

determining the background count rate of a beta d

1. General ambient background

2 L ti ifi bi t b k d

Background Count Rate

2. 

Location specific ambien

t

bac

kgroun

d

3. Material specific background4. Location specific ambient and material specific 

background
1. General Ambient Background

• The detector background is determined in a low 

background area, or an area typical of the facility. 

determined by holding the detector in the air and the instrument reading.

Background Count Rate• The background count rate is primarily due to pho

(gamma rays and x-rays), to a lesser extent cosmand to a very minor extent, radioactive contaminadetector.
2. Location Specific Ambient Background

• A potential problem with the previous approach: it 

account for spatial variability in background. If bacvariability is small, this approach is acceptable. 

• Where background variability is large (e.g., in fac

hi h ti it itt ) it i ht b b tt t

Background Count Rate

high activity gamma emitters), it might be better to 

determine a background for each measurement lo

• This can be done by holding the probe far enough 

the surface where the measurement is performed detector cannot respond to surface contaminationmethod would be to make the background measuwith a plastic shield between the surface and the 
3. Material Specific Background

• A gross beta or alpha measurement on an uncon

ceramic tile surface can be very different from a measurement on uncontaminated drywall or wood

• This reflects the differences in the concentrations 

t ll i di lid i diff t th 

Background Count Rate

na

turally occurring radionuclides in differen

t the m

• To account for this, some facilities assign a uniqu

background count rate to each material type. In scases, the same background count rate might be for a group of materials (e.g., wood and drywall).

• The table on the following slide(after NUREG 150

illustrates some of these different backgrounds.
Background Count Rate

3. Material Specific Background
4. Location Specific Ambient and Material Spec

Backgrounds

At each measurement location two counts are perfo

R

G is the gross count rate with the detector on a 

contaminated surface. This is the detector respon

d h t f th t i ti b t d 

Background Count Rate

an

d p

h

o

tons 

from the con

tamination, 

b

e

tas an

d p

from the material (e.g., ceramic tile), and backgrophotons. R

S is the shielded count rate with a plastic shield 

the detector and the surface. This is the detector to photons from the contamination and backgroun
4. Location Specific Ambient and Material Spec

Backgrounds

R

M, the material specific background (e.g., for cera

subtracted from the gross count rate. 

RN1 = R

G – R

M

Background Count RateRN1 is the net instrument response to the betas and 

emitted by the contamination and to background phThe shielded count rate is subtracted from RN1 to g

instrument’s response to the betas from the contam

RN2 = RN1 – R

S