VIII-Ⅱ-1. Project Research
Project 5PR5Studies on Radiation Safety Control at Accelerator Facilities

S. Takahashi
Research Reactor Institute, Kyoto University
Objectives and Allotted Research Subjects
A Fixed-Field Alternating-Gradient (FFAG) proton
synchrotron (max energy 150 MeV, max mean current 1nA) has been constructed next to the Kyoto University
Critical Assembly (KUCA) to study the technical development for the accelerator driven subcritical reactor(ADSR). The proton beam was led to the A-core of
KUCA to conduct the experiment of ADSR on March 4,
2009. On the other hand, the commissioning of a 30 MeV
proton cyclotron was completed at the end of March,
2009, for the boron neutron capture therapy (BNCT).
And other high energy accelerators are scheduled to
conduct as neutron sources in the master plan of KURRI.
In these situations, the radiation safety control at accelerator facilities is a key issue in the workplaces and environment.
In these projective studies, five research subjects
were carried out in three facilities (the electron linear
accelerator (LINAC), the Co-60 gamma irradiation facility and the proton cyclotron) as substitutes related to theaccelerator fields.
The allotted research subjects (ARS) are as follows:
ARS-1 (23P5-1): Development of Passive Neutron Dosimeter with Good Energy Response.
(T. Iimoto, K. Shimada, K. Tani, Y. Fujimichi, K.
Yamasaki and T. Takahashi)
ARS-2 (23P5-2): Production and Behavior of Tritium in
Accelerator Laboratory.
(M. Ohta, S. Kimura, S. Fukutani and K. Okamoto)
ARS-3 (23P5-3): Corrosion of Metals and Colloid Formation in Water under Intense Radiation Field.
(K. Bessho, H. Matsumura, K. Masumoto, Y. Oki, N.
Akimune, S.Sekimoto,K. Yamasaki and N. Osada)
ARS-4 (23P5-4):Adsorption of Radioactive Gas on a
Membrane Filter in an Electron Linear Accelerator.
(Y. Oki, N. Osada and K. Yamasaki)
ARS-5 (23P5-5): Time Dependencies of Size Distributions of Radioactive Aerosols Produced in Accelerators.
(K. Yamasaki, Y. Oki, N. Osada, M.Shimo,S. Yokoyama, S. Tokonami, A. Sorimachi, C. Kranrod and S.
Takahashi)

Main Results
ARS-1: The uncertainty of external dose measurements
by energy and angular response with dosimeter andworker was discussed using a passive neutron monitor
consisted of CR-39 and one millimeter thickness
poly-ethylene sheet. If the upper limit of confidence interval was set to 95 % of Cumulative Distribution Function (CDF), in the case of KURRI linac neutron field, thedosimeter value should be set the value of 30 to 50 percent to conform the dose limit of 50 mSv/y.
ARS-2:The concentration of radioactive particles containing of exhaust gases from accelerator for BNCT wascontinuously measured using a radioactive gas monitor.
The concentration of exhaust gas was higher continuously for the limited period of the working of BNCT. The
concentration of atmosphere was not affected by theworking of BNCT. The tritium compounds from radioactive particles containing of exhaust gases from BNCT
appear to be not detected and is considered to be Ar-41.
ARS-3: In the electron LINAC experiment, the soluble(0-3 nm) and colloidal (3-7, 7-16, 16-200,200- nm) concentrations of Cu and Fe were measured after irradiation
time for 2 h and 12h. Dependence of photon intensity on
the size profiles showed that high-energy photons promote the transfer of Cu, Fe into water phase. At the 60Co
gamma-ray irradiation to Cu powder/water samples,
dominant Cu species in water were colloidal species,
which were identified to the copper oxides (Cu2O, CuO)
by XRD analysis.
ARS-4: The screen-type diffusion battery consists of a
stack of stainless steel wire screens and a backup filter.
The particle size distribution is calculated from the activity of the backup filter. The size is overestimated when
the radioactive gas is adsorbed on the backup filter. The
influence of the adsorption was very high. The particle
size is overestimated to be two times or more the correct
size in the case of aerosols with 50-nm geometric mean
diameter.
ARS-5: A comparative measurement of the size distributions were conducted in Linac and Cyclotron. Main artificial radio-nuclide was N-13 in the Linac target room.
Owing to its relatively long time of operation, observed
geometrical mean diameters (GMD) were relatively large
and varied with the time of operation. On the other hand,owing to very short operation time of Cyclotron, observed radio-nuclides Mg-27 and Na-24 had very small
GMD. It is clarified that GMDs based on the volumes areproportional to operation period of accelerator.

採択課題番号 23P5
加速器施設における放射線安全管理に関する研究（京大・原子炉） 高橋千太郎

プロジェクトPR5-1Development of Passive Neutron Dosimeter With Good Energy Response

T. Iimoto, K. Shimada1, K.Tani1,Y. Fujimichi1,
K. Yamazaki2 and T. Takahashi2
Division for Environment, Health and Safety, The University of Tokyo
1
Graduate School of Engineering, The University of Tokyo
2
Research Reactor Institute, Kyoto University

Radiation workers exposing to neutrons should becontrolled by the radiation safety regulation. Personaldose of radiation workers should be monitored andadequately estimated. When energy of neutron distributes over ten-digit range, in addition when incident
angle to workers is not stable, then existing personal
dosimeters could not succeed in realistic dosimetry.
This study aims to discuss a new radiation control
method using a CR-39 personal dosimeter in neutron
fields with wide energy range. Basic experiments on aneutron personal passive dosimeter using CR-39
combined with polyethylene had been studied. Multiple radiators structure has been designed in order toelevate its detection sensitivity to neutrons with wide
energy range. Detection efficiency of CR-39 to neutrons depending on incidence angles has been simulated and the calculated results fit our experiment data.
In addition, dosimetric method has been developedfor unidentified situations on incident angle of neutron to personal detectors. Combination of these
items succeeds in calculation of probabilistic density distribution of whole body dose for each energy
range of neutron. The result is multiplied by realenergy spectrum under an exposure situation. This
leads to probabilistic distribution of whole bodydose in each neutron work place.
Figure 1 indicates a probabilistic density distribution of whole body dose of each energy range of neutron when indication dose value of a personal dosimeter is 30 mSv, for example. Probabilistic distributionof whole body dose in a target radiation field can becalculated after multiplying the probabilistic density
distribution with real neutron spectrum information.
Figure 2 indicates an accumulated distribution function of whole body dose for neutrons. This figure
shows that the probability of a real effective dose being less than 50 mSv is about 30 % when a personal
dosimeter indicates 30 mSv. We conclude that dose
limit of radiation workers can be fully kept
when the alarm level or reporting level of thepersonal dosimeter is set as the value of 30 to
50 % of effective dose limit value determinedby the radiation safety regulation. This certainty probability is estimated as about 90 to

95 %. The method we have developed realizes
and ensures more adequate personal dose control of radiation workers using neutrons.

Fig.１. A probabilistic density distribution of wholebody dose of each energy range of neutron when indication dose value of a personal dosimeter is 30 mSv.

Fig.2. An accumulated distribution function of wholebody dose for neutrons under the indication of 30mSv.

Fig.3. Neutron Spectrum from Ta target by the
KURRI-LlNAC.

採択課題番号 23Ｐ5-1 エネルギーレスポンスの良好なパッシブ型中性子線量計の開発 プロジェクト（東大・環境安全本部）飯本武志 （東大・工）嶋田和真、谷幸太郎、藤通有希（京大・原子炉）山崎敬三、高橋知之

PR5-2

Production and Behavior of Tritium in Accelerator Laboratory

M. Ohta, S. Kimura1, S Fukutani2 and K. Okamoto2
Niigata University,
1
Osaka University of Pharmaceutical Sciences,2
Research Reactor Institute, Kyoto University
INTRODUCTIONRadioactive particles are known to generate in theworking field of accelerator. Then, the concentrationof radioactive particles in the working field of Fixed
Field Alternating Gradient Accelerator (FFAG) is necessary to be measured before and after working FFAG.
However, the concentration of gaseous radioactive
particles exhausted from working FFAG in 2011 was
too low to be measured as monitoring gas. The present
work was measured the concentration of radioactive
particles containing of exhaust gases from theaccelerator for boron neutron capture therapy(BNCT).

Research Laboratory on October 22 (Tuesday) in
2011. The radioactive particles concentration of
exhaust gas was higher continuously for thelimited period of the working of BNCT. The alternate radioactive particles concentration of thegas permeated into Vycor glass wall used asgas separator and the atmosphere outside Innovation Research Laboratory increased slightly due
to the working of BNCT.
The permeability of a trace of tritium or argon in nitrogen into Vycor glass wall wasmeasured. Tritium permeated fast but argon
did slowly into Vycor glass wall. Therefore, Theradioactive particles containing of exhaust gas isconsidered to argon-41.

EXPERIMENTAL
Gaseous radioactive particles were provided fromthe exhaust gas from the accelerator for BNCT.
They were filtered with pre filter and heap filter, andthen were used as monitoring gas. The concentration of exhaust gases from BNCT, the gas permeated into Vycor glass wall used as gas separator and the atmosphere outside Innovation Research Laboratory was used as reference gas were
measured alternately.
A activity of gaseous radioactive particles wasmeasured by using radioactive gas monitor(Ohkura Electric Co., RD-1,200) and ion
chamber (Ohkura Electric Co. I-409602,
1,000cm3). The output of ion chamber was
digitally recorded by a detalogger (Graphtec
Co., midi LOGGER GL200).
RESULTSThe concentration of radioactive particles containing of exhaust gases from Accelerator forboron neutron capture therapy (BNCT) was
continuously measured from October 2 (Sunday) in 2011 to October 8 (Saturday) in 2011.
Figure 1 shows the radioactive particles concentration of exhaust gases from BNCT, the gas
permeated into Vycor glass wall used as gas
separator and the atmosphere outside Innovation

Fig. 1. The concentrations of gaseous radioactive particles contained in the exhaust gas of BNCT
and atmosphere outside Innovation Research Laboratory.

採択課題番号 23P5-2
加速器施設内外のトリチウム生成・動態 3
プロジェクト
（新潟大・工）太田雅壽（大阪薬科大）木村捷二郎（京大・原子炉）福谷 哲、岡本賢一

Corrosion of Metals and Colloid Formation in Water under Intense Raiation Field

Ta target (50Φ x 62) t5

40

0.8

Irrad.: 2.0 h 0.8

Irrad.: 2.0 h 0.8

Irrad.: 2.0 h0.8

0.4

0.4

0.4

0.4

0.0

Activation foils: Au, Al

Fig. 1. Experimental setup for the irradiation of thesamples at the electron LINAC.

採択課題番号 23P5-3

0 3

0.0

7 16 200

Particle size (nm)

Water (21 ml) in
Metal vessel( I.D. 19Φ x 75 )

0 3

0.0

7 16 200

Particle size (nm)

0.0

0 3

7 16 200

Particle size (nm)

1.2

1.2

1.2

1.2

0.8

Irrad.: 12 h 0.8

Irrad.: 12 h 0.8

Irrad.: 12 h0.8

0.4

0.4

0.4

0.4

0.0

0 3

0.0

7 16 200

Particle size (nm)

0 3

0.0

7 16 200

Particle size (nm)

0 3

0.0

7 16 200

Particle size (nm)Irrad.: 2.0 h

0 3

7 16 200

Particle size (nm)

2.0

0 3

Irrad.: 12 h

7 16 200

Particle size (nm)Fig. 2. Soluble (0-3 nm) and colloidal concentrations (3-7, 7-16, 16-200 nm) of Cu in water without
irradiation, after the irradiation at Co-60 -ray irradiation facility, and after the irradiation at electron
LINAC. Irradiation time : 2.0 h, 12 h

加速器冷却水中における放射性核種およびコロイド

プロジェクト

化学種の挙動解析３（KEK・放射線）別所光太郎、松村宏、桝本和義 （京大・原子炉）沖雄一、関本俊（京大院・工）秋宗尚弥、長田直之

e-LINAC
10 A (0 ˚)
1.2

4030 MeV

electron

Co-60 -ray
2.9 kGy/h
22 kGy/h
1.2

Cu (ppm)～15

Without
irradiation

1.2

1.2

Cu (ppm)(2) Irradiations at the 60Co -ray irradiation facility
Cu vessels filled with water, same size as used in the
LINAC experiments, were irradiated by -rays using the60
Co -ray irradiation facility, KURRI. The dose rates
were 2.9 kGy/h or 22 kGy/h and irradiation times were 2- 72 h.

Cu (ppm)(1) Irradiations at the electron LINAC
Irradiation was carried out using bremsstrahlung andneutrons generated by 30 MeV electron beam hitting on a
Ta target (50 x 62 mm) using an electron linear accelerator (LINAC) at the KURRI. A pair of Cu vessels (I.
D.19x75mm) filled with pure water was fixed at thedownstream position (0 deg: 40 mm from Ta target) andperpendicular position (90 deg: 40 mm from Ta target), as
shown in Fig. 1. Electron beam currents and the irradiation times were 10 - 110 A and 2 - 24 h, respectively.
Intensity of high energy photons, fast neutrons, andthermal neutrons was monitored by activation method
using 197Au(,n)196Au, 27Al(n,)24Na and 197Au(n,)198Au
reactions, respectively.

Cu (ppm)

EXPERIMENTS:

RESULTS: Figure 2 shows soluble (0-3 nm) andsize-separated colloidal concentrations (3-7, 7-16, 16-200,
200- nm) of Cu in water without irradiation and after theirradiation at -ray irradiation facility or electron LINAC
facility. The plots for the LINAC experiments in the figure are selected as the results obtained at the downstream(0-deg) position in order to evaluate the effect of photon
intensity, where flux of neutrons can be neglected compared to flux of bremsstrahlung. The results in Fig. 2
demonstrate that irradiation of high-energy photons( -ray or bremsstrahlung ) clearly affects the elution of
Cu into water and formation of Cu-related colloid / particle in water phase.
Concentration of soluble Cu species increased withphoton intensity. Formation of colloidal species was also
noticeable at intense photon-fields. It implies thathigh-energy photons induce corrosion of Cu materials inwater, transfer of Cu species into water phase as a soluble
species or colloidal species, and growth of colloidal species in water.
Time dependence of size-profiles for Cu species
formed at constant dose rates imply that dissolution of Cu
metal and formation of Cu-related colloid promoted byradiation progress in the time scale of several hours tohundreds hours.

Cu (ppm)

INTRODUCTION: At high-intensity accelerator facilities, it is possible that intense radiation fields affectchemical states of elements around beam-lines and targets. In the cooling-waters for magnets and targets, formation of metal-related colloid in water is one of the important subjects in the radiation managements. In thiswork, metals contacted with water were irradiated bybremsstrahlung and neutrons, or -rays, as a model environment inside accelerator facilities. Radiation effects oncorrosion and colloid formation were investigated.

Cu (ppm)

Radiation Science Center, KEK
1
Research Reactor Institute, Kyoto University
2
Graduate School of Engineering, Kyoto University(3) Analysis of soluble and colloidal concentrations of
Cu in water after the irradiations
After the irradiations, water samples in the Cu vessels
were poured out and treated with four kinds ofultrafiltra-tion (UF) units for particle size separation. Estimated pore sizes of the UF units were 200, 16, 7 and 3
nm. Concentrations of metal elements in the filtrates were
determined by ICP-AES analyses.

CuCu(mg/L)(ppm)

K. Bessho, H. Matsumura, K. Masumoto, Y. Oki1,
N. Akimune2, S. Sekimoto1, K. Yamasaki1 and N. Osada2

CuCu(mg/L)
(ppm)

PR5-3

PR5-4 Adsorption of Radioactive Gas on a Membrane Filter in an Electron Linear Accelerator
Y. Oki, N. Osada and K. Yamasaki
Research Reactor Institute, Kyoto University
INTRODUCTION: Membrane filters are widely employed for air filtration. They are suitable for collectionof radioactive aerosols and the following radioactivity
measurement. However, some material of the filters collects gaseous compounds by adsorption in addition to theparticulate matter. The adsorption interferes correct estimation of radioactivity of radioactive aerosols.
In accelerator facilities, radioactive airborne species
are formed in air of the accelerator rooms during machine
operation. Oxygene-15 (half life: 2 min), 13N (10 min)and 11C (20 min) are principal radionuclides in the air.
They are contained in both gaseous molecules and aerosol particles. Both species are formed through radiolysis
processes of the air. Especially in electron linear accelerators (linacs), radioactive gaseous nitrogen species, suchas nitric oxides and nitric acid, are dominantly formed in
the air. Therefore, corrosion of accelerator hardware
takes place in the accelerator rooms. Besides the corrosion problem, the information on radioactive airborne
species is also important for protection of internal exposure of workers and design of exhaust systems of the facilities. The membrane filters are used in the size measurement of the aerosols, such as diffusion battery or cascade impactor. The particle size is indispensable information to estimate correct internal doses.
In this work, collection efficiency of the gaseous species of 13N was estimated to correctly measure the activity of the aerosols using the radioactive gas formed in anelectron linac.
EXPERIMENTS: The irradiation experiment was carried out in the 46-MeV electron linear accelerator of Research Reactor Institute, Kyoto University. In this work
the adsorption of radioactive gas was estimated for Millipore HA filter (a mixture of cellulose acetate and cellulose nitrate, pore size 0.45 µm). A tantalum target was
bombarded with a 30-MeV electron beam in the irradiation room. The beam current was ca. 100 µA. During theirradiation, the air was exposed to bremsstrahlung of
maximum energy of 30 MeV and neutrons which were
produced in the target.
The Irradiated air was sampled from the irradiation
room, and was introduced to a membrane filter assemblyat the flow rate of 20 L/min. The filter assembly wascomprised of a PTFE (polytetrafluoroethylene) filter,without adsorption ability of radioactive gas, and theMillipore filter. Their diameter was 47 mm. After theparticulate fraction was removed by the PTFE filter (pore
	
 
size,
0.8 µm), the gas fraction was passed through theMillipore filter.
The activity of the filters was measured 10 min after
the end of the sampling. The 511-keV annihilation γ-rays
from the e+-emitters were measured with a coincidence
system of two bismuth germanate (BGO) detectors. The
activity of 13N was determined by analyzing decay curvesof the activity of the filters.
RESULTS AND DISCUSSION: The radionuclide detected on the filters was found to be 13N and almost all
15
O was decayed at the time of 10 min after the end ofsampling. Unlike high-energy proton accelerator, carbon-11 was not observed in air the 30-MeV electron irradiation. The efficiency was expressed as the activity ratioof the gas collected on the Millipore filter to the aerosol
particles on the PTFE filter. The efficiency was found to
be 65 %.
The screen-type diffusion battery consists of a stackof stainless steel wire screens and a backup filter. Afterthe aerosol particles in the sample air penetrate thescreens, all the particles are collected on the backup filter.
The percentage of particles which can pass through thestack of the screens is governed by a function of particle
size, screen mesh size, the number of screens and otherparameters. The particle size distribution is, therefore,
calculated from the activity of the backup filter. The size
is overestimated when the radioactive gas is adsorbed on
the backup filter. The influence of the adsorption was
estimated as shown in Fig.1. [1] As the obtained efficiency in this work was very high, the particle size isoverestimated to be two times or more the correct size inthe case of aerosols with 50-nm geometric mean diameter.

Fig. 1. Influence of the gas adsorption for 50-nm particles on the particle size measurement with the diffusion battery.
REFERENCES:[1] N. Osada, Y. Oki, K. Yamasaki and S. Shibata, Prog.
Nucl. Sci. Tech., 1 (2011) 483-486.

採択課題番号 23P5-4	
 大強度加速器内で発生する放射性ガスの性状測定 3	  プロジェクト	 （京大・原子炉）沖	  雄一、関本俊、山崎敬三、丸橋晃、田中浩基（京大院・工）長田直之、（藤田保健衛生大医療科学部）横山須美、（保健衛生大院保健学研究科）青木克憲	
 PR5-5

Varieties of Radio-Nuclides and Size Distributions of Radioactive Aerosol Produced in
Different Types of Accerelators III

K. Yamasaki, Y. Oki, N. Osada1, M. Shimo2, S. Yokoyama2, S. Tokonami3, A. Sorimachi3 , C. Kranrod3 andS. Takahashi
Research Reactor Institute, Kyoto University
1
Graduate School of Engineering, Kyoto University
2
Fujita Health University
3
National Institute of Radiological Sciences
INTRODUCTION: The radiation protection toward
the induced airborne particulate radio-nuclides is a key
issues for radiation safety of the workers and maintenance of the accelerator facilities. Ultra fine particle generation and particulate radioactivity in high energy andhigh dose accelerator have been examined using electron
Linac in this institute [1]. Recently, a proton cyclotron for
BNCT has been installed. This report describes mainly
the experimental results which were obtained at both accelerators.
EXPERIMENTS: Exposure experiments were carriedout in the ambient air
near target (Ta:Linac,
Be:Cyclotron). Both accelerators were operated at theconditions of maximum energy 30 MeV and maximum
mean current 90 μA to 1mA. Sampling points wereabout 1 m apart from the target in both cases. At the linac,
sample air was introduced to the experimental room withflexible tube made of stainless steel of 2.5 cm dia. andabout 6 m in length through radiation shield of 2.5 m
thick concrete. At the cyclotron, sample air was introduced to the basement room using flexible tube made ofcharge proofing rubber of 1.2 cm dia. and about 20 m inlength through a labyrinth. Sampling flow rate was about
25 ℓ /min. Number and activity-weighted size distributions which were induced high dose and high energy accelerator radiation were measured using SMPS (TSI,

Model 3936), CPC (TSI, Model 3025A), laser particle
counter (RION, KC-18) and low pressure cascade
impactor (Tokyo Dylec, LP-20RS)
The aerosol attached N-13, Mg-27, Na-24 andRn-progeny were sampled on the 13 stages of the
impactor for thirty minutes with flow rate of 22.2 ℓ /min.
The beta ray from N-13, Mg-27, Na-24 and alpha particles from Rn-progeny were sequentially measured with
an automatic sample changer (Aloka, Model JDC-551S)
equipped with ZnS(Ag) scintillation counter and GM
counter for 1 minute after 15 minutes waiting for the decay of 218Po. After decay correction, number fractions ofradioactive particles were found for each stage of the
impactor. Since the size distribution was close to alog-normal distribution, the data of the cumulative fraction vs. the aerodynamic diameter were plotted on a logarithmic probability section paper. The smooth line
through those data points was used to find the geometric
median diameter (GMD, dg), and geometric standard deviation (GSD, σg).
RESULTS and DISCUSSION: Table 1 shows typicaltime variation data of the measured radio-nuclides andtheir size distributions in the electron Linac and the proton Cyclotron in KUR. Both data seems to be somewhat
different. Here, N-13 aerosols which exist in the target
room of the Linac are considered to coexist with largest
amount of gaseous N2 and N-13. On the other hand,
Mg-27 and Na-24 are considered to be produced throughnuclear reactions of high energy neutron and main constitutes of Al near the target material Be in the proton
Cyclotron.
REFERENCE:[1] S. Yokoyama et al. Jpn. J. Health Phys. 43(4), 2008,
333-340

Table 1. Typical time variation data of the measured radio-nuclides and their size distributions in theelectron Linac and the proton Cyclotron in KUR.

ElapsedTimefrom Beam “ON”
hrs

Electron Linac
13Ndg(μm)
σg(－)

0.17

Proton Cyclotron27
Mg 24Nadg(μm)
σg(－)
0.083
1.70

Remarks
Target Room

0.50

0.11

2.45

Chamber

1.3

0.21

1.46

Target Room

16.7

0.40

1.73

Target Room

38

0.48

1.77

Target Room

採択課題番号 23P5-5 高エネルギー放射線場で発生する放射性ナノ粒子の測定・評価 3 プロジェクト（京大・原子炉）山崎敬三、沖雄一（京大院・工）長田直之（藤田保健大）下 道国、横山須美（放医研）床次真司、反町篤行、C. Kranrod（京大・原子炉）高橋千太郎