PR5 Behavior of Radioactive Nuclides in Intense Radiation Fields in Accelerator Facilities
Y. Okitive aerosols in the target room of the KUR-LINAC. The
size and radioactivity of the aerosol sampled from two
sampling positions (40 cm and 230 cm apart from the Ta
target) were compared. The target was irradiated with the
30-MeV electron beams of 10, 50, and 100-µA currentsfor ~2 h per experiment. Radioactive aerosols were collected with a low-pressure cascade impactor to obtain theparticle size distribution. Under 10 µA and 50 µm, theparticle size distribution for radioactive aerosols showedno significant difference between the two sampling positions. Total radioactivity at both positions increased withbeam current.

Research Reactor Institute, Kyoto University
OBJECTIVES AND RESEARCH SUBJECTS:
High-energy and high-intensity accelerators are widelyused for many fields such as physics, chemistry and cancer therapy. The high-energy proton accelerators produce
a variety of radionuclides through nuclear reactions including spallation reactions in high-energy accelerator
facilities. The activation takes place in accelerator hardware, air, cooling water and other materials such as soil
outside of shielding concrete walls. From the viewpointsof radiation safety and safe accelerator operation, themanagement of the radionuclides is very important. The
behavior and property of the radionuclides are the mostimportant information to estimate radiation exposure andto ensure the accelerator safety.
In this work, the behavior and property were investigated in the air of the accelerator rooms and the coolingwater.
The following problems are studied in this work.
1. The property of radioactive airborne species (radioactive aerosols and radioactive gases) in the air.
2. The behavior of dissolved metals from cooling watertubes and radioactive nuclides formed in the water.
3. Problems related to activation in accelerator facilities
such as development of new radiation detectors forhigh energy accelerators and measurement of formation cross section of the principal radionuclides fordose estimation.

PRS-2
An air irradiation experiment was performed in the
150-MeV FFAG proton accelerator using an
air-irradiation chamber under various beam conditions.
The size and concentration of the aerosol particles produced in the irradiation were studied for applications to
the instrument calibration and other experiments using
standard aerosol particles. The size was increased as the
air supplying flow rate to the chamber was decreased. In
other words, the particles grew as the irradiation time wasincreased. The size was possible to be varied by changing
the flow rate to the chamber. In the case of 1 nA, beam
current, the size was able to be changed from approximately 10 to 20 nm in geometric mean diameter. The sizeand concentration were also dependent on the beam current. An increase in size and concentration was observed
above the proton current of approximately 300 pA andthey were almost saturated above 1 nA at the flow rate of
18 L/min

The participating research subjects (PRS) in the final
year of this project research (Fiscal 2014) and co-workers
in each subject are listed below.

PRS-3
In this work, experimental metal vessels filled withpure water were irradiated by -rays or bremsstrahlung /neutrons generated at electron linear accelerator (LINAC)
facility as model environments for cooling water used
inside accelerator facilities. Radiation effects on corrosion of various metals in water and colloid/particle formation of metal elements were systematically studied.
After the irradiation of -rays or bremsstrahlung, soluble(<3 nm), colloidal (3-200 nm), and particulate (>200 nm)
metal elements were detected in water. The size profiles
for each element in water and characteristics in radiation
effects were dependent on vessel materials. In the experiments using Al and Fe vessels, total Al/Fe concentrations became higher dependent on photon irradiation intensity. In the water supernatant obtained after the irradiations, Al and Fe were found to be mainly present as relatively-large particles (>200 nm). Concentrations of soluble species and fine colloidal species are quite small
compared to those of the large particle species. Theirchemical states were are also discussed in this work.

PRS-1 (26P5-1) Radioactivity Size Distribution of Airborne Aerosols Formed in Target Room Estimatedfrom Number Size Distribution(S. Yokoyama, Y. Oki and S. Sekimoto)PRS-2 (26P5-2) Production of Airborne Nano-Particles
by Proton Irradiation in an FFAG Accelerator(Y. Oki, N. Osada, S. Yokoyama, Y. Ishi, T. Uesugi, Y.
Kuriyama and M. Sakamoto)PRS-3 (26P5-3) Corrosion of Various Metals in Water
and Formation of Metal-related Colloidal Particles under Intense Photon-Radiation Field(K. Bessho, H. Matsumura, Y. Oki, S. Sekimoto, K.
Masumoto and N. Abe)
MAIN RESULTS:
PRS-1
The present study analyzed a distribution of radioac-

19PR5-1

Radioactivity Size Distribution of Airborne Aerosols
Formed in Target Room Estimated from Number Size Distribution

S. Yokoyama,1 Y. Oki,2 and S. Sekimoto2
1
2

rays induced by electrons.
Under 50 A, the peak radioactivity count collected at
port 2 was 1.3 times higher than that at port 1, as shownin Fig. 1. The number size distributions of aerosols simultaneously measured by a Scanning Mobility Particle
Sizer (TSI, Model 3080) showed a similar result. Radioactive aerosols are formed by deposition of radionuclides
on non-radioactive aerosols. Thus, the number of radioactive aerosols at port 2 under 50 A should increase. No
clear difference existed between median diameters ofradioactive size distributions at ports 1 and 2. This meansthat the non-radioactive aerosols were generated not onlyaround the target, but also throughout the target room.

School of Health Science, Fujita Health University
Graduate School of Engineering, Kyoto University

INTRODUCTION: To assess internal exposure of accelerator facility workers due to inhaling radioactive aerosols and gases, the radioactivity size distribution and theamount of radioactive aerosols formed in the facilities
must be estimated [1–4]. In previous studies, aerosol radioactivity and number size distributions were measured
in the target room of KUR-LINAC and the radioactivity
size distributions were estimated from the number-size
distributions [3, 4]. In addition, the relationship between
radioactivity size distribution of aerosols and beam currents was investigated. The present study analyzes a distribution of radioactive aerosols in a target room.

15000

dA/dlogDp

EXPERIMENTS: Two sampling ports were prepared 40
cm (port 1) and 230 cm (port 2, near the wall surface)from the target of KUR-LINAC. Electron beams weregenerated under a 30-MeV voltage and 10-, 50-, and100-μA currents for ~2 h per experiment. A water-cooled
Ta target was placed at the end of the beam line as a neutron generator. Radioactive aerosols were collected by a
13-stage low-pressure cascade impactor (Tokyo Dylec
Corp.). Stainless steel plates coated with grease were set
in each stage, except for the lowest stage, in which a filter
was set. The collection started at 60 min after irradiation
began and continued for 30 min. After collection, theplate and filter radioactivities were measured by a GM
survey meter (TGS123-C, Aloka). Radionuclides formedin the target room confirmed that 13N contributed significantly to total activity, when compared with the lower
radioactivity measured in the previous study [4].
RESULTS: Figure 1 shows the radioactivity size distribution of aerosols under 10- and 50-A beam currents at
ports 1 and 2. Under 10 A, the median diameters of radioactive aerosols were 270 and 189 nm (and 1.2)
at ports 1 and 2, respectively. Under 50 A, median diameters of radioactive aerosols were 270 and 229 nm(and 1.4) at ports 1 and 2, respectively. In the previous study, the median diameter of radioactive aerosols
collected near the target was 261±3.9 nm under 20-100
A [3, 4]. Figure 2 illustrates the total radioactivity ofaerosols under 10, 50 and 100 A. Total radioactivity at
ports 1 and 2 increased with beam current.
Radionuclides are mainly generated by interaction between neutrons and the atmospheric nitrogen and oxygen
proximal to the target just after the electron beam hits thetarget. Non-radioactive aerosols were formed by irradiation by electrons leaked from the beam line and gamma

10A, at 40 cm
10A, at 230 cm
50A, at 40 cm
50A, at 230 cm

10000

5000

0

100

1000

10000

Diameter (nm)F
ig. 1. Activity size distribution of radioactive aerosols
collected at ports 1 and 2.

Total activity (Counts)

60000
50000
40000
30000
20000

at 40 cm
at 230 cm

10000
0

0

20

40

60

80

100

Beam current (A)

Fig. 2. Total activity of radioactive aerosols at ports 1 and
2.
REFERENCES:[1] S. YOKOYAMA et al., Jpn. J. Health. Phys., 43(2008) 333–340.
[2] S. YOKOYAMA et al., Rad. Prot. Dosi., 127 (2007)
392–397.
[3] S. YOKOYAMA et al., KURRI progress report 2012,
PR11-1 (2013), http://www.rri.kyoto-u.ac.jp/JRS/.
[4] S. YOKOYAMA et al., KURRI progress report 2013,
http://www.rri.kyoto-u.ac.jp/PUB/report/PR/ProgRep201
3/Project8.pdf

採択課題番号 26P5-1
加速器施設内生成粒子の粒径分布に関する研究（藤田保衛大・医科）横山 須美（京大・原子炉）沖 雄一、関本 俊

20

プロジェクトPR5-2 Production of Airborne Nano-Particles by Proton Irradiation in an FFAG Accelerator
Y. Oki, N. Osada1, S. Yokoyama2, Y. Ishi, T. Uesugi, Y.
Kuriyama and M. Sakamoto

the beam dump of the specimen irradiation beam line.
The 1-mm thick aluminum plates were used as both endsof the chamber. The aerosol-free air was prepared by filtration and was introduced to the chamber at the constantflow rate, and the irradiated air was sampled from thechamber at the same flow rate.
The size distribution and the total concentration of theaerosol particles were measured with SMPS (Scanning
Mobility Particle Sizer).

Research Reactor Institute, Kyoto University
Advanced Science Research Center, Okayama University
2
School of Health Science, Fujita Health University
1

INTRODUCTION: In accelerator facilities, very fineradiation-induced aerosol particles were often producedin air of accelerator rooms during machine operation. The
size and concentration of the particles are generally very
stable under a given beam condition. This particle generation may be applicable to calibration of size-measuring
instrument for the fine particles in the diameter range ofnm to 0.1 m.
In this work, an air irradiation experiment was performed in an FFAG (Fixed Field Alternating Gradient)
proton accelerator under various beam conditions. The
size and concentration of the aerosol particles producedin the irradiation were studied for applications to the instrument calibration and other experiments using standard aerosol particles.

RESULTS AND DISCUSSION: The size of formed
aerosol particles showed very steady mono-modal
log-normal distributions. The size was increased as the
air supplying flow rate was decreased. In other words,
the particles grew as the irradiation time was increased.
The size was possible to be varied by changing the flowrate to the chamber. In the case of 1 nA, beam current,
the size was able to be changed from approximately 10
nm (the flow rate: 18 L/min) to 20 nm (8 L/min) in geometric mean diameter. The size and concentration werealso dependent on the beam current. An increase in sizeand concentration was observed above the proton currentof approximately 300 pA and they were almost saturated
above 1 nA at the flow rate of 18 L/min [1].
During the air irradiation, principal radionuclides
formed in the accelerator air, 15O (half life: 2 min), 13N(10 min), 11C (20 min) [2] and 7Be (53 d), are formed
together with the radiation-induced aerosol particles. The
aerosol particles form radioactive aerosols by incorporating the radioactive atoms into the radiation-induced particles. The size distribution of 7Be-bearing aerosol particles were successfully measured with a graded screen
array system in the same air-irradiation chamber [1]. The
7
Be aerosol particles can be also used in various research
including calibration of aerosol instruments for radioactive fine particles.

EXPERIMENTS: The irradiation experiment was performed in the 150-MeV FFAG proton accelerator of Research Reactor Institute, Kyoto University (KURRI). The
FFAG accelerator system consists of the 11-MeV H– linear accelerator (Injector) and the FFAG main ring. The
injected protons are accelerated in the main ring to 150
MeV after conversion of H– ions to protons. The nominal
150-MeV proton beams were extracted to an air irradiation chamber in the specimen irradiation beam line. Figure 1 shows the irradiation chamber together with thespecimen irradiation beam line and the main ring.

In conclusion, the air-irradiation chamber was capable of producing aerosol particles in the diameter rangeof 10 to 20 nm by the 1-nA proton irradiation carried out
in the FFAG accelerator.
REFERENCES:[1] Y. Oki, N. Osada, Y. Ishi, T. Uesugi, Y. Kuriyama and
M. Sakamoto, KEK Proceedings 2014-7, 52-57.
[2] A. Endo, Y. Oki, Y. Kanda, T. Oishi, and K. Kondo,
Radiat. Prot. Dosim., 93 (2001) 223-230.

Fig.1 Irradiation Chamber
The air-irradiation chamber was a 1-m long stainlesssteel cylinder (i.d. 15 cm). It was installed upstream of

加速器室の空気生成する放射性化学種の生成挙動
採択課題番号 26P5-2（京大・原子炉）沖 雄一、関本俊、（藤田保健衛生大医療科学部）横山須美
21

プロジェクトPR5-3

Corrosion of Various Metals in Water and Formation of Metal-related
Colloidal Particles under Intense Photon-Raiation Field

K. Bessho, H. Matsumura, Y. Oki1, S. Sekimoto1,
K. Masumoto, N. Abe1

alloys). In this report, some characteristics observed forpure Al, Fe and Cu are described.
In the experiments using Al and Fe vessels, irradiations
were carried out at LINAC with two kinds of beam currents (20, 100 A) and the irradiation times of 2 h. Total
Al/Fe concentrations became higher dependent on photon
irradiation intensity. In the water supernatant obtained
after the irradiations, Al and Fe were found to be mainlypresent as relatively-large particles (>200 nm). Concentrations of soluble species and fine colloidal species arequite small compared to those of the large particle species.
Al and Fe in non-degassed water are considered to be in
the oxidation states of III (Al3+, Fe3+), which tend to formhydroxide precipitations in neutral pH conditions. It canbe supposed that photon irradiation facilitates the corrosion (oxidation) of pure Al and Fe metals in water, consequently Al and Fe are released as Al3+, Fe3+ ions fromthe metal surface to water, finally form Al(OH)3 andFe(OH)3 particles in water phase.
In case of the experiments using Cu metal vessels, effects of radiation were mainly observed as increase insoluble Cu species (<3 nm) and production of large particle Cu species (>200 nm). Under irradiation conditions,soluble Cu concentration increased with time depend on
photon doses and finally reached to plateau, which may
be originated from hydrolysis of Cu(II) ions. On the other
hand, production of particle Cu species was observed
remarkably after long irradiation times (> 20-30 h). These
characteristic time-dependence imply that particle Cu
species were initially generated at the Cu/water interface
as particle-like corrosion products. These products grewup at the interface in a time scale of several tens hours,
and were finally released into water phase as particles (>200 nm). The particle production processes at the interface were also promoted by photon irradiations [3].
Radiation effects on corrosions of metals in water are
explained by production of oxidative reactive species,
such as OH radicals and H2O2, induced by radiolysis ofwater molecules. By using water quality testing kits, it
was demonstrated that several mg/L of H2O2 and O3 were
produced by irradiation of water by -rays or bremsstrahlung, and these oxidative species should induce various radiation effects clarified by this work.

Radiation Science Center, KEK
1
Research Reactor Institute, Kyoto University
INTRODUCTION: At high-energy accelerator facilities, intense radiations affect chemical states of elements
including radionuclides inside the facilities. In the cooling-waters for various accelerator components, corrosionof metal components and formation of metal related colloids/particles in water are important subjects in the radiation safety managements at accelerator facilities, because some radionuclides are incorporated in colloidal
species and it complicate the behavior of nuclides [1,2].
In this work, experimental metal vessels filled withpure water were irradiated by -rays or bremsstrahlung /neutrons generated at electron linear accelerator (LINAC)
facility as model environments for cooling water used
inside accelerator facilities. Radiation effects on corrosion of various metals in water and colloid/particle formation of metal elements were systematically studied.
EXPERIMENTS: Metal vessels (I. D. 19 x 75 mm)
filled with pure water were irradiated by -rays generated
at the 60Co -ray irradiation facility, or bremsstrahlung /neutrons generated by 30 MeV electron beam hitting on a
Ta target (50 x 62 mm) at the LINAC facility. Samples
at the LINAC experiments were placed at the downstream position (40 or 80 mm from Ta target) and perpendicular position (40 or 80 mm from Ta target).
Monte Carlo calculations and activation experiments using metal foils (Au, Al) demonstrated that radiation effects observed in the present LINAC experiments could
be ascribed to the effects of photon irradiations (maximum fluxes; 3 MeV for 0-deg and 0.7 MeV for 90-deg).
Contribution of neutrons was found to be much smaller
than those of photons in these experiments.
After the irradiations, water in metal vessels werepoured out and treated with four kinds of ultrafiltration(UF) membrane units for particle size separation contained in water supernatant. Estimated pore sizes of the
UF units were 200, 16, 7 and 3 nm. Concentrations ofmetal elements in the filtrates and unfiltered samples
were determined by ICP-AES analyses.

REFERENCES:[1] K. Bessho et al., J. Radioanal. Nucl. Chem., 303(2015) 1719-1725.
[2] H. Matsumura et al., Progress in Nucl. Sci. Technol.,
4 (2014) 372-375.
[3] K. Bessho et al., J. Radioanal. Nucl. Chem., 303(2015) 1117-1121.

RESULTS: After the irradiation of -rays or bremsstrahlung, soluble (<3 nm), colloidal (3-200nm), andparticluate (>200nm) metal elements were detected inwater. The size profiles for each elements in water andcharacteristics in radiation effects were dependent on
vessel materials (pure Fe, Al, Cu, and SUS-304, A6061

採択課題番号 26P5-3

高線量放射線場における水中金属材料の腐食およびプロジェクトコロイド生成挙動の解析２（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
22