VIII-Ⅱ-1. Project Research
Project 8

PR8

Irradiation Effects on Microstructural Evolution in Materials Irradiatedby Particles with High Energy

Q. Xu
Research Reactor Institute, Kyoto University
OBJECTIVES: Maintenance the safety of nuclear reactors is important. Neutron irradiation degrades mechanical properties of materials. Thus the study of nucleationand growth of irradiation defects in materials is significant to predict irradiation effect. Kyoto University research reactor, and other irradiation facilities, such asions, electrons and  rays, have also been used in the present project research to clarify the damage structural development.
RESULTS: The allotted research subject (ARS) andthe name of co-researches in each ARS are listed below.
A number of important data were already obtained. Details are presented in this progress reports.
ARS-1
Persistent photoconductivity in electron-irradiated single
crystal ZnO bulk: dual light illumination effect(K. Kuriyama, T. Oga, T. Ida, K. Kushida, and Q. Xu)
ARS-2
X-ray diffraction analysis of ZnO implanted with Sn+ atroom temperature and 110 K(G.T. Dang, N. Nitta, M. Taniwaki and T. Yoshiie)
ARS-3
Study on formation and recovery of damage in irradiatedcrystalline materials(A. Kinomura, K. Sato, Q. Xu and T. Yoshiie)
ARS-4
Orange emission of calcites by gamma rays
(T. Awata, T. Kishino, F. Maki and Q. Xu)
ARS-5
Annealing behavior of thermal diffusivity and positronannihilation lifetime in 30MeV electron-irradiated ceramics(M. Akiyoshi, I. Takagi, T. Yoshiie, Q. Xu, K. Sato)
ARS-6

採択課題番号 23P8

Defects in a Zr-Nb alloy studied by positron annihilation
and atom probe tomography(Y. Nagai, T. Toyama, Y. Matsukawa, Y. Shimizu, A.
Kuramoto, H. Takamizawa, Y. Kakubo, K. Inoue, T.
Yoshiie, Q. Xu and K. Sato)
ARS-7
Defects study for iron alloys damaged by electron irradiation(F.Hori, M.Maruhashi, N. Onodera, A.Ishii, S.Mineno,
A.Iwase, Q.Xu, K.Sato and T.Yoshiie)
ARS-8
Recovery process of neutron-irradiated vanadium alloys
in post-irradiation annealing treatment(K. Fukumoto, M. Iwasaki and Q. Xu)
ARS-9
Damage evolution in neutron-irradiated metals during
neutron irradiation at elevated temperatures(I.Mukouda, K. Yamakawa, T. Yoshiie, Q. Xu)
ARS-10Effects of thermal aging and irradiation on mechanicalproperties of Fe-Cr ferritic alloys(R. Kasada, Y. Sakamoto, K. Yabuuchi, A. Kimura, K.
Sato, Q. Xu, T. Yoshiie)
ARS-11
Radiation resistance of nanocrystalline Ni by neutron
irradiation(H. Tsuchida, A. Itoh, K. Sato, T. Yoshiie, Q. Xu)
ARS-12
Interaction between deuterium and defects in tungsten(K. Sato, R. Tamiya, Q. Xu and T. Yoshiie)
ARS-13
Irradiation effects on stress loading property of refractory
metal at high temperature(K. Tokunaga, K. Araki, T. Fujiwara, T. Hotta, Q. Xu, T.
Yoshiie)

材料の組織変化に及ぼす高エネルギー粒子線の照射効果（京大・原子炉）徐 虬

プロジェクトPR8-1

Persistent Photoconductivity In Electron-irradiated Single Crystal ZnO Bulk:
Dual Light Illumination Effect

K. Kuriyama, T. Oga, T. Ida, K. Kushida1 andQ. Xu2

infrared LED. Thus, the slight increase in thephotocurrent observed here is not directly related to
PPC observed in the present study.

College of Engineering and Research Center of Ion
Beam Technology, Hosei University
1
Osaka Kyoiku University
2
Research Reactor Institute, Kyoto University
INTRODUCTION: Some models of Persistent
Photoconductivity (PPC) mechanism have beentheoretically proposed [1, 2], indicating that theoxygen vacancies (VO) with various charge states(VO+ or VO2+) are related to PPC in ZnO. In thepresent study, in order to study the origin of the PPC,
we use the dual light illumination (DLI), namely,
the illumination with blue LED and subsequently,
the illumination with red or infrared LED.
EXPERIMENT: The ZnO single crystals used in thepresent study were grown at Tokyo Denpa Co, Ltd.
using the hydrothermal method. A 30 MeV
electron-irradiation was performed at room
temperature, using an electron linear accelerator
facility at Kyoto University Research Institute. A
beam current and irradiation dose were 18 μA/cm2
and 5 × 1017 e−/cm2, respectively.
RESULTS: Fig. 1 shows the decay of PPC under the
DLI (first, the illumination with blue LED for 20 min
and subsequently, with red or infrared LEDs for 20
min). All these spectra were normalized after
subtracting the dark current. The excitation with red
and infrared LED showed the remarkable reduction of
PPC, suggesting that electrons in the origin of the
PPC were excited to higher unoccupied states.
Fig. 2(a) shows PPC spectra measured at various
temperatures between 90 and 300 K. To study
variations of PPC under the DLI, after turning off theblue LED, the sample was held in the dark for 60 min
and subsequently exposed to the infrared LED for 20
min. Both the current reduction in PPC and the slightincrease in the photocurrent were observed. The
threshold temperature for the increase and decrease in
the photocurrent was ∼160 K. These results imply
that the electrons in the origin of PPC are sensitive tothe sample temperature. PPC curves of 250 and 300
K were fitted by the least square method with thestretched exponential function [3], I(t) = I(0)exp[−(t/τ )β ], which was used in our previous study[4], as shown in Fig. 2. The fitting parameters, τ and β
values, were 2.4 × 105 s and 0.11 at 250 K and 1.0 ×
104 s and 0.27 at 300 K, respectively. The stretchedexponential functions were well fitted with theexperimental values except for the slight increase in
the photocurrent caused by the exposure to theFig. 1. Persistent Photoconductivity (PPC)
measured at 90 K under the dual light illumination(DLI), namely, the illumination with blue LED for
20 min and subsequently, the illumination with red
or infrared LED for 20 min.

Fig. 2. PPC decay measured at various temperatures
under the DLI. The fitting curves at 250 and 300 K
show the least squares fit of data by thestretch-exponential function [3].
REFERENCES:[1] A. Janotti, C.G. Van de Walle, Phys. Rev. B 76
(2007) 165202.
[2] S. Lany, A. Zunger, Phys. Rev. B 72 (2005)
035215.
[3] H.X. Jiang, J.Y. Lin, Phys. Rev. Lett. 64 (1990)
2547.
[4] T. Oga, Y. Izawa, K. Kuriyama, K. Kushida, and Q.
Xu, AIP Conf. Proceedings, Vol. 1399, (2011) 67.
30th International Conference on the Physics of
Semiconductors (Soule, Korea).

採択課題番号 23P8-1 化合物半導体の照射効果と電気的・光学的特性に関する研究 プロジェクト(法政大院) 栗山一男、尾賀孝宏、伊田孝寛 (大阪教育大) 串田一雅
(京大・原子炉) 徐 虬

PR8-2

X-ray Diffraction Analysis of ZnO Implanted with Sn+
at Room Temperature and 110 K

G. T. Dang, N. Nitta, M. Taniwaki, and T.
Yoshiie1
Department of Environmental Systems Engineering, Kochi University of Technology
1
Research Reactor Institute, Kyoto University
Ⅱ - Ⅵ comINTRODUCTION: Nowadays,
pound semiconductors are noticed because of
its potential applications in (opto)electronic
devices. Particularly ZnO has regained research interest in the field of opt-electronic devices working in the blue and ultraviolet regions. However, wide applications have been
impeded by difficulty in achieving p-type conductivity ZnO. Better understanding of defectstructures is necessary to overcome this difficulty. Ion implantation, which is a standard
technique in semiconductor device process atpresent, is an artificial way to produce defects
in semiconductors. In this study, ZnO wafers
were implanted with 60 keV Sn+ ions. The wafers were examined by means of X-ray diffraction (XRD).

0003 reflection. Its appearance indicates that thesesamples contained some defects (probably twins), because the 0003 Bragg reflection is forbidden in thewurtzite-type perfect crystals. The fine-scans of the0002 peak for the unimplanted sample and all RT
samples are illustrated in Fig.1 a. By implantation atroom temperature, a broad line component appeared
around the 0002 peak and its width increased withimplantation dose. However the results for LT samples were different from RT samples. Figure1 b displays the fine-scans for the LT samples. The changewith implantation dose was not discernible. This will
be due to the difference in migration of the implantation-induced defects between RT and LT samples.
Movement of the implantation-induced point defects
depends on temperature; that is, the active migrationof the implantation-induced defects at room temperature disturbs the lattice structures leading to thebroadening of the reflected line.

EXPERIMENT: 99.99% pure ZnO samples withdimensions of 10×10×0.54 mm3 were implanted with60 keV Sn+ ions to doses of 2×1014, 4×1014, 8×1014,
and 1.5×1015 ions/cm2 at room temperature (RT samples) and 4×1014, 8×1014, and 1.5×1015 ions/cm2 at 110
K (LT samples). The zinc surface of the (0001) planeof all samples was implanted, except for the 2×1014
ions/cm2 RT sample, whose oxygen surface was implanted. XRD patterns (   2 scan) were measured in these samples by an ATX Rigaku XRDdiffractometer using the Cu K line (=1.5418 Å).
RESULTS: In the wide-range XRD patterns of theunimplanted, 1.5×1015 ions/cm2 RT, and 1.5×1015
ions/cm2 LT samples, two strong peaks were observed
at 34.42o, and 72.58o. These peaks correspond to 0002
and 0004 reflections, respectively. A weak peak at
52.70o was observed in all samples except for the
1.5×1015 cm2 LT sample. This peak corresponds to the

採択課題番号 23P8-2

Fig.1

Fine-scans of the XRD 0002 peak: RT sam-ples and b) LT samples. (Referred from G. T. Danget al., AIP Conf. Proc. 1321, 270 (2011) )半導体イオン照射によって導入される点欠陥挙動の解明とプロジェクトナノセル技術の開発（高知工科大） 谷脇雅文、新田紀子、 Dang Tchai Giang、 石川 修、 横山和弘、 横田正博
(京大・原子炉) 義家敏正、徐 虬

PR8-3

Study on Formation and Recovery of Damage in Irradiated Crystalline Materials

A. Kinomura, K. Sato1, Q. Xu1 and T. Yoshiie1
National Institute of Advanced Industrial Science andTechnology (AIST)
1
Kyoto University Research Reactor Institute (KURRI)

INTRODUCTION: Radiation effects of ion irradiation
have been extensively studied for various materials.
Irradiation-induced damage degrades crystallinity andgives harmful effects on material properties. However,under appropriate irradiation or annealing conditions, theradiation and/or damaging effects can induce interesting
effects and useful structures in materials. A typical caseof such effects is the ion beam annealing in Si, where
implantation-induced damage layers are recrystallized
under other ion irradiation at elevated temperatures.
Thus, it is important to investigate the radiation effects
for the application and fundamental studies oninteractions of energetic particles (ions and neutrons)with materials.
EXPERIMENTS: Two types of samples were studied inthis year: (1) Hydrogen-implanted multicrystalline Si toobserve the gettering of metal impurities tohydrogen-induced nanocavities; (2) ion-irradiated Ni toinvestigate the difference between the calculated ion
range and the actual depth of damage. Some of these
irradiated samples have been characterized by neutron
activation analysis or positron annihilation spectroscopy.
We performed cross-sectional transmission electron
microscopy (TEM) to understand the nature of theradiation damage. It is difficult to make thinned
samples for cross-sectional TEM observation, when theamounts of samples are limited. To obtain sufficient
TEM samples from such samples, we used an FIB(focused ion beam) milling system. The FIB milling
method is also good for multicrystalline samples like thisstudy. The TEM observation was performed at anelectron energy of 200 keV.
RESULTS: The multicrystalline Si observed was
implanted with 50 keV H+ to a dose of 3×1016 cm-2 andannealed at 850 ºC for 1h. Cross-sectional TEM
samples were taken from the positions overriding grainboundaries as shown in Fig. 1(a). Pt protective layers
were deposited on the sampling point (approximately 12
× 2 µm) prior to the cutting process to protect the surface
side of the cross-sectional sample during the FIB milling.
The thickness of the sample was about 2 µm at the
beginning and further thinned by FIB milling. Fig. 1(b)shows the TEM image after the FIB milling. This
image almost covers the whole area exposed to the ion
milling (about 10 µm wide). A continuous band ofnanocavities was clearly observed around the projected
range of 50 keV H+ (~0.5 µm) as shown in Fig. 1(b).
The grain boundary should be at the middle of theobserved region. However, interestingly, there was noinfluence of the grain boundary on the nanocavity band.
TEM samples were also made from a pure Ni sample
irradiated with 150 keV Ar+ to a dose of 1×1015 cm-2 atroom temperature. This sample was observed by EBSD(Electron BackScatter Diffraction) in advance. It is
confirmed that the crystal grains observed in EBSD wereprecisely identified in SIM (secondary ion microscopy)
images and the grains of interest can be chosen for the
FIB milling method. The sampling of the TEM sample
was successfully performed in the same way as the Si
samples. We plan to perform electrochemical etching to
remove the damage caused by the FIB milling.
In summary, the TEM sample preparation by the FIB
milling was performed for multicrystalline-Si andpure-Ni samples in this study. The hydrogen-induced
nanocavities were successfully observed for the Si
samples around the grain boundary.
ACKNOWLEDGMENT: We would like to thankcolleagues in AIST for their assistance on this study.

(a)

(b)
Fig. 1. Images of the multicrystalline Si sample after
H-implantation and annealing. (a) Plan-view SIM
image showing the sampling position for TEM. (b)Cross-sectional TEM image of the thin specimen
obtained after milling.

採択課題番号 23P8-3 照射下の結晶材料における損傷形成と回復過程の研究（産総研）木野村淳（京大・原子炉）佐藤紘一、徐、義家敏正

プロジェクトPR8-4

Orange Emission of Calcites by Gamma Rays

T. Awata, T. Kishino, F. Maki and Q. Xu1
Department of Physics, Naruto University of Education
1
Research Reactor Institute, Kyoto University
INTRODUCTION: The calcite (CaCO3) has beenstudied since 1940’s [1-3], because the intensity of thermoluminescence of calcite is higher than other famous
minerals (e. g. fluorite) and it has the possibility of radiation dosimeter. V. Ponnusamy et al. [4] reported that theintensity of luminescence of calcite irradiated by gamma
rays was depend on the annealing and the emission spectra have an emission band at 610nm (orange), and might
be assumed that the recombination are always in involves
Mn2+ ions. Last year, we reported thermoluminescence of
natural calcite irradiated by gamma rays and it was
shown that the spectra had only one orange emission
peak at 620nm and that may be originated from impurity
Mn2+[5]. In this study, we have performed trace element
analysis of natural calcite using NAA (Neutron Activation Analysis), XRF (X-ray Fluorescence Analysis) and
ICP-AES (Inductively Coupled Plasma Atomic Emission
Spectroscopy) to clear the relationship with orange emission bands and impurities of calcite.

(Futagoyama, Saitama, JAPAN) irradiated by neutron at
Pn-3 for after 1 day. It is shown that manganese, lanthanum and sodium were detected in the calcite. On the two
weeks after measurements, no element without calcium
was detected. Figure 2 shows the X-ray fluorescence
spectrum of natural calcite. In this figure, it can be shownthat manganese and iron are dominant impurities in the
calcite. To clear the impurity concentration of the calcite,
ICP-AES was performed. From the experimental results,
impurities of manganese (57.1ppm), sodium (9.12ppm),
iron (4.73ppm) and Copper (0.345ppm) are contained incalcite. At the all experimental results, Mn was always
detected and was dominant impurity of calcite. V. Ponnusamy et al. had concluded the orange emission around
610nm is originated from the electron transition from 4G
to 6S state of Mn2+. In our results, thermoluminescence
spectra of calcite has emission peaks at 620nm, andslight different from their results. We have to clear thereason this difference and influence of other impurities(especially Fe and Cu) in the near future.

EXPERIMENTS:The samples were some natural calcites and were irradiated neutron at Pn-3 of KUR for
NAA. The gamma-rays spectra were taken by Ge detector at KUR after 1day for short-lifetime element and after
two weeks for long-lifetime elements. ICP-AES(iCAP6300Duo, Themo Fisher) was also performed tomeasure element concentration of calcites at KUR. To
analyze the element characterization of calcites, we had
used XRF (Simultix 14, Rigaku).
RESULTS and DISCUSSION: Fi gur e 1 s ho ws t he
gamma-ray energy spectrum of typical natural calcite

Fig.2 .X-ray fluorescence spectrum of calcite.
ACKNOWLEDGEMENT: We would like to thankProfessor Dr. Fukutani (KURRI) for assistance on thisstudy.

Fig. 1. Gamma-ray energy spectrum of natural calcite.

REFERENCES:[1] W. L. Medlin, J. Opt. Soc. Am. 53(1963) 1276-1285.
[2] W. L. Medlin, J. Chem. Phys. 30, pp451-458 (1959).
[3] W. L. Medlin, Phys. Rev, 135, pp.A1770 (1964).
[4] V. Ponnusamy, V. Ramasamy, M. Dheenathayalu, etal., Nucl. Instr. and Meth. B 217 (2004)611-620.
[5] T. Awata and Q. Xu, KURRI Progress Report 2010
p.183.

採択課題番号 23P8-4
高エネルギー粒子線による絶縁体の照射効果
プロジェクト
（鳴門教育大学）粟田高明，岸野哲也，牧文哉（京大・原子炉）義家敏正，徐虫しAnnealing Behavior of Thermal Diffusivity and Positron Annihilation Lifetime in
30MeV Electron-irradiated Ceramics

RESULTS:
After the spectrum analysis, average positron lifetime<> was obtained as <> = 1 I1 + 2 I2, where i are theanalyzed positron lifetimes and I i are the intensities forthe components. The average lifetime <> of electron
irradiated -Al2O3 and AlN indicated significant increment same as neutron irradiated specimens. On the other
hand, -Si3N4 and -SiC showed almost no change inlifetime same as neutron irradiated specimen.

採択課題番号 23P8-5

180

0.8
Unirradiated TD

175
170

Unirradiated PAL

160
0

0.7
0.6

165

→
Thermal diffusivity←
Average PAL
Electron irradiated AlN KURL-0708

500
1000
Annealing Temperature / ℃

2

EXPERIMENTS:
Typical structural ceramics (-Al2O3, AlN, Si3N4 and-SiC) were irradiated by 30MeV electron using the
KURRI-LINAC up to 1.5x1024e/m2 (correspond to
0.01dpa) at 300K in the water-cooled specimen holder.
Thermal diffusivity was measured by laser flash method
at the room temperature, and as-irradiated specimen
showed about 20%, 40%, 30%, 75% degradation in-Al2O3, AlN, -Si3N4 and -SiC respectively.
Positron annihilation lifetime was also measured using
conventional -fast coincidence method in Radiation
Laboratory, Uji. The irradiated specimen was ax0.5mm disk. Positron source was specially ordered
1MBq 22Na sealed by Ti foil, and the active diameter was
1mm.
The obtained PAL spectrum was analyzed with PALSfit
program, with FWHM about 230ps. In analyze of thespectrum, a source component that represents annihilation in the Ti foil was not resolved, and only two or threecomponent was guessed in the analysis.
After the measurement for the as-irradiated specimens,
isochronal annealing was conducted every 100℃ up to
1100℃ in a vacuum. After the each step of annealing,
specimens were cooled to the room temperature and thenthermal diffusivity and PAL measurements were performed at the room temperature.

-4

INTRODUCTION:
Measurement of thermal diffusivity and positron annihilation lifetime were performed on 30MeV electron irradiated ceramics. In this study, electron irradiation was
performed to 0.01 dpa via 30MeV KURRI-Linac. The
electron irradiated specimens showed obvious degradation in thermal diffusivity and increment in positron annihilation lifetime. In addition, isochronal annealing was
conducted every 100℃ up to 1100℃ in a vacuum. The
annealing behavior of several specimens showed that
positron annihilation lifetime gives good correlation withthermal diffusivity.

Thermal Diffusivity / 10 m /s

Faculty of Engineering, Kyoto University
1
Research Reactor Institute, Kyoto University

The annealing behavior of PAL showed almost same
trend as that of thermal diffusivity in -Al2O3 and AlN.
On the other hand, PAL in -Si3N4 and -SiC showed
different behavior from the thermal diffusivity. This trend
fit to the correlation between thermal diffusivity and PAL
measured for specimens irradiated several different conditions in the previous work.
AlN showed most clear correlation between thermal
diffusivity and PAL during the annealing. On the other
hand, the thermal diffusivity of unirradiated -Al2O3
specimen was no so high, so the annealing behavior was
not clear. -SiC specimen showed clear recovery inthermal diffusivity but the specimen was p-type SiC,
therefore the PAL did not show obvious change after theirradiation and the annealing. Now n-type SiC was irradiated using the LINAC, and it is expected that the specimen show clear correlation even in a covalent bond ceramics.

Average PAL <τ> / ps

M. Akiyoshi, I. Takagi, T. Yoshiie1, Q. Xu1 and K. Sato1

0.5

Fig 1: Annealing behavior of thermal diffusivity and PAL
in electron-irradiated AlN.

Average PAL <τ> / ps

PR8-5

180

Tokuyama AlN SH-30
Unirradiated
KURL-0708 Electron irradiated

170

160
0.4

0.5
0.6
0.7
Thermal Diffusivity / 10 -4 m2/s

0.8

Fig 2: Correlation between thermal diffusivity and PAL
obtained from an electron-irradiated AlN specimen withisochronal annealing.

照射セラミックスの熱拡散率及び陽電子消滅法による欠陥評価（京大・工）秋吉 優史、高木 郁二（京大・原子炉）義家 敏正、徐 虬、佐藤 紘一

プロジェクトPR8-6 Defects in a Zr-Nb Alloy Studied by Positron Annihilation and Atom Probe Tomography

INTRODUCTION: Zr-Nb alloy is an advanced nuclear
material recently developed for fuel cladding tubes that
store uranium pellets in light-water nuclear reactors operated at extended fuel burn-up rates such as 65~70
GWdt-1, which is 20~30% greater than the current
standard, for improving economic efficiency. The originof the excellent properties on corrosion resistance andsuppression of hydride formation considered to be related
to Nb precipitates, however the detail is not understoodyet. In this work, we employed positron annihilation andatom probe tomography (APT) to study the defects related to the Nb precipitates in Zr-Nb alloy.
EXPERIMENTAL: The samples used in this study arean Zr-1.8wt%Nb alloy. A part of the samples were irradiated at 77K by 28MeV electrons to a fluence of about
5×1018 e/cm2 using the KUR-LINAC.
RESULTS & DISCUSSION: Fig. 1 shows positron
coincidence Doppler broadening (CDB) ratio spectra for
the unirradiated and the electron-irradiated Zr-Nb normalized by pure-Zr. CDB ratio spectra for pure Nb andFe are also shown as references. For the unirradiatedsample, a broad peak around 18×10-3mc is clearly observed. This peak originates from positron annihilation
with Fe electrons which is contained as impurities in
Zr-Nb alloy due to zirconium’s high chemical reactivity.
Judging from the peak height, the fraction of positrons
annihilated with Fe electrons was estimated to be about
30 at.%. On the other hand, for the irradiated sample,
such a broad peak around 18×10-3mc is not observed asshown in Fig. 1. Fig. 2 shows mean positron lifetime forthe unirradiated and the electron-irradiated Zr-Nb. In theelectron-irradiated sample mean positron lifetime is almost same as that for vacancy in Zr, which indicates that
positrons are mainly trapped at the vacancies in the Zr
matrix introduced by the electron-irradiation. Fig. 3
shows APT elemental maps for the unirradiated sample.
Fe segregation on the interface between Zr matrix and a
Nb precipitate is clearly observed.
These results of positron annihilation and APT strong-

採択課題番号 23P8-6

5

PureFeIrrad.
Unirrad.

4
3
2

PureNb

1
0
0

10

20

30

PL [×10-3 mc]

Fig. 1. CDB ratio spectra for the unirradiated and electron-irradiatedZr-Nb normalized by pure-Zr. CDB ratio spectra for pure Nb and Fe arealso shown as references.

Mean Positron Lifetime[ps]Institute for Materials Research, Tohoku University
1
Department of Materials Science and Engineering, Kyoto
University
2
Research Reactor Institute, Kyoto University

ly suggest that positrons are mainly trapped at the precipitate-matrix interface decorated with Fe atoms for theunirradiated sample, while for the irradiated sample positrons are mainly trapped at the irradiation induced vacancies in the Zr matrix rather than the precipitate-matrix
interface, because the vacancies are more abundant andattractive than the precipitate-matrix interface for positrons. This is consistent with the result that broad peakoriginated from positron annihilation with Fe electrons is
not observed for the irradiated sample.

Ratio to Pure Zr

Y. Nagai, T. Toyama, Y. Matsukawa, Y. Shimizu, A.
Kuramoto, H. Takamizawa, Y. Kakubo, K. Inoue1, T.
Yoshiie2, Q. Xu2, K. Sato2

300
V1(Zr)
V1(Nb)

200

Bulk(Zr)
Bulk(Nb)

100
0

Unirrad.

Irrad.

Fig. 2. Positron lifetime results for the unirradiated and electron-irradiated Zr-Nb.

Fig. 3.

APT elemental maps for the unirradiated Zr-Nb.

陽電子消滅および 3 次元アトムプローブによるプロジェクト
低温照射効果の研究（東北大・金研）永井康介、外山健、松川義孝、清水康雄、蔵本明、高見澤悠、鹿窪勇太（京大・工学研究科）井上耕治（京大・原子炉）義家敏正、徐虬、佐藤紘一

Defects Study for Iron Alloys Damaged by Electron Irradiation

F. Hori, M. Maruhashi, N. Onodera, A. Ishii, S. Mineno,
A. Iwase, Q. Xu1, K. Sato1 and T. Yoshiie1
Dept. of Mater. Sci., Osaka Prefecture University
1
Research Reactor Institute, Kyoto University

INTRODUCTION: It is well known that theirradiation damage of the metal under high-energy
particles irradiation makes various effects with thealloy compositions. Especially, the mechanism ofradiation embrittlement in the pressure vessel steels of
the light water reactor is one of the most important
subjects which are related to the lifetime extension of
the nuclear reactors. The embrittlement of the pressure
vessel steels during irradiation is partly due to copper
precipitation, many researches of the irradiation effectabout the precipitation process of copper atom in thesolid solution of Fe-Cu alloy have been studied in thepast. However, copper precipitation is previously
formed in the welding part in the reactor pressure
vessel, and there are few discussions on the irradiation
effect for existing Cu precipitation.
EXPERIMENTS: The specimens were annealed at
850℃ for 2 hours, followed by quenching into 0℃
water, then the Fe-Cu alloys with the copper
concentration of 0.6 and 1.2 wt.% forming solid
solution were prepared. Moreover, the Fe-Cu alloys
were aged at 500℃ for 48 hours, in order to form Cu
precipitation in the iron matrix. These specimens were
irradiated 30 MeV electrons at 77K up to 5.0×1017
e-/cm2 and 1MeV neutrons at 4K using the research
reactor at Kyoto University Research Reactor Institute.
Electrical resistivity in-situ measurement has been
performed for neutron irradiation at 4 K during
irradiation. After irradiation, electrical resistivity andpositron annihilation measurements have also been
performed.

precipitation occurred. In general, irradiation induced
point defects make Cu atoms aggregation in Fe-Cu
alloys with solid solution. Fig. 1 shows the electric
resistivity change, which is normalized by the value
before irradiation, for each Fe-Cu alloy during neutron
irradiation. In this figure, neutron flux increases withconstant rate until 3800 sec and becomes constantafter that. In case of neutron irradiation, it appears thedifferent trend of change in the electrical resistivity
between these alloys. This difference may come fromthe dissociation of some Cu precipitation and the local
re-precipitation of dissociated Cu atoms occurred inbalance. These phenomena inhibited the increase ofelectrical resistivity by neutron irradiation.

-10

3.5 10solid solution alloy
alloy including Cu precipitation

change in electric resistivity(Ωm)

PR8-7

3 10

-10

-10

2.5 10

-10

2 10

-10

1.5 10

1 10

-10

-11

5 10

0

0

2000

4000

6000

8000

10000

Time (sec)Fig. 1 Change in electric resistivity for solid solution andannealed (Cu precipitation formed) alloys during neutron
irradiation.

RESULTS: The results of electrical resistivity
measurement show that the electrical resistivity
increases by the electron and neutron irradiation, andthe change in resistivity in solid solution alloy is larger
than that in same alloy including Cu precipitation.
This result suggests that the dissociation of some Cu	
 採択課題番号 23P8-7	
 金属合金における照射効果の研究	
  	
  	
  	
 
（阪府大・工）堀史説、丸橋基邦、小野寺直利、石井顕人、峯野慎也、岩瀬彰宏	
 	
 (京大・原子炉)徐虫 L	
 、義家敏正、佐藤紘一	
 プロジェクト	 PR8-8 Recovery Process of Neutron-Irradiated Vanadium Alloys in Post-Irradiation Annealing

Treatment
K. Fukumoto, M. Iwasaki1 and Q. Xu2
RINE, Univ. of Fukui
Graduate school of Eng., Univ. of Fukui
2
KUR, Kyoto Univ.
1

INTRODUCTION:
In this study, experiments to determine thepost-irradiation annealing effect on the mechanical properties and microstructures of neutron-irradiated V-Cr-Ti
were conducted in this study. Two groups of specimens(as-irradiated specimens and specimens which underwent
the post-irradiation annealing treatment) were subjected
to tensile tests at room temperature and 500°C.
Post-irradiation annealing experiments were carried out
for long periods (up to 50 hrs) in an effort to restore theoriginal strength and ductility. In order to understand thethermal stability of the defect clusters, and investigate arecovery method for irradiation hardening and embrittlement, post-irradiation annealing experiments were
performed to evaluate the recovery of the microstructure
and mechanical properties of vanadium alloys irradiatedbelow 300°C.
EXPERIMENTS: The majority of test specimens forthis study were prepared from V-4Cr-4Ti alloys. The tensile specimens had nominal gauge dimensions of
0.25mm(t) x 1.2mm(w) x 5mm(l). Before irradiation, allspecimens were annealed in vacuum at 1000°C for 2hrs.
The specimens were irradiated at 228°C to 280°C with 3
to 5 di splacements per atom (dpa) in the ATR-A1.
Post-irradiation annealing was carried out for 2 to 50 hr
at 500°C and 600°C in a vacuum. Tensile tests wereconducted at room temperature and 500°C. TEM samples
were punched from non-deformed areas of tested specimens. The microstructural TEM observations were performed in KUR/Kyoto Univ.
RESULTS: Tensile behavior was reported in the last
KURRI progress report 2010. From TEM observation,
the density of defect clusters was very high and the sizeof each cluster was very small, about a f ew nm, in theas-irradiated specimens. With increasing annealing timeat 500°C, the density of defect clusters decreased gradually. The clusters grew into large dislocation loops on

採択課題番号 23P8-8

annealing for 50 hrs at 500°C. With increasing annealing
time, the density of defect clusters showing as black dots
decreased and the defect clusters grew into dislocation
loops. The yield stress increases were estimated by analyzing the microstructural changes. This estimation was
carried out using the well-known dispersed barrier hardening equation,∆σy = Mαµb(Nd)1/2 (1)where ∆σy is the increase in strength from the unirradiated value, µ is the shear modulus, and b is the magnitude of the a/2[111] Burgers vector of the dislocation
loops; N and d are the density and size of the defectclusters, respectively; M is the Taylor factor, which is set
to M= 3. The calculated value of the barrier strength forthe dislocations was 0.35 according to the previous datarevised using the M=3 estimation. Fig.1 shows the comparison of yield stress increases estimated from the experimental results and microstructural analyses as a function of annealing time. The estimated values of yieldstress increase were consistent with the experimental
results and the irradiation hardening corresponded to themicrostructural changes due to the neutron irradiationand the following post-irradiation annealing treatment. In
the case of the as-irradiated sample, the fracture of thetensile specimen occurred before the stress level reachedthe ultimate tensile stress; that is, a plastic instability due
to local propagation of the deformation proceeded and it
was considered that the stress increase was underestimated in the experimental data.

Fig. 1. Comparison of yield stress increases estimatedfrom experimental results and microstructural analyses, asa function of annealing time for the post-irradiation annealed V-4Cr-4Ti alloys

中性子・イオン照射を用いたバナジウム合金の熱処理による損傷回復過程（福井大院工）福元 謙一、岩崎将大 （京大・原子炉）徐 虫 Lプロジェクト研究

Damage Evolution in Neutron-irradiated Metals
during Neutron Irradiation at Elevated Temperatures

採択課題番号 23P8-9

Tq=400℃

1.58

1.56

1.54

100

1.26

1.24

1.22

0

200

100

Fig. 1(a)Au3Cu Isochronal 10K/100min
)

Au3Cu Isochronal 10K/100min
a3c29
1.30
Liq.N2

(10

–1

1.40

1.38

–0.04()
1.28

1.36

1.34
0℃
1.32

1.26

1.24

Liq.He

1.22
20

80

140

200

260

20

An neal ing Temp erat ure ( ℃ )a3c61–0

Fig. 1(b)a3c28–hcb

a3c29

200

An neal ing Temp erat ure ( ℃ )An neal ing Temp erat ure ( ℃ )a3c28–0cb

Tq=400℃

10K/20min
10K/100min
10K/300min
TM=Liq.He–1(10 )10K/20min
10K/100min
10K/300min
TM=0℃

1.52
0

Isochronal

1.28

Electrical Resistance–1(10 )1.60

Isochronal

Electrical Resistance

RESULTS: The isochronal resistance curves withdifferent heating rates, for the quenched specimen from
400oC is shown in Figs.1(a)~(b) for various measuring
temperatures, respectively. The measuring temperatures
are 0oC(Fig.1(a)) and liquid helium temperature(Fig.1(b)).
The resistance in Fig.1 increases with the temperatureand then decreases around the critical temperature. The
curve shifts to high temperature side with heating rate.
The curves at 10oC/300min do not bend smoothly but
bend clearly as composed by two stages. The dissociation

1.62

Electrical Resistance

EXPERIMENTS: Two types of specimen were preparedin the present experiment. One of which was thequenched specimen from 400oC and the other was thefast cooled specimen from 230oC or 250oC.
On the quenching, the specimens were quenched fromthe high temperature by falling down into water in a
vertical furnace with flowing Ar+3%H2 gas mixture. On
the fast cooling, the stainless steel tube, in which thespecimen was set, filled with helium gas was quenched
into ice water. The fast cooling rate of the specimen from230~250oC was 15~30oC/sec.
The electrical resistance was measured isochronallyat 3 constant temperatures (ice water temperature, liquid
nitrogen temperature and liquid helium temperature)
during the annealing. The heating rates were 10K/20min,
10oC/100min and 10oC/300min for the quenchedspecimen, and 10oC/100min for the fast cooled specimen,
respectively.

)

INTRODUCTION: A structural ordering of atoms in
Au3Cu alloy has been investigated by the electricalresistivity measurements. The isochronal resistance curve
has been investigated experimentally during ordering anddisordering. In many investigations the electricalresistance of the specimen was measured in situ atconstant rate of heating but it was not measured
isochronally at the same temperature. In the present
experiment the electrical resistances of the Au3Cu alloy
are measured isochronally at 3 constant temperaturesduring ordering and disordering for various heating
treatments.

–1

Hiroshima International University
1
Faculty of Engineering, Ehime University
2
Research Reactor Institute, Kyoto University

to two stages of the resistance curve during ordering is
first observed in this isochronal curve at low heating rate.
This dissociation becomes clear with lowering of themeasuring temperature.
The isochronal resistance curves of the fast cooled
specimen from 250oC are shown in Figs.2(a)~(b) together
with the resistance curves of the quenched specimen forvarious measuring temperatures. The measuring
temperatures are 0oC(Fig.2(a)), and liquid nitrogentemperature and liquid helium temperature(Fig.2(b)). It
must be noted that the resistance maximums of fast
cooled specimen appear at the same annealing
temperatures for the main maximums of quenchedspecimen and sub-maximums as in quenched specimen
are not found. Even at this low heating rate such as
10oC/100min the curve increases smoothly and does notdissociate to two stages different from the quenched case.
The excess vacancies obtained by the quenching would
enhance the ordering by help atomic diffusion during theisochronal annealing. However the excess vacancies
would be gradually consumed during the annealing at
low heating rate and would become to equilibrium value.
Therefore, the rate of resistance increase would beslow down at one time and be appeared 2 stages likechange in the resistance. In fact, the number of atomic
jumps, at 120oC in the quenched specimen is roughly thesame order of magnitude at 180oC in the quenchedspecimen and the fast cooled specimen.

(10

I. Mukouda*, K. Yamakawa1, T. Yoshiie2 and Q. Xu2

Electrical Resistance

PR8-9

Fig. 2(a)

80

140

200

260

An neal ing Temp erat ure ( ℃ )a3c61nhFig. 2(b)高温での中性子照射金属中の点欠陥集合体動的挙動とプロジェクト
損傷組織発達過程（広島国際大学）向田一郎、（愛媛大）山川浩二、(京大原子炉) 義家敏正、徐 虬Effects of Thermal Aging and Irradiation on Mechanical Properties of Fe-Cr
PR8-10)HUULWLF$OOR\V

R. Kasada, Y. Sakamoto, K. Yabuuchi, A. Kimura,
K. Sato1, Q. Xu1 and T. Yoshiie1
Institute of Advanced Energy, Kyoto University

Research Reactor Institute, Kyoto University
INTRODUCTION: Fe-Cr binary system is an importantbasis for the structural materials of energetic power
plants such as fossil fuel ones, next generation fission
reactors and fusion reactos. However, such high-Cr steels
may suffer from thermal aging embrittlement, which iswell-known 475 °C embrittlement, due to phase separation of Fe and Cr. Recently, Kasada and Sato are widely
investigating the positron trapping behavior in the Fe-Cr
alloys under “the Strategic Promotion Program for Basic
Nuclear Research by the Ministry of Education, Culture,
Sports, Science and Technology of Japan”. So the present
collaborative research has moved to investigate the neutron irradiation effect on the phase separation of Fe-Cr
ferritic alloys. In the FY2011 we have irradiated the
Fe-Cr alloys in KUR. The post-irradiation experiments
including hardness test and positron annihilation spectrometry will be done in FY2012.
Here, we reports the ion-irradiation results for the
Fe-Cr alloys as a reference data for the neutron irradiation in KUR

Experimental Procedure: Materials used in the present
study is Fe-Cr binary alloys (Fe-xCr; x = 0, 0.09, 0.16,
0.31, 0.47, 0.51, 0.70, 0.84, 1). Thermal aging treatment
on these materials was carried out at 475 °C up to 100 h.
Some of the materials were ion-irradiated at 290 °C up to
5 dpa, in DuET facility, Institute of Advanced Energy,
Kyoto University. Nano-indentation hardness tests were
performed using Nano-Indenter G200 with a continuous
stiffness measurement method to obtain the hardness
depth profile.
Results and Discussions: As previously shown in theFig. 1 [1], the Cr-dependence of the H0 is very similar tothat of the micro-Vickers hardness obtained for the similar materials. The depth-dependence of the nanoindentation hardness of ion-irradiated Fe-9Cr were analyzed
using the extended Nix-Gao model [2]. These data sets
will be provided for the reference data of the following
neutron irradiation experiments in KUR.

Fig. 2. Depth-dependence of a bulk-equivalent hardness,
H0, converted from nano-indentation hardness of
ion-irradiated Fe-9Cr binary alloy.

Fig. 1.Cr-dependence of a bulk-equivalent hardness, H0,
converted from nano-indentation hardness of Fe-Cr
binary alloys [1].

REFERENCES[1] R. Kasada et al., KURRI progress report 2010. 1[2] W. D. Nix and H. Gao: J. Mech. Phys. Solids 46(1998), p. 41

採択課題番号 23P8-10
Fe-Cr 合金の相分離に及ぼす照射効果（京大・エネ研）笠田 竜太、木村晃彦、藪内聖皓、坂本雄太（京大原子炉）佐藤 紘一、義家 敏正、徐 虬

プロジェクトRadiation Resistance of Nanocrystalline Ni by Neutron Irradiation

Quantum Science and Engineering Center, Kyoto University
1
Depertment of Nuclear Engineering, Kyoto University
2
Research Reactor Institute, Kyoto University
INTRODUCTION: Studies of radiation resistance of
nuclear reactor materials are of technological importanceto perform evaluation of age-related deterioration of thematerials. Irradiation induces production of radiation defects and their accumulation, resulting in a change of
microstructure in materials. It is well known that ananocrystalline material with grain size of less than a few
tens micrometers has high resistance to radiation damaging effects. This is due to the fact that grain boundary acts
as effective sinks that absorb radiation-induced defects. A
recent simulation study has showed a new mechanism ofradiation resistance in nanocrystalline materials:
self-healing of radiation damage occurs via interstitialemission near grain boundary, resulting in suppression of
defect accumulation [1].
In this work, radiation damaging effects in
nanocrystalline Ni under neutron irradiation were studied.
Defect microstructure was analyzed by conventional positron annihilation lifetime spectroscopy.
EXPERIMENTS: Samples were nanocrystalline (NC)Ni with an average grain size of about 30 nm, which wasmeasured by a TEM observation. The samples were irradiated with neutrons from KUR operated at 1 MW. To
investigate microstructure of the sample after irradiation,
we performed measurements of positron annihilation
lifetime spectroscopy (PALS) as a function of displacement per atom (dpa) estimated from neutron fluence,
ranging from 3.8×10-5 to 1.8×10-3. We also performed
the same experiment for coarse-grained polycrystalline
Ni annealed at 1523 K for 1 h under a high vacuum condition.
RESULTS: Figure 1 shows results of dpa-dependenceof positron lifetime for NC Ni. Positron lifetime spectra
were analyzed by two components τ1 and τ2, where thefirst lifetime τ1 is attributed to positron trapping at thefree volumes in the crystalline interfaces and the second
lifetime τ2 is due to the free volumes at the intersectionsof two or three crystallites interfaces. It is seen that thevalues of τ1 remain unchanged with increasing the dpa,
while the τ2 increases slightly at above 4.6×10-4 dpa.
The former result indicates that defect accumulation at
crystalline interfaces is strongly suppressed under irradiation. The latter suggests that microstructure offree-volume at intersections changes with increasing the
dpa. From these results, we concluded that radiation resistance of NC materials is related with no change in mi-

採択課題番号 23P8-11

crostructure of crystalline interface.
Comparing results for NC Ni and coarse-grained counterpart, we found that a completely different
dpa-dependence of the positron lifetime is observed depending on grain size: for the coarse-grained specimen,
the lifetime increase monotonically with increasing the
dpa. This is due to defect accumulation or formation of
defect cluster.
In order to understand interface-microstructure of NC
materials after irradiation in more detail, it is necessary to
perform further experiment by combined analysis ofThermal desorption spectroscopy and Positron lifetime
spectroscopy.

Intensity (%)

H. Tsuchida, A. Itoh1, K. Satoh2, T. Yoshiie2 and Q. Xu2

Lifetime (ps)PR8-11

100
80
60
40
20
0
400
300
200
100
0
0

Mean lifetime
Short lifetime
Long lifetime

10
20
30
40
Irradiation time (h)50Fig. 1. Experimental results of positron lifetime as afunction of dpa, where dpa per 1 h was 3.8×10-5.

REFERENCES:[1] Bai et al., “Effective annealing of radiation
damage near grain boundaries via interstitialemission”, Science 327 (2010) 1631

水素イオン照射に伴う材料欠陥生成挙動の陽電子解析に関する研究（京大院工）土田秀次、伊藤秋男（京大・原子炉）義家敏正、徐 虬、佐藤紘一

プロジェクトInteraction between Deuterium and Defects in Tungsten

K. Sato, R. Tamiya1, Q. Xu and T. Yoshiie
Research Reactor Institute, Kyoto University
Graduate School of Engineering, Kyoto University

1

INTRODUCTION: In a fusion reactor, plasma-facing
materials (PFMs) must withstand the damage producedby hydrogen and helium at up to 10 keV of energy andheat loads from the plasma, in addition, the neutrons withhigh energy, high flux and high fluence similar to thestructural components. Hydrogen isotopes retain in vacancy-type defects in PFMs, and this is a critical problem
for fusion reactors. To know the interaction between vacancy-type defects and hydrogen isotopes is very important. In this study, the size and density of vacancy-type defects in tungsten was obtained by positron annihilation lifetime (PAL) measurements. Next, thermal
desorption spectra of deuterium was obtained after deuterium charging. From these results, trapping site anddissociation energy of deuterium were identified.
EXPERIMENTS: The samples were 99.95% puretungsten (A.L.M.T. Corp.). The 0.2-mm-thick sheet waspunched to 5mm in diameter. These samples were annealed at 1773 K for 1 h in a vacuum of less than 10−4 Pa.
Electron and deuterium ion irradiations were carried out
to introduce defects. Electron irradiation of 8 MeV was
performed at Electron Linear Accelerator of Research
Reactor Institute, Kyoto University. Deuterium ion irradiation was performed at Low-energy ion irradiation system of Research Reactor Institute, Kyoto University. 5
keV D2+ ions were irradiated up to 1.0×1018 /cm2 (20 dpa
at defect peak) at room temperature (R.T.) and 673 K. A
displacement threshold energy used for irradiation dose
calculation was 42 eV [1]. After that, 1 keV D2+ ions,which do not induce irradiation defects, were implanted
by low-energy ion irradiation system. Thermal desorption
spectroscopy (TDS) was carried out from R.T. to 1523 K
in order to detect elimination behavior of deuterium fromtungsten.
RESULTS: TDS spectra of 8 MeV electron- and 5 keV
D2+ ion-irradiated samples are shown in Fig. 1. The spectrum of sample annealed at 1273 K for 5 hours, whichmainly includes dislocations, is also shown in Fig. 1. Because single vacancies are mainly formed by electron
irradiation, a peak around 550 K denotes elimination of
deuterium from single vacancies. Peak separation analysis was performed to spectra of 5 keV D2+ ion irradiation
by data analysis software Origin, and the results wereshown in Fig. 2 and 3. Spectra of 5 keV D2+ ion irradiation at R.T. and 673 K were resolved into three gaussfunctions. Peak of them is around 450 K, 560 K and 640
K. 450 K peak denotes the elimination of deuterium fromsurface. It is expected that 560 K peak denotes the elimination of deuterium from single vacancies from result ofelectron-irradiated sample. Because 5 keV D2+ ion irradiation is likely to form small vacancy clusters, the peakaround 560 K may include the elimination from small
vacancy clusters. This possibility is considered in next
step. 640 K peak denotes the elimination of deuterium
from dislocations, because the peak was obtained in sample annealed at 1273 K for 5 hours.
D2 desorption rate [×1016/m2s]

PR8-12

Electronirr.
D2++5keV RT
D2 5keV 673K
1273K 5h anneal

2

1

0

300

400

500

600

700

Temperature [K]

800

900

Fig. 1. TDS spectra of 8 MeV electron- and 5keV D2+
ion- irradiated and annealed samples.

Fig. 2. Peak separation of TDS spectrum of sample
irradiated with 5 keV D2+ ions at R.T.

Fig. 3. Peak separation of TDS spectrum of sample
irradiated with 5 keV D2+ ions at 673 K.
REFERENCES:[1] F. Maury, M. Biget, P. Vajda, A. Lucasson and P.
Lucasson, Radiat. Eff. 38 (1978) 53.

採択課題番号 23P8-12 電子照射された金属の損傷組織の照射温度依存性の研究（京大・原子炉）佐藤紘一、徐虬、義家敏正（京大院・工）田宮怜

プロジェクトPR8-13 Irradiation Effects on Stress Loading Property of Refractory Metal at high Temperature
K. Tokunaga, K. Araki, T. Fujiwara, T, Hotta1,
Q. Xu2 and T. Yoshiie2
Research Institute for Applied Mechanics,
Kyushu University
1
Interdisciplinary Graduate School of Engineering
Sciences, Kyushu University
2
Research Reactor Institute, Kyoto University
INTRODUCTION: Tungsten is one of refractory
metal and will be used as armor material of the firstwall/blanket and divertor in the fusion reactor because of
its low sputtering yield and low hydrogen retention. The
plasma facing armor materials will be subjected to highflux bombardment of low energy particles including thehydrogen fuel and helium ash. In addition, stress by disruption and ELMs will be loaded on the armor materialof the first wall/blanket and divertor of at high temperature. This is a concern because it is well known that helium implanted in tungsten does not release until hightemperatures, due to strong interaction with lattice defects. Helium drastically enhances the formation of bubbles due to the strong bonding to vacancies and theirclusters. As a result, local swelling and degradation of
mechanical properties of bulk materials take place. It is
anticipated that implanted helium influences the responseof tungsten to stress loading at high temperature by thepulsed high heat loading such as disruption and ELMs.
Very little information is available on the combined effects of helium implantations and the pulsed high heatloading. In the present work, helium pre-implanted tungsten has been exposed to pulsed electron beams to examine synergistic effects of helium irradiation and stressloading at high temperature by the pulsed high heat loading.
EXPERIMENTS: Tungsten samples used in the present experiment are powder metallurgy tungsten. The
sample sizes and purity are 20 mm x 20 mm x 5 mm and99.99%, respectively. The sample surface was mechanically and electrochemically polished. Helium beam irradiations were performed in an ion beam facility. The
samples were mechanically mounted on a Cu holder
which was actively water cooled. The helium energy was
18.7 keV. The helium beam flux and heat flux at thebeam center was 2.0 x 1021 He/m2s and 6.0 MW/m2, respectively. The beam duration was 2.8–3.0 s. The samples were irradiated to a fluence between 1023 ～ 1024
He/m2 by 130–150 pulse irradiations cycles. The beam
diameter on samples was 16 mm, defined using apertures.
The surface temperature of the sample was measured
with a two-color optical pyrometer and the two dimen-

sional surface temperature distribution of the samples
was also monitored with an IR camera. After the helium
irradiation, the samples were exposed to pulse heat loading by electron beam irradiation. The heat flux was 1
GW/m2, with duration of 1, 1.5 or 2 ms. The half width
value of the electron beam was 8 mm. The electron beam
area on the tungsten surface was defined by a beam limiter with an aperture of 4 mm. The net electron current
induced by the electron beam irradiation was also measured, the electron beam energy was 70 keV, and the heat
flux was measured by the calorimetric method. Before
and after the helium and electron beam irradiation, thesample surfaces were examined using a scanning electron
microscope (SEM).
RESULTS: As shown in Fig. 1, formation of blisters,
exfoliation and small pin hole are observed in boundary
area of melted and non-melted zone. These surface modifications are considered to be due to the formation, coalescence and migration of helium bubbles near the surface under stress loading at high temperature during thepulse high heat loading of 1 ms. In addition, the pin holes
may be formed by the migration of helium bubbles to thesurface at a high temperature. On the other hand, surface
smoothing at high temperature did not occur; however,partial exfoliation of blister caps with a diameter of about
1 µm and cracking along grain boundaries are formed in
the non-melted zone on the electron beam irradiated area.
It is possible that helium implantation in tungsten suppresses the migration of atoms at high temperature because radiation damage, such as helium bubbles act as
obstacle to the atom migration.

10µm
Fig. 1. SEM image taken from in boundary between melted and unmelted zone of the surface irradiated by an electron beam with a heat flux of 1
GW/m2 and a duration of 1 ms. Sample is irradiated with 3.3 x 1023 He/m2 at the peak temperatureof 973 K before the electron bombardment.

採択課題番号 P8-13 高融点金属材料の高温下における応力負荷特性に及ぼす照射効果 プロジェクト（九大・応力研）徳永和俊、荒木邦明、藤原正、（九大・総理工）堀田智宏（京大・原子炉）徐 虬、
義家敏正