Project Research
Project 1

PR1

Irradiation Effects on Nuclear Advaced Materials Irradiatedby Particles with High Energy

Q. Xu

intermetallic alloys(F. Hori, Y. Ueno, T. Ishiyama, K. Kobayashi, A. Iwase,
K. Ohsawa, Q. Xu and N. Abe)
Before irradiation, the single Al-vacancy remains in
Fe-50Al alloy. After irradiation, however, the differnent
types of vacancy were produced into Fe-Al compoundalloy.

Research Reactor Institute, Kyoto University
OBJECTIVES: High dose neutron irradiation is usuallyused to investigate radiation effects in solid materials anddevelop new materials. Unfortunately, KUR could notsupply the neutron irradiation field and the laboratory forneutron-irradiated samples was closed in 2015. The research activities were severely restricted. Most of researchers had to change their research purpose to get theresults. Therefore, instead of neutron irradiation, electronand  ray irradiations were used to estimate the damage
induced by the irradiation in materials.

ARS-8
Effects of high energy particle irradiation on hydrogen
retention in refractory metals(K. Tokunaga, M. Matsuyama, S. Abe, H. Osaki, K.
Araki, M. Hasegawa, K. Nakamura, Q. Xu and K. Sato)
The amount of tritium increases with increasing the irradiation dose. In addition, tritium is easy to diffuse parallel
direction for rolling direction after irradiation.

RESULTS: The carried out research subject (ARS) andthe name of co-researches in each ARS are listed below.
ARS-1
Modification of the yellow luminescence in gamma-ray
irradiated GaN bulk single crystal(K. Kuriyama, A. Shikawa, N. Nishikata, K. Kushida,
and Q. Xu)
The results show that gamma-ray induced shallow donor
relating to nitrogen vacancy is located at about 50 meV
below the conduction band.

ARS-9
Positron annihilation spectroscopy of Ferritic/Martensitic
steels irradiated with protons and spallation neutrons(K. Sato, Q. Xu, T. Yoshiie, Y. Dai and K. Kikuchi)
Vacnacy clusters are formed by the irradiation in F82H.
The vacancy clusters including small and latge amount of
He atoms up to 15 dpa of irradiation.

ARS-2
Photoluminescence of natural and synthesized calcites(T. Awata, S. Tanaka and Q. Xu)
Photoluminescence (PL) of natural calcites and impurities of these, and compared spectra of artificially synthesized calcite in chemical reaction have been measured.

ARS-10
Positron annihilation behavior in Fe-Cr alloys(R. Kasada, K. Sato and Q. Xu)
In unaged Fe0.91Cr0.09 and Fe0.84Cr0.16 alloys, there are notenhancement of positron density. In contrast, an enhancement of annihilation in Fe cell in other Fe-Cr alloys,
such as, Fe0.7Cr0.3, Fe0.55Cr0.45 and Fe0.5Cr0.5.

ARS-3
Thermal diffusivity measurement of small specimens toachieve the measurement of heavily neutron irradiatedtungsten(M. Akiyoshi and Q. Xu)
The measurement results of thermal diffusivity between
small specimen and 10 mm standard specimen are different. The result of small specimen is small even above
373 K compared with 10 mm standard specimen.
ARS-4
Electron

irradiationinduceddamagestrcutre

CONCLUSIONS: The defects induced by irradiation
degrade the physical mechanical properties of solid materials. Some experimental results are important for development of nuclear industry. For example, the resultsof ARS-8 indicate that the retention of tritium, which is
the isotope of hydrogen, in refractory metals used in fusion reactor may be an important issue because the plasma-facing materials suffer two types of damage: displacement damage caused by high energy neutrons andsurface damage.

in

27P1

-3-

PR1-1

Modification of the Yellow Luminescence in Gamma-ray Irradiated GaN
Bulk Single Crystal

K. Kuriyama, A. Shinkawa, N, Nishikata, K. Kushida1,
and Q. Xu2cated at about 1.1 eV above the valence band [6], thegamma-ray induced shallow donor is located at about
50 meV bellow the conduction band. This energy levelis close to a donor level (64 ± 10 meV [7]) relating to
VN. Figure 1 shows the YL model estimated from theCollege of Engineering and Research Center of Ion
Beam Technology, Hosei University
1
Osaka Kyoiku University
2
Research Reactor Institute, Kyoto University

photoluminescence at 77 K.

INTRODUCTION: Examining the defects caused byvarious radiations to GaN under the space environment is important. In our previous study [1, 2], we
reported that the energy levels relating to nitrogenvacancy (VN) and gallium vacancy (VGa) were inducedby neutron and proton irradiated GaN. The neutron
irradiation has been used as the neutron transmutation
doping into semiconductors such as GaAs [3], GaP [4],and GaN [5]. Atoms in semiconductors mainly transmute by a (n, γ) reaction. Therefore, to survey the radi-

ation effect of gamma ray alone is meaningful. In thepresent study, we report the variation of the yellow
luminescence (YL) in GaN bulk single crystals by
gamma-ray irradiation.
Fig.1 Yellow luminescence estimated from the photoluminescence at 77 K. The gamma-ray induced shallow
donor relating to nitrogen vacancy is located at about 50
meV below the conduction band.

EXPERIMENTS: GaN bulk single crystals with athickness of 450 ± 50 µm were purchased from Furukawa Co. Ltd. The crystals were irradiated at room
temperature with gamma-rays of 1.17 and 1.33 MeV
from a cobalt-60 source of Kyoto University Research
Reactor Institute. Samples were irradiated with an absorption dose rate of 1.771 KGy/h. Total gamma-ray
dose was 160 kGy. The resistivity varied from 30 Ωcm
for an un-irradiated sample to 104 Ωcm for gamma-ray
irradiated one. Photoluminescence (PL) spectra were
measured at 77 K using a He-Cd laser.

REFERENCES:[1] K. Kuriyama, M, Ooi, A. Onoue, K. Kushida, and Q.
Xu, Appl. Phys. Lett. 88, 132109 (2006).
[2] T. Nakamura, N. Nishikata, K. Kamioka, K. Kuriyama, and K. Kushida, Nucl. Instrum, Method Phys.
Res. B 371, 251 (2016).
[3] M. Satoh, K. Kuriyama, and T. Kawakubo, J. Appl.
Phys. 67, 3542 (1990).
[4] K. Kuriyama, Y. Miyamoto, T. Koyama, O. Ogawa,and M. Okada, J. Appl. Phys. 86, 2352 (1999).
[5] K. Kuriyama, T. Tokumasu, J. Takahashi, H. Kondo,
and M. Okada, Appl. Phys. Lett. 80, 3328 (2002).
[6] J. Neugebauer, C. G. Van de Walle, Appl. Phys. Lett.
69, 503 (1996).

RESULTS: The band edge emission was observed at
3.48 eV in both un-irradiated and gamma-ray irradiated samples. The YL from the un-irradiated GaN with apeak at 557 nm (2.22 eV) was observed at around 440
nm to 800 nm, whereas that of the gamma-ray irradiated GaN showed a peak at 532 nm (2.33 eV) although the YL spectrum is almost overlapped with
un-irradiated ones. Therefore, the modification of YL
observed here would be attributed to a transition fromthe shallow donor induced by the gamma-ray irradiation to a native VGa. Since the usual YL has been proposed as a transition from a shallow donor to VGa lo-[7] D. C. Look, D. C. Reynolds, J. W. Hemsky, J. R.
Sizelove, R. L. Jones, and R. J. Molnar, Phys. Rev.
Lett. 79, 2273 (1997).

27P1-1-4-

Photoluminescence of Natural and Synthesized Calcites

T. Awata, S. Tanaka and Q. Xu1
Department of Physics, Naruto University of Education
1

Research Reactor Institute, Kyoto University

INTRODUCTION: Thermoluminescence (TL) of natural calcite irradiated by gamma rays have only one orange emission peak and that may be originated from an
impurity of Mn2+ in calcite [1-2]. At photoluminescence(PL) of natural calcite irradiated UV rays, the spectra of
PL have 620nm emission peak and 270nm emission peakwhich is related Mn2+ and Pb2+, respectively [3]. In thecase of calcites, it has been shown the impurity plays amajor role for luminescence. In this study, we first havemeasured PL of natural calcites and impurities of these,and compared spectra of artificially synthesized calcite inchemical reaction with resulted major impurities.

a strongest and most sharp (FWHM=4%). From ICP-AES
results, Colorado calcite has impurities (ppm) of Sr (5.1),
Mn (N.D.) and Pb (0.05). Nevertheless almost calcite haslarge amount of Mn impurity, Colorado calcite has very
little amount. There is no peak at 620nm in figure 1, that is
related to little Mn amount. Photoluminescence data reference [5] reported that emission peak at 560nm for defectcenter of carbonate ion. From experimental results, wehave synthesized calcite artificially with controlled impurities. Fig 2 shows that PL spectra of synthesized calcitewith an impurity of Sr and Sr + Mn. It is shown that both

[ 10-5]Intensity(Arb.)

PR1-2

EXPERIMENTS: Natural calcite with colored pink wascollected at Colorado State in USA. Artificial calcite
was synthesized by a chemical reaction method in water
solution [4]. 1.5% of (NH4)2CO3･2H2O(1.5g in 100mL
pure water) and 1.8% of CaCl2･6H2O (2g in 100mL
pure water) with 0.01g element impurity were mixed atroom temperature. After mixed, these solutions wereprecipitated by holding for two weeks and filtering. After filtering, samples were shaped by a tablet machine.
PL spectra have been taken using PL-84 (Seishin,
SOEX1702/04, PM:Hamamatsu R928) with He-Cd laser (Kinmon 325nm). ICP-AES (iCAP6300Duo, Themo
Fisher) was also performed to measure impurity elements concentration of calcite.

Sr
Sr,Mn*2

4
3
2
1
0

400

500 600 700
Wavelength(nm)

800

900

Fig. 2 Photoluminescence spectra of synthesized calcite with an impurity of Sr and Sr + Mn.
spectra have four peaks at 427nm, 493nm, 560nm and756nm. Comparing PL spectra of natural and synthesized
calcite, both spectra are almost same. PL spectra of synthesized calcite with Sr and Sr + Mn are almost same andthere is no effect of presented Mn ion. Sidike et al., reported [3] that Mn ion cannot be an activator alone for PL,
but can be activator with co-activator as Ce ion or Pb ion
which can absorb UV rays. Relatively large amount impurity in Colorado calcite, Sr ion, is not activator but alsoco-activator for Mn ion.

RESULTS and DISCUSSION: Figure 1 shows the PL
spectra of Colorado natural calcite irradiated 325nm UV
rays. It is shown that a spectrum has three peaks at
396nm, 564nm, 760nm and 564nm peaks. 564nm peak is[ 10-5]
2

Intensity(Arb.)

5

ACKNOWLEDGEMENT: We would like to thankProfessor S. Fukutani (KURRI) for using ICP-AES on
this study.
1

0

400

500

600

Wavelength(nm)

700

800

REFERENCES:[1] T. Awata et al., KURRI Progress Report 2014 27.
[2] W. L. Medlin, J. Opt. Soc. Am. 53(1963)1276.
[3] A. Sidike et al., Phys. Chem. Minerals 33(2006)559.
[4] G. R. Fonda, J. Phys. Chem. 44(1940)435.
[5] Colin M. MacRae et al., Microsc. Microanal. 14(2008)184.

900

Fig. 1 Photoluminescence of natural Colorado calcite.

27P1-2-5-

PR1-3

Thermal Diffusivity Measurement of Small Specimens to Achieve the Measurementof Heavily Neutron Irradiated Tungsten

M. Akiyoshi and Q. Xu1

after a laser flashing, and the Netzsch LFA-457 system
uses IR detector to measure the temperature. Intensity of
the IR is changed with a temperature according to the
Planck radiation formula, and also with measuring area ofa specimen. The back side area of a 6mm specimen is
only 36% of a 10mm specimen. Then the wave-shapefrom the IR detector was noisy at around room temperature, while above 373K, the intensity of IR was increased
enough to evaluate the thermal diffusivity correctly.
This result is almost same for a 3mm specimen shownin Fig.2, however measurement result of this small
specimen is obviously small even above 373K comparedwith 10mm standard specimen. The difference in the
shape of these specimens is not only the surface area but
also the thickness, 0.973mm for 10mm diameter and0.598mm for 3mm diameter specimen. The later thickness is too thin to evaluate correctly for tungsten before
neutron irradiation. The difference between the thermal
diffusivity of 10mm diameter and 3mm diameter getting
smaller at higher temperature, because the uprising timeof IR after the laser flashing getting longer and analyzed
better. Neutron irradiated tungsten shows smaller thermal
diffusivity than the unirradiated specimens here, so thedifference is expected to be enough small with thespecimen of 0.5mm thickness.
80

Radiation Research Center, Osaka Prefecture University
1
Research Reactor Institute, Kyoto University

Thermal Diffusivity / mm2/s

INTRODUCTION:
Usually, heat is mainly carried by free electrons in metals. On the other hand, it is well known that irradiationinduced damages in ceramics showed significant degradation in thermal diffusivity unlike metals, because inceramics, heat is mainly carried by phonon that is scattered by irradiation induced defects. In these days, development of materials for divertor in future fission reactor is very important and concerned study. Most of studies are focused on SiC ceramics and tungsten based materials. Tungsten is a metal, of cause, however heat is
carried by phonon in tungsten partly. Then, thermal diffusivity of tungsten after severe neutron irradiation mustbe estimated in the same way as ceramics.
In addition, tungsten shows far stronger radioactivity
after a neutron irradiation than SiC ceramics. In the
PHENIX project for development of divertor materials in
fusion reactor, many SiC and W specimens were loaded
to HFIR reactor in ORNL, USA. To reduce the level ofradioactivity, specimens for thermal diffusivity measurement is limited to 6mm in diameter or further small 3mm
in diameter disk specimens with 0.5mm thickness.
Measurement of thermal diffusivity after the neutron irradiation in HFIR is must to be operated using Netzsch
LFA-457 Micro Flash thermal analyzer in ORNL, which
can measure 6mm disk specimens using commercial jigs,
while measurement of 3mm small disk is not certified.
EXPERIMENTS:
To achieve a measurement of small specimens 3mm indiameter using Netzsch LFA-457, special jigs were designed and manufactured. The jigs shade the incident
laser flash to 2.4mm in diameter and also cut the infrared
respond signal radiated from the back side of the specimen to 2.6mm in diameter.
Measurements of thermal diffusivity using small disks
were performed at ORNL, USA using Netzsch LFA-457,
and also 10mm in diameter standard sample was measured using Ulvac TC-7000 at the Radiation Laboratory,
Uji, Kyoto University. Specimens were ITER grade puretungsten (supplied by A.L.M.T. Corp.) with the size of
6mm and 10mm in diameter and commercial grade puretungsten (supplied by Nilaco) with the size of 3mm and10mm in diameter. The measurements were operated atroom temperature to 773K using Netzsch LFA-457, andto 973K using Ulvac TC-7000, respectively.

φ6x1mm ITER Grade Pure W→ at low temperature
φ10x1mm ITER Grade Pure W

70

φ6: Sample, t=1.088mm
φ10: Sample , t=1.078mm

60
50
40

300 400 500 600 700
Measurement Temperature / K

800

Thermal diffusivity / mm2s-1

Fig.1 Validation of thermal diffusivity measurement
using a specimen of 6mm in diameter.

RESULTS:
Fig.1 shows thermal diffusivity of ITER Grade tungsten
with the size of 6mm and 10mm in diameter. The measurement result of a 6mm sample showed large dispersion
at around room temperature. The laser flash method uses
uprising curve of temperature on the back side surface

＠300K α=66.34mm2/s

60
40
20

α = k/xn + c
k=4.515e+02
n=6.011e-02
c=-2.540e+02|r|=9.925e-01

＠300K α=54.85mm2/s
α = k/xn + c
k=2.229e+02
b=1.336e-01
c=-4.918e+01| r|=9.958e-01

Measured by Netzsch LFA-457
Pure W φ3×0.598mm around RT
Pure W φ3×0.598mm
Measured by TC-7000
Pure W φ10×0.973mm（Pure W: Nilaco）

0

400
600
800
Measurement temperature / K

1000

Fig.2 Validation of thermal diffusivity measurement
using a specimen of 3mm in diameter.

27P1-3-6-

PR1-4

Electron Irradiation Induced Damage Structure in Intermetallic Alloys
broadening measurements. The positron lifetime spectra
were analyzed by using POSITRONFIT program. Also,
the positron lifetimes in B2 type Fe-Al alloys were
calculated using the superimposed atom method [2].

F. Hori, Y. Ueno, T. Ishiyama, K. Kobayashi, A. Iwase,
K. Ohsawa1, Q. Xu2 and N. Abe2
Dept. of Mater. Sci., Osaka Prefecture University
1

Res. Inst. of Appl. Mech., Kyushu University
Res. Reactor Inst., Kyoto University

2

RESULTS: Before irradiation, positron lifetime of thisalloy was 186 psec showing that single vacancy still
remains in this alloy. This positron lifetime value is close
to that in Al-vacancy by the calculation. The positronannihilation lifetime value of this alloy increases to 200
psec after 2 MeV electron irradiation and decreases to
172 psec after 9 MeV electron irradiation, respectively.
Also, the Doppler broadening S-parameter showed
different changing trend for each electron irradiation withdifferent energy. That is S-parameter increases for 2 MeV
irradiation and decreases for 9 MeV irradiation case.
Figure 1 shows the changing relation between positron
lifetime and S-parameter for each energetic electron
irradiations. This result suggests that different types ofvacancy were produced into Fe-Al compound alloy byelectron irradiation with different energies.

INTRODUCTION: It is well known that intermetallic
compound alloys possibly include more than two types ofvacancies basically, that is A-vacancy and B-vacancy in
A-B compound alloy. Thermally equilibrium defects andchemically deviated structural defects in these compoundalloys are very complicated. However, the amount ofdefect and the defect structure affects the various
characteristic features, such as strength and electronic
conductivity and so on. Moreover, first principle
calculation shows that different number of hydrogenatoms can be trapped by Al- or Fe-vacancy in B2 type
Fe-Al alloy. On the other hand, although the electron
irradiation produces vacancies and interstitials in metallic
alloys, the threshold energy of displacement for eachelemental atom in compound alloys is not necessarily
same. Then the defect type introduced by electron
irradiation depends on its incident energy. Kosugi et al.
reported that the type of defects produced by electron
irradiation in B2 type Fe-Rh intemetallic alloy changes
with increasing of incident electron energy [1]. Then we
supposed that radiation induced vacancy type defects canbe controlled by changing the energy of electron
irradiation. In this study, we have performed electron
irradiation with different energy for Fe-Al alloys.
EXPERIMENTS: Fe-50%Al alloy specimens with B2
structure were prepared by arc melting method. Sliced
samples with the thickness of 0.5 mm were annealed at
973 K for 120 h followed by air-quenched in vacuum.
These specimens were irradiated with 2 MeV electron
to the fluence of 1×1017 and 1×1018 /cm2 at
JAEA-Takasaki and with 9 MeV electron to thefluence of 5×1017 and 3×1018 /cm2 at KURRI, Kyoto
University. In both cases, irradiations were carried out
at about 330 K controlled by water flow system. Afterand before irradiation, samples were examined bypositron annihilation lifetime and coincidence Doppler

Fig. 1 Positron lifetime and S-parameter relation for before
and after electron irradiated Fe-Al alloy.
REFERENCES[1] S. Kosugi, N. Ishikawa, Y. Saitoh, F. Hori, A. Iwase, J. ofNucl. Mater. 411 (2011) 171–173[2] M. J. Puska and R.M. Nieminen, J. Phys. F: Met. Phys. 13(1983) 333–346.
Acknowledgement
We would like to express cordial thanks to Dr. K.Sato(Kagoshima University) for his help and kind advice forelectron irradiation experiments.

27P1-4-7-

PR1-5

Effects of High Energy Particle Irradiation on Hydrogen Retention in
Refractory Metals

K. Tokunaga, M. Matsuyama1, S. Abe1, H. Osaki2, K.
Araki, M. Hasegawa, K. Nakamura, Q. Xu3 and K Sato4

3.26 x 10-3. Temperature during the irradiation wasmeasured by thermocouples which was contacted with abackside of the W samples. After the electron beam irradiation, T exposure experiments have been carried out
using a T exposure device in University of Toyama.
Pressure of the T gas was 1.3 kPa and T exposure was
kept for 4 h. T concentration in the gas was about 5 %.
Temperatures of pre-heating and T exposures were 100
oC. After the exposure to T gas, T amount retained insurface layers of the sample was evaluated by
-ray-induced X-ray spectrometry (BIXS) and imaging
plate (IP) measurements.

Research Institute for Applied Mechanics, Kyushu
University
1
Hydrogen Isotope Research Center, University of
Toyama2
Interdisciplinary Graduate School of Engineering
Sciences, Kyushu University
3
Research Reactor Institute, Kyoto University
4
Faculty of Engineering, Kagoshima University
INTRODUCTION: It is of importance to clarify phenomena of implantation, retention, diffusion and permeation of tritium on surface of the armor materials of thefirst wall/blanket and the divertor on fusion device from aviewpoint of precise control of fuel particles, reduction oftritium inventory and safe waste management of materials contaminated with tritium (T). Refractory metals suchas tungsten (W) is potential candidate for an armor of thefirst wall and the divertor plate of the fusion reactor because of its low erosion yield and good thermal properties.
The armor material will be subjected to heavy thermalloads in the steady state or transient mode combined withhigh energy neutron irradiation that will cause serious
material degradation. In addition, high energy runaway
electrons would bombard the armor materials along theequatorial plane in fusion device. It is considered thatthese cause radiation damage and enhance tritium retention. In the present works, T exposure experiments havebeen carried out on W samples which were irradiated byhigh energy electrons using LINAC in KURRI of Research Reactor Institute, Kyoto University to investigate
effects of high energy electrons irradiation and microstructure on tritium retention of W. In the repot of the last
fiscal year, results of T exposure experiments on ITER
grade W which was fabricated by powder metallurgy. In
the present report, results of T exposure experiments on
W which was fabricated by Hot Isostatic Pressing(HIP-W) and comparison of results with ITER grade W
and HIP-W will be described.
EXPERIMENTS: W samples used were ITER grade
W (IG-W) and Hot Isostatic Pressing W (HIP-W). In thecase of IG-W, one was W sample (ITER grade W(1))
which the surface were manufactured to be oriented parallel to the rolling surface and rolling direction. The otherW sample (ITER grade W(3)) which the surface were
manufactured to be oriented perpendicular to the rollingsurface and rolling direction. On the other hand, structureof HIP-W is equiaxed deriving from the nature of theconsolidation process. The sizes of W samples were10mm x 10mm x 1mm. The surface of the both samples
were polished to be mirrored． High energy electrons
irradiation has been carried out using LINAC in KURRI
of Research Reactor Institute, Kyoto University. An energy of electron irradiated was 10 MeV and DPA was

RESULTS: In the condition of 10 MeV electrons irradiation, electrons go through in 10 mm thickness W sample. As a result, uniform defects were formed in the W
samples. Fig. 1 shows IP images of HIP-W, IG-W(3) andIG-W(1). It can be seen that amount of T near surface
depends on kinds of W. Fig. 2 shows amount of T as afunction of DPA. In general, the amount T increases withincreasing DPA. In addition, it is considered that T iseasy to diffuse parallel direction for rolling direction fromcomparing with IG-W(3) and IG-W(1) after the electron
irradiation.

Fig. 1. Tritium image of HIP-W, ITER grade W(3) (IGW(3) and ITER grade W(1)(IG W(1). Upper parts are
standard samples.

Fig. 2. Amount of tritium as a function of DPA

27P1-8-8-

PR1-6

Positron Annihilation Spectroscopy of Ferritic/Martensitic Steels
Irradiated with Protons and Spallation Neutrons

K. Sato, Q. Xu1, T. Yoshiie1, Y. Dai2 and K. Kikuchi3
Graduate School of Science and Engineering, Kagoshima
University
1
Research Reactor Institute, Kyoto University
2
Spallation Neutron Source Division, Paul Scherrer Institut
3
Frontier Research Center for Applied Atomic Sciences,
Ibaraki University
INTRODUCTION: In fusion reactors and spallation
neutron sources, irradiation damage is significantly more
serious than fission reactors. There is a need for use ofirradiation resistant materials in high neutron dose facilities. Due to its good thermal and mechanical properties,
the reduced-activation ferritic/martensitic steel, F82H is acandidate material for the first wall and blanket of the
future fusion reactor [1]. There have been a number ofstudies on the void swelling behavior of structural materials after neutron irradiation [2,3]. Recent theoretical andexperimental analyses have revealed the importance of
incubation period, a transient stage before the steady
growth of voids. Positrons are very sensitive to vacancy
type defects, and even single vacancies can be detected inpositron annihilation lifetime measurements. In this study,
defect structures in both F82H and SS316 steels during
the incubation period were studied after proton irradiation
using positron annihilation lifetime measurements.
EXPERIMENTS:
The reduced activated ferritic/martensitic steel F82H was used in this experiment.
F82H was irradiated in the second program (STIP-II).
More details of the STIP-I and STIP-II experiment werepreviously reported [4]. Table 1 shows sample ID, irradiation dose, average irradiation temperature and calculated
production of H and He. It should be noted that the actual
H contents can be much lower than the calculated values
due to fast diffusion of H in steels [5]. The chucks of tensile test samples of F82H were used for positron annihilation lifetime measurements at Paul Scherrer Institut.

creases to less than 200 ps when the vacancy clusters
contain a large amount of He atoms. The short and long
lifetime at 5.9 dpa is almost the same as the calculated
lifetime of V1 and V15, respectively, due to a lot of gas
atoms are produced during the irradiation. Therefore, thelong lifetime and short lifetime up to 15 dpa denote vacancy clusters including small and large amount of He
atoms, respectively. Decrease of long lifetime and mean
lifetime up to 15 dpa is due to the absorption of He atoms.
The concentration of vacancy clusters including small
amount of He atoms decreases up to 10 dpa because they
absorb He atoms and are classified into the short lifetime.
After that, the concentration of vacancy clusters including small amount of He atoms increases again. In thisstage, small vacancy clusters, which are classified into
the short lifetime up to 10 dpa, grow more prominently
and are classified into the long lifetime. From TEM observation, He bubbles grow with increasing irradiationdose above 10 dpa, but the positron lifetime does not increase. The absorption of He atoms is also large. If V341
(about 1.5 nm in diameter) contains 341 and 682 He atoms, the positron lifetime changes from 441 ps to 242
and 187 ps in Fe, respectively [6]. These results suggestthat vacancy clusters contains more He atoms than number of vacancies which make up the vacancy clusters
above 15 dpa.
Table 1. Irradiation condition of F82H.
Tempera- Irradiation
He
H
ID
ture (K)dose (dpa) (appm) (appm)
L11-L
371
5.9
413
1680
L12-L
L11-H
397
8.5
650
2530
L12-H
L13-L
406
9.2
715
2850
L14-L
L13-H
L14-H
L15-H
L16-H
L17-H
L18-H

RESULTS: Before irradiation, the long lifetime ofabout 150 ps denotes the lifetime of the dislocations andthe lath boundaries. Vacancy clusters are formed by theirradiation. In F82H, He bubbles formed by the irradiation above 443 K and about 500 appm He are visible by
TEM. He bubble size increases and the concentration
decreases with increasing the irradiation dose and temperature by TEM. However, the long lifetime intensity
does not increase with increasing the irradiation dose.
Therefore, it is also possible to detect invisible He bubbles by positron annihilation lifetime measurements. The
positron annihilation lifetime of vacancy clusters de-

448

12.3

1015

4200

513

17.2

1505

6200

560

20.4

1795

7720

REFERENCES:[1] M. Tamura et al., J. Nucl. Mater. 141−143 (1986)
1067.
[2] F.A. Garner, Materials Science and Technology, Vol.
10 (VCH Weinheim, 1994), p. 419.
[3] T. Okita et al., J. Nucl. Mater. 307−311 (2002) 322.
[4] Y. Dai et al., J. Nucl. Mater. 343 (2005) 33.
[5] Y. Dai et al., J. Nucl. Mater. 318 (2003) 167.
[6] T. Troev et al., Phys. Stat. Sol. C 6 (2009) 2373.

27P1-9-9-Positron Annihilation Behavior in Fe-Cr Alloys

PR1-7
R. Kasada, K. Sato1 and Q. Xu2

where  Fe is the enhancement of positron density in the
Fe cell of Fe-Cr alloy compared with the constituent pureFe.
Figure 1 presents the normalized W-parameter of
the CDB measurement against the Cr content x in theFe1-xCrx alloys. In Figure 1 the curve 1, which linearly
connects the Fe and Cr, represents the simplest casethat corresponds to no enhancement of positron density in
the Fe-Cr alloys. The unaged Fe0.91Cr0.09 and Fe0.84Cr0.16
are well fitted to the curve 1. In contrast, the other unaged
Fe-Cr alloys indicate an enhancement of annihilation in
Fe cell. The nonlinear function of Cr content for theunaged Fe1-xCrx alloys suggests a presence of preferential
positron annihilation (PPA) in Fe cell at their disorderedstate. Further experiments and discussion on the aged
Fe-Cr alloys are now going.

Institute of Advanced Energy, Kyoto University
1Department of Mechanical Engineering, Kagoshima

University
2Research Reactor Institute, Kyoto University

INTRODUCTION: Ferritic steels containing Cr are
expected to be used for the first-wall component of thefusion reactors as well as for the fuel pin cladding of theGeneration IV nuclear fission systems [1]. However,high-Cr steels may suffer from thermal aging embrittlement, which is well-known 475 °C embrittlement. This ismainly due to hardening phenomenon through the phaseseparation of Fe and Cr as shown in the phase diagram.
In the previous study [2], we applied a positron annihilation spectrometry to detect the phase separation in the
Fe-Cr alloys after thermal aging at 475 °C. Currently, thiscollaborative research is investigating neutron irradiation
effect on the positron annihilation behavior of Fe-Cr alloys. Here, we reports a new model to explain the positron annihilation behavior in Fe-Cr binary alloys.
Experimental Procedure: Positron annihilation coincidence Doppler broadening (CDB) measurement were
performed at the hot laboratory of KURRI.
Results and Discussions: Based on the theoretical modelof positron annihilation in binary alloys suggested by
Lock and West [3], we modeled the effect of Cr concentration and aging on positron annihilation in disordered(unaged) Fe-Cr alloys. The expression for the
W-parameter of the Fe-Cr alloys may be represented by
W FeCr  f Fe
W Fe  f Cr
WCr

Fig. 1 Normalized W parameter of Fe-Cr alloys.
(1)

as the weighted sum of the W parameter of the constituent pure metals ( WFe and WCr ). The fractions f denotethe fractions of positron density in the Fe cell and Cr cell.
The normalized W-parameters of Fe1-xCrx alloys can be
written as following equation:

WFeCr  WFe f Cr 1  f Fe
 1  (1  x) Fe
WCr  W FeREFERENCES:[1] A. Kimura, et al., Journal of Nuclear Science andTechnology, 44 (2007) 323-328.
[2] R. Kasada and K. Sato, submitted.
[3] Lock, D.G. & West, R.N. Positron annihilation in disordered binary alloys, J. Phys. F: Metal Phys. 4,2179-2188 (1974).

(2),

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