PR12

Project Research on Nuclear Spectroscopy and Condensed Matter
Physics Using Short-Lived Nuclei

Y. Ohkubo

annealed in vacuum at various temperatures. Theyobserved no clear signal of such complexes in the
TDPAC spectra. However, the TDPAC spectra indicatethat Ce and He form complexes having a variety ofgeometrical structures. Comparison with TDPAC results
reported by another research group on 111Cd arising from111
In in He-doped stainless steel shows that the parent
atoms (La and Ba) of 140Ce trap He atoms more
efficiently than In atoms do, indicating stronger bondingof He to the former atoms, while different from thepresent case, 111Cd (In)‒He complexes form a uniquegeometrical structure. A part of the results are describedin the following second page.
S. Komatsuda et al. (PRS-3) investigated thermal
behavior and interacting nature of 100-ppm Al and~100-ppt In impurities doped in a semiconductor ZnO
by means of the TDPAC technique with the 111In(→
111Cd) probe. They observed the following contrasting
interactions between Al and In impurities depending on
different atmospheric conditions: (1) in air, Al and In
impurities irreversibly associate with each other in theprocess of thermal diffusion of these two species, but (2)in vacuum, these bound states formed in air dissociate byheat treatment at temperature higher than 873 K, and thedissociation reaction is enhanced with increasing
temperature. Considering that the dissociation is triggeredby the oxygen vacancy formation near the locallyassociated In‒Al structure and using the TDPAC dataobtained, they estimated the activation energy of theoxygen‒vacancy formation to be 0.72(6) eV. A part of
the results are described in the following third page.
Superionic conductivity observed for AgI emerges onlyat the high-temperature (≥ 420 K)  phase because of
temperature-dependent crystal structures, which is abarrier to the practical applications of this compound.
Recently, this problem was attacked by a novel technique:powder AgI coated with poly-N-vinyl-2-pyrrolidone(PVP) can drastically enhance the ionic transport property
at room temperature. W. Sato et al. (PRS-4) studied
dynamic behavior of the extranuclear field relative to the111
Cd(← 111Ag) probe nucleus incorporated in AgI, using
the TDPAC method. For PVP-coated AgI nanoparticles,
they observed nuclear spin relaxation of the probe atroom temperature, which indicates that Ag+ ions in the
PVP-coated sample make hopping motion from site tosite at this low temperature. From the TDPAC dataobtained, they estimated the activation energy for the
dynamic motion to be 46(10) meV. A part of the results
are described in the following fourth page.

Research Reactor Institute, Kyoto University
Objective and Participating Research Subjects
The main objectives of this project research are theinvestigation of the nuclear structure of unstableneutron-rich nuclei and also the local properties ofmaterials using short-lived nuclei.
This period is the first year of the project.
Unfortunately, no experiments in all six research subjectsof the project (26P12) were executed owing to thesuspension of the reactor operation. Here, we report someresults which were obtained in previous periods and havealready been published in journals.
The research subjects (PRS) reported here are as
follows:
PRS-1  Decay of 150Ce to 150Pr
PRS-2 Interaction between He and Elements with A =140 in Fe
PRS-3 Atmosphere Dependence of Stability of Local
Fields in Al-Doped ZnO
PRS-4 Extranuclear Dynamic Motion of 111Cd(← 111Ag)
Doped in AgI Nanoparticles
Main Results and Contents of This Report
At KUR-ISOL (the on-line isotope separator installedat the Kyoto University Research Reactor), Y. Kojima etal. (PRS-1) studied the  decay of 150Ce having ahalf-life of 6.05(7) s produced by the thermal-neutroninduced fission of 235U. From -ray singles and ‒coincidence measurements, they newly found 9 excitedstates and 37-rays and constructed a decay scheme
containing 18 excited states and 55 -rays which include
the newly found excited states and -rays. They
concluded that the dominant -feeding at the 110-keV
excited state of 150Pr arising from the  decay of 150Ce to
be an allowed unhindered spin-flip transition. They
furthermore proposed the Nilsson configurations of theground state and the 110-keV excited state of 150Pr. A
part of the results are described in the next page.
In order to examine whether Ce (or rather, La and Ba)
and He form complexes having a definite geometricalstructure in Fe as suggested in first-principles density
functional theory calculations, Y. Ohkubo et al. (PRS-2)
projected 100-keV 140Cs+ at KUR-ISOL and then 4-keV
He+ using an ion beam gun into an Fe foil and tooktime-differential perturbed-angular-correlation (TDPAC)
spectra at room-temperature of 140Ce arising through140
Ba-140La from 140Cs in He-doped Fe, unannealed and

採択課題番号 26P12
短寿命 RI を用いた核分光と核物性研究（京大・原子炉）大久保嘉高
70

プロジェクト decay of 150Ce to 150Pr

Y. Kojima, K. Kosuga1, Y. Shima2, A. Taniguchi3,
H. Hayashi4 and M. Shibata

0
0

2000

4000

789

688

x5

558

1000

380

Counts2000

100

INTRODUCTION: Decay data provide valuable information about unstable nuclides. In particular, the branching ratio I is one the most important properties
from the nuclear structure viewpoint. For even-even 150Ce,
Fogelberg et al. briefly reported an intense -transition to
the 110-keV level in 150Pr [1]. If this -feeding is an allowed unhindered transition, it will lead to the assignment of the Nilsson orbital for 150Pr. However, it is uncertain whether this transition is firmly an allowed unhindered transition because of the following reasons.
First, ref. [1] did not provide detailed experimental dataon 150Ce. Second, the other published data for 150Ce arevery scarce and partly inconsistent with each other [2,3].
In the present work, decay studies on 150Ce have been
performed using the on-line isotope separator at KUR(KUR-ISOL) [4] to investigate low-energy level structures in150Pr. Note that this work was recently published[5]. This report is an outline of the paper.
EXPERIMENTS: The 150Ce nuclides were producedby the thermal neutron induced fission of 235U. The
mass-separated source was periodically moved to a detector port with time intervals of 12.2 s.
Time-dependent -ray singles and  coincidence measurements were performed with two Ge detectors in ameasurement period of 46 h. The energy and efficiency
calibrations were made using standard -ray sources.
RESULTS: The half-life and coincidence relationships
with the Pr KX-ray were analyzed to assign the parent
nuclide of each -ray observed in this work. From theseanalyses, 57 -rays including 39 new -transitions were
found to be due to the decay of 150Ce.
Energy spectra gated on the-rays from 150Ce were analyzed to establish -ray cascade relations. For example,
Fig. 1 is a spectrum gated on the 110-keV -ray. This
spectrum shows that the 110-keV -ray is coincident with
13 -rays. From these cascade relations and also fromenergy sum rules, the excited levels in 150Pr and the -ray
placements were unambiguously proposed. The decay
scheme includes 18 excited levels. Nine levels of themwere newly proposed. The 717-keV level seen in ref. [3]was not observed in this work.
The -ray intensities relative to that of the 110-keV tran-

106
169
180
200
231
279.2

Radioisotope Research Center, Nagoya University
School of Engineering, Nagoya University
2
Graduate School of Engineering, Nagoya University
3
Research Reactor Institute, Kyoto University
4
Institute of Biomedical Science, The University of Tokushima Graduate School
1

KX

sition were deduced from peak counts observed in the
singles spectrum or in coincident spectrum. Multipolarities of three -rays were also estimated from the intensity
ratio between KX and -ray peaks observed in the coincident spectrum: M1/E2 for the 103- and 154-keV -rays,
and E1 for the 110-keV -ray.
Finally, the I and log-ft values were calculated from thetransition intensity ( and conversion electron) imbalance
for each excited level. A small log-ft value of 4.9 wasobserved for the 110-keV level. It leads to spin-parity J= 1+ for this level.
DISCUSSION: The very intense -feeding to the
110-keV level is an allowed transition, and should be
explained by selection rules for -decays of deformed
nuclei [6]. Near the Nilsson orbitals observed in theneighboring nuclides, only the spin-flip transition between 3/2[532] and 5/2[532] satisfies the selection
rules. Thus, this -transition is interpreted as one of thecoupled neutron in 3/2[532] orbital in 150Ce changing toa proton in the vacant 5/2[532] orbital in 150Pr. This configuration yields J = 1+, and agrees with our spin-parity
assignment. The configuration of 5/2+[413]-3/2[521]
was also proposed for the ground state of 150Pr from thesystematics of the neighboring nuclides and from coupling rules.
CONCLUSIONS: A detailed decay scheme of 150Ce,
which includes 37 new -rays and 9 new excited levels,
was proposed from -ray measurements. On the basis of
the systematics and observation of the allowed spin-flip
transition, the Nilsson configurations were newly proposed for the ground and 110-keV level in 150Pr.

62, 63

PR12-1

6000

Channel number (0.125 keV/ch)

Fig. 1. A -ray spectrum gated on the 110-keV
-transition. Coincident -rays are indicated with
their energies in units of keV.
REFERENCES:[1] B. Fogelberg et al., Nucl. Phys. A 453 (1986) 15-25.
[2] K. Yamauchi et al., KURRI-KR-3 (1996), pp.51-53(in Japanese).
[3] K. S. Basu et al., Nucl. Data Sheets 114 (2013) 435.
[4] A. Taniguchi et al., Nucl . Instr. and Meth. A 351(1994) 378-382.
[5] Y. Kojima et al., J. Phys. Soc. Jpn. 84 (2015)
054201/1-8.
[6] G. Alaga, Phys. Rev. 100 (1955) 432-433.

採択課題番号 26P12-3

核分裂生成物に対する線直線偏光度測定を中心としたプロジェクト
核分光実験（名大・RI）小島康明、柴田理尋（名大院・工）嶋 洋佑、常少亮太 （名大・工）小菅数人（徳島大・医）林 裕晃 （京大・原子炉）谷口秋洋
71

PR12-2

Interaction between He and Elements with A = 140 in Fe
He-doped(1)140CeFe (4 × 1013/cm2 He corresponding to
only 0.0003 dpa), it is unlikely for He ions to directly
displace them. We think that He atoms diffused andbonded to the parent atoms of "good" 140Ce (interstitial
He atoms diffuse much more easily than vacancies: thecorresponding calculated activation energies are 0.06 and0.68 eV, respectively). As the dose of He increases, thenumber of the parent atoms of "good" 140Ce decreases. If
140
Ce‒He complexes take one or a few definite
geometrical structures, these would be reflected in the
TDPAC spectra and it may be possible to determine
whether He atoms are at substitutional or interstitial sites.
The observation that the oscillation amplitude is only
reduced but not damped with time under the He
implantation indicates that 140Ce‒He complexes take avariety of geometrical structures, accordingly these 140Ce
bonded by He feeling various electric field gradients due
to He. It is natural to think that many He atoms surroundthe parent atom and that there is a distribution of thenumber of He atoms attached to it.

Y. Ohkubo, A. Taniguchi, Q. Xu, M. Tanigaki and K.
Sato
Research Reactor Institute, Kyoto University
INTRODUCTION: As far as we know, the state of
impurities He and Ce in Fe has not been studied
experimentally until our recent work [1]. This knowledge
is important in materials science related to nuclear fusion
reactor materials. With a nuclear spectroscopic technique,the time-differential perturbed angular correlation (TDPAC)
technique, we obtained the result that the parent atoms(La and Ba) of 140Ce very efficiently trap He and they
form complexes in Fe, which do not have a definite
geometrical structure. The present report describes thelatter result. See [1] for the full description.
EXPERIMENTS: 100-keV 140Cs+ (~1.4 × 1012/0.2 cm2)
were projected into an Fe foil at KUR-ISOL. 140Cs decays
through 140Ba and then 140La to 140Ce. We name thissample 140CeFe. Three additional samples were preparedusing the 140CeFe. The first, second and third wereprepared by projecting 4-keV He+ of ~4 × 1013, ~5 × 1014
and ~2 × 1016/cm2 in this sequence into the 140CeFe. We
name them He-doped(1)140CeFe, He-doped(2)140CeFe
and He-doped(3)140CeFe, respectively. The profile of the
He concentration in Fe overlaps that for 140Cs.
Room-temperature TDPAC spectra of 140Ce were taken
for these four samples.

-0.10

no He
[1.93(1)Grad/s, -0.042(3)]

-0.05
0.00
-0.10

A22 G22 (t)-0.05

RESULTS: Fig. 1 (from top to bottom) shows the
TDPAC spectra obtained at room temperature for 140CeFe,
He-doped(1)140CeFe, He-doped(2)140CeFe and He-doped(3)140CeFe, all four with no annealing. The top spectrum
is the one appearing in [2]. As explained there, theoscillation pattern seen in the spectrum is due to a uniquestatic magnetic hyperfine interaction at 140Ce occupying
the Fe substitutional site with no lattice defects nearby(the Larmor frequency equals 1.927(7) Grad/s). Hereafter,
we call these 140Ce "good" 140Ce. From the value of theamplitude of the oscillation, "good" 140Ce are only about
30% of the 140Ce implanted in Fe. In Fig. 1 are also
shown the characteristic values for each oscillation
component seen in the TDPAC spectra. As the dose of He
increases to ~5 × 1014/cm2, the oscillation amplitude gets
reduced more and more (note that the amplitude is not
damped with time), and at the dose of ~2 × 1016/cm2(He-doped(3)140CeFe) no clear oscillation is observed.
The dose of 2 × 1016/cm2 corresponds to 0.15 dpa(displacement per atom) at the maximum. This large
number may imply that He ions directly displace theparent atoms of "good" 140Ce from the substitutional sites.
However, based on the fact that the oscillation amplitude
is reduced by as much as ~50% even for the

1st He irrad.
[1.90(1), -0.020(3)]

0.00
-0.10

2nd He irrad.
[1.91(1), -0.013(3)]

-0.05
0.00

-0.10
3rd He irrad.

-0.05
0.00
0

5

10

15

20

25

t (ns)

Fig. 1. Room-temperature TDPAC spectra for 140CeFe before
He irradiation, He-doped(1)140CeFe, He-doped(2)140CeFe, andHe-doped(3)140CeFe, all with no annealing. The two values inthe square brackets in each panel are the Larmor frequency(Grad/s) and the amplitude of the oscillation component.

REFERENCES:[1] Y. Ohkubo, A. Taniguchi, Q. Xu, M. Tanigaki and K.
Sato, Phil. Mag. Lett. 94, 470-477 (2014).
[2] Y. Ohkubo, A. Taniguchi, Q. Xu, M. Tanigaki, N.
Shimizu and T. Otsuka, Phys. Rev. C 87, 044324(2013).

採択課題番号 26P12-4 鉄中での不純物原子と 140Ce 不純物原子核との相互作用 プロジェクト（京大・原子炉）大久保嘉高、谷口秋洋、谷垣 実、徐 虬（京大院理）常山正幸、谷口良徳

72

PR12-3

Atmosphere Dependence of Stability of Local Fields in Al-Doped ZnO

S. Komatsuda, W. Sato1 and Y. Ohkubo2

G22 t the time-differential perturbation factor as a function of the time interval, t, between the relevant cascade
γ-ray emissions, and N(θ,t) the number of the coincidence
events observed at angle, θ. The spectrum in Fig.1(a)shows that 100 ppm Al and 100 ppt 111In are locally-associated in ZnO matrix, suggesting that there is astrong attractive force between Al and In in ZnO [1,2].
For the spectrum in Fig. 1(b), two different components
were observed: one is that appearing in the spectrum in
Fig. 1(a) and the other is that observed for undoped
ZnO[3]. This observation implies that the probe graduallyresides solely at the substitutional Zn site after annealing
under argon gas in the same way as the case for the sample heat-treated in vacuum. These observations suggestthat the drastic change of local structure formed by Al
and In ions is closely related to the presence of O2 gas. In
oxide compounds, in general, oxygen vacancies are likely
to be formed during annealing process at a lower partialpressure of atmospheric oxygen. Therefore, it is suggested that the local association of Al and 111In becomes unstable in anaerobic atmosphere due to the formation ofoxygen vacancies in the sample. For further informationon the stability of the local structure, dependence of partial pressure of oxygen for the dissociation process needs
to be investigated.

Department of General Education, National Institute ofTechnology, Ichinoseki College
1
Institute of Science and Engineering, Kanazawa University
2
Research Reactor Institute, Kyoto University
INTRODUCTION:
Impurity-induced
properties
emerging in ZnO has been attracting increasing attention
toward its application to functional materials in a wide
field of industry. For a practical use of ZnO as a conduction-controlling device, it is of great importance to study
the physical and chemical states of doped impurities
and/or oxygen vacancies. From this point of view, wehave investigated the factors determining the local structures and their stability of Al-doped ZnO samples synthesized on different conditions by means of thetime-differential perturbed angular correlation (TDPAC)
method. In a series of our TDPAC studies, drastic changeof the local structure was observed for Al-doped ZnO
sample heat-treated in vacuum [1,2]. In order to provide
further insight into the above atmosphere dependence, inthe present work, we performed an additional TDPAC
measurement for 100 ppm Al-doped ZnO annealed underargon gas flow.
EXPERIMENTS: For the synthesis of 100 ppm
Al-doped ZnO, stoichiometric amounts of Al(NO3)3・
9H2O and ZnO powder were mixed in ethanol. The suspension was heated to evaporate the ethanol until dryness.
The powder was pressed into two disks and sintered in air
at 1273 K for 3 h. For TDPAC measurements, commercially available 111In solution was added in droplets onto
the sintered disks at the concentration of 100 ppt. The
disks again underwent heat treatment in air at 1373 K for
2 h. After that, a TDPAC measurement was performed
for one of these samples prepared in air. The other sample was ground into powder and annealed under argon
gas flow at 1373 K for 24 h. A TDPAC measurement was
carried out for the 111In(→111Cd) probe on the 171-245
keV cascade γ rays with the intermediate state of I = 5/2
having a half-life of 85.0 ns.
RESULTS: Fig. 1 shows the TDPAC spectra of 111In(→
111Cd) probe in 100 ppm Al-doped ZnO annealed (a) in
air and (b) in argon gas. The directional anisotropy on theordinate, A22 G22 t , was deduced by the following relation for delayed coincidence events of the cascade:Fig. 1. TDPAC spectra of 111In( → 111Cd) in 100 ppm
Al-doped ZnO annealed (a) in air and (b) in argon gas. The
TDPAC measurements were performed at room temperature.

REFERENCES:[1] S. Komatsuda et al., J. Appl. Phys., 116 (2014)
183502/1-5.
[2] S. Komatsuda et al., J. Radioanal. Nucl. Chem., 303(2015) 1249-1252.
[3] W. Sato et al., Phys. Rev. B, 78 (2008) 045319/1-5.

2 [ N (π , t )－N (π / 2, t )]A22G22 (t ) =.
N (π , t ) + 2 N (π / 2, t )Here, A22 denotes the angular correlation coefficient,

採択課題番号 26P12-5	  	  	  金属酸化物中不純物サイトの局所構造観察	
 プロジェクト	 （金沢大・理工研究域）佐藤	  渉（金沢大院・自然）小松田沙也加（京大・原子炉）大久保嘉高	
 73

PR12-4

Extranuclear Dynamic Motion of 111Cd(← 111Ag) Doped in AgI Nanoparticles

W. Sato, R. Mizuuchi1, N. Irioka2, S. Komatsuda3, S.
Kawata4, A. Taoka and Y. Ohkubo5

were performed for the synthesized sample at various
temperatures. The directional anisotropy, A22G22(t), wasdeduced with the following relation:

Institute of Science and Engineering, Kanazawa
University
1
Graduate School of Natural Science and Technology,
Kanazawa University
2
School of Chemistry, Kanazawa University
3
Department of General Education, National Institute ofTechnology, Ichinoseki College
4
Department of Chemistry, Faculty of Science, Fukuoka
University
5
Research Reactor Institute, Kyoto University

A22G22( t) =Here, A22 denotes the angular correlation coefficient,
G22(t) the time-differential perturbation factor as afunction of the time interval, t, between the relevant
cascade γ-ray emissions, and N(θ, t) the number of thedelayed coincidence events observed at an angle, θ.
RESULTS: It was found that TDPAC spectra of the111
Cd( ← 111Ag) probe introduced in PVP-coated AgI
measured at different temperatures show exponential
relaxation of the directional anisotropy, which signifies
that the probe is dynamically perturbed by the
extranuclear field. This phenomenon is understandable
for the spectra of the sample as in the α phase (> 420 K).
What is to be noted here is that the spectral relaxation
was also observed even at room temperature. It was
found from this observation that Ag+ ions surrounding
the probe nuclei exhibit site-to-site hopping motion in the
PVP-coated AgI nanoparticle even at this low
temperature. Fig. 1 shows the temperature dependenceof the relaxation constants. From a least-squares fit to
the data with an Arrhenius-type equation, the activationenergy, Ea, of the hopping motion was successfully
estimated to be Ea = 46 (10) meV. This value shows
fair agreement with that obtained for the superionic
conductivity: Ea = 60 meV [1]. The present result issignificant in that superionic conduction can be probedwith local dynamics observed through nuclear spin
relaxation.

INTRODUCTION: Silver iodide, AgI, is a promising
metal halide showing superionic conductivity as in its αphase, and its application to functional materials such as
solid electrolytes is thus highly expected.
The
conducting phenomenon, however, only emerges atelevated temperature (> 420 K) because the crystal
structure depends on temperature; this has indeed been abarrier to the practical applications of this compound.
Recently, an epoch-making technique has broken
through this situation: powder AgI coated with
poly-N-vinyl-2-pyrrolidone (PVP) can drasticallyenhance the ionic transport property at room temperature,
recording the conductivity of 1.5 × 10 2 Ω-1 cm 1[1].
According to the report, this achievement is due tosuccessful control of the particle size as small as€ nanoscale. In addition to the property in the bulk, it isof great importance to obtain complementary informationon the site-to-site hopping motion of Ag+ ions on an
atomic scale for a detailed understanding of ionic
conductivity of this binary solid. For that purpose, inthe present work, we have applied the time-differential
perturbed angular correlation (TDPAC) technique withthe 111Cd( ← 111Ag) probe nuclei to observe dynamic
behavior of Ag+ ions. We here report successful
evaluation of the activation energy of the dynamic
motion of Ag+ ions [2,3].
EXPERIMENTS: Pd foil was irradiated with thermal
neutrons in Kyoto University Reactor to produce the
TDPAC probe. After radioequilibrium was achieved
between 111Pd and 111Ag, the Pd foil was dissolved in
HNO3 aq. solution, and carrier-free 111Ag was isolated byan anion-exchange chromatography.
The separated
111
Ag was incorporated together in PVP-coated AgI
sample when the powder sample was synthesized by
precipitation of their raw materials. We confirmed bytransmission electron microscopy that microscopic
particles with sizes of 10-100 nm were expectedly
synthesized for 111Ag-free PVP-coated AgI.
TDPAC measurements of the 111Cd(←111Ag) probe
−

10

6 -1

 (10 s )−2[N ( π , t) − N (π /2,t)] 	
  	
  (1)
.
N( π ,t) +2N (π /2,t)

Ea = 46 (10) meV

1

2

2.2

2.4

2.6

2.8

3

3

3.2

3.4

3.6

-1

1/T (10 K )Fig. 1. Temperature dependence of the relaxation constant.
The line is the result of a least-squares fit with an
Arrhenius-type equation.

REFERENCE:[1] R. Makiura et al. Nature Mater. 8 (2009) 476-480.
[2] W. Sato et al. Chem. Phys. Lett. 609 (2014) 104-107.
[3] W. Sato et al. Hyperfine Interact. 231 (2015) 107-113.

採択課題番号 26P12-6	  	 	  超イオン伝導体ヨウ化銀中 111Ag の核スピン緩和	
 	
 	
 	
 	
 	
 プロジェクト	 （金沢大・理工研究域）佐藤	  渉（金沢大院・自然）藤澤	  照功（京大・原子炉）大久保	  嘉高	
 74