PR12 Project Research on Nuclear Spectroscopy and Condensed Matter Physics Using Short-Lived Nuclei Y. Ohkubo annealed in vacuum at various temperatures. They observed no clear signal of such complexes in the Research Reactor Institute, Kyoto University TDPAC spectra. However, the TDPAC spectra indicate that Ce and He form complexes having a variety of geometrical structures. Comparison with TDPAC results Objective and Participating Research Subjects reported by another research group on 111Cd arising from The main objectives of this project research are the 111In in He-doped stainless steel shows that the parent investigation of the nuclear structure of unstable atoms (La and Ba) of 140Ce trap He atoms more neutron-rich nuclei and also the local properties of efficiently than In atoms do, indicating stronger bonding materials using short-lived nuclei. of He to the former atoms, while different from the This period is the first year of the project. present case, 111Cd (In)‒He complexes form a unique Unfortunately, no experiments in all six research subjects geometrical structure. A part of the results are described of the project (26P12) were executed owing to the in the following second page. suspension of the reactor operation. Here, we report some S. Komatsuda et al. (PRS-3) investigated thermal results which were obtained in previous periods and have behavior and interacting nature of 100-ppm Al and already been published in journals. ~100-ppt In impurities doped in a semiconductor ZnO The research subjects (PRS) reported here are as by means of the TDPAC technique with the 111In(→ follows: 111Cd) probe. They observed the following contrasting interactions between Al and In impurities depending on PRS-1 Decay of 150Ce to 150Pr different atmospheric conditions: (1) in air, Al and In PRS-2 Interaction between He and Elements with A = impurities irreversibly associate with each other in the 140 in Fe process of thermal diffusion of these two species, but (2) PRS-3 Atmosphere Dependence of Stability of Local in vacuum, these bound states formed in air dissociate by Fields in Al-Doped ZnO heat treatment at temperature higher than 873 K, and the PRS-4 Extranuclear Dynamic Motion of 111Cd(← 111Ag) dissociation reaction is enhanced with increasing Doped in AgI Nanoparticles temperature. Considering that the dissociation is triggered by the oxygen vacancy formation near the locally Main Results and Contents of This Report associated In‒Al structure and using the TDPAC data obtained, they estimated the activation energy of the At KUR-ISOL (the on-line isotope separator installed oxygen‒vacancy formation to be 0.72(6) eV. A part of at the Kyoto University Research Reactor), Y. Kojima et the results are described in the following third page. al. (PRS-1) studied the decay of 150Ce having a Superionic conductivity observed for AgI emerges only half-life of 6.05(7) s produced by the thermal-neutron- at the high-temperature (≥ 420 K) phase because of induced fission of 235U. From -ray singles and ‒ temperature-dependent crystal structures, which is a coincidence measurements, they newly found 9 excited barrier to the practical applications of this compound. states and 37-rays and constructed a decay scheme Recently, this problem was attacked by a novel technique: containing 18 excited states and 55 -rays which include powder AgI coated with poly-N-vinyl-2-pyrrolidone the newly found excited states and -rays. They (PVP) can drastically enhance the ionic transport property concluded that the dominant -feeding at the 110-keV at room temperature. W. Sato et al. (PRS-4) studied 150 150 dynamic behavior of the extranuclear field relative to the excited state of Pr arising from the decay of Ce to 111 111 be an allowed unhindered spin-flip transition. They Cd(← Ag) probe nucleus incorporated in AgI, using furthermore proposed the Nilsson configurations of the the TDPAC method. For PVP-coated AgI nanoparticles, 150 they observed nuclear spin relaxation of the probe at ground state and the 110-keV excited state of Pr. A + part of the results are described in the next page. room temperature, which indicates that Ag ions in the In order to examine whether Ce (or rather, La and Ba) PVP-coated sample make hopping motion from site to and He form complexes having a definite geometrical site at this low temperature. From the TDPAC data structure in Fe as suggested in first-principles density obtained, they estimated the activation energy for the functional theory calculations, Y. Ohkubo et al. (PRS-2) dynamic motion to be 46(10) meV. A part of the results projected 100-keV 140Cs+ at KUR-ISOL and then 4-keV are described in the following fourth page. He+ using an ion beam gun into an Fe foil and took time-differential perturbed-angular-correlation (TDPAC) spectra at room-temperature of 140Ce arising through 140Ba-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 プロジェクト （京大・原子炉）大久保嘉高 70 PR 12-1 decay of 150Ce to 150Pr Y. Kojima, K. Kosuga1, Y. Shima2, A. Taniguchi3, sition were deduced from peak counts observed in the H. Hayashi4 and M. Shibata singles spectrum or in coincident spectrum. Multipolari- ties of three -rays were also estimated from the intensity Radioisotope Research Center, Nagoya University ratio between KX and -ray peaks observed in the coin- 1 School of Engineering, Nagoya University cident spectrum: M1/E2 for the 103- and 154-keV -rays, 2 Graduate School of Engineering, Nagoya University and E1 for the 110-keV -ray. 3Research Reactor Institute, Kyoto University 4 Finally, the I and log-ft values were calculated from the Institute of Biomedical Science, The University of To- transition intensity ( and conversion electron) imbalance kushima Graduate School for each excited level. A small log-ft value of 4.9 was observed for the 110-keV level. It leads to spin-parity J + = 1 for this level. INTRODUCTION: Decay data provide valuable in- DISCUSSION: The very intense -feeding to the formation about unstable nuclides. In particular, the - 110-keV level is an allowed transition, and should be branching ratio I is one the most important properties explained by selection rules for -decays of deformed from the nuclear structure viewpoint. For even-even 150Ce, nuclei [6]. Near the Nilsson orbitals observed in the Fogelberg et al. briefly reported an intense -transition to 150 neighboring nuclides, only the spin-flip transition be- the 110-keV level in Pr [1]. If this -feeding is an al- tween 3/2[532] and 5/2[532] satisfies the selection lowed unhindered transition, it will lead to the assign- rules. Thus, this -transition is interpreted as one of the ment of the Nilsson orbital for 150Pr. However, it is un- coupled neutron in 3/2[532] orbital in 150Ce changing to certain whether this transition is firmly an allowed un- a proton in the vacant 5/2[532] orbital in 150Pr. This con- hindered transition because of the following reasons. + First, ref. [1] did not provide detailed experimental data figuration yields J = 1 , and agrees with our spin-parity 150 150 assignment. The configuration of 5/2+[413]-3/2[521] on Ce. Second, the other published data for Ce are 150 very scarce and partly inconsistent with each other [2,3]. was also proposed for the ground state of Pr from the In the present work, decay studies on 150Ce have been systematics of the neighboring nuclides and from cou- pling rules. performed using the on-line isotope separator at KUR 150 (KUR-ISOL) [4] to investigate low-energy level struc- CONCLUSIONS: A detailed decay scheme of Ce, tures in150Pr. Note that this work was recently published which includes 37 new -rays and 9 new excited levels, [5]. This report is an outline of the paper. was proposed from -ray measurements. On the basis of EXPERIMENTS: The 150Ce nuclides were produced the systematics and observation of the allowed spin-flip by the thermal neutron induced fission of 235U. The transition, the Nilsson configurations were newly pro- 150 mass-separated source was periodically moved to a de- posed for the ground and 110-keV level in Pr. tector port with time intervals of 12.2 s. Time-dependent -ray singles and coincidence meas- 2000 urements were performed with two Ge detectors in a KX 100 measurement period of 46 h. The energy and efficiency 180 231 1000 789 calibrations were made using standard -ray sources. 688 106 558 62, 63 169 x5 200 279.2 Counts RESULTS: The half-life and coincidence relationships 380 with the Pr KX-ray were analyzed to assign the parent 0 0 2000 4000 6000 nuclide of each -ray observed in this work. From these Channel number (0.125 keV/ch) analyses, 57 -rays including 39 new -transitions were 150 Fig. 1. A -ray spectrum gated on the 110-keV found to be due to the decay of Ce. 150 -transition. Coincident -rays are indicated with Energy spectra gated on the-rays from Ce were ana- their energies in units of keV. lyzed to establish -ray cascade relations. For example, Fig. 1 is a spectrum gated on the 110-keV -ray. This REFERENCES: spectrum shows that the 110-keV -ray is coincident with [1] B. Fogelberg et al., Nucl. Phys. A 453 (1986) 15-25. 13 -rays. From these cascade relations and also from [2] K. Yamauchi et al., KURRI-KR-3 (1996), pp.51-53 energy sum rules, the excited levels in 150Pr and the -ray (in Japanese). placements were unambiguously proposed. The decay [3] K. S. Basu et al., Nucl. Data Sheets 114 (2013) 435. scheme includes 18 excited levels.