Searcharxiv⌕ Search

arXiv subjects

K. Ishizaki

Publications and source records attributed to K. Ishizaki.

6 recordsLinked to original sources
arXiv2024

Transverse asymmetry of individual $γ$-rays in the $^{139}$La($\vec{n}$, $γ$)$^{140}$La reaction

The enhancement of the parity-violating asymmetry in the vicinity of $p$-wave compound nuclear resonances was observed for a variety of medium-heavy nuclei. The enhanced parity-violating asymmetry can be understood using the $s$-$p$ mixing model. The $s$-$p$ mixing model predicts several neutron energy-dependent angular correlations between the neutron momentum $\vec k_n$, neutron spin $\vecσ_n$, $γ$-ray momentum $\vec k_γ$, and $γ$-ray polarization $\vecσ_γ$ in the $(n,γ)$ reaction. In this paper, the improved value of the transverse asymmetry of $γ$-ray emissions, corresponding to a correlation term $\vecσ_n\cdot(\vec k_n\times\vec k_γ)$ in the $^{139}\mathrm{La}(\vec n,γ)^{140}\mathrm{La}$ reaction, and the transverse asymmetries in the transitions to several low excited states of $^{140}\mathrm{La}$ are reported.

nucl-ex↗
arXiv2022

Angular distribution of $γ$ rays from the p-wave resonance of $^{118}$Sn

The neutron energy-dependent angular distribution of $γ$ rays from $^{117}{\rm Sn}(n,γ)$ reaction was measured with germanium detectors and a pulsed neutron beam. The angular distribution was clearly observed in $γ$-ray emissions with an energy of 9327 keV which corresponds to the transition from a neutron resonance of $^{117}{\rm Sn}+n$ to the ground state of $^{118}{\rm Sn}$. The angular distribution causes an angular-dependent asymmetric resonance shape. An asymmetry $A_{\rm LH}$ was defined as $(N_{\rm L}-N_{\rm H})/(N_{\rm L}+N_{\rm H})$, where $N_{\rm L}$ and $N_{\rm H}$ are integrated values for lower- and higher-energy regions of a neutron resonance, respectively. We found that the $A_{\rm LH}$ has the angular dependence of $(A \cos θ_γ+B)$, where $θ_γ$ is the $γ$-ray emission angle with respect to the incident neutron momentum, with $A=0.394 \pm 0.073$ and $B = 0.118 \pm 0.029$ in the 1.33 eV p-wave resonance.

nucl-ex↗
arXiv2021

Measurement of nuclear spin relaxation time in lanthanum aluminate for development of polarized lanthanum target

The nuclear spin-lattice relaxation time ($T_1$) of lanthanum and aluminum nuclei in a single crystal of lanthanum aluminate doped with neodymium ions is studied to estimate the feasibility of the dynamically polarized lanthanum target applicable to beam experiments. The application of our interest is the study of fundamental discrete symmetries in the spin optics of epithermal neutrons. This study requires a highly flexible choice of the applied magnetic field for neutron spin control and favors longer $T_1$ under lower magnetic field and at higher temperature. The $T_1$ of $^{139}{\rm La}$ and ${}^{27}{\rm Al}$ was measured under magnetic fields of $0.5$-$2.5$ T and at temperatures of $0.1$-$1.5$ K and found widely distributed up to 100 h. The result suggests that the $T_1$ can be as long as $T_1 \sim$ 1 h at $0.1$ K with a magnetic field of $0.1$ T, which partially fulfills the requirement of the neutron beam experiment. Possible improvements to achieve a longer $T_1$ are discussed.

physics.ins-det↗
arXiv2021

Energy dependent angular distribution of individual $γ$-rays in the $^{139}$La($n$, $γ$)$^{140}$La* reaction

Neutron energy-dependent angular distributions were observed for individual $γ$-rays from the 0.74 eV p-wave resonance of $^{139}$La+$n$ to several lower excited states of $^{140}$La. The $γ$-ray signals were analyzed in a two dimensional histogram of the $γ$-ray energy, measured with distributed germanium detectors, and neutron energy, determined with the time-of-flight of pulsed neutrons, to identify the neutron energy dependence of the angular distribution for each individual $γ$-rays. The angular distribution was also found for a photopeak accompanied with a faint p-wave resonance component in the neutron energy spectrum. Our results can be interpreted as interference between s- and p-wave amplitudes which may be used to study discrete symmetries of fundamental interactions.

nucl-ex↗
arXiv2020

Monitoring the build-up of hydrogen polarization for polarized Hydrogen-Deuteride (HD) targets with NMR at 17 Tesla

We report on the frozen-spin polarized hydrogen--deuteride (HD) targets for photoproduction experiments at SPring-8/LEPS. Pure HD gas with a small amount of ortho-H2 (~0.1%) was liquefied and solidified by liquid helium. The temperature of the produced solid HD was reduced to about 30 mK with a dilution refrigerator. A magnetic field (17 T) was applied to the HD to grow the polarization with the static method. After the aging of the HD at low temperatures in the presence of a high-magnetic field strength for 3 months, the polarization froze. Almost all ortho-H2 molecules were converted to para-H2 molecules that exhibited weak spin interactions with the HD. If the concentration of the ortho-H2 was reduced at the beginning of the aging process, the aging time can be shortened. We have developed a new nuclear magnetic resonance (NMR) system to measure the relaxation times (T1) of the 1H and 2H nuclei with two frequency sweeps at the respective frequencies of 726 and 111 MHz, and succeeded in the monitoring of the polarization build-up at decreasing temperatures from 600 to 30 mK at 17 T. This technique enables us to optimize the concentration of the ortho-H2 and to efficiently polarize the HD target within a shortened aging time.

physics.ins-det↗