Mar 24 – 25, 2022
Europe/Paris timezone

Measurement of prompt $\gamma$-rays from the neutron capture reaction of Pd isotopes in the eV energy range

Mar 24, 2022, 9:15 AM


Mr Hiromoto Yoshikawa (Osaka University)


In the compound process of neutron-induced nuclear reactions, the parity symmetry (P-violation) is violated due to the effect of the weak interaction. It has been experimentally found that the helicity dependence of the reaction cross section due to the P-violating nucleon-nucleon interaction is enhanced by up to six orders of magnitude compared to the bare effect observed in few-nucleon reactions[1]. This amplification effect has been explained by using a statistical model based on the Random Matrix Theory. In this model, transition matrix element is expected to be inversely proportional to the square-root of the level density $N$. The accuracy of the existing experimental data of $W$, however, are not sufficient to verify the model, and thus more accurate data are demanded. $W$ is related to the asymmety ${A_{\rm L}}$ of the helicity-dependent reaction cross section as the following equation;

$A_L \approx -\frac{2xW}{E_{\rm p}-E_{\rm s}}\sqrt{\frac{\Gamma^{\rm n}_{\rm s}}{\Gamma^{\rm n}_{\rm p}}}\hspace{1cm} \left(x\equiv\sqrt{\frac{\Gamma^{\rm n}_{\rm p,j=1/2}}{\Gamma^{\rm n}_{\rm p}}}\right),\hspace{3cm} (1)$

where ${E_{\rm s}}$ and ${E_{\rm p}}$ are the resonance energies of the s-wave and the p-wave resonances, respectively. ${\Gamma^{\rm n}_{\rm s}}$ and ${\Gamma^{\rm n}_{\rm p}}$ are the corresponding neutron widths, respectively. $x$ is the ratio of the partial p-wave neutron width to the total neutron width, it can be determined by measuring the angular dependence of the emitted $\gamma$-rays of the (n,$\gamma$) reaction [2]. Therefore, by measuring ${A_{\rm L}}$ and $x$, one can determine $W$ experimentally from Eq. (1).

In this study, we focus on Pd isotopes which have relatively small values of $N$, and consequently $N$ dependences of $W$ are rather significant. To obtain $x$, the angular distributions of the prompt $\gamma$-rays from the p-wave resonance of the Pd isotopes were measured at the J-PARC MLF BL04 in February 2021. As a preliminary result, the following values of $x$ were obtained for $^{108}$Pd;

$x = 0.9986^{+0.0003}_{-0.0099}\hspace{1cm}{\rm or}\hspace{1cm}x = -0.9986^{+0.0099}_{-0.0003}.\hspace{2cm} (2)$

In this contribution, the experimental procedure and the result will be presented.

[1] G. E. Mitchell et al., Phys. Rep. 354, 157 (2001).

[2] V. V. Flambaum et al., Nucl. Phys. A 435, 352 (1985).

Primary authors

Mr Hiromoto Yoshikawa (Osaka University) Mr Ryota Abe (Nagoya University) Mr Kohei Ishizaki (Nagoya University) Mr Yuki Ito (Nagoya University) Mr Shunsuke Endo (JAEA) Dr Takuya Okudaira (Nagoya University) Mr Kento Kameda (Tokyo Institute of Technology) Dr Masaaki Kitaguchi (Nagoya University) Dr Atsushi Kimura (JAEA) Dr Kenji Sakai (JAEA) Dr Tatsushi Shima (Osaka University) Prof. Hirohiko Shimizu (Nagoya University) Mr Shusuke Takada (Kyushu University) Mr Asuka Nakai (Osaka University) Dr Katsuya Hirota (KEK) Mr Takuhiro Fujiie (Nagoya University) Dr Hiroyuki Fujioka (Tokyo Institute of Technology) Dr Tamaki Yoshioka (Kyushu University)

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