Single-particle and collective motions from nuclear many-body correlation (PCM2025)

Measurements of Isomer Ratio for 12Be beams and Precise Branching Ratio and Half-Life

5 Mar 2025, 15:30

1m

Main Lecture Hall (University of Aizu)

Poster session

Speaker

Ryo Taguchi (Osaka University)

Description

The study of isomeric states in nuclei is crucial for understanding the nuclear structure, as these states often exhibit structures significantly different from their ground states. The neutron-rich nucleus ${}^{12}$Be has an isomeric $0_2^{+}$ at $E_x=2.3$ MeV with a half-life of 230 ns (see level diagram in the upper right of Fig. 1). This state undergoes deexcitation via an E2 transition through an intermediate $2_1^{+}$ state or via an E0 transition directly to the $0_1^{+}$ ground state, accompanied by positron annihilation $\gamma$-rays produced through E0 internal pair production.
Previous studies$[1,2]$ have indirectly suggested that the isomeric state in ${}^{12}$Be exhibits a large nuclear radius based on $\gamma$-ray measurements. However, it is still an open problem due to the uncertainties of that discussion. Thus, we propose a direct measurement of the radius of the isomeric state in ${}^{12}$Be via its interaction cross section. Since producing a pure beam of isomeric ${}^{12}$Be is challenging, we aim to measure interaction cross sections using beams with different isomer ratios, where the isomer ratio represents the fraction of isomeric nuclei within the beam.
In this study, ${}^{12}$Be beams were produced at the HIMAC synchrotron facility through the projectile fragmentation of ${}^{13}$C and ${}^{18}$O beams on Be or Al targets at 250 MeV/nucleon. The isomer ratios of the ${}^{12}$Be beams were measured, and the branching ratio and the half-life of the isomeric state were determined with high precision by analyzing delayed $\gamma$-rays emitted from stopped ${}^{12}$Be. The time spectrum of these delayed $\gamma$-rays is shown in Fig. 1. The results of these measurements will be presented and the dependence of the isomer ratio on beam conditions will be discussed.

Reference
$[1]$ S. Shimoura et al., Phys. Lett. B. 654, 87 (2007).
$[2]$ I. Hamamoto and S. Shimoura, J. Phys. G: Nucl. Part. Phys. 34, 2715 (2007).

Presentation materials

poster - 田口諒.pdf