Speaker
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).
| Type of contribution | poster |
|---|---|
| Are you a student or postdoc? | yes |
