Speaker
Description
High-spin nuclear isomers in rare unstable beams are important for studies in nuclear structure, nuclear astrophysics, and applied research. While fragmentation reactions, widely used at in-flight rare-isotope beam facilities, can produce a diverse range of nuclides, the selective and high-intensity production and separation of specific isomer states remain challenging. This study aimed to experimentally investigate the correlation between parallel momentum transfer and angular momentum transfer in fragmentation reactions, contributing to the development of selective beam production techniques for isomer states.
We focused particularly on previous studies [1] that showed an increase in the isomer ratio by selecting the tail of the fragment momentum distribution, with the goal of clarifying its physical origin. In this research, we investigated the correlation between angular momentum and parallel momentum transfer by selecting events from high-spin isomer states and comparing their momentum distributions with those of events primarily in the ground state.
The experiment was conducted at the SB2 beamline of the High-Energy Heavy-Ion Accelerator Facility (HIMAC). Primary beams of $^{58}$Ni and $^{59}$Co accelerated to 350 MeV/u irradiated a 14 mm thick $^{9}$Be target to produce nuclides around $^{52}$Fe through fragmentation reactions. The produced fragments were separated by a fragment
separator (two dipole magnets) and identified using the time-of-flight (ToF), energy loss($\Delta$E), and magnetic rigidity (B$\rho$) method. Among the identified nuclides, de-excitation gamma rays from high-spin isomers $^{52m}$Fe(12$^+$), $^{53m}$Fe(19/2$^-$) and $^{54m}$Co(7$^+$) were measured using four Ge detectors placed at the end of the
flight path with the particle identification.
As a result of the analysis, a clear tendency was observed for the relative production of high-spin isomers to increase in the region of large momentum transfer away from the center of the fragment momentum distribution (the tail of the distribution), consistent with previous studies [2][3]. Furthermore, by comparing the measured properties of multiple isomer states, a clear positive correlation was found between the magnitude of the imparted angular momentum and the parallel momentum transfer.
In this presentation, we will report these experimental results in detail and discuss the current understanding of the angular momentum generation mechanism in fragmentation reactions and its potential application to the production of high-purity, high-intensity isomer beams.
[1] Schmidt-Ott, et al., Zeitschrift für Physik 350 215-219 (1994)
[2] Daugas, J. M. et al., Phys. Rev. C 63 064609 (2001)
[3] M. Notani et al., Phys. Rev. C 76 044605 (2007)
| Email address | kkawata@rcnp.osaka-u.ac.jp |
|---|---|
| Supervisor's Name | Yako Kentaro |
| Supervisor's email | yako@cns.s.u-tokyo.ac.jp |
| Classification | Isotope production, target, and ion source techniques |
