Ponente
Descripción
The study of neutron-rich osmium isotopes has revealed a gradual transition from prolate to oblate deformation as neutrons are added. Among the most neutron-rich even-even isotopes where first excited states have been observed, 196Os (N=120) was studied via in-beam gamma-ray spectroscopy following multinucleon transfer reactions [1], while 198Os (N=122) was populated through fragmentation, with its level scheme built from isomeric decay gamma rays [2].
Comparisons with beyond-mean-field calculations suggest a shift from axial rotational behavior in lighter isotopes (e.g., 188Os) to vibrational spectra in heavier ones (e.g., 198Os), passing through gamma-soft or triaxial configurations, as observed in 196Os. The key question now is: what happens near the neutron shell closure at N=126? Will 200Os and 202Os be spherical, or will deformation persist?
To address this, we propose to measure the gamma rays from the first excited states of 200Os and 202Os following the isomeric decay of expected isomers using the new decay spectrometer at RIBF. A crucial aspect will be selecting the most effective fragmentation reaction, either 238U to populate 200Os and 202Os or cold fragmentation of 208Pb.
This experiment will provide critical insights into nuclear shape evolution near N=126, testing shell closure robustness and advancing our understanding of nuclear deformation and collectivity in heavy neutron-rich nuclei.
[1] P.R. John et al., PRC 90, 021301(R) (2014).
[2] Zs. Podolyak et al., PRC 79, 031305(R) (2009).
