Speaker
Description
Understanding the global Z-N-dependence of the γ strength functions (γsf) is important for reliably predicting reaction rates in astrophysical and technical applications. For this reason, the Notre Dame-HZDR-Kashmir collaboration has calculated the M1 and E2 γsf for extended series of the Sn, Ge, Gd and Sm isotopes using the conventional spherical shell model (SSM) and, as a new tool, the triaxial projected shell model (TPSM). The appearance of the strong enhancement of the M1 γsf (low energy magnetic radiation-LEMAR) is demonstrated for the semi magic isotope chain $_{~~~~~~~~~~50}^{106-130}$Sn. The SSM calculations for $_{~~~~~~~32}^{64-80}$Ge show the LEMAR spike for all cases, except for $_{32}^{64}$Ge, where isospin conservation suppresses it. Approaching the midshell region the bimodal structure of the LEMAR spike and a bump around 3 MeV, interpreted as the scissors resonance (SR), develops, which disappears again toward the shell closure. The calculated E2 γsf and $B(E2,2_1^+\rightarrow 0_1^+)$ values indicate that the bimodal structure appears as a consequence of quadrupole deformation, which reaffirms the results for the Fe and Sm isotopes found by the collaboration before [1,2]. The TPSM calculations for $_{~~~~~~~~~~64}^{154-164}$Gd demonstrate the transition from the monomodal LEMAR spike for the transitional N=90 isotope to the bimodal LEMAR+SR profile for the well deformed N=100 isotope. The TPSM calculations for the odd-A Sm isotopes provide analogue results.
The number of studied examples suggests that the LEMAR spike is commonly ![enter image description here][1]present, except special conditions like isospin conservation in N=Z nuclei suppress it. Deformation causes a partial shift of the M1 strength from the LEMAR to the SR. Possible interpretations of the nature of LEMAR will be discussed.
[1] R. Schwengner et al., Phys. Rev. Lett. 118, 092502 (2017)
[2] F. Naqvi et al., Phys. Rev. C 99, 054331 (2019)
| Contribution category | Theory |
|---|---|
| Presenter status | Faculty/Staff |