Speaker
Description
The isovector giant dipole resonance (IVGDR) serves as a crucial tool for probing a wide range of phenomena, from r-process nucleosynthesis to the determination of the strength of gravitational waves. Generally, the width of the IVGDR ($\Gamma_G$) increases with temperature ($T$) in the range of 1 MeV $\lesssim T\lesssim 3$ MeV, with the possibility of saturation at higher temperatures [1]. However, in the low-temperature regime (T$\lesssim$ 1 MeV), studying $\Gamma_G$ is particularly challenging due to the difficulty of achieving low excitation energies. Limited investigations in this regime suggest that the behavior of $\Gamma_G$ is ambiguous, influenced by microscopic effects such as shell effects and pairing fluctuations, which hinder the expected thermal broadening of $\Gamma_G$ [2, 3] .
Motivated by these challenges, we conducted a detailed study of $\Gamma_G$ in the low-to-intermediate temperature range for nuclei near the $N=Z=28$ shell closure, where detailed analyses are currently lacking. Our work elucidates the relative importance of neutron-to-proton ratio ($N/Z$), shell closure, and thermal fluctuations in shaping the temperature dependence of $\Gamma_G$ for nuclei near the doubly magic $^{56}$Ni. To isolate these effects, we studied $^{62}$Zn and $^{68}$Zn nuclei, populated via $\alpha$-induced fusion reactions. High-energy $\gamma$-rays ($E_\gamma>$4 MeV) emitted from IVGDR decay were detected using the Large Area Modular $\text{BaF}_2$ Detector Array (LAMBDA) [4]. The measured spectra were analyzed using statistical model calculations implemented in TALYS.
A contrasting thermal behavior of $\Gamma_G$ was observed for the two nuclei. For $^{68}$Zn, the width ($\Gamma_G$) increases monotonically with temperature from its ground-state value. In contrast, $^{62}$Zn exhibited a suppressed width at low temperatures, consistent with the behavior of nearby nuclei with neutron and/or proton numbers close to 28. This suggests that the suppression of $\Gamma_G$ at low temperatures is not a universal feature but is influenced by proximity to magic numbers, rather than $N/Z$ asymmetry.
