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Description
Nuclei near the doubly magic nucleus $^{100}$Sn (N = Z = 50) have been extensively studied to investigate nuclear structure, including shell evolution, seniority effects, and proton–neutron interactions. In this work, $^{94}$Pd with N = Z + 2 was investigated with a focus on isovector (T = 1) and isoscalar (T = 0) neutron-proton pairing using the fast-timing measurement. Half-lives of yrast excited states in $^{94}$Pd were measured using isomeric decay spectroscopy.
The experiment was performed at RIBF (Radioactive Isotope Beam Factory), RIKEN, where $^{94}$Pd ions were produced via in-flight fragmentation of a $^{124}$Xe beam impinging on a $^{9}$Be target. These ions were implanted into the GARi active stopper array, and isomeric delayed $\gamma$-rays were detected with the IDATEN fast-timing array consisting of 48 LaBr$_3$(Ce) detectors. The half-lives were determined using the generalized centroid difference method, yielding the T$_{1/2}$ values of $\leq$ 15 ps, 13(11) ps, $\leq$ 13ps, 693(72) ps, and $\leq$ 19 ps for the (2$_1^+$), (4$_1^+$), (6$_1^+$), (8$_1^+$), and (10$_1^+$) states, respectively. The half-lives of the (2$_1^+$), (4$_1^+$) and (10$_1^+$) states are reported here for the first time, and the uncertainties of the half-lives of the (6$_1^+$) and (8$_1^+$) states have been improved compared to previous measurements.
Reduced transition probabilities B(E2) were deduced from the measured half-lives and discussed in the context of shell-model calculations employing the JUN45 effective interaction, including T = 0, T = 1 and full interaction. The results suggest that $^{94}$Pd, with N = Z + 2, lies in a transitional regime between the N = Z isoscalar-pairing domain $^{92}$Pd and the N = 50 isovector-dominated region ($^{96}$Pd).