Giant quadrupole resonances within neutron-induced α-particle emission?

The particular conditions for the recent measurement of 91 Zr ( n , α ) 88 Sr reaction cross sections at incident energies below 5.3 MeV [Phys. Rev. C 106 , 064602 (2022)] as well as a previous detailed analysis of other reaction channels involving neutrons incident on 91 Zr, using a consistent set of model parameters, have two main advantages. First, the close agreement between the calculated and experimentally obtained data for the incident energy associated mainly with the ground-state activation provides strong support for the α -particle optical potential involved in this analysis. Second, a further underestimation of the cross section is observed around the energy corresponding to the isoscalar giant quadrupole resonance (ISGQR), beyond any model parameter uncertainty. This underestimation is consistent with previous observations of ISGQR- like α -particle decay of excited nuclei for neutron-induced reactions in the mass range 54≤ A ≤98. To phenomenologically identify the ISGQR- like behavior, a comparison is made between their strengths and the ISGQR strengths measured through the ( γ , α ) reaction and inelastic scattering of 3 He and α -particles. Additionally, an isotope effect, possibly related to the decrease in Q -value with the target-nuclei asymmetry parameter, supports the observation of a low energy-weighted sum rule (EWSR) fraction for the ISGQR- like strength function in the excited nucleus 92 Zr.