Probing the j dependence of angular distributions and N = 20 shell rigidity via the 36S(p, d) 35S reaction

Abstract

An investigation of the 𝑁=2036S nucleus has been performed through a detailed study of the 36S⁡(𝑝,𝑑)⁢35S neutron-removal reaction, employing a 66-MeV proton beam at iThemba Laboratory for Accelerator Based Sciences and an innovative target design. Using the high-resolution 𝐾 = 600 magnetic spectrometer, 98 states in 35S were identified up to 16-MeV excitation energy, including 47 previously unobserved states. Angular distributions and spectroscopic factors, including isobaric analog-state contributions, were extracted for 81 levels. A pronounced 𝑗 dependence in the angular distributions of ℓ=2 states provide refined insights into the spin-orbit splitting. Finite-range adiabatic distorted-wave approximation calculations qualitatively reproduce the observed 𝑗 dependence. Comparisons of the measured 1⁢𝑑5/2 spectroscopic strength distribution with large-scale shell-model and ab initio calculations show good agreement overall, and the robustness of the 𝑁=20 shell closure in 36S is confirmed when comparing the relatively low 𝑓⁡𝑝 orbital occupancies in 40Ca and 36S across the Fermi surface. This study underscores the utility of neutron-removal reactions in probing nuclear structure and the Fermi surface of 𝑠⁢𝑑 nuclei and beyond. The findings advance our understanding of shell evolution and offer constraining data for theoretical models.