Graduate Student Seminar with Nicolas Dronchi on Breakdown of the Z=20 Shell Gap Closure in 36/38Ca

In a pair of experiments, the B(E2; 0⁺_g.s –>2⁺₁) was measured for ³⁶Ca. The first experiment measured a cross section for the Coulomb excitation of a ³⁶Ca beam where only gamma decays were detected. The second experiment measured the p/g branching ratio required as a correction to this cross section because the 2⁺₁ state of ³⁶Ca is above the proton separation energy. The corrected B(E2) was measured to be 130(20) e²fm⁴ and the proton branching ratio was measured to be 0.087(8). These B(E2) and branching-ratio values can be reproduced in the shell-model with the ZMB2 interaction, an interaction that predicts the Z = 20 shell closure is incomplete with large proton pf -shell occupancies in the ground state. These occupancies are at odds with other shell-model and energy-density-functional calculations of ³⁶Ca. The new data are used to provide an update on the determination of the slope of the symmetry energy with density L using the charge radii of the 36Ca/36S mirror pair as well as help reduce uncertainties of an rp-process waiting point.