Effective Charges in thefpShell

Abstract

Following the heavy-ion fusion-evaporation reaction 32S+24Mg at 95 MeV beam energy the lifetimes of analogue states in the T(z)=+/-1/2 A=51 mirror nuclei 51Fe and 51Mn have been measured using the Cologne plunger device coupled to the GASP gamma-ray spectrometer. The deduced B(E2;27/2(-)-->23/2(-)) values afford a unique opportunity to probe isoscalar and isovector polarization charges and to derive effective proton and neutron charges, epsilon(p) and epsilon(n), in the fp shell. A comparison between the experimental results and several different large-scale shell-model calculations yields epsilon(p) approximately 1.15e and epsilon(n) approximately 0.80e.

Thick-target inverse-kinematics proton scattering fromAr46and theN=28shell belowRiley1, Abdelqader2, Bazin3 et al. 2005Phys. Rev. C

“…The former set is the standard isoscalar choice that can be related to the mixing of the isoscalar giant quadrupole resonance into the model-space wave functions. The latter set contains a significant isovector component related to mixing with the isovector giant quadrupole resonance [49] and is close to that suggested from a recent study of mirror nuclei in the pf shell [50].…”

“…→ 2 + 1 excitation of 46 Ar and combine our result with the most recent Coulomb excitation result [13] to obtain M n /M p . A variety of measurements have yielded M n /M p < N/Z for the 2 + 1 states of 50 Ti, 52 Cr, and 54 Fe, the stable even-even N = 28 isotones above 48 Ca [16,17]. However, our result of M n /M p = 1.19(25)N/Z for the 2 + 1 state of 46 Ar indicates a greater neutron contribution to the excitation.…”

“…The choice e p = 1.2e and e n = 0.8e clearly leads to a better description of the ratio of the matrix elements. However, the comparison of experimental and theoretical B(E2 ↑) values reveals striking discrepancies for 46 Ar and 50 Ti (see Fig. 5) pointing to deficiencies of the present effective interactions which are most apparent in the structure of the two N = 28 isotones just two protons outside doubly magic 48 Ca.…”

“…The 2 + 1 energies show a dramatic increase in the doubly magic nucleus 48 Ca flanked by a smaller, relatively uniform increase in the other N = 28 isotones, as expected based on the shell closures at Z = 20 and N = 28. The E 3 − 1 energies in 48 Ca, 50 Ti, and 52 Cr fall within a very narrow range centered at about 4500 keV, with no distinguishing increase at Z = 20. This can be explained in terms of the details of the shell structure.…”

Coulomb Excitation ofSn104and the Strength of theSn100Shell Closure

“…A common polarization charge of 0:5e for protons and neutrons was used. The recently discussed [35][36][37][38][39] isovector dependence of E2 polarization charges due to coupling to the giant quadrupole resonance outside the model space will lead to at most a marginal increase of BðE2Þ values since at N $ Z the isoscalar part dominates. However, the agreement with the global 100-132 Sn trend, i.e., the asymmetry with respect to the middle of the N ¼ 50-82 neutron shell [9][10][11], is improved by this effect.…”