Thick-target inverse-kinematics proton scattering fromAr46and theN=28shell below

L. A. Riley

¹

,

M. A. Abdelqader

²

,

D. Bazin

³

et al.

Abstract

Low-lying excited states of 46 Ar have been studied via inverse-kinematics proton scattering with a thick target. Coupled-channels calculations have been used to extract the deformation length of the 2 + 1 state. This result, combined with existing Coulomb excitation data, yields a ratio of the neutron-to-proton transition matrix elements of M n /M p = 1.19(25)N/Z, showing a departure from the proton dominance observed in the N = 28 isotones above 48 Ca. The status of the N = 28 shell below 48 Ca is discussed.

Shell-model study for neutron-richsd-shell nuclei

“…Figure 7 shows the first excited 2 + energies as a function of neutron number for the Ca, Ar, S, and Si isotopes. The EPQQM calculations agree well with the known experimental data, except for 34 Si and 44 S. The SDPF-NR calculations also agree with the data for the Ca and Ar isotopes but cannot reproduce those of the Si isotopes. The calculated first excited 2 + states lie higher than experimental results show.…”

“…Moreover, considerable differences between the EPQQM and SDPF-NR (and also SDPF-U, SDPF-U1) can be seen around the neutron number N = 34, where no experimental data are currently available to discriminate the predictions. We note that none of the interactions can reproduce the first excited 2 + energy level of 34 Si with N = 20. This suggests that it would be necessary to include the neutron excitations from the sd shell to the pf shell across the N = 20 energy gap.…”

“…9. (Color online) Experimental and calculated energy levels for even-even argon isotopes [24,31,33,34]. The left (black) and right (red) bars denote the experimental and calculated energy levels, respectively.…”

Coulomb excitation ofCa44andAr46

“…This ratio has been derived for the 36,40,42,44 Ar nuclei by Khan et al [50] and for the 46 Ar nucleus by Riley et al [51]. Adding the information on the B(E2) values, the neutron transition matrix elements M n have been deduced.…”

Low-lying2+states generated bypn-quadrupole correlation andN=28shell quenching

“…One of the interesting examples is the N = 28 shell gap which is known to be quenched in the vicinity of 44 S and which has been given considerable experimental [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and theoretical attention [22][23][24][25][26][27][28][29][30][31][32]. Since the the orbital angular momenta of f 7/2 and p 3/2 differ by two, the quench of the N = 28 shell gap will lead to the strong quadrupole correlation of neutrons.…”