Scissors modes and spin excitations in light nuclei including △N = 2 excitations: Behaviour of 8Be and 10Be

M. S. Fayache, S. Shelley Sharma, L. Zamick

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Abstract

Shell model calculations are performed for magnetic dipole excitations in 8Be and 10Be, first with a quadrupole-quadrupole interaction (Q • Q) and then with a realistic interaction. The calculations are performed both in a 0p space and in a large space which includes all 2ℏω excitations. In the 0p with Q • Q we have an analytic expression for the energies of all states. In this limit we find that in 10Be the L = 1 S = 0 scissors mode with isospin T= 1 is degenerate with that of T = 2. By projection from an intrinsic state we can obtain simple expressions for B(M1) to the scissors modes in 8Be and 10Be. We plot cumulative sums for energy-weighted isovector orbital transitions from J = 0+ ground states to the 1+ excited states. These have the structure of a low-energy plateau and a steep rise to a high-energy plateau. The relative magnitudes of these plateaux are discussed. By comparing 8Be and 10Be we find that contrary to the behaviour in heavy deformed nuclei, B(M1)orbital is not proportional to B(E2). On the other hand, a sum rule which relates B(M1) to the difference (B(E2)isoscalar - B(E2)isovector) succeeds in describing the difference in behaviours in the two nuclei. The results for Q • Q and the realistic interactions are compared, as are the results in the 0p space and the large (0p + 2ℏω) space. The Wigner supermultiplet scheme is a very useful guide in analyzing the Shell model results.

Original languageEnglish (US)
Pages (from-to)123-154
Number of pages32
JournalAnnals of Physics
Volume251
Issue number1
DOIs
StatePublished - Oct 10 1996

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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