High-spin Structure of $^{87}$Sr and $^{87}$Zr Nuclei: Shell-model Interpretation

Abstract

In the present work we report a comprehensive analysis of shell model results for high-spin states of 87 Sr and 87 Zr for recently available experimental data within the full f 5/2 pg 9/2 model space using JUN45 and jj44b effective interactions developed for this model space. In this work we have compared the energy levels, electromagnetic transition probabilities, quadrupole and magnetic moments with available experimental data. We have confirmed structure of high-spin states of these two nuclei which were tentatively assigned in the recent experimental work. In the case of 87 Sr, for positive parity states up to ∼ 7.5 MeV, both interactions predict very good agreement with experimental data, while negative parity states are slightly suppressed in jj44b calculation. For the 87 Zr nucleus, the jj44b interaction predicts higher energies for the negative parity states beyond J ≥ 27/2 − . The configuration, which have one hole in νg 9/2 orbital, is responsible for generating the states in 87 Sr. In the case of 87 Zr, low-lying positive parity states come with the configuration having three holes in the νg 9/2 , while the odd-parity states have configuration ν(f −1 5/2 g −2 9/2 ). PACS numbers: 21.60.Cs, 27.50.+e * pcsrifph@iitr.ac.in Experimental information on low-lying single-particle excited states are available for many nuclei. Because of the advancement in experimental techniques now it is possible to populate high spin states of nuclei beyond Ni. These experimental results are stringent test for the predicting power of shell model for high spin excited states. It is possible to test two-body matrix elements for predicting the high-spin states which are generated by aligning the angular momenta due to broken nucleon pairs. The nuclei in Sr-Zr region show many interesting features, such as spherical shell, isomeric states, candidates of double and neutrinoless double beta decay [1-12].High spin states of 88 Zr have been recently populated up to ∼ 20 and an excitation energy of 10 MeV was measured in 80 Se( 13 C,5n) 88 Zr fusion evaporation reaction [13]. Similarly, the high spin states of 89 Zr were populated using the fusion evaporation reaction 80 Se( 13 C,4n) 89 Zr. The observed high-spin states up to 10 MeV excitation energy and spin ∼ 37/2 are reported in Ref. [14]. The dominance of single-particle excitations is shown for both positive and negative parity states. The high-spin band structure of 85 Sr was populated in the reaction 76 Ge( 13 C,4n) 85 Sr [15]. The spin and parity of different levels up to the spin of ∼ 35/2 and an excitation energy ∼ 7.5 MeV were established. Here shell model explains various features, such as the odd-even staggering, very well. In the case of 86 Sr the high-spin states were populated using 76 Ge( 13 C,3n) 86 Sr reaction. The level scheme up to 10.9 MeV excitation energy and maximum spin of ∼ 19 have been reported in Ref. [16].Experimentally, the high-spin structure of 87 Sr previously was studied in Refs. [17,18].Recently, using the fusion-evaporation reaction 82 Se( 9 Be,4n...