Coulomb excitation of the even-mass selenium nuclei

Abstract

The properties of the low-lying states of the doubly even selenium nuclei have been investigated via multiple Coulomb excitation effected with 39.2 MeV oxygen projectiles. The excitation probabilities of the first 2 + states of 76Se, 78Se and 80Se have been determined directly by resolving inelastically and elastically scattered 4He projectiles on thin targets. These measurements yielded values of B(E2; 0 + → 2 +) equal to 0.421 ± 0.009 ( 76 Se), 0.321 ± 0.009 ( 78 Se) and 0.248 ± 0.005 ( 80 Se) e 2 · b 2 . The multiple Coulomb excitation experiments enabled us to detect 2 + and 4 + levels in all isotopes studied up to 2.1 MeV. Moreover the double Coulomb excitation of 0 +' states at 854.1 keV ( 74Se), 1498.5 keV ( 78Se), and 1478.3 keV ( 80Se) was also observed. The enhancement of the E2 transition between these 0 +' levels and the first 2 + states decreases rapidly with the increase of the neutron number, i.e., B( E2; 0 +′ → 2 +)/B( E2; 2 + → 0 +) = 2.04 ± 0.08 ( 74 Se), 0.91 ± 0.08 ( 78Se), and 0.28 ± 0.04 ( 80 Se) . States interpreted as the result of direct E3 Coulomb excitation have been observed at 2350.2, 2429.2, 2507.6, and 2717.6 keV in 74Se, 76Se, 78Se and 80Se, respectively. Their B(E3; 0 + → 3 −) values are 2.1 ± 0.5 ( 74 Se), 4.0 ± 0.5 ( 76 Se), 2.7±0.3 ( 78 Se) and 0.9 ± 0.2 ( × 10 −2 e 2 · b 3 which represent enhancements of 9.2 ± 2.2, 16.6 ± 2.1, 10.8 ± 1.2 and 3.2 ± 0.7 respectively. Furthermore, angular distribution measurements of γ-rays following Coulomb excitation with 42 MeV 16O ions in 78Se and 80Se have been performed. The E2 content of the 2 +' → 2 + transition in these two nuclei is 87.9 % ( 78Se), and 96.2 % or 33.5 % ( 80Se).