Recoil-βtagging study of theN=Znucleus66As

Abstract

An in-beam study has been performed to further investigate the known isomeric decays and to identify T = 1 excited states in the medium-heavy N = Z = 33 nucleus 66 As. The fusion-evaporation reaction 40 Ca( 28 Si,pn) 66 As was employed at beam energies of 75 and 83 MeV. The half-lives and ordering of two known isomeric states in 66 As have been determined with improved accuracy. In addition, several prompt γ -ray transitions from excited states, both bypassing and decaying to the isomeric states in 66 As, have been observed. Most importantly, candidates for the 4 + → 2 + and 6 + → 4 + transitions in the T = 1 band have been identified. The results are compared with shell-model calculations using the modern JUN45 interaction in the pf 5/2 g 9/2 model space.alignment of the valence nucleons [5], shape changes as a function of spin [6], and the evolution of nuclear radii along the yrast line [7].Two isomeric states have been previously identified in 66 As [8]. In more recent studies, the decay of the isomers was used as a tag to identify excited states above the isomeric states [9] and new prompt γ rays were associated with 66 As, without the ability to observe delayed transitions, in Ref.[10]. In the current work, both the isomeric and the prompt T = 0 and T = 1 structures have been studied. The half-lives and ordering of the isomeric states have been determined with improved accuracy and internal conversion coefficients have been deduced for the transitions deexciting the isomers, allowing the determination of the corresponding experimental B(E2) transition strengths. Recent experimental [10] and theoretical [11] work has investigated the CED in the A = 66 ( 66 As/ 66 Ge) and A = 70 ( 70 Br/ 70 Se) systems. The present work agrees with some of the findings reported in Ref.[10], but differs for the T = 1, I π = 6 + state resulting in a positive CED behavior.The odd-odd N = Z nuclei in the mass A ∼ 60-70 region provide an opportunity to test shell-model (SM) interactions and model spaces for these midmass nuclei. In the present work SM calculations have been performed using the modern JUN45 interaction [12] and a pf 5/2 g 9/2 model space. The experimental results are compared with the SM predictions in terms of level energies, CED, and B(E2) values.

Spectroscopy of Kr70 and isospin symmetry in the T=1 fpg shell nuclei

“…13 in Ref. [12]. The normal, positive, trend in the behavior of the CED as a function of spin has previously been attributed to Coriolis antipairing effects [13].…”

“…This technique has been successfully employed to study several other nuclei in the region, see [12,15,17,18,23].…”

Spectroscopy of proton-rich66Se up toJπ=6+: Isospin-breaking effect in theRuotsalainen1, Jenkins2, Bentley3 et al. 2013Phys. Rev. CSelf Cite

“…The γ rays detected in the focal plane germanium detectors in delayed coincidence with a recoil implantation or in prompt coincidence with β decay can be utilized as an additional veto, in a similar manner to the charged particles. The β decay of 65 Ga feeds excited states in 65 Zn, which are deexcited by various γ rays, as are the isomeric structures in 66 As [15]. After the final focal plane veto only three γ rays remain, as can be seen in Fig.…”

“…This technique, entitled recoil-β tagging (RBT), is suitable for studying exotic proton-rich nuclei and was first demonstrated for 74 Rb [13] at the University of Jyväskylä (JYFL). This initial work has been extended at JYFL to the previously unknown case of 78 Y [14] and recently provided additional information on excited states in 66 As [15]. To reach the most exotic nuclei on the proton-rich side of the N = Z line in fusion-evaporation reactions, the experimental sensitivity needs to be increased further.…”

“…(b) Same as (a) but for the MEDs. Data are taken from the present work and from Refs [5,6,15,26,[29][30][31][32][33][34][35][36][37]…”