The deformed 0⁺state in³⁴Si

Abstract

Abstract. The energy of the lowest deformed 2-particle 2-hole (2p2h) 0 + state in even-even N = 20 nuclei is a key observable directly related to the size of the neutron N = 20 shell closure. 34 Si, with 14 protons and 20 neutrons, lies at the boundary of the "island of inversion", where the deformed 2p2h 0 + state is the ground state in even-A nuclei. In 34 Si, the 2p2h 0 + state is expected to be particularly low lying -in some theories it is even predicted to lie below the first 2 + state. While there have been a number of attempts, using various techniques, no experiment to date has been able to firmly locate the 34 Si 2p2h 0 + state although a number of candidates have been suggested. Here we present, for the first time, data obtained from a fusion-evaporation reaction 18 O( 18 O, 2p) to produce 34 Si. Gammasphere and Microball were used to detect γ-γ coincidences and charged particles (two protons), respectively. The increased sensitivity of this experiment using γ-γ coincidences and a high charged-particle detection efficiency helped to exclude previously reported candidates and provided a stringent limit on the anticipated γ decay from the first 2 + state to the 2p2h 0 + state.

β-decay study of neutron-rich nucleus 34Al

“…Due to the combination of high γ-detection efficiency and a low back ground level, a γ line at 1193 keV was found to be coincident with the 3326-keV ray (Figure 4(b)). This 1193-keV line has been reported in several previous experiments [25][26][27][28][29][30], and based on the observed coincidence between the 1193-and 3326-keV transitions, a 4519-keV level was established [26,28,29]. However, in the previous studies, no spin-parity was assigned to this 4519-keV level.…”

“…The coincidence between the 1193-and 3326-keV transitions as well as the observation of the 1800-keV de-excited γ-ray transition from the 4519-keV state to the 0 2 + state at 2719 keV in the present work further confirm the measurements reported in refs. [26,28,29].…”

Level structure of the double-shell closure system with Z = 14 and N = 20: 34Si*

“…The levels at 4379 and 4969 keV were tentatively assigned (3 -, 4 -, 5 -) on the basis of logft values [4]. The 4519 keV level was also observed in β-decay measurements [4,8]. Conversely, the levels at 4920 and 6233 keV were observed only in a fusion-evap-oration reaction, 18 O ( 18 O, 2p) 34 Si [5].…”

“…The 2 + and 3 states were firstly identified through the β-decay of 34 Al [2−4]. The levels at 4379 and 4969 keV were tentatively assigned (3 -, 4 -, 5 -) on the basis of logft values [4]. The 4519 keV level was also observed in β-decay measurements [4,8].…”

Structure of Si33 and the magicity of the N=20 gap at Z=14Jongile1, Lemasson2, Sorlin3 et al. 2020Phys. Rev. C10030View full textAdd to dashboardCite

“…For example, the nearby 34 Al nucleus has ground and intruder configurations separated by only 46.6 keV [9]. It follows that deformed configurations, shape coexistence [6,10], and possibly triaxial shapes were predicted [11] and searched for [6,12,13] in the properties of the first few excited states of 34 Si. The abrupt transition from the closed-shell ground state of 34 Si to the intruder-dominated ground state of 32 Mg [14][15][16], with only two protons removed from the 0d 5/2 orbit, is attributed to the subtle balance between the magnitude of the proton and neutron shell gaps that prevent nuclear excitations and the pairing and quadrupole correlations that scale with the amount of particle-hole excitations across these gaps.…”