Lowest Excitations inTi56and the PredictedN=34Shell Closure

Abstract

Recent experimental characterization of the subshell closure at N=32 in the Ca, Ti, and Cr isotones has stimulated shell-model calculations that indicated the possibility that the N=34 isotones of these same elements could exhibit characteristics of a shell closure, namely, a high energy for the first excited 2(+) level. To that end, we have studied the decay of 56Sc produced in fragmentation reactions and identified new gamma rays in the daughter N=34 isotone 56Ti. The first 2(+) level is found at an energy of 1127 keV, well below the expected position that would indicate the presence of an N=34 shell closure in 56Ti.

Single-particle and collective structures inCr55andV55Deacon1, Steppenbeck2, Zhu3 et al. 2011Phys. Rev. CSelf Cite11120View full textAdd to dashboardCite

“…The neutron-rich f p-shell nuclei, bounded by 20 ≤ Z ≤ 28 and 28 ≤ N ≤ 40, represent one region of the nuclear chart where significant developments have occured recently. For example, experimental evidence points to the opening of a new shell gap at N = 32 in neutron-rich nuclei close to Ca; systematics of E(2 + 1 ) values beyond N = 28 [1][2][3][4][5][6][7] show a sharp rise at N = 32 associated with a relatively large p 3/2 −p 1/2 separation. This effect weakens for nuclei with increasing Z as movements of the neutron f 5/2 orbital, due to increasing interactions with f 7/2 protons, effectively destroy the gap The theoretical understanding of shell evolution has progressed in a number of ways, and includes the development of new effective interactions for shell-model calculations within large extended model spaces.…”

“…GXPF1 calculations also predict an additional shell gap to arise at N = 34; experimental evidence for this effect, however, remains elusive. The lack of an observed gap between the νp 1/2 and νf 5/2 orbitals [5,6,11] and measurements of the B(E2; 0 + g.s. → 2 + 1 ) transition rate in 56 Ti [7] suggest that a substantial sub-shell closure does not persist above Z = 20.…”

“…These observations prompted modifications resulting in a more refined interaction, GXPF1A [12], where the effective single-particle energies of the νf 5/2 and νp 3/2 states are closer and in which five T = 1 matrix elements of the interaction are adjusted. This led to significant im-provements in the predictive power of the calculations; the value of E(2 + 1 ) in 56 Ti, for example, is reduced to give much better agreement with experiment than was the case with the GXPF1 interaction, and a consistent description of the structure of all the neutron-rich Ti isotopes [5,10,11,13] is achieved. More recently, further modifications to the GXPF1 family of interactions [14] have produced closer fits to experimental data on 51−53 Ca [15].…”

Computational nuclear quantum many-body problem: The UNEDF project

“…For this reason, studies on the evolution of structure in neutron-rich semi-magic isotopes of oxygen, calcium, nickel, and tin are central to experimental and theoretical efforts. With 40,48 Ca being doubly magic nuclei, many studies were aimed at understanding the structure of the rare isotopes 52,54 Ca and questions regarding the N = 32, 34 shell closures [50,51,52,53,54].…”

Magnetic rotation and quasicollective structures in58Fe: Influence of theνg9/2orbital

“…Another important manifestation of the GXPF1 Hamiltonian is the prediction of a significant subshell closure at N = 34 along the Ti and Ca isotopic chains; however, this was not verified by experiment in the case of 56 Ti [6,11]. The interaction was modified as a result, leading to a new version, GXPF1A [12], by changing the strength of five T = 1 matrix elements mainly associated with the νp 1/2 orbital.…”