Beta decay of the new isotopesK52,Ca

Abstract

The nuclides ' K, Ca, and ' Sc have been produced by fragmentation of a uranium target with a 600 MeV proton beam. The subsequent P decays to the daughter nuclei '2Ca, ' Sc, and ' Ti have been studied by neutron and y spectroscopy on sources obtained from on-line mass separation. P decay energies have been determined by P-y coincidence spectroscopy. In addition to the short halflife of K (Tl&2 --110+30 ms), we attributed two different half-lives (Tlq2 --4.6+0.3 s and Tl~2 --8.2+0.2 s) to ' Ca and ' Sc, respectively. A decay scheme has been established for ' K involving five P branches to delayed neutron emitting states between 6.6 and 10.3 MeV and one P branch to a bound level at E"=2.56 MeV. The ' Ca decay scheme accounts for 13 branches to four levels at 1.64, 2.75, 3.46, and 4.27 MeV for which the deduced logft values restrict the angular momentum and parity to J =1+. For the "Sc ground state, strong P transitions to the 2+ (1.05 MeV) and the (4+) (2.32 MeV) levels in '2Ti strongly favor a J =3+ attribution. The measured gp values for the Ca (5.7+0.2 MeV) and Sc (8.02+0.25 MeV) decay are noticeably lower than expected from mass systematics. The energy level diagrams of ' Ca, Sc, and ' Ti nuclei have been calculated in the framework of the shell model with a realistic interaction. Good agreement between theory and experiment is achieved as well for excitation energies as for mass excesses, assuring then the applicability of the theory to this region of nuclei far from stability.

Cross-shell excitation in two-proton knockout: Structure ofCa52

“…These observations can be reproduced qualitatively by calculations which assign the 3 − level to the promotion of protons across the Z = 20 shell gap. In addition, the data confirm the presence of a neutron sub-shell closure at N = 32, the subject of much recent attention [8,9,10,11,12,13].…”

“…These observations can be reproduced qualitatively by calculations which assign the 3 − level to the promotion of protons across the Z = 20 shell gap. In addition, the data confirm the presence of a neutron sub-shell closure at N = 32, the subject of much recent attention [8,9,10,11,12,13].The 54 Ti secondary ions were produced by fragmentation of a 130 MeV/nucleon 76 Ge beam, delivered by the Coupled Cyclotron Facility of the National Superconducting Cyclotron Laboratory, onto a 9 Be fragmentation target. The ions were selected in the A1900 largeacceptance fragment separator [14], which was operated with two settings during different phases of the experiment; 1% momentum acceptance and no momentum restriction, respectively.…”

Shell model study of the isobaric chains A=50, A=51 and A=52

“…It is important to remark that, for the nuclei already studied with KB3, KB3G produces equivalent results. In the case of FPD6, the gaps are nearly correct and the monopole defects amount to having the 1f 5/2 orbit too low and the 2p 1/2 orbit too high, both in 49 Ca and 57 Ni. The modifications that repair that are:…”

“…Both interactions use very similar single particle energies; ǫ 7/2 =0.0 MeV, ǫ 3/2 =2.0 MeV, ǫ 1/2 =4.0 MeV and ǫ 5/2 =6.5 MeV for KB3 and ǫ 7/2 =0.0 MeV, ǫ 3/2 =1.89 MeV, ǫ 1/2 =3.91 MeV and ǫ 5/2 =6.49 MeV for FPD6. The two body matrix elements Notice that KB3 does definitely better than FPD6 for the single particle spectra of 49 Ca and 57 Ni, while for the 56 Ni gap, FPD6 is better.…”

Tracking changes in shell structure in neutron-rich nuclei as a function of spin

“…This effort was prompted primarily by the observation of an N = 32 subshell closure in 52 Ca [17], 54 Ti [18], and 56 Cr [19], which has been inferred from mounting experimental evidence such as systematic variations in E(2 + 1 ) energies and B(E2) values in the even-even Ca, Ti and Cr isotopes [20]. The two physical quantities are found to be anti-correlated; while the E(2 + 1 ) energies increase significantly at N = 32, the B(E2) strengths are lowest.…”