B. Pritychenko

Role of intruder configurations in 26,28Ne and 30,32Mg

Abstract The energies and reduced transition probabilities B(E2;0g.s.+→2+) for the lowest Jπ=2+ excited states in the neutron-rich radioactive isotopes 26,28 Ne and 30,32 Mg were measured via intermediate energy Coulomb excitation. The data suggest that the interaction between coexisting 0ℏω (normal) and 2ℏω (intruder) configurations significantly perturbs the energy of the 21+ state in 28 Ne, while the data on 26 Ne and 30 Mg can be well understood in the context of 0ℏω configurations alone. Nilsson model calculations suggest that if these nuclei have static axially symmetric deformations, they are prolate.

Spectroscopy of the 21+ state in 22O and shell structure near the neutron drip line

Abstract The energy and electromagnetic matrix element B(E2↑) for the 21+ state in 22O have been determined via inelastic scattering of a beam of these radioactive nuclei from a 197Au target. These results provide strong evidence for the existence of the N=14 subshell closure in 22O. This demonstrates that the shell structure in 22O is similar to that of stable oxygen isotopes, even though this nucleus is only two neutrons away from the neutron drip line. These results are reproduced in the standard sd shell model as well as with a an expanded space which also includes the f7/2 and p3/2 orbitals.

Structure of the weakly-bound nucleus 6He studied via the 6Li(t, 3He)6He reaction

Abstract The 6Li(t,xa03He)6He charge-exchange reaction leading to the weakly-bound nucleus 6He has been studied at 336 MeV. Beyond the strong peaks for the known ground state (Jπ=0+) and first excited state (Jπ=2+, Ex=1.8 MeV), a broad asymmetric structure around Ex∼5xa0MeV has been observed. The angular distribution of this structure exhibits the dominance of a ΔL=1 transition, indicating the existence of intruder states at low excitation energies in 6He.

Spectroscopy of [Formula Presented] via the one-neutron knockout reaction

The single-nucleon knockout reactions 9Be(14B, 13B + gamma)X and 197Au(14B, 13B + gamma)X, at an incident energy of 60 MeV per nucleon, have been used to probe the structure of 14B and of the core fragment 13B. A dominant 2s configuration is deduced for the neutron in the ground state of 14B. The longitudinal momentum distribution for this state is consistent with neutron halo structure. Spin assignments for 13B excited states at 3.48 and 3.68 MeV are proposed based on the observed spectroscopic factors for one-neutron removal.

Study of 34,35Si and 37S with single-neutron removal reactions

Preliminary results of one-neutron removal reactions on the nuclei 34,35Si and 37S at the intersection of the 1s0d and 1p0f neutron shells are reported. Momentum distributions of the projectile residues have been measured at the National Superconducting Cyclotron Laboratory at Michigan State University. The populated final states in the neutron removal reactions could be resolved by measuring the γ rays from the de-excitation of bound states using a position-sensitive NaI(T1) array. Partial cross sections to specific final states have been deduced. A comparison of the cross sections in the reactions (35Si,34Si) and (37S,36S) shows differences that point to the influence of intruder configurations in the vicinity of 34Si.

Intermediate-energy Coulomb excitation of 28,29,30,31Na

The neutron-rich radioactive isotopes {sup 28,29,30,31}Na have been produced by nuclear fragmentation of {sup 48}Ca and {sup 40}Ar primary beams at intermediate energies. The energies and excitation cross sections to the lowest excited states were measured via intermediate-energy Coulomb excitation on a {sup 197}Au target. Experimental results suggest a large degree of collectivity in {sup 31}Na. Intrinsic ground state and transition quadrupole moments in {sup 28,29,30,31}Na are compared.

Mass dependence of the effective isovector charge in the sd-shell

In order to map out a possible mass and isospin dependence of the effective charges in the sd-shell, we performed an intermediate energy Coulomb excitation experiment with the semi-magic, proton-rich nucleus 38Ca. The transition between the first excited state (21+, E*=2206u200akeV) and the ground state (0gs+) was studied, and the reduced transition strength and the proton transition matrix element were deduced. The nucleus 38Ca was chosen for this study, as it is at the upper mass end of the sd-shell, and will together with already existing high precision data for the lower mass end of the shell most clearly show a systematic trend in the effective charges. Our study also helps to fill the void of available high quality data for proton-rich nuclei in this mass region. We compare our data to theoretical shell model predictions with mass dependent, and mass independent effective charges, and to experimental values of the neutron-rich mirror nucleus 38Ar.