G. Rotbard

Proton occupancies in the even Se ground states via the (d, 3He) reaction

Abstract The spectroscopic factors for the levels of73,75,77,79,81As have been measured in the Se(d, 3He)As reactions at 25.2 MeV. The proton occupation numbers deduced for the even Se isotopes show that the striking change in proton configuration, observed for the Ge isotopes between N ⩽ 40 and N ⩾ 42, does persist for the Se isotopes. This change is not reproduced, either by a model calculation using spectral distribution methods or by proton wave functions recently suggested for the Se isotopes to explain the results of the Se(d, 6Li)Ge reactions.

Evidence for a change of structure in the heavy mercury isotopes around 200Hg

Abstract The (p, t) reaction has been performed on natural Hg and separated 196,198–202,204Hg targets, using a 25 MeV proton beam from the Orsay MP tandem accelerator and a split-pole spectrometer. In an excitation energy region below 2 MeV, new excited 0+ levels have been found. The enhancement factors of the populated 0+ states have been extracted. The resulting set of data exhibits striking discontinuities. In particular, both the energy and the (p, t) cross section of the 02+ level show a pronounced extremum in 200Hg. This observation, together with the previous experimental evidence, suggests a quite dramatic change in intrinsic structure of the Hg-isotopes at A=200. Microscopic calculations based on the deformed-shell-model approach suggest an explanation in terms of the Subshell closures at Z=80 and N=120 at weakly deformed oblate shapes, and a possible oblate-to-spherical shape transition. Qualitative theoretical arguments are confronted with the properties of pairing excitations calculated within a variant of the one broken-pair method. Within this approach the lowest excited 0+ states are interpreted as pairing vibrations. Energy positions of 0+ states and the pair transfer matrix elements are compared with the available experimental data.

One-nucleon pickup reactions on 32S: Experimental results and shell-model calculations

Abstract The 32S(d,3He)31P and 32 S ( 3 He ,α) 31 S reactions have been investigated at incident energies of Ed = 27 MeV and E3He = 25 MeV. The experimental values of excitation energies (0 ⩽ Ex(MeV) ⩽ 8) have been compared with the predictions of a complete sd-shell space, shell-model calculation. Spectroscopic factors obtained for 22 levels of 31S through the DWBA analysis of the experimental angular distributions have also been compared with the shell-model predictions. In order to reconcile the experimental and shell-model predicted values of the spectroscopic factors, the geometrical parameters of the spin-orbit part of the transferred nucleon potential are required to be smaller than those of the central part as it was previously observed in studies of the one-proton (3He,d) stripping reaction. The experimental fragmentation of the 1d 5 2 and 2s 1 2 strengths is correctly reproduced by the shell-model calculations. Twenty pairs of levels were identified as mirror states in the 31S and 31P nuclei and the ambiguities concerning the Jπ-values of eleven 31S levels could be removed.

Étude du pick-up d'un neutron sur les isotones N = 20 40Ca, 39K et 37Cl

Abstract Neutron pick-up in the N = 20 closed shell has been studied for the three isotones 40 Ca, 39 K and 37 Cl using the ( 3 He, α) reaction. The results have been analyzed with previously determined optical potentials and the spectroscopic factors compared to theoretical values calculated from several models. New levels have been observed in 38 K. and 36 Cl. Spins, parities and isospins have been tentatively assigned to some of them.

(p,t) strengths in the Ga isotopes

Abstract The (p, t) reaction on the two stable Ga isotopes has been performed at 25 MeV, with 11 keV energy resolution. Levels up to 3.5 MeV in 67Ga and 4.3 MeV in 69Ga were measured. Differences observed between the distribution of the L = 2 (p, t) strength and the distribution of the B(E2)↑ strength may be explained by a mixed character of the 7 2 2 − level wave function. The distribution of the L = 0 strength indicates that the striking change in the ground-state structure shown between N = 40 and 42 already begins, although weakly, between N = 38 and 40.

Potentiels optiques moyens 3He et α pour les noyaux de la couche s-d

Abstract Average 3 He and α potentials have been determined which permit a quantitative analysis of the ( 3 He, α) reaction. Only one parameter is changed from one nucleus to another: the real potential depth, V , related to the nuclear radius R = rA 1 3 by the empirical formula VR 1.5 = K . The parameter K independent of the mass number A and of the radius r characterizes a family.

Étude de la Réaction 40Ca(3He, α)39 Ca

Abstract The ( 3 He, α) reaction on 40 Ca has been analysed at several energies using the DWBA method. Optical potentials have been found which reproduce the angular distribution of α-particles corresponding to the ground and first excited states of 39 Ca. Values for the spectroscopic factors of the ground and first two excited states using a normalization constant N = 20 are compared with other experimental and theoretical values. A rather large disagreement is observed for the ground state of 39 Ca; the spectroscopic factor deduced from the ( 3 He, α) reaction is not independent of the incident energy. The value obtained at E 3He = 8 MeV is much too large.

States inPt193using the (p,t) reaction

Levels in /sup 193/Pt were populated by the ( p,t) reaction using 25 MeV protons and an isotopically enriched /sup 195/Pt target. A number of low-lying negative parity states are observed. By far the most strongly populated is the 1/2/sup -/ ground state. Some of these states are qualitatively interpreted assuming Coriolis coupling and rotation-vibration coupling between the 1/2/sup -/vertical-bar530vertical-bar, 3/2/sup -/vertical-bar532vertical-bar, and 5/2/sup -/vertical-bar532vertical-bar Nilsson states and an oblate core. L=0 angular distributions for states in /sup 193/Pt appear to be associated with the excited J/sup ..pi../=0/sup +/ states in the even-even Pt cores.

Levels ofGe68excited by the (p, t) reaction

The /sup 70/Ge(p,t)/sup 68/Ge reaction has been studied at 26 MeV incident energy with an overall resolution of 10 keV using a split-pole spectrometer. Forty-one /sup 68/Ge levels, among which twenty-eight are observed for the first time, are populated below 5.2 MeV excitation energy. Angular distributions are obtained, and comparison with distorted-wave Born approximation calculations allows spin and parity assignments. An interesting result is the discovery of the first excited 0/sup +/ level at 1.753 MeV as well as seven other 0/sup +/ levels above 2 MeV energy. Five J/sup ..pi../ = 2/sup +/ and four J/sup ..pi../ = 4/sup +/ levels are observed for the first time. We also establish the position of the first J/sup ..pi../ = 3/sup -/ level at 2.651 MeV and the possibility of a J/sup ..pi../ = 6/sup +/ level at 4.456 MeV excitation energy.

States in /sup 193/Pt using the ( p,t) reaction

Levels in /sup 193/Pt were populated by the ( p,t) reaction using 25 MeV protons and an isotopically enriched /sup 195/Pt target. A number of low-lying negative parity states are observed. By far the most strongly populated is the 1/2/sup -/ ground state. Some of these states are qualitatively interpreted assuming Coriolis coupling and rotation-vibration coupling between the 1/2/sup -/vertical-bar530vertical-bar, 3/2/sup -/vertical-bar532vertical-bar, and 5/2/sup -/vertical-bar532vertical-bar Nilsson states and an oblate core. L=0 angular distributions for states in /sup 193/Pt appear to be associated with the excited J/sup ..pi../=0/sup +/ states in the even-even Pt cores.