J. Kalifa

Spectroscopic factors from one-proton stripping reactions on sd-shell nuclei: experimental measurements and shell-model calculations

Abstract The (3He,d) reaction has been investigated at 25 MeV on the target nuclei 16O, 18O, 19F, 23Na, 24Mg, 25Mg, 26Mg, 27Al, 28Si, 29Si, 30Si, 31P, 32S, 34S, 35Cl, 37Cl and 39K. Attention is restricted to the few even-parity levels in each final nucleus which are strongly populated. Values of the single-nucleon Spectroscopic factors C2S are obtained from the differential cross sections measured for these levels by analyzing them in the framework of the DWBA theory of nuclear reactions. The DWBA calculations use sets of 3He and deuteron optical-potential parameters which are experimentally validated and internally consistent. The absolute values of C2S thus extracted are rather insensitive to which sets of equivalent optical-model parameters are used in the DWBA analyses (variations of the order of ±15%) and the variations in the relative values for the different transitions are very insensitive to these choices. Most of the sensitivity which does exist can be traced to the specification of the absorptive part of the deuteron potential. The values of C2S are not sensitive to the presence of spin-orbit terms in either the deuteron or the 3He potential. Contrary to the case for optical-model potentials, however, absolute values of C2S are very sensitive to the radius parameter r0 chosen for the potential which binds the transferred proton, although relative values are almost completely insensitive to this choice. The effects of the spin-orbit part of this bound-state potential on j = l + 1 2 and j = l − 1 2 transitions have also been carefully investigated. Evidence is developed that the radius parameter rs.o. of the spin-orbit part of the bound-state potential should be smaller than that of the central part. The values of C2S extracted from the present data both with standard DWBA analyses (r0 = rs.o. and a0 = as.o.) and with analyses which incorporate a modified treatment of the spin-orbit term of the bound-state potential (r0 ≠ rs.o. and a0 ≠ as.o.) are compared with the predictions of the USD shell-model hamiltonian. The ratios between the experimentally based spectroscopic factors and the model predictions exhibit a marked difference between transitions into the 1 d 3 2 orbit and transitions into the 1 d 5 2 orbit when the standard DWBA analysis is used. However, this difference between 1d 3 2 and 1d 5 2 transitions is greatly reduced if, while the conventional values r0 = 1.25 fm and a0= 0.65 fm continue to be used for the central component of the bound-state potential, values of rs.o. = 1.00 fm and as.o. = 0.52 fm are used for the spin-orbit part.

Optical model analysis of 3He elastic scattering from s-d shell nuclei at 25 MeV

Abstract Angular distributions of elastically scattered 3 He particles from 16 O, 18 O, 19 F, 23 Na, 24 Mg, 25 Mg, 26 Mg, 27 Al, 28 Si, 29 Si, 30 Si, 31 P, 35 Cl, 37 Cl, 39 K and 40 Ca nuclei were measured at 25 MeV bombarding energy. The absolute differential cross-section data were analysed in the framework of the standard optical model with either a volume or a surface imaginary part. Three families of parameters were considered. For all these families, the real potential volume integral j r per interacting nucleon pair decreases as the mass number A increases. The family with j r = 380 MeV · fm 3 for 40 Ca and j r = 590 MeV · fm 3 for 16 O has been identified with the unique family obtained at higher energies, and is therefore considered as the “physical” family. The matter and charge radii deduced from the analysis are presented. The charge radii are compared with the ones obtained from muonic X-ray transitions and electron scattering measurements.

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.

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.

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.

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.

States in Pt-193 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.