G.J. Wagner

Elastic scattering of 52 MeV deuterons

Abstract Strongly excited levels of the nuclei 12 C, 14 N, 20 Ne, 22 Ne, 27 Al, 28 Si, 32 S, 40 Ar, 48 Ti, 54 Fe, 58 Ni, 64 Ni, 208 Pb and 209 Bi have been investigated by means of inelastic scattering of 52 MeV deuterons. The angular distributions have been analysed in terms of the DWBA. The description of the excited states in the collective model yields good fits and values of the deformation parameter β L which agree with independent measurements. Satisfactory fits are obtained in an attempt to apply a microscopic theory of inelastic deuteron scattering. An effective nucleon-nucleon interaction of Wigner type V ( r ) = V N exp(− r 2 / γ 2 ) is assumed to induce the scattering. From target nuclei where shell-model functions for the ground and excited states are available, we deduce the parameters V N = 38±5 MeV and γ = 1.7 fm. For other target nuclei, information about the collective enhancement of the excited states is obtained which is more sensitive to the details of the nuclear structure than the β L values.

Proton separation energies derived from the (d, 3He) reaction on f-p shell nuclei at 52 MeV

Abstract The (d, 3 He) reaction was investigated by 52 MeV deuterons on 45 Sc, 54 Fe, 58 Ni, 60 Ni, 63 Cu, and 65 Cu. The measured angular distributions were compared with local zero-range DWBA calculations from which the angular momenta of the transfered protons and the spectroscopic factors were deduced. The centres of gravity of the binding energies were determined for the 1 f 7 2 , 1 d 3 2 and 2 s 1 2 proton hole states. Taking into consideration the results of proton pick-up experiments on ten other f-p shell nuclei partly investigated by us previously, it was possible to study the systematic behaviour of the binding energies. In the lower f-p shell for nuclei with A ⩽ 48, the 2 s 1 2 protons are in the average more tightly bound than the 1 d 3 2 protons, and the reverse is true for A > 48. A Bansal and French type calculation based on an average particle-hole interaction E ph = − E + ΔE (t p ·t h proved to reproduce the observed data. The parameters E and ΔE have been determined for the 1 d 3 2 − f 7 2 and the 2 s 7 2 − f 7 2 interaction by means of a least-squares fit procedure considering the experimental binding energies in altogether 16 nuclei.

Proton pick-up from 19F, 20Ne and 22Ne

Abstract Energy spectra and angular distributions of the 3He particles from the (d, 3He) reactions on 19F, 20Ne and 22Ne have been measured at an incident energy of 52 MeV. Excitation energies up to 15 MeV (18O), 7 MeV (19F) and 9 MeV (21F) and pick-up from seven different shell-model orbits have been observed. Several previously unknown negative parity states have been found in 18O. A ( 3 2 , 1 2 ) − level at 4.56 MeV was found in 19F, while the known J = 3 2 level at 3.91 MeV was not observed which suggests a positive parity assignment. The hole state spectrum of 21F resembles closely that of 19F. The spectroscopic factors are compared to the predictions from a simple rotational model and from various effective shell-model calculations. All models describe the positive parity transitions leading to 19, 21F reasonably well, but those leading to 18O are only understood by the inclusion of excited core contributions of 4p-2h character in 18O. The low-lying negative parity states, containing essentially the 1p 1 2 hole strengths, are also nicely described by the weak coupling calculations. Higher excited negative parity states show deviations which are discussed in terms of 2p particle-1p hole admixtures.

Proton shell structure of mass 28-32 nuclei

Energy spectra of3He-particles from the (d,3He) reaction on28, 29, 30Si,31P and32S have been measured at an incident energy of 52 MeV. Spectroscopic factors have been determined by comparison of measured and DWBA angular distributions. The results are compared with predictions of recent shell model calculations. Excitation energies and spectroscopic strengths of low lying positive parity states are fairly well described. The 1d5/2 hole strengths distributions are not reproduced. The measured 1p hole strength decreases rapidly from28Si to28S. The occupation numbers of the different subshells show a considerably smoothed Fermi surface of these nuclei.

Proton pick-up from the 1p and 2s-1d shells of 27Al

Energy spectra and angular distributions of 3He particles from the 27Al(d, 3He)26Mg reaction have been measured at an incident energy of 52 MeV. An 11 MeV excitation range in 26Mg has been covered. Below 4 MeV final excitation, the DWBA spectroscopic factors agree with shell-model predictionsbut disagree with those from a simple rotational model. Above 4 MeV, we have found some evidence in favour of a rotational band structure of the hole states. Negative-parity hole states have been observed at an energy much lower than expected from (p, 2p) experiments. The application of the DWBA to the pick-up of strongly bound protons requires optical potentials with modified radii in the exit channel.

1p hole-states in 16O and 16N and the mass dependence of the 1p spin-orbit splitting

Abstract The 1p hole strength distributions in mass 16 nuclei, measured in parallel 17O(d,t)16O and 17O(d,τ)16N experiments, exhibit differences of the effective 1d 5 2 1p 1 2 and 1d 5 2 1p 3 2 interactions which lead to a 1p orbit splitting increasing strongly with the number of 1d 5 2 nucleons.

Energy levels in 30Si from the 29Si(d, p)30Si reaction

Energy levels in 30Si up to 9.6 MeV have been studied with the 29Si(d, p)30Si reaction at incident energies of 11.5 MeV, 16 MeV and 20 MeV. The protons were recorded with the aid of magnetic spectrographs of the Browne-Buechner type and the Enge split-pole type. A previously unreported level was found at 7637 ± 10 keV. New spin and parity assignments and spectroscopic factors were obtained. The dominant features of the proton spectrum are interpreted within a simple two-particle model with an inert 28Si core; e.g. evidence for (2s12−1f72) and (2s12−2p32) doublets in 30Si was derived from the strong excitation of the Jπ = 3− (5.49 MeV) and 4− (6.50 MeV) states, and the 1− (6.75 MeV) and (2)− (7.51 MeV) states, respectively.

Shell effects in potential radii deduced from (d, 3He) angular distributions

Abstract Systematic phase displacements between measured (d, 3He) angular distributions and conventional DWBA calculations are observed. They can be removed by shell-dependent optical parameters. The j-effect on l = 2 angular distributions is interpreted as a shell effect. Arguments are given that there is some geometrical shell structure nuclei.

Comparative spectroscopy with the (d, τ) reaction on even Ar isotopes

Abstract The (d, τ) proton pick-up reactions on 36 Ar and 38 Ar have been studied at an incident energy of 52 MeV. Differential cross sections were measured and spectroscopic factors were extracted for transitions to 14 states of 35 Cl and 13 states of 37 Cl, respectively. Many new 5 2 + states and nearly the complete 1 d 5 2 strength have been observed in both nuclei. The width of the 1 d 5 2 spectral distribution is appreciably smaller for the semi-closed shell nucleus 38 Ar than for 36 Ar and 40 Ar. The results are compared with those from the 40 Ar(d, τ) reaction and proton stripping reactions on each of the three argon isotopes. Recent shell model calculations proved to be well suited to describe excitation energies as well as spectroscopic factors for the low-lying positiveparity states. Mirror relations were established for the nuclei 35 Ar and 35 Cl. In 37 Cl we succeeded in observing a weak component of a 1p proton hole state at a separation energy of only 18 MeV.

STUDY OF

Ten states of17N have been excited via the18O(d,3He)17N reaction atEitd=52 MeV. Thel-transfer values are presented for eight of these states. Based on the subsequent spin and parity assignments severalT=3/2 isobaric multiplets are proposed.