G. Mairle

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.

The quasihole aspect of hole strength distributions in odd potassium and calcium isotopes

Abstract The 40,42,44,48 Ca ( d , ρ) 39,41,43,47 K and 40,44 Ca(d, t) 39,43 reactions have been studied at 52 MeV. Angular distributions have been taken and spectroscopic factors have been extracted by means of a DWBA analysis for states with excitation energies up to typically 10 MeV. Analog relations are proposed for mass-39 and mass-43 nuclei. A discussion of proton occupation numbers for various shells above and below the Fermi surface shows a substantial and about equal core excitation for 42Ca and 44Ca. Typically 70 % of the 1 d 5 2 hole strengths have been located. The corresponding energy averaged strength distributions show quasihole structures whose widths are dominated by phonon-hole coupling to the first 2+ state in the target nucleus.

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 the magnesium isotopes: 24, 25, 26Mg(d, τ)23, 24, 25Na

Abstract Energy spectra and angular distributions of the 3 He particles from the (d, τ) reaction on 24, 25, 26 Mg have been measured at E d = 52 MeV with an energy resolution of about 80 keV. Excited states up to 11 MeV have been observed in 23 Na. High-lying l = 1 transitions were excited by pick-up from the 1 p 3 2 shell. Discrepancies of 1p proton separation energies determined by quasi-free scattering and proton pick-up are discussed. The l -values have been determined for transitions to a variety of states with unknown spins in the doubly odd 24 Na nucleus. A spin 5 + can be attributed to the 1.51 MeV level which is then the second member of the 4 + ground state rotational band. Several previously unknown spins could be determined in the 25 Na level scheme. There is an apparent similarity in the proton-hole spectra of 23Na and 25Na and consequently a similar rotational structure. The spectra of 23 Na, 24 Na and 25 Na are discussed in the framework of the Nilsson model. The spectroscopic factors are compared with shell-model calculations and predictions from a simple rotational model. States which are excited by pick-up from Nilsson orbit no. 7 contain approximately 75 % of the total sd strength. This contradicts the rotational model and requires strong band mixing. On the other hand the shell-model calculations account for excitation energies and spectroscopic factors of low-lying positive parity states. The data provide information about T = 1 and T = 3 2 states in mass-24 and mass-25 nuclei respectively.

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. n nBelow 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. n nThe application of the DWBA to the pick-up of strongly bound protons requires optical potentials with modified radii in the exit channel.

The decrease of ground-state correlations from 12C to 14C☆

Abstract The (d, τ) reactions on 12C, 13C and 14C have been investigated with 52 MeV deuterons. Spectroscopic factors have been extracted from a DWBA analysis of the measured angular distributions. The derived proton occupation numbers show that the addition of 1 p 1 2 . neutrons leads to a consolidation of the 1 p 1 2 proton shell closure: The number of protons in the 1 p 1 2 . shell of the target wave function decreases from 0.7 in 12C to about 0.4 in 13C and 0.3 in 14C. This decrease is understood as the result of (i) a blocking of proton scattering into the 1 p 1 2 shell due to the presence of 1 p 1 2 neutrons or (ii) a decreasing deformation with increasing neutron number.

Spins of proton hole states from analyzing powers of (d, τ) reactions at 52 MeV

Large and characteristic vector-analyzing powers of the (d, τ) reactions on 16O, 28Si and 40Ca at 52 MeV have been observed and utilized to determine the spins of 1p hole states in 15N and 27Al and of 1d hole states in 39K. The results are pertinent to the empirical determination of the 1p and 1d spin-orbit splittings.

The optical potential for vector-polarized deuterons of 52 MeV

Abstract The vector analysing power for elastic scattering of 52 MeV polarized deuterons was measured for 12 C, 16 O, 20 Ne, 28 Si, 32 S, 40 Ar, 58 Ni, 90 Zr and 197 Au. The data were analysed together with previously measured differential cross sections in the framework of the optical model. Best-fit and average optical-model parameters were obtained both for surface and volume absorption. Fits with surface absorption are superior to those with volume absorption, especially for heavier nuclei. Typical parameters of the spin-orbit part of the best-fit optical potentials are found to be V s.o. ∼- 5.5 MeV, r s.o. ∼- 1.15 fm and a s.o. ∼- 0.4 fm, and there is no evidence for an imaginary component. The volume integrals and rms radii of real, imaginary and l · s potentials show a smooth mass dependence and differ insignificantly for different sets of potentials.