D.L. Friesel

Microscopic and macroscopic aspects of 135 MeV proton scattering from 16O

Abstract Differential cross sections have been measured for the scattering of 135 MeV protons from 16 O and data from the transitions to 13 states (up to 19.5 MeV excitation) have been analysed using microscopic and macroscopic nuclear reaction models. Extensive collective model calculations have been made of the transitions to all natural-parity states. The deformation parameters for the 4p4h rotational band are in good agreement with theoretical models. The inelastic scattering data from the excitation of the negative-parity states have also been analysed in the distorted-wave approximation using microscopic (shell and RPA) models of nuclear structure and with density-dependent two-nucleon t -matrices. For positive-parity states, we report the first shell-model calculation using the complete 2ħω basis space and find that the triplet of 2p2h states (4 + , 2 + , 0 + ) around 11 MeV excitation is quite well described by this model, as may be a 1 + state which is observed for the first time by proton scattering from 16 O.

Density-dependent forces and large-basis structure models in the analyses of 12C(p, p') reactions at 135 MeV

Abstract Differential cross sections have been measured for the elastic and inelastic scattering of 135 MeV protons from 12C. The data from the transitions to 9 selected states up to 18.3 MeV in excitation have been analysed using a distorted wave approximation with various microscopic model nuclear structure transition densities and free and density-dependent two-nucleon t-matrices. Clear signatures of the density dependence of the t-matrix are defined and the utility of selected transitions to test different attributes of that t-matrix when good nuclear structure models are used is established.

The (3He, t) reaction at 197 MeV on 12C, 24Mg, 28Si and 40Ca

Abstract Spectra have been measured for the (3He,t) reaction on 12C, 24Mg, 28Si and 40Ca at Elab = 197 MeV and θlab = 15°. The analog of the giant dipole resonance (GDR) is strongly populated in the charge-exchange reaction for each of the targets used in this study. Differences between the spectral shape of the GDR known in 12C, 28Si, 24Mg and 40Ca from photonuclear work and their analogs in 12N, 28P, 24Al and 40Sc are discussed. No evidence is seen for the population of a compact isovector giant quadrupole resonance (GQR) in any of these targets. Angular distributions have been measured at this energy for the 40Ca(3He, 3He), 40Ca(3He, 3He′)40Ca and 40Ca(3He, t)40Sc reactions. The elastic 3He scattering from 40Ca is reasonably described by a volume Woods-Saxon optical potential that is very similar to one known from lower-energy studies. Collective DWA calculations using this potential reproduce the inelastic scattering to the 3− and isoscalar GQR states of 40Ca and an additional calculation using the Goldhaber-Teller model roughly reproduces the measured charge-exchange angular distributions of the GDR in 40Sc. Data for the inelastic-scattering and charge-exchange reactions to a few low-lying discrete states and the region including the GDR in mass 40 have also been examined in DWA calculations using a microscopic double-folding model with a realistic effective interaction and particle-hole wave functions. Where possible these results are compared with results for other probes and rough consistency is found. The decomposition of the strength observed in the GDR region via (3He, t) is considered in some detail and it is estimated that 30% of this strength is ΔS = 1.

Comparison of the noncoplanar 6Li(p, pd)4He reactions at 120 and 200 MeV

Abstract The 6 Li(p, pd) 4 He reaction was studied at 200.2 MeV, at the quasi-free angle pair ( θ p , θ d ) = (54°, −48.9°), for noncoplanarity angles φ from 0° to 28°. 6 Li αd spectroscopic factors of 0.84 and 0.76 are deduced from our coplanar data at this energy and 120 MeV, respectively, for ground-state 2S Woods-Saxon wave functions. A recent microscopic three-body calculation predicts spectroscopic factors from 0.70 to 0.75; using the ground-state wave functions from this study, we deduce a factor of 0.76 from the 200 MeV data. DWIA calculations fit the measured integrated cross sections versus φ for spectator momenta P α ≲ 100 MeV/ c at both bombarding energies, but underpredict them for larger P α . Momentum form factors were better reproduced with 1S αd cluster wave functions for a soft-core bound-state potential than with the 2S Woods-Saxon wave functions, but the former wave functions generate unphysically large (∼1.25) spectroscopic factors.

The spectroscopy of 13C by inelastic proton scattering

Abstract At 135 MeV incident energy, differential proton scattering cross sections have been measured for many states of 13 C, up to 23 MeV in excitation. These data are supplemented by analysing power data for states up to 10 MeV in excitation, measured at 119 MeV incident energy. Distorted wave analysis using a density-dependent form of the nucleon-nucleon interaction has provided a thorough assessment of the model predictions of the nuclear structure of many of these excited states.

The 48Ca(d→, 3He)47K reaction at 80 MeV

Abstract A high-resolution measurement of the 48Ca(d→, 3He)47K reaction has been carried out. Seventeen final states are found, up to an excitation of 8.35 MeV. The measured vector analysing powers allow spin determination for most of these states. The 2s1/2 and ld3/2 hole strengths observed are found to exhaust the respective sum rules, while 64% of the sum-rule strength for 1d5/2 hole states is found. It is surmised that the remainder of this strength resides at higher excitation energies. The amount of proton ground-state correlations is deduced from the strength of a newly observed 7/2− state in 47K.

Neutron-knockout reactions from 2H, 40Ca and 48Ca

Abstract The reactions 2H(p, pn)1H and 40,48Ca(p,pn)39,47Ca were studied at 149.5 MeV in coplanar geometries. An overall separation-energy resolution of about 1 MeV was achieved. In addition to valence neutron-hole states ( lf 7 2 , ld 3 2 , 2 s 1 2 ) , probable neutron-hole strength is seen for ld 5 2 and 1p shell knockout for both calcium targets. The 2H and 40,48Ca data are compared with PWIA and DWIA calculations, respectively. Spectroscopic factors and rms radii are extracted for neutron-hole states.

The noncoplanar 6Li(p, pd)4He reaction at 120 MeV, and the 6Li cluster momentum wave function☆

Abstract The 6Li(p, pd)4He reaction was studied at 119.6 MeV, at the quasifree angle-pair (θp, θd) = (40°, 59°), for noncoplanarity angles 0° ⩽ φ ⩽ 36°. The deduced 6Li αd spectroscopic factor (0.75) and momentum distribution (73 MeV/c) FWHM) agree reasonably well with most other intermediate-energy measurements. A minimum and adjacent secondary maximum in the integrated cross section versus φ, predicted by the DWIA theory, was observed for the first time. Cross sections at large φ are about 2.5 times greater than the DWIA predictions, suggesting contributions of higher-order processes not included in the DWIA treatment of the reaction, or larger momenta than the cluster wave function contains.

The noncoplanar 7Li(p, pd)5He and 7Li(p, pt)4He reactions at Ep = 200 MeV, and evidence for deuteron clustering in 7Li

Abstract The 7Li(p, pd)5He reaction was studied at 200 MeV, at the quasi-free angle pair θ p θ d = 64° −47.4° , for noncoplanarity angles from 0° to 16°. Data were fitted with DWIA calculations, which gave a spectroscopic factor Cd of 1.1 for deuterons in 7Li if entrance-channel absorption was neglected, and 1.4 if it was not. The Cd deduced from plane-wave analysis (by comparison with 6Li(p, pd) data) is 0.9. The deuteron cluster momentum distribution is characterized, at small momentum, by an FWHM of 140 MeV/c. At large momentum there is an excess of measured cross section over predictions, as is true also for 6Li(p, pd) at intermediate energies. Cross sections for 7Li(p, pt)4He at the same experimental conditions are very small but are consistent with unit spectroscopic factor for t + α; these cross sections show the expected minimum at zero relative cluster momentum, and are adequately fitted by DWIA predictions.

Detection efficiency of Ge telescopes for 35 to 105 MeV deuterons

Abstract The probability of deuterons detected in Ge telescopes giving anomalously small pulse heights, due to their undergoing inelastic interactions and possibly elastic scattering, was measured from about 35 to 105 MeV. The loss factors, determined to 0.5% or better, increase from 3.1 to 12.2% in this region, and are consistent with a nearly energy-independent d + Ge total reaction cross section of about 2000 mb.