L.W. Swenson

The elastic scattering of intermediate energy protons from 40Ca and 208Pb

Abstract Elastic scattering of protons from 40 Ca and 208 Pb has been studied using the MRS facility at TRIUMF. Cross section and analyzing power ( A y ) angular distributions to 50° in the center of mass have been measured for incident proton energies of 200, 300, 400 and 500 MeV. Comparisons of the experimental results are made with calculations based on relativistic and non-relativistic phenomenological models, and with relativistic and non-relativistic microscopic models. The differences between the results of the non-relativistic and relativistic models manifest themselves in the spin observables. They are found to be smaller in the phenomenological approach than in the microscopic one and they depend on energy.

Validity of collective model DWBA analysis for intermediate energy proton scattering to low-lying states of 208Pb

Abstract New measurements of inelastic proton scattering to low-lying collective states of 208 Pb at 200 and 400 MeV are reported. Deformation lengths ( δ H = βR ) extracted from angular distributions for the 3 − (2.614), 5 − 1 (3.198 MeV), 5 − 2 (3.709 MeV), 2 + (4.086 MeV) and 4 + (4.324 MeV) states are in good accord with values extracted at other incident proton energies. The fact that the deformation lengths for these levels are independent of incident proton energy within experimental uncertainty provides further support of the validity of the collective DWBA for medium energy proton scattering to strongly excited states. Advantage is taken of this to extract more precise values for the ratio of neutron to proton multipole matrix elements for both the low-lying states and the giant quadrupole resonance at 10.6 MeV.

Pion double charge exchange on 3He and 4He

Abstract We have measured the differential cross section d 2 σ/ d Ω d T for the double charge exchange reactions 4He(π+, π−)4p and 3He(π−, π+)3n at 140, 200 and 295 MeV. By fitting this data with a simple phase-space model we have estimated the integrated cross section d σ/ d Ω and the total cross section. The 4He data agree qualitatively with the predictions of a meson exchange calculation and with one version of the successive single charge exchange model. The 3He cross sections are considerably larger than those of 4He and in some cases the missing mass plot shows a strong enhancement, which resembles a broad three-nucleon resonance.

A surface-delta description of analyzing power measurements for collective states of Ni and Zn isotopes☆

Abstract Analyzing powers and differential cross sections for the inelastic scattering of 15 MeV polarized protons to the stronger collective states of 58, 60 Ni and 64 Zn have been measured. The data were compared to detailed microscopic reaction calculations using a central plus spin-dependent effective interaction. The nuclear structure wave functions used were obtained from a quasiparticle random-phase appoximation calculation using a spin-dependent surface delta interaction and a basis set containing both neutron and proton configurations. The overall quality of the fits strongly suggests that the surface-delta wave functions provide a good representation for spherical nuclei in this intermediate mass range. The effects of exchange and further modifications to the microscopic effective interaction are discussed.

Relativistic medium effects for 208Pb(p,p′) at intermediate energies

Abstract Analyzing power and spectral data for the inclusive quasifree ( p ,p ′) reaction on 208Pb at 290 MeV are presented. Cross sections were measured over an angular range of 4°–26° and for excitation energies up to 160 MeV. The free surface response model provides a good description of the shape of the continuum. At the quasifree peak the large angle Ay(θ) data drop below the free nucleon values. This difference is a possible indication of relativistic medium effects.

Elastic and inelastic scattering of 280 and 489 MeV protons from 58Ni

Abstract Nonrelativistic and relativistic collective deformed potential models have been used to study the excitation of seven states in 58Ni by 280 and 489 MeV unpolarized protons. Optical model potentials were determined at each energy by fitting elastic scattering data using both of the models. Deformation lengths were also obtained using both models with no dependence on incident energy observed for either model. The average value of the hadronic deformation lengths along with the charge deformation lengths were used to calculate neutron to proton multipole matrix elements ( M n M p ). Five transitions, 2+1, 1.45 MeV; 2+3, 3.04 MeV; 2+4, 3.26 MeV; 4+1, 2.46 MeV; and the 4+5, 4.75 MeV state were determined to be isoscalar, i.e. M n M p = N Z . The 4+2, 3.63 MeV state was observed to be a proton-like transition with M n M p = 0.43 ± 0.18. At small scattering angles, the relativistic model gave consistently larger cross sections than the nonrelativistic model. This effect was much larger at 280 MeV than at 489 MeV.

Analyzing powers and cross sections of inclusive polarized proton scattering on 208Pb

Abstract Inclusive polarized proton-nucleus scattering on 208 Pb has been studied at 290 and 500 MeV. The measurements cover a broad range (0–250 MeV) of excitation energy over the 4°–27° angular range. The measured analyzing powers and cross sections for the continuum were compared with recent relativistic and nonrelativistic distorted-wave impulse approximation calculations. The cross section in the continuum region is found to be dominated by single-step quasi-free scattering. Differences of up to 40% between the analyzing powers measured at the quasi-free peak as opposed to free NN values strongly support the relativistic impulse approximation predictions for the quasi-free region, and indicate the presence of relativistic medium effects. Analyzing powers and cross sections of several low-lying states were compared with both nonrelativistic and relativistic distorted-wave Born approximation predictions.

Multipole matrix elements for 208Pb

New measurements of inelastic proton scattering to low‐lying states of 208Pb at 200 and 400 MeV are reported. Deformation lengths extracted from angular distributions for the 3− (2.614 MeV), 5−1 (3.198 MeV), 5−2 (3.209 MeV), 2+ (4.086 MeV) and 4+ (4.324 MeV) states are in good accord with values extracted at other incident proton energies. The fact that the deformation lengths are independent of incident proton energy within experimental uncertainty provides support for the validity of the collective DWBA for medium energy proton scattering to strongly excited states. Advantage is taken of this to extract statistically more precise values of the ratio of neutron to proton multipole matrix elements (Mn/Mp). Different methods of determining the appropriate average value of Mn/Mp are discussed.

Collective model distorted-wave Born approximation analysis of 500-MeV proton scattering from 40Ca.

A vibrational collective model has been used to analyze 15 bound states in /sup 40/Ca excited by inelastic scattering of 500 MeV polarized protons. It is shown that for those states which have surface peaked charge transition densities the collective model describes the shape and magnitude of the angular distributions quite well. The hadronic deformation lengths extracted are shown to be constant over the incident proton energy range of 25--800 MeV with the exception of data at 185 MeV. The average values for the hadronic deformation lengths are used to calculate the ratio of the neutron to proton multipole matrix elements for five states. Elastic scattering and the 3/sub 1//sup -/, 2/sub 1//sup +/, and 5/sub 1//sup -/ transitions have also been studied using the relativistic collective model.

T=1, spin-dipole strength in40Ca

Spin-dipole strength in40Ca has been studied by inelastic scattering of 500-MeV protons and the dipole response in40Ca is compared with the spin-dipole data from the40Ca(p, n) reaction and nonspin-dipole data from photonuclear studies.