J. Lisantti

The nuclear spin response to intermediate energy protons

Abstract Measurements of the spin-flip probability S nn for inclusive inelastic proton scattering around 300 MeV from nuclei between 12 C and 90 Zr show that an enhanced spin response near 40 MeV excitation at q ∼ 100 MeV/ c is a general feature of nuclear structure. Data for 40 Ca at 800 MeV confirm that the enhancement is not a peculiarity of 300 MeV scattering. In addition, measurements in 44 Ca up to 75 MeV show that the enhancement cannot be attributed solely to a relatively narrow resonance. Continuum RPA calculations suggest that the enhancement is due to the exhaustion of most S = 0 strength at lower energy and a shift of S = 1 strength to higher 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.

Analyzing power for the inelastic continuum with 200 MeV protons

Abstract Inelastic proton scattering from targets of 60 Ni, 90 Zr, and 208 Pb has been studied using 200-MeV polarized and unpolarized protons. The behavior with angle of a narrow region at the peak of the continuum underneath the giant resonance spectra follows that expected for free nucleon-nucleon scattering, modified by an energy shift dependent on target mass. Analyzing power results support the hypothesis that single-step quasifree scattering represents a significant fraction of the overall inelastic scattering for the excitation region near the proposed quasifree peak, but indicate that other processes start to dominate above this excitation region.

P-Ay for excitation of natural and unnatural-parity states of 12C by 400 MeV protons

Abstract Differences of the polarization ( P ) and analyzing power ( A y ) have been measured between 5° and 14° for the lowest isoscalar 1 + and isovector 1 + and 2 + states in 12 C excited by 400 MeV protons. This is the first measurement of P - A y in an energy regime where the impulse approximation is most valid. Values of P - A y for all states are compared to both nonrelativistic and relativistic model calculations, which only qualitatively describe the data.

On the validity of microscopic calculations for inelastic proton scattering

Abstract Recent measurements of transition rates for low-lying collective states and giant resonances in 208 Pb using inelastic scattering of 200 and 334 MeV protons are in accord with accepted values. This is in sharp disagreement with earlier medium-energy proton inelastic scattering studies in which the validity of the collective model formalism was questioned. Combining these results with measurements at other energies, we conclude that the extraction of deformation lengths with the collective distorted wave Born approximation formalism is satisfactory to at least 800 MeV. The present results bring into question the microscopic calculations of inelastic scattering using RPA wave functions.

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.

Spin-transfer measurements for the 24Mg(→p, →p′)24Mg∗ reaction at 250 MeV

Abstract For the 24 Mg ( →p . →p ′) reaction at Ep=250 MeV and small momentum transfers we have measured cross sections, analysing powers and spin-transfer probabilities up to 40 MeV of excitation in 24Mg. Because of the strong suppression of the S=0 excitations in the spin-flip cross sections, the analogs of Gamow-Teller transitions could be cleanly observed. Up to Eexc=15 MeV about 80% of the L=0 strength predicted by large-scale shell model calculations has been found.