NUCLEAR RESPONSE IN THE FE-54(P-],P-]') REACTION AT 290 MEV

Cross sections, analyzing powers and spin-flip probabilities have been measured for inclusive inelastic scattering of 290 MeV protons from Fe-54 at laboratory angles between 3.1-degrees and 20-degrees. The momentum transfers vary from small values (q approximately 0.2 fm-1) where individual giant resonances of low multipolarity are observed, to larger values (q approximately 1.4 fm-1) where quasielastic scattering dominates. Complete measurements of spin observables at 20-degrees are discussed, which show that present impulse approximation models based on either the Dirac or the Schrodinger equation for the nucleon are not capable of reproducing all the data. At all momentum and energy transfers the measured analyzing powers A(y) are smaller than predictions from nonrelativistic calculations. Relativistic calculations explain this reduction of A(y) for data near the quasielastic point (omega = q2/2m) as an effect of the attractive scalar field in the nuclear medium; however, they fail to reproduce the observed slopes [d(A(y))/d-omega at fixed angle], assuming for the nuclear response a simple Fermi gas model. For the observed range of momentum and energy transfers (omega less-than-or-equal-to 96 MeV at 20-degrees; less-than-or-equal-to 45 MeV at smaller angles) the spin-flip probabilities S(nn) and spin-flip strengths sigma-S(nn) appear to be rather insensitive to assumptions about the reaction mechanism and are qualitatively described by a nonrelativistic model of quasielastic scattering, which approximates the nuclear response by that of a semi-infinite slab with random phase approximation (RPA) correlations. Strongly enhanced S(nn) values are observed for omega > 25 MeV and q congruent-to 100 MeV/c in agreement with similar observations for several other nuclei. The slab model gives a reasonable account of cross sectons and angular distributions for the Fe-54(n,p)Mn-54 reaction at 298 MeV. The inclusion of damping of the response by two-particle-two-hole excitations and of contributions from two-step processes improves the agreement with the (n,p) data. Using the experimental cross sections for (p,p') and (n,p) reactions and the measured spin-flip strengths in (p,p'), we have separated the nuclear response into spin (DELTA-S = O, DELTA-S = 1), isopin (T(f) = 1,2) and angular momentum (L = 0,1,2,...) components. The distribution and strengths of the Gamow-Teller, the isovector giant dipole, and the (isoscalar) giant quadrupole resonances have been determined from this analysis and are compared to results from complementary reactions. Relative to quasiparticle RPA calculations the Gamow-Teller quenching factors deduced from the sigma-S(nn) data are slightly smaller than those from (p,n) and (n,p) reactions.