[en] Giant Dipole Resonances (GDR's) built upon excited states in ¹²C and ¹⁵O are studied. The Second Harmonic GDR is a resonance whose excitation function is centered at a 2ℎw excitation in ¹²C and is built upon 1p-1h states at a 1ℎw excitation. Data on ¹¹B(p,γ)¹²C taken at six beam energies from 37 MeV to 80 MeV are analyzed and evidence is presented for a Third Harmonic GDR in ¹²C which is centered at a 3ℎw excitation energy and is built upon 1p-1h states at 2ℎw excitation. Integrated capture strengths for both the Second Harmonic and Third Harmonic GDR's agree well with dipole strengths calculated by using a simple schematic model. Data for the ⁹Be(³He,γ)¹²C taken at an incoming excitation energy in ¹²C of 43 MeV are compared to data on ¹¹B(p,γ)¹²C taken at the same incoming excitation energy. The capture reactions lead primarily to final states which are similar in structure to the incoming state. Comparison of the capture cross sections of these two reactions indicates a large contribution to the structure of ¹²C excited states from configurations which are more complicated than 1p-1h configurations and which are primarily 3p-3h in nature. Data for the ⁹Be(³He,γ)¹²C reaction covering four ³He beam energies from 23 MeV to 40 MeV including a differential cross section angular distribution taken at 23 MeV are presented. Data for the ¹²C(³He,γ)¹⁵O reaction covering three ³He beam energies between 25 MeV and 40 MeV including a differential cross section angular distribution taken at 26 MeV are also presented

[en] The (p,n) reaction at intermediate energies provides a direct determination of nuclear weak-interaction matrix elements which are often unobtainable from decay studies. Calibration of this strong-interaction probe for quantitative measure of such matrix elements has been based primarily on study of the well-known Fermi and GT transitions in the ¹⁴C(p,n)¹⁴N reaction. The energy dependence of the ratio of the strengths of the isovector spinflip and non-spinflip central components of the effective nucleon-nucleon interaction using this reaction has been extended to higher energies than previously investigated using the recently commissioned 600 meter neutron flight path at the NTOF facility of LAMPF. This study will further improve our understanding of the (p,n) reaction as a probe of matrix elements related to beta decay

[en] The region of excitation in ¹⁶O near 9.85 MeV has been investigated for evidence of a doublet, expected from tetrahedral symmetry arguments, by using the ¹²C(⁴He,γ₃)¹⁶O and ¹²C(⁴He,⁴He)¹²C reactions. Energy-matched measurements of the pair of reactions show no evidence for cascade gamma-ray decay of any but the known D-wave resonance observed in the elastic channel. The gamma-ray decay width of a possible second nondegenerate level to the 2₁⁺ state is determined to be less than 5 x 10^-4 eV

[en] The angular distributions of cross section and analyzing power for the radiative capture reaction ¹⁵N(rvec p,γ₀)¹⁶O have been measured at excitation energies of 35.0 and 39.0 MeV in ¹⁶O. Gamma rays were detected in a large, self-shielded NaI spectrometer at eight angles from 23 degree to 155 degree. The complex reaction amplitudes associated with the capture channels leading to dipole, quadrupole, and octupole radiation have been extracted. The data at 39 MeV excitation indicate a quadrupole component σ_E2/σ_E1=0.124±0.015, and an octupole component σ_E3/σ_E1=0.0051±0.0026. The observation of high multipolarity radiation is discussed within the context of microscopic calculations which locate large components of the isovector quadrupole and octupole resonances within this region of excitation in ¹⁶O

[en] In this paper, we present the measured differential cross sections for the transition between the 1/2^-,¹³C(g.s.) and the 1/2⁺, ¹³N(2.34 MeV) state, excited in the (p,n) reaction at E_p=160 MeV and at E_p=186 MeV. The ΔL=1, ΔS=1, ΔJ=0^- contribution in the 1/2^-→1/2⁺ transition, which provides direct information on pionlike transitions, was the main motivation of these studies

[en] A complete set of polarization transfer observables for quasifree scattering in the (rvec p, rvec n) reaction at 495 MeV is reported. Measurements were carried out on CD₂, natural carbon, and calcium targets at a momentum transfer of 1.72 fm^-1 using the new Neutron Time-of-Flight facility at LAMPF. The spin-longitudinal and spin-transverse responses are extracted from the data. The ratio of these responses are compared to DWIA-RPA calculations in which the particle-hole interaction is taken to be of the form g'+π+ρ. No evidence for these RPA correlations is seen in the data at this momentum transfer. 8 refs., 2 figs

[en] The polarization transfer observable D_LL(0 degree) has been measured for ²H(rvec p,rvec n)2p, ¹²C(rvec p,rvec n)¹²N, and ¹⁴C(rvec p,rvec n)¹⁴N reactions with beam energies of 318 and 494 MeV. The deuterium results are in close agreement with free NN scattering constrained to the ΔJ^π=1⁺ channel. The results for the carbon targets, however, are systematically more negative than those for deuterium, which suggests a difference between the free and effective nucleon-nucleon interactions. Such a medium modification of the spin-dependent interaction may have important implications for intepretation of other intermediate-energy scattering experiments

[en] Complete sets of polarization transfer coefficients have been measured for quasifree (rvec p,rvec n) scattering from ²H, ¹²C, and ⁴⁰Ca at 494 MeV and scattering angles of 12.5 degree, 18 degree, and 27 degree (q=1.2,1.7,2.5 fm^-1). These measurements yield separated transverse (σ at sign x/Iq) and longitudinal (σ at sign ·/Iq) isovector spin responses. Comparison of the separated responses to calculations and to electron-scattering responses reveals a strong enhancement in the spin transverse channel. This excess transverse strength masks the effect of pionic correlations in the response ratio

[en] Results from a complete set of polarization-transfer observables for quasifree (rvec p,rvec n) scattering at 495 MeV are reported. Measurements were carried out on CD₂, carbon, and calcium targets at a laboratory scattering angle of 18 degree using the new neutron time-of-flight facility at LAMPF. The ratio of spin-longitudinal to spin-transverse responses at a momentum transfer of approximately 1.72 fm^-1 is extracted from the data and compared to distorted-wave calculations incorporating a random-phase approximation description of the nuclear response. No enhancement is observed in the experimental ratio

[en] A complete set of polarization-transfer observables has been measured for quasifree (rvec p,rvec n) reactions on ²H, ¹²C, and ⁴⁰Ca at a bombarding energy of 495 MeV and a laboratory scattering angle of 18 degree. The data span an energy-loss range from 0 to 160 MeV, with a corresponding momentum transfer range of q_c.m.=1.7--1.9 fm^-1. The laboratory observables are used to construct partial cross sections proportional to the nonspin response and three orthogonal spin responses. These results are compared to the transverse spin response measured in deep inelastic electron scattering and to nuclear responses based on the random phase approximation. The polarization observables for all three targets are remarkably similar and reveal no evidence for an enhancement of the spin-longitudinal nuclear response relative to the spin-transverse response. These results suggest the need for substantial modifications to the standard form assumed for the residual particle-hole interaction