A. A. Cowley | Searcharxiv

arXiv2014

Pre-equilibrium mechanisms in the93Nb(p,alpha) inclusive reaction at incident energies from 65 to 160 MeV

The reaction mechanism of pre-equilibrium proton-induced $α$-particle emission from 93Nb at an incident energy of 100 MeV was investigated with polarized projectiles. A formalism based on the statistical multistep direct emission model of Feshbach, Kerman and Koonin was found to give a reasonably good reproduction of cross section and analyzing power angular distributions at various emission energies. Existing experimental distributions for the same reaction at an incident energy of 65 MeV were also analyzed with the same model. The incident-energy variation from 65 MeV up to 160 MeV was found to be consistent with the predictions of the basic model. However, whereas knockout of an $α$ cluster is the dominant reaction mechanism in the final stage at the lowest- and highest incident energies, at 100 MeV a pickup process competes with comparable intensity in yield.

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arXiv2006

Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV

Intermediate mass fragments (IMF) from the interaction of $^{27}$Al, $^{59}$Co and $^{197}$Au with 200 MeV protons were measured in an angular range from 20 degree to 120 degree in the laboratory system. The fragments, ranging from isotopes of helium up to isotopes of carbon, were isotopically resolved. Double differential cross sections, energy differential cross sections and total cross sections were extracted.

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arXiv2003

Relativistic predictions of exclusive $^{208}Pb(\vec{p},2p) ^{207}T\ell$ analyzing powers at an incident energy of 202 MeV

Within the framework of the relativistic distorted wave impulse approximation (DWIA), we investigate the sensitivity of the analyzing power - for exclusive proton knockout from the 3s$_{1/2}$, 2d$_{3/2}$ and 2d$_{5/2}$ states in $^{208}$Pb, at an incident laboratory kinetic energy of 202 MeV, and for coincident coplanar scattering angles ($28.0^{\circ}$, $-54.6^{\circ}$) - to different distorting optical potentials, finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as medium-modified coupling constants and meson masses. Results are also compared to the nonrelativistic DWIA predictions based on the Schrödinger equation. Whereas the nonrelativistic model fails severely, both ZR and FR relativistic DWIA models provide an excellent description of the data. For the FR predictions, it is necessary to invoke a 20% reduction of sigma-nucleon and omega-nucleon coupling constants as well as for $σ$-, $ρ$- and $ω$-meson masses, by the nuclear medium. On the other hand, the ZR predictions suggest that the strong interaction in the nuclear medium is adequately represented by the free nucleon-nucleon interaction associated with the impulse approximation. We also demonstrate that, although the analyzing power is relatively insensitive to the use different relativistic global optical potential parameter sets, the prominent oscillatory behavior of this observable is largely attributed to distortion of the scattering wave functions relative to their plane wave values.

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