(Stellenbosch : University of Stellenbosch, 2010-03) Mabiala, Justin; Cowley, A. A.; Fortsch, S. V.; University of Stellenbosch. Faculty of Science. Dept. of Physics.

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ENGLISH ABSTRACT: The (p, pα) reaction on 12C was investigated experimentally using polarized incident protons
of 100 MeV. Coincident data, which were obtained at ten quasifree angle pairs for
proton angles ranging from 25◦ to 110◦, were analyzed in terms of the distorted-wave impulse
approximation (DWIA). Calculated energy-sharing cross section and analyzing power
distributions reproduce the data reasonably well. The observed agreement allows the extraction
of distorted momentum distributions from experimental data. These distributions
are very consistent over a wide range of angle pairs at which cross section energy-sharing
distributions vary considerably.
Since measurements of analyzing powers were made, spin-orbit distortions were included
in the DWIA calculations. The effects of spin-orbit distortions were found to be very
small near zero recoil momentum and did not destroy the validity of the factorization
approximation where the two-body p-α cross section enters as a multiplicative factor in
the three-body (p, pα) cross section expression. Spectroscopic factors derived from the
data are fairly consistent with the trend of the theoretical predictions.
Analyzing power data also follow the trend of free p-4He scattering data, and comparisons
with DWIA predictions are in reasonable agreement. The theory reproduces also very
well analyzing power angular distributions of the projectile-cluster two-body scattering at
large angular momentum of the residual nucleus. This indicates that a quasifree knockout
mechanism dominates the reaction.
The two-body interaction response between the projectile and the α cluster was found to
resemble the scattering of protons from a free α particle to a remarkable degree, the present
results strongly imply the existence of preformed α clusters in 12C.