Issue
EPL
Volume 85, Number 2, January 2009
Article Number 22001
Number of page(s) 5
Section Nuclear Physics
DOI http://dx.doi.org/10.1209/0295-5075/85/22001
Published online 07 January 2009
EPL, 85 (2009) 22001
DOI: 10.1209/0295-5075/85/22001

Analyzing power distribution in the 12C(p, p$\alpha$)8Be(g.s.) reaction at an incident energy of 100 MeV

A. A. Cowley1, 2, J. Mabiala1, 2, E. Z. Buthelezi1, S. V. Förtsch1, R. Neveling1, F. D. Smit1, G. F. Steyn1 and J. J. van Zyl2

1   iThemba Laboratory for Accelerator Based Sciences - PO Box 722, Somerset West 7129, South Africa
2   Department of Physics, Stellenbosch University - Private Bag X1, Matieland 7602, South Africa

aac@sun.ac.za

received 17 November 2008; accepted in final form 12 December 2008; published January 2009
published online 7 January 2009

Abstract
The analyzing power distribution in the 12C(p, p$\alpha$)8Be(g.s.) reaction at an incident energy of 100 MeV is investigated. The experimental coincidence data measured under quasifree kinematic conditions are in remarkable agreement with the trend of free p + 4He elastic scattering, and also with a distorted-wave impulse approximation prediction. Thus the projectiles interact with the clusters as if they were free entities, with the rest of the target nucleons acting merely as spectators to the reaction. This result provides compelling and direct evidence for the existence of preformed $\alpha$-clusters in 12C, as has often been postulated for this nucleus.

PACS
25.40.-h - Nucleon-induced reactions.
24.70.+s - Polarization phenomena in reactions.
21.60.Gx - Cluster models.

© EPLA 2009