Dr. DeYoung and Dr. Peaslee (Nuclear Group)
Supported by the NSF-REU
Statistical emission of intermediate mass fragments (IMF) from excited nuclei is an area of nuclear physics needing clarification. Measurements of evaporation residue (ER) cross sections, from compound nucleus decay, have been shown to diverge from predicted cross sections, particularly at larger angles . A possible explaination for this discrepancy may be the statistical model's exclusion of IMF emission.
Evidence for the existance of IMF emission is seen in alpha-alpha and d-alpha correlations functions from 16O+27Al at beam energies ranging from 80MeV to 250MeV . Large enhancements in these correlations can be seen at relative momenta that correspond to the breakup of 8Be and 6Li^* respectively. In light of these facts, an experiment to measure IMF and ER coincedences was conducted by P. A. DeYoung, G. F. Peaslee and M. A. Barton with the Tandem VanderGraaff Accelerator at the University of Notre Dame in June of 1996.
A 72MeV beam of 16O was collided with an 27Al target. Two arrays of 8 telescopes, each array spanning 10 degrees, were used for detection. Each telescopes consisted of two 1.35micron Si wafer detectors (3 by 3cm). One array was held at a constant angle of 25 deg throughout data collection and the other array was positioned at angles 35, 40, 45 and 60 degrees.
My summer research consisted of furthering the data analysis from this experiment. Angular distributions of single alpha, IMF and ER have been extracted showing encouraging agreement with statistical models such as MODGAN. The angular distribution of ERs reproduce the trend of augmented counts at large angles as compared to model results. A significant amount of work has been done towards attaining angular distributions of coincdence events and results are forthcoming.
G. P. Gilfoyle et al Phys Rev C46, 265(1992) Phys Rev C46, R1 (1992)