Matt Barton's pictureMatt Barton

Hope College

Dr. DeYoung, Dr. Peaslee, Dr. Mader (Nuclear Group)

Supported by NSF-RUI

Since I am a member of the Hope College Nuclear Group, the focus of my summer research has been nuclear physics. In specific, I have been studfocus of myying coincidences between intermediate mass fragments (IMFs) and evaporation residues. When a beam of nuclei hit a target, occasionally a nucleus in the beam collides directly with a nucleus in the target, the result is an excited compound nucleus. Since the excited compound nucleus is unstable, it must emit particles and gamma rays until the nucleus' spin and excitation energy reach a stable level; one such particle the compound nucleus could emit is an IMF, that is, any isotope heavier than Lithium, but lighter than Carbon. Once the nuclei has reached a stable level, it is called an evaporation residue (ER).

Various researchers have attempted to model this process. One such attempt was done by G. P. Gilfoyle et al [Phys. Rev. C., Vol. 46, No. 1, July 1992]. In this report, an attempt was made to measure and predict the average fraction of ERs scattered into an infinitesimal solid angle per unit time per unit flux of beam nuclei as a function of angle (i.e. the differential cross section of ERs as a function of angle). They found that their predicted differential cross section of ERs was lower than the measured cross section at large angles (i.e. greater than 20 deg.). One possible explanation of this discrepancy lies in their choice of model; their model did not include IMFs. The inclusion of IMFs in their model could have provided the momentum kick necessary to drive ER to larger angles. In another paper P. A. DeYoung et al [Phys. Rev. C, Vol. 52, No. 6, Dec. 1995] attempted to model the emission of IMFs from excited nuclei; they used the models MODGAN and GEMINI, both of which are statistical models. In both cases, the models overpredicted the production of IMFs. So then, the question presents itself, what is the differential cross section of IMF -ER coincidences? Are IMFs providing the momentum kick to drive ERs to large angles, or is there something else?

To answer these questions and others, P. A. DeYoung and myself designed an experiment to measure IMF-ER coincidences; the experiment was performed the second week of June at Notre Dame University. A Tandem Van de Graff accelerator was used to accelerate Oxygen-16 nuclei to 72 MeV, and then smash them onto an Aluminum-27 target. The reaction products were measured via two detector arrays 27.5 in from the target. Both arrays contained eight telescopes, and each telescope consisted of two 0.135 millimeter thick Silicon wafers. From time of fight information and the energy of the first element we are able to identify ERs, and from the energy of the first and second elements of the telescope, we are able to identify IMFs.

Results are on their way.

bartonm@hope.edu