Oak Ridge National Laboratory

Physics Division

Physics Division Seminars

Physics Division Seminars bring us speakers on a variety of physics related subjects. Usually these are held in the Building 6008 large Conference Room, at 3:00 pm on the chosen day, but times and locations may vary. For more information, contact our seminar chairman,

Alfredo Galindo-Uribarri
Tel (Office): (865) 574-6124  (FAX): (865) 574-1268

Thu., July 01, 2010, at 3:00 p.m. (refreshments at 2:40 p.m.)

Nuclear temperatures from the evaporation fragment spectra and possible lifetime effect

Amlan Ray, Variable Energy Cyclotron Center, Kolkata (India)
Building 6008 Conference Room

The temperature of a compound nucleus should decrease for the higher values of its spin angular momentum; thus, the spectra of the heavier evaporation fragments emitted from the compound nucleus should have progressively steeper slopes. To test this idea, we formed the same compound nucleus 105Ag at the same excitation energy (EX=76 MeV) and with very similar spin distribution by 16O+89Y and 12C+93Nb reactions and studied back-angle alpha, lithium, boron and carbon emissions. The compound nucleus character of the reaction was established from the observed 1/sinTHETAc.m. angular distribution of the emitted fragments (in the center of mass frame) and the lack of any entrance channel dependence of the angle-integrated yields of the fragments. It was found that the temperatures as obtained from the slopes of alpha, lithium, boron, carbon spectra remain about 3.0 MeV in most cases and higher for the lithium emission (approximately 4.2 MeV), whereas statistical model codes predict continuous decrease of the corresponding temperatures from approximately 3.0 MeV (for alpha) to approximately 1.7 MeV (for carbon). The temperature of the exit channel nuclei is expected to drop for the emission of the heavier nuclei because the heavier nuclei carry higher orbital kinetic energy and hence the available thermal energy becomes smaller. An analysis of the alpha and heavier ion emission from 35Cl+24Mg reaction at E(35Cl)lab=260 MeV also showed that the temperatures extracted from the slopes of the carbon and oxygen spectra did not decrease compared to that obtained from the slope of the alpha spectra. These results could not be understood by adjusting the parameters of the statistical models and might imply the effect of the lifetime of the exit channel fragment plus residual dinuclear system.