Nuclear Theory Seminars at Texas A&M: Spring 2007

Location: Cyclotron Building (434), Seminar Room

Friday, February 23, Dissertation Defense 4:00pm

When targets and projectiles are chosen to have a wide distribution in neutron to proton ratio (N/Z), the quasiprojectiles formed should have a mean N/Z somewhere between that of the N/Z of the target and the N/Z of the projectile depending on the amount of N/Z equilibration that occurred during the deep inelastic collision (DIC). Six systems at two beam energies (32 and 45 MeV/nucleon) were collected. The systems in order of increasing difference between target and projectile N/Z (shown in parentheses) are ⁴⁰Ar + ¹¹²Sn (ΔN/Z = 0.018), ⁴⁸Ca + ¹²⁴Sn (ΔN/Z = 0.080), ⁴⁸Ca + ¹¹²Sn (ΔN/Z = 0.160), ⁴⁰Ca + ¹¹²Sn (ΔN/Z = 0.240), ⁴⁰Ar + ¹²⁴Sn (ΔN/Z = 0.258) and ⁴⁰Ca + ¹²⁴Sn (ΔN/Z = 0.480).

Two techniques were used to determine the N/Z of the quasiprojectiles. The first technique uses the isotopically resolved fragments to reconstruct the quasiprojectile sources. Reconstruction also provides a means for source determination by requiring that the charge of the quasiprojectile source equals the charge of the projectile used. The second technique, developed in this work, uses fragment yield ratios and a simple relationship to simultaneously fit all six systems to determine the N/Z of the quasiprojectile sources. Using simulations and a filter of the FAUST array, the neutron loss was measured and found to account for the observed difference between these two techniques. In the simulation the N/Z of the quasiprojectile source is known and can be compared to the results using the newly developed technique to provide a means of validation for this procedure.

To study the fragmentation of quasiprojectiles the fragment yields were used to look at the isobaric, isotopic, fractional and mean N/Z yields. The results show that more neutron-rich systems produce more neutron-rich fragments and the more neutron-poor systems produce more neutron-poor fragments. Evidence for an inhomogeneous distribution of N/Z between the light charged particles (LCPs) and intermediate mass fragments (IMFs) was observed using the multiplicity of LCPs and IMFs, the mean N/Z of the IMF divided by the mean N/Z of the LCP, and mirror nuclei ratios.

This research was funded in part by the Department of Energy through grant DE-FG03-93ER40773 and the Robert A. Welch Foundation through grant A-1266.