l-forbidden Gamow-Teller beta decay of Cu-57

Journals published by the American Physical Society can be found at http://publish.aps.org/Absolute branching ratios for the beta decay of Cu-57 to excited states up to 3.3 MeV in Ni-57 have been determined, including the rho-forbidden Gamow-Teller transition to the first excited state in Ni-57. Four transitions to excited states at 0.768, 1.113, 2.443, and 3.007 MeV are observed in addition to the superallowed decay to the ground state of Ni-57. The, measured branching ratio to the ground state is 89.9 +/- 0.8% and the branching ratios to the four excited states are 0.94 +/- 0.09%, 8.6 +/- 0.6%, 0.17 +/- 0.03%, and 0.35 +/- 0.04%, respectively. In addition we have measured the Cu-57 half-life and find it to be 196.3 +/- 0.7 ms, which is in good agreement with the most recent measurement. B(GT) values have been extracted from the new results and are compared to shell model calculations

Intermediate mass fragments and isospin dependence in Sn-124,Xe-124+Sn-124,Sn-112 reactions at 28 MeV/nucleon

Intermediate mass fragment (Z>2) emission in Sn-124,Xe-124+Sn-124,Sn-112 reactions at 28 MeV /nucleon were studied using neutron ion multidetector for reaction oriented dynamics, a 4pi charged particle detection system. A number of observables, such as isotopic yield distributions, energy spectra of light charged particles and intermediate mass fragments, isotopic and isobaric yield ratios, and average neutron to proton ratios are investigated. These observables show significant dependence on the isospin N/Z of the reacting system. It is observed that the formation of neutron-rich clusters are correlated with the excess neutrons in the composite system and depends on the temperature of the emitting source. The origin of light particles and fragments was studied through observations of rapidity distribution as a function of collision violence. With increasing centrality, the heavier He-6 isotope is found to be emitted closer to the midrapidity region than the lighter He-3 isotope. The emission of heavy fragments from the midrapidity region becomes increasingly favorable for fragments with higher charge Z . The results suggest that the midrapidity region is not only neutron rich but also a rich source of heavy fragment (cluster) formation

Evidence of critical behavior in the disassembly of nuclei with A similar to 36

A wide variety of observables indicate that maximal fluctuations in the disassembly of hot nuclei with Asimilar to36 occur at an excitation energy of 5.6+/-0.5 MeV/nucleon and temperature of 8.3+/-0.5 MeV. Associated with this point of maximal fluctuations are a number of quantitative indicators of apparent critical behavior. The associated caloric curve does not appear to show a flattening such as that seen for heavier systems. This suggests that, in contrast to similar signals seen for liquid-gas transitions in heavier nuclei, the observed behavior in these very light nuclei is associated with a transition much closer to the critical point

Reaction dynamics and multifragmentation in Fermi energy heavy ion reactions

The reaction systems, Zn-64+Ni-58, Zn-64+Mo-92, Zn-64+Au-197, at 26, 35, and 47 A MeV, have been studied both in experiments with a 4pi detector array, NIMROD, and with antisymmetrized molecular dynamics model calculations employing effective interactions corresponding to soft and stiff equation of state (EOS). Direct experimental observables, such as multiplicity distributions, charge distributions, energy spectra and velocity spectra, have been compared in detail with those of the calculations and a reasonable agreement is obtained for both EOS's. No conclusive preference for either EOS has been observed. Neither of the above direct observables nor the strength of the elliptic flow are also sensitive to changes in the in-medium nucleon-nucleon cross sections. A detailed analysis of the central collision events revealed that multifragmentation with cold fragment emission is a common feature predicted for all reactions studied here. A possible multifragmentation scenario is presented; after the preequilibrium emission ceases in the composite system, cold light fragments are formed in a hotter gas of nucleons and stay cold until the composite system underdoes multifragmentation. For reaction with Au-197 at 47A MeV a significant radial expansion takes place. For reactions with Ni-58 and Mo-92 at 47A MeV semitransparency becomes prominent. The differing reaction dynamics drastically change the kinematic characteristics of emitted fragments. This scenario gives consistent explanations for many existing experimental results in the Fermi energy domain