Search Results (10 total)

Generalized isoscaling relationships which may permit one to relate the isotopic distributions of systems that may not be at the same temperature are proposed. The proposed relationships are applied to multifragmentation excitation functions for central Kr+Nb and Ar+Sc collisions.

Emission of intermediate mass fragments (IMFs) (Z>~3) from central collisions of ⁴⁰Ar+⁴⁵Sc  (E/A=35–115 MeV), ⁵⁸Ni+⁵⁸Ni (E/A=35–105 MeV), and ⁸⁶Kr+⁹³Nb (E/A=35–95 MeV) was studied. For each system, the average number of IMFs per event increased with beam energy, reached a maximum, and then decreased. The beam energy of peak IMF production increased linearly with the combined mass of the system. The number of IMFs emitted at the peak also increased with the system mass. Percolation calculations showed a weaker dependence of the peak beam energy and the number of IMFs on the total mass of the system.

The balance energy at which repulsive nucleon-nucleon scattering balances the attractive force due to the nuclear mean field is measured for the first time for the Au+Au reaction. The observed balance energy of 42±3_stat±1_sys MeV/nucleon agrees with the previously established power law dependence of E_bal on system mass, providing evidence that the Coulomb interaction does not suppress the attractive mean field near the balance energy, in contrast to recent theoretical predictions.

Intermediate mass fragment (IMF) production is different for the reaction pair ⁵⁸Fe+⁵⁸Fe and ⁵⁸Ni+⁵⁸Ni for which the only difference is the ratio N/Z, 1.23 for ⁵⁸Fe and 1.07 for ⁵⁸Ni. For beam-velocity fragments at 5.4° with Z from 3 to 15 the more proton-rich Ni reaction produces more even-Z IMFs than the Fe reaction. The ratio (number of IMFs from ⁵⁸Ni+⁵⁸Ni)/(number of IMFs from ⁵⁸Fe+⁵⁸Fe) as a function of Z is about 10% larger for even-Z values than for odd-Z values. The magnitude of this odd-even effect is about the same for beam energies with E/A=45, 75, and 105 MeV.

We present measurements of the multiplicity of charged particles ( N_c) and intermediate mass fragments (IMFs) for ⁵⁸Fe+⁵⁸Fe and ⁵⁸Ni+⁵⁸Ni at incident energies of 45 to 105 MeV/nucleon. We find that the neutron-rich system emits more IMFs as a function of N_c at low incident energies while at the highest energy we observe a much smaller difference between the two systems. Expanding emitting source and statistical multifragmentation simulations reproduce the difference between the two systems at low energies while a charge percolation simulation describes the results at the highest energy.

Ratios of the populations of ground and excited states of ⁴He, ⁵Li, and ⁸Be and double ratios constructed from the yields ^3,4He, ^6,7,8Li, ^11,12,13C isotopes were measured for central Kr+Nb collisions at E/A=35, 70, 100, and 120 MeV. These ratios were analyzed to estimate an apparent temperature for emission. Consistent and approximately constant apparent temperatures were obtained from the excited states of ⁴He, ⁵Li, and ⁸Be nuclei and from thermometers based upon the yields of carbon isotopes. In contrast, apparent temperatures obtained from thermometers based upon the ratios using helium isotopes increase monotonically with incident energy.

Systematic experimental evidence is presented for the decay of nuclear matter from toroidal geometries using reactions of ⁸⁶Kr+⁹³Nb at incident energies ranging from 35 to 95 MeV/nucleon. The decay of noncompact geometries is established through two charge-related observables, and the distinction between toroidal and bubblelike geometries is achieved through event shape analysis. Indications of these exotic geometries appear for beam energies between 60 and 75 MeV/nucleon.

The energy at which collective transverse flow in the reaction plane disappears, the balance energy E_bal, is found to depend on the isospin of the system using the reactions ⁵⁸Fe+⁵⁸Fe and ⁵⁸Ni+⁵⁸Ni. The more neutron-rich system exhibits higher balance energies for all measured impact parameters, in agreement with the predictions of a transport model which incorporates an isospin dependent mean field and isospin dependent in-medium nucleon-nucleon cross sections.

Collective transverse flow of nuclear matter was measured as a function of the ratio of neutrons to protons ( N/Z) of the interacting system for the first time. The collisions of three isotopically pure beams of A  =  58 nuclei with two A  =  58 targets were studied at 55 MeV/nucleon. The results for the flow variables demonstrate the sensitivity of transport models to elementary aspects of the nucleon-nucleon collisions.

The energy at which the collective transverse flow in the reaction plane disappears, the balance energy E_bal, is found to increase linearly as a function of impact parameter for ⁴⁰Ar+⁴⁵Sc reactions. Comparison of our measured values of E_bal(b) with predictions from quantum molecular dynamics (QMD) model calculations agrees better with an approach incorporating momentum dependence in the nuclear mean field. © 1996 The American Physical Society.