Power law behavior of the isotope yield distributions in the multifragmentation regime of heavy ion reactions

Abstract

Isotope yields have been analyzed within the framework of a Modified Fisher Model to study the power law yield distribution of isotopes in the multifragmentation regime. Using the ratio of the mass dependent symmetry energy coefficient relative to the temperature, asym/T , extracted in previous work and that of the pairing term, ap/T , extracted from this work, and assuming that both reflect secondary decay processes, the experimentally observed isotope yields have been corrected for these effects. For a given I = N -Z value, the corrected yields of isotopes relative to the yield of 12 C show a power law distribution, Y (N, Z)/Y ( 12 C) ∼ A −τ , in the mass range of 1 ≤ A ≤ 30 and the distributions are almost identical for the different reactions studied. The observed power law distributions change systematically when I of the isotopes changes and the extracted τ value decreases from 3.9 to 1.0 as I increases from -1 to 3. These observations are well reproduced by a simple de-excitation model, which the power law distribution of the primary isotopes is determined to τ prim = 2.4 ± 0.2, suggesting that the disassembling system at the time of the fragment formation is indeed at or very near the critical point.

Experimental reconstruction of excitation energies of primary hot isotopes in heavy ion collisions near the Fermi energy

“…The size of the fragmenting source is evaluated from the NN source multiplicities of all particles, determined by a moving source fit described in Ref. [34,44]. The excitation energy of the fragmenting system is chosen to give an average value roughly similar to those of the experiment.…”

“…As discussed in detail in Ref. [34], the events measured by this IMF trigger belong essentially to the event class of semicentral collisions. The telescope consisted of four Si detectors.…”

“…When fragments are formed, many of them are in excited states and cool by evaporation processes before they are detected. These secondary cooling processes may also significantly alter the information of the hot nuclear matter, carried by the primary fragments [33][34][35]. Even though the statistical decay process itself is rather well understood and well coded, it is not a trivial task to combine it with a dynamical code.…”

Temperature determined by isobaric yield ratios in heavy-ion collisions

“…(1) was applied to the cold fragments in Ref. [41], they showed that useful information can be extracted to elucidate the effects of the secondary decay process. In that case, T and other parameters do not correspond to those in the primary hot nuclear matter but do correspond to those modified by the secondary decay process.…”

Isobaric yield ratio difference between the140AMeVNi58+BeQiao1, Wei2, Ma3 et al. 2015Phys. Rev. C12070View full textAdd to dashboardCite

“…Based on the isobaric yield ratio (IYR), the IBD method provides cancellation of both the system dependence parameters [8][9][10][11], the free energies of isobars [3], and the terms contributing to the free energy of fragments [8,[12][13][14][15][16] in the formula determining the cross sections of fragment. The target dependence of IBD has been studied by investigating the measured fragments in 140A MeV 40,48 Ca and 58,64 Ni projectile fragmentation reactions on the 9 Be and 181 Ta targets [17], which have been performed by Mocko et al at the National Superconducting Cyclotron Laboratory (NSCL) in Michigan State University [18].…”