Isobaric yield ratio difference in heavy-ion collisions, and comparison to isoscaling

Abstract

An isobaric yield ratio difference (IBD) method is proposed to study the ratio of the difference between the chemical potential of neutron and proton to temperature (∆µ/T ) in heavy-ion collisions. The ∆µ/T determined by the IBD method (IB-∆µ/T ) is compared to the results of the isoscaling method (IS-∆µ/T ), which uses the isotopic or the isotonic yield ratio. Similar distributions of the IB-and IS-∆µ/T are found in the measured 140A MeV 40,48 Ca + 9 Be and the 58,64 Ni + 9 Be reactions. The IB-and IS-∆µ/T both have a distribution with a plateau in the small mass fragments plus an increasing part in the fragments of relatively larger mass. The IB-and IS-∆µ/T plateaus show dependence on the n/p ratio of the projectile. It is suggested that the height of the plateau is decided by the difference between the neutron density (ρn) and the proton density (ρp) distributions of the projectiles, and the width shows the overlapping volume of the projectiles in which ρn and ρp change very little. The difference between the IB-and IS-∆µ/T is explained by the isoscaling parameters being constrained by the many isotopes and isotones, while the IBD method only uses the yields of two isobars. It is suggested that the IB-∆µ/T is more reasonable than the IS-∆µ/T , especially when the isotopic or isotonic ratio disobeys the isoscaling. As to the question whether the ∆µ/T depends on the density or the temperature, the density dependence is preferred since the low density can result in low temperature in the peripheral reactions.

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

“…For the 58 Ni reaction, if ρ n1 /ρ p1 = 1 can be assumed [3], ∆µ/T = lnρ n2 − lnρ p2 ≡ ∆lnρ np for the asymmetric 64 Ni system can be obtained. According to the IBD plateaus for the I =0 and 1 chains, in the 64 Ni + 9 Be reaction, ∆µ/T ≈ 1 will result in ∆lnρ np = 1 for the measured reaction, and ∆µ/T ≈ 0.5 will result in ∆lnρ np = 0.65 for the AMD + GEMINI simulated reaction.…”

“…Considering two reactions where the measurement situations are the same (where the temperature of the reactions can be assumed as the same), the IYR difference between the reactions, i.e., IBD, is defined as [3][4][5][6],…”

“…In a typical IBD distribution, there is a plateau part plus a changing (increasing or decreasing) part as the function of the mass numbers A of fragments [3][4][5][6]. The plateau part is explained as denoting the region where the chemical potential (or the density) difference of neutrons and protons changes very little.…”

“…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].…”

“…The isobaric yield ratio difference (IBD) method, which is similar to the isoscaling method [1,2], has been developed to study chemical potentials of neutrons and protons [3,4] or the nuclear density [5][6][7] in heavy-ion collisions. 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.…”