Gamma-ray multiplicity studies for 40Ar and 86Kr induced reactions leading to Er compound nuclei at limiting angular momenta

Abstract

The moments of the γ-ray multiplicity distributions as a function of evaporation residue and of E γ have been determined from γ-multiplicity measurements for the 116, 120, 122, 124Sn( 40Ar, xn) reactions at 161 ≦ E(Ar) ≦ 236 MeV and for the 76Ge( 86Kr, xn) reaction at 314 ≦ E(Kr) ≦ 376 MeV. Even at the highest incident energies where l gr ≈ 120 units, it is not possible to populate nuclei with l > 65 units, the limiting l predicted for a rotating liquid drop. For the lowest incident energies these data are in agreement with the decay of a compound system. At the highest incident energy, however, significant deviations are observed from the expected decay of an equilibrated system. Such deviations are indicative of pre-equilibrium particle decay. Statistical calculations utilizing the code GROG12 are used to substantiate these conclusions. No evidence for a lower l-cut in the population of the compound system is observed; however, these data would not be sensitive to an l cut ≲ 10 units. The moments of inertia extracted from the edge of the “collective E2 bump” in the 〈 M γ 〉 versus E γ data are in agreement with those predicted for a rotating liquid drop. The average multiplicity of the noncompound processes is estimated to be 8–11 for l gr ≲ 100 units and increasing to 21 for l gr ≲ 120 units.