Fusion–evaporation cross-sections for the⁶⁴Ni+¹⁰⁰Mo reaction using the dynamical cluster-decay model

Abstract

The decay of hot and rotating compound nucleus 164 Yb * , formed in heavy ion reaction 64 Ni+ 100 Mo at both below-and above-barrier energies, is studied on the basis of the dynamical cluster-decay model (DCM) with effects of deformations and orientations of nuclei included in it. There is only one parameter in this model, namely the neck-length parameter, which varies smoothly with the temperature of the compound nucleus at both below-and above-barrier energies, and its value remains within the range of validity of the proximity potential. The emission of light particles (xn, x-neutrons, x = 1-4) as well as the energetically favoured intermediate mass fragments (IMFs) of both the light (5 A 2 20) and heavy (40 A 2 50) masses, together with the symmetric fission (SF) channel ((A/2) ± 20), is considered as the dynamical collective mass motions of preformed fragments or clusters through the barrier. The light-mass IMFs, the heavy-mass fragments (HMFs) and SF, constituting the fusion-fission (ff) cross-section, contribute only at above-barrier energies, and are compatible with the CASCADE analysis of experimental data. A best fit to data is obtained for two different neck-length parameters, one for light particles (LPs) and another for all other decay channels, the ff crosssection. The barrier height corresponding to the neck-length parameter for LPs gives 'barrier lowering' in a straightforward way for the best-fitted fusionevaporation cross-sections in DCM, and, in contrast to the (statistical model) analysis of experimental data, results in largest contribution for 1n emission. A further study is called for both the LPs and ff channels.

Decay analysis of compound nuclei with massesA≈30–200formed in reactions involving loosely bound projectiles

“…The DCM, for the decay of compound systems, is non-statistical description of dynamical mass motion of preformed clusters through the interaction barrier which treats all types of emissions i.e. evaporation residues (or equivalently light particles LPs (A ≤ 4)), intermediate mass fragments IMFs (5 ≤ A 2 ≤ 20) and fusion-fission ff fragments, on the same footing [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. But the statistical models treat all these emissions on different footing, where these emissions are treated differently on the basis of mass of compound nucleus [28][29][30].…”

“…It is relevant to mention here that the neck length parameter ∆R emp is the only parameter of this model, which is fixed empirically. Gupta and Collaborators successfully presented interaction barrier modification characteristic of ∆R in significant studies [17][18][19][20]24]. Interestingly, these works point out that the empirically fitted ∆R emp simply result in the corresponding 'barrier lowering' ∆V emp B for the given reaction.…”

Dynamical cluster-decay model for fusion cross-sections below the barrier

“…, and relative separation R. For the decoupled η-, R-motions, in terms of the -partial waves, the DCM defines the fragment formation or compound-nucleus decay cross section for oriented nuclei as [3,5,6] σ…”

“…The only acceptable explanation so-far is the "modification of the shape of the inner part of the potential in terms of a thicker barrier and shallower pocket" [2]. This property of "lowering of barriers" at sub-barrier energies is also supported by the dynamical cluster-decay Model (DCM) of pre-formed clusters by Gupta and Collaborators [3], where "barrier lowering" ΔV B arises in a natural way in its fitting of the neck-length parameter ΔR ( Fig. 1(a)).…”

Compound nucleus formation probabilityPCNdefined within the dynamical cluster-decay model

“…Some attempts (see, e.g., [2][3][4]) were made to use P CN in determining the evaporation residue cross section σ ER , given as the product of the capture cross section σ capture , the CN formation probaility P CN and the survival probability W sur , each term treated and calculated separately [3]. In this contribution, we introduce for the first time the definition of P CN in to the dynamical clusterdecay model (DCM) of Gupta and collaborators [5][6][7][8][9][10][11][12][13], applied to reactions having non-zero nCN contribution.…”