Measurement of evaporation residue excitation functions for theF19+Pt194,196,198

Abstract

Experimental measurements of evaporation residue (ER) cross sections for the 19 F + 194,196,198 Pt reactions forming 213,215,217 Fr compound nuclei are reported. The cross sections are measured at beam energies in the range of 101-137.3 MeV. The survival probability of the 213 Fr compound nucleus with neutron number N = 126 is found to be lower than the survival probabilities of 215 Fr and 217 Fr with neutron numbers N = 128 and 130 respectively. Statistical model analysis of the ER cross sections show that an excitation energy dependent scaling of the finite-range rotating liquid drop model fission barrier is necessary to fit the experimental data. The fitted scaling factors for 213 Fr are found to be smaller than those of 215 Fr and 217 Fr for almost the entire range of excitation energies.

Probing nuclear dissipation via evaporation residue excitation functions for theO16,18+Pt198reaction

“…This is reflected in smaller values of dissipation strength obtained from ER studies than those from analyses of pre-scission multiplicity data. For a number of systems, enhancement of fission width is achieved by reducing the height of the liquid drop model (LDM) fission barrier [9,10]. The above observations suggest that improvements in fission modeling are necessary where effects such as the roles of excitation energy and shape (of the CN) dependence of dissipation need to be further investigated [7], Experimental data on both pre-scission multiplicities and ER cross sections of a large number of systems are therefore required for a better understanding of the fission process of heavy nuclei with large excitation energies.…”

Detailed statistical model analysis of observables from fusion-fission reactions

“…The escape rate across the potential barrier or the fission rate was obtained by Kramers [100] many years ago. A reduction in fission width is obtained from the dissipative stochastic dynamical model of fission developed by Kramers where the fission width is given as [100] Kram f (E * , , K ) 64 Ni + 92 Zr [30,31], 12 C + 158 Gd [32,33], 16 O + 154 Sm [17,32,[34][35][36], 20 Ne + 150 Nd [33,[37][38][39], and 4 He + 188 Os [40][41][42]. Neutron multiplicities of 12 where β is the reduced dissipation coefficient (ratio of dissipation coefficient to inertia) and ω s is the local frequency of a harmonic oscillator potential which approximates the nuclear potential at the saddle configuration and depends on the spin of the CN [101].…”

“…4. Comparison of measured σ ER , σ fiss , and ν pre with SM predictions for the reactions 16 O + 176 Yb [42,43], 16 O + 181 Ta [5,[44][45][46][47], 19 F + 178 Hf [47], 16 O + 184 W [36,[48][49][50][51], 19 F + 181 Ta [17,18,52], and 30 Si + 170 Er [18,53,54]. Continuous (black) lines indicate the SM predictions including shell correction both in B f and LD, CELD and K-orientation effects.…”

“…One naturally wonders if there is a way to reproduce data without ad hoc manipulation of the SM parameters. (2) While a speeding up of fission, by means of reducing the fission barrier, was required to reproduce measured σ ER [14][15][16], a slowing down of fission was necessary to reproduce experimental ν pre [17,18]. Does this contradiction point to an inadequate modeling of CN decay?…”

Statistical model calculations for evaporation residue and fission cross-section for48Ti +122Sn system

“…E i is the initial excitation energy of the CN and B f is the fission barrier, which is obtained from the finite-range liquid drop model (FRLDM) [13]. Now, we have introduced a scaling factor (K f ) for the FRLDM barrier and treated it as an adjustable parameter to fit the experimental ER and fission cross-section [14,15]. The K f is varies between 0.5 to 1.0 as shown in Figure 2 and we have adjusted K f value to reproduce the experi- mental cross-section at every energy point.…”