Search for fusion suppression in reactions having entrance-channel mass-asymmetry values around the Businaro-Gallone point

Abstract

Available data on evaporation residue (ER) production and fission in a wide region of compound nucleus (CN) masses and entrance-channel mass-asymmetry values have been analyzed in search for the "starting point", where the fusion suppression due to the quasi-fission (QF) effect starts to show up. Comparing cross sections for the ER production and fission in reactions leading to the same CN, but having different values of entrance-channel mass-asymmetry, one can extract the fusion probability for a more symmetric combination with respect to quite an asymmetric one, where no limitation seems to occur. An attempt to find correlations between the fusion probabilities derived for the considered combinations and some entrance-channel characteristics is undertaken.The heavy ER production demonstrates a visible entrance channel effect of fusion suppression in quite asymmetric combinations of interacting nuclei. Such fusion suppression is quite unexpected, especially for the reaction induced by 19 F and 22 Ne [1, 2], since the QF effect, which is responsible for the lowering of the ER production cross section, appears in reactions with Mg and heavier projectiles, as follows from the fission reaction studies [3,4]. An explanation of the fusion suppression effect was proposed in [1], in the framework of the liquid-drop (LD) model. It is suggested that a transition from the contact configuration to the CN configuration is determined by an existence of the conditional barrier along the mass-asymmetry coordinate [5], or the entrancepoint position with respect to the Businaro-Gallone (BG) point [6]. Extrapolations in [1] of calculations [5] show that the mass-asymmetry values for the F + Au and Ne + Pt combinations leading to the Ra * compound nuclei are in the vicinity of the BG point. Calculations in the framework of the Generalized Liquid-Drop Model (GLDM) [7] show a similar behavior of the asymmetric fission barriers, which implies that the fusion suppression is starting to appear in the reactions with Ne and heavier projectiles.It is of interest to search for correlations between the heights of the asymmetric fission barrier or the entrance-channel mass-asymmetry values and the fusion probability values

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

“…They have used a shellcorrected fission barrier while we have used FRLDM barrier which is lower. Consequently, our ER cross-sections are smaller than that found in [16], which means a higher value of best-fit K f in our case. Further, we included the shell-correction in level density parameter which was taken from the work of Ignatyuk et al [17].…”

“…We found an energy dependence of K f as we fitted the individual data point and the best-fitted K f value 0.8 lies between the dispersion of K f ( 0.6-1.0) values. It is to be noted that in another recent calculation by Sagaidak et al [16], best-fit value of K f is reported to be 0.8 at higher excitation energies. Our results show a better fit at K f = 0.8 for lower excitation energies.…”

Measurement of the fusion probability,PCN, for hot fusion reactions

“…Some of the systems studied in this work have been studied previously, i.e., the reaction of 18 O with 197 Au [25,32,55]. In [32], the fragment angular distributions were measured for the reaction of 78-97 MeV 18 O with 197 Au.…”

“…A number of calculations of P CN for cold fusion reactions have been made using the "fusion by diffusion" approach [5,[44][45][46] that differ from both the DNS and Zagrebaev and Greiner approaches. There have also been a number of attempts [25,44,46,47] to make semi-empirical estimates of P CN using one or another models for σ capture , W sur and using measured values for σ EVR to get values of P CN for both hot and cold fusion reactions. Other aspects of quasifission , such as the time scale and the role of deformation effects in the entrance channel have been treated [38,[48][49][50].…”

“…Primarily this task becomes one of identifying quasifission, the re-separation of the contacting nuclei before moving inside the fission saddle point. There the product of the atomic numbers of the reacting nuclei, Z 1 Z 2 , exceeds 1600 [1,16,[18][19][20][21] and (c) when the asymmetry, α, of the reacting system is less than the mass asymmetry associated with the Businaro-Gallone point [22][23][24][25][26]. Unfortunately there are known exceptions to each of these general rules, i.e., (a) [24,27,28] (b) [29][30][31] (c) [31,32].…”