Energy dependence of fusion evaporation-residue cross sections in theSi28+

Abstract

Fusion evaporation-residue cross sections for the 'Si+ ' C reaction have been measured in the energy range 18~E,~136 MeV using time-of-Aight techniques. Velocity distributions of mass-identified reaction products were used to identify evaporation residues and to determine the complete-fusion cross sections at high energies. The data are in agreement with previously established systematics which indicate an entrance-channel mass-asymmetry dependence of the incomplete-fusion evaporation-residue process. The complete-fusion evaporation-residue cross sections and the deduced critical angular rnomenta are compared with earlier measurements and the predictions of existing models. PACS number(s): 25.70.Jj For more than a decade fusion evaporation-residue cross sections for the Si+' C system have been measured [1 -5] at center-of-mass energies ranging from 14 to 80 MeV. With one exception [1], the grouping and trend of the low-energy (E,~3 1 MeV) data are in reasonable agreement. Higher-energy cross sections measured byHarmon et al. [5] show a rapid decrease with increasing energy. The critical angular momenta extracted from their complete-fusion evaporation-residue cross sections show a saturation at 22A' which indicates an entrancechannel limitation of the fusion cross section at high energy when compared to other systems forming the same compound nucleus. The authors reported that this value for the critical angular momentum saturation is consistent with the results of an orbiting analysis of deepinelastic scattering of Si+' C [6] and supports the idea that the binary cross sections found in this reaction can be attributed to a dinuclear orbiting mechanism [7].In this work we present evaporation-residue cross-IL 60439. section measurements for Si+ ' C in the center-of-mass energy range from 18 to 136 MeV. Initially, data were taken at Si bombarding energies of 309, 397, and 452 MeV as part of a systematic study [8,9) of the energy and target dependence of the incomplete-fusion evaporationresidue process. Additional measurements were then performed at lower energies resulting in data extending over one of the largest energy ranges ever measured for a light system. The fusion evaporation-residue cross sections reported here at Si bombarding energies between 60 and 178 MeV were measured at the Florida State University Superconducting Accelerator Laboratory. The Si beams ranged in intensity from 5 to 30 particle nA and were incident on self-supporting (200 pg/cm ) ' C foils mounted in a 36-cm scattering chamber. The targets were monitored using a 500-pm Si surface-barrier detector positioned at 14.5 above the reaction plane.Mass identification of the reaction products was obtained with the use of a time-of-flight system consisting of a carbonfoil (10 pg/cm ) channel plate to provide the start signal and a 500-pm Si surface-barrier detector to obtain the stop signal and energy of each particle. With a flight path of 2.7 m the detection system subtended a solid angle of 44 psr. Angular distributions were measured over a ran...

Role of deformation in the decay of 56Ni and 40Ca di-nuclei

“…The data analysis was performed using CACARIZO, the Monte Carlo version of the statistical-model code CASCADE [6]. The angular momenta distributions, needed as the principal input to constrain the calculations were taken from compiled 28 Si+ 28 Si [7] and 28 Si+ 12 C [8,9] complete fusion data. The other ingredients for the realistic statisticalmodel calculations such as the nuclear level densities and the barrier transmission coefficients, are usually deduced from the study of the evaporated light particle spectra.…”

Towards a unified description of evaporation-residue fusion cross-sections above the barrier

“…Despite a broad coverage in the α and N sys /Z sys variables many of data are for the mass symmetric systems and, in particular, for the systems with the equal number of neutrons N sys and protons Z sys . About 100 additional data points from those measurements which have reported existence of a non-negligible fusion-fission component will be presented p-1 [18,19] 20Ne+16O [20] 24Mg+12C [21] 12C+27Al [22] 16O+24Mg [23] 20Ne+20Ne [20] 28Si+12C [24,25] 14N+27Al [26] 16O+26Mg [23] 18O+24Mg [23] 16O+27Al [27][28][29] 32S+12C [30][31][32][33][34] 20Ne+26Mg [35] 20Ne+27Al [28,36] 20Ne+27Al [28,36] 35Cl+12C [37][38][39] 16O+32S [28] 16O+40Ca [40,41] 28Si+28Si [42][43][44][45][46] 28Si+28Si [42][43][44][45][46] 32S+24Mg [47,48] 19F+40Ca [49,50] 32S+27Al [28,49] 35C...…”

Comprehensive analysis of fusion data well above the barrier

“…Data of the same experiments discussed in the case of incomplete fusion results belonging to group 1 in Fig. 7, namely 3 points of the 28 Si + 12 C [31] and a single data point of the 32 S + 12 C reaction [41], are again outside the general data trend. Thus, they are labeled by lighter colors of the symbols.…”