Hot fusion-evaporation cross sections ofSc45-induced reactions with lanthanide targets

Abstract

Background: 45 Sc has rarely been studied as a projectile in fusion-evaporation reactions. The synthesis of new superheavy elements with Z > 118 will require projectiles with Z > 20, and 45 Sc could potentially be used for this purpose.Purpose: Cross sections were measured for the xn and pxn exit channels in the reactions of 45 Sc with lanthanide targets for comparison to previous measurements of 48 Ca reacting with similar targets. These data provide insight on the survival of spherical, shell-stabilized nuclei against fission, and could have implications for the discovery of new superheavy elements. Methods:Beams of 45 Sc 6+ were delivered from the K500 superconducting cyclotron at Texas A&M University with an energy of ≈5 MeV/nucleon. Products were purified using the Momentum Achromat Recoil Spectrometer, and excitation functions were measured for reactions of 160 Gd, 159 Tb, and 162 Dy at five or more energies each. Evaporation residues were identified by their characteristic α-decay energies. Experimental data were compared to a simple theoretical model to study each step in the fusion-evaporation process. 2.4 + − , and 1.8 ± 0.6 μb, respectively. Proton emission competes effectively with neutron emission from the excited compound nucleus in most cases. The α, αn, and α2n products were also observed in the 45 Sc + 162 Dy reaction.Conclusions: Excitation functions were reported for 45 Sc-induced reactions on lanthanide targets for the first time, and these cross sections are much smaller than for 48 Ca-induced reactions on the same targets. The relative neutron-deficiency of the compound nuclei leads to significantly increased fissility and large reductions in the survival probability. Little evidence for improved production cross sections due to shell-stabilization was observed. PACS number(s): 25.70.Gh, 25.70.Jj

Hot fusion-evaporation cross sections ofCa44-induced reactions with lanthanide targets

“…(1) in Ref. [3] was then performed to determine if the number of data counts in the peak was above background. Regions of interest (ROIs) were identified for each of the possible reaction products based on the PSSD resolution, and a flat background was fit to each spectrum to determine the number of background counts per bin.…”

“…The experimental setup was nearly identical to that described in our previous work [3], so only important details and differences are presented here. The desired reaction products were physically separated using the Momentum Recoil Achromat…”

“…Previously, we have reported results using 48 Ca [1], 50 Ti [2], 54 Cr [2] and 45 Sc [3] projectiles, respectively, to bombard lanthanide targets and produce compound nuclei (CN) with Z = 84-90. EvR cross sections for xn exit channels ranged over four orders of magnitude for these reactions, and theoretical modeling emphasized the role of the neutron separation energy and the fission barrier in determining the magnitude of these cross sections.…”

“…However, the influence of CELD may negate this effect, and the cross section enhancement may not be observed. This effort is part of a systematic study of this region using projectiles with Z ≥ 20 to bombard lanthanide targets [1][2][3]. 44 Ca (Z = 20) has one less proton than 45 Sc (Z = 21), which was the focus of a recent investigation [3], and both projectiles are N = 24 isotones.…”

“…This effort is part of a systematic study of this region using projectiles with Z ≥ 20 to bombard lanthanide targets [1][2][3]. 44 Ca (Z = 20) has one less proton than 45 Sc (Z = 21), which was the focus of a recent investigation [3], and both projectiles are N = 24 isotones. The CN produced by the 44 Ca-induced reactions are more neutronrich than the CN in the 45 Sc-induced reactions on the same targets, which increases the fission barrier relative to the neutron separation energy.…”