Ho with the maxima at 12.6 ± 1.9 mb, 12.6 ± 1.7 mb, and 9.4 ± 1.3 mb, respectively. For the reaction with 154 Gd, the maximum is slightly lower at 4.0 ± 0.6 mb. A simple model to describe the measured production cross sections was employed. Capture was estimated using the "diffused barrier formula" from the "fusion by diffusion" model proposed byŚwiątecki et al. The fusion probability was estimated using a phenomenological expression presented by Siwek-Wilczyńska et al. The survival probability was calculated according to the formula of Vandenbosch and Huizenga, derived from transition-state theory. Best agreement is reached between calculation and experiment upon inclusion of collective effects in the calculation of the survival probability, shown previously to be important for production of weakly deformed nuclei. This, in turn, challenges the expectation of strong shell-stabilization benefiting the production cross section. The present data is compared with earlier studies on production of neutron-deficient nuclei in Ca-induced reactions with lanthanide targets. PACS number(s): 25.70.Gh, 25.70.Jj

We have measured the K-shell and total internal conversion coefficients, αK and αT , for the 150.8-keV E3 transition in 111 Cd to be 1.449 (18) and 2.217(26) respectively. The αK result agrees well with Dirac-Fock calculations in which the effect of the K-shell atomic vacancy is accounted for; it extends our precision tests of αK calculations to Z = 48, the lowest Z yet measured. However, the result for αT disagrees by about two standard deviations from the calculated αT value, whether or not the atomic vacancy is included.

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

Background: Previously reported cross sections of 45 Sc-induced reactions with lanthanide targets are much smaller than 48 Ca-induced reactions on the same targets. 44 Ca is one proton removed from 45 Sc and could be used to produce nuclei with a relative neutron content between those produced in the 45 Sc-and 48 Ca-induced reactions.Purpose: As part of a systematic investigation of fusion-evaporation reactions, cross sections of 44 Cainduced reactions on lanthanide targets were measured. These results are compared to available data for 48 Sc-induced fusion-evaporation cross sections on the same lanthanide targets. Collectively, these data provide insight into the importance of the survival against fission of excited compound nuclei produced near spherical shell closures. Gd once differences in capture cross sections and compound nucleus formation probabilities are corrected for. Methods Conclusions: Excitation functions were measured in44 Ca-induced reactions on lanthanide targets. Evaporation residue cross sections were two orders of magnitude larger than 45 Sc-induced reactions on the same targets due to an increase in the survival probability of the compound nucleus. However, little evidence of cross section enhancement due to shell stabilization of the compound nucleus was observed.

Cross sections for the production of shell-stabilized evaporation residues in the 50

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Abstract. The possibility of forming new superheavy elements with projectiles having Z > 20 is discussed. Current research has focused on the fusion of 48 Ca with actinide targets, but these reactions cannot be used for new element discoveries in the future due to a lack of available target material. The influence on reaction cross sections of projectiles with Z > 20 have been studied in so-called analog reactions, which utilize lanthanide targets carefully chosen to create compound nuclei with energetics similar to those found in superheavy element production. Dy have been studied at the Cyclotron Institute at Texas A&M University using the Momentum Achromat Recoil Spectrometer. The results of these experimental studies are discussed in terms of the influence of collective enhancements to level density for compound nuclei near closed shells, and the implications for the production of superheavy elements. We have observed no evidence to contradict theoretical predictions that the maximum cross section for the 249

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