Cross sections of 102 element isotopes formation in the reactions of22Ne+236U and26Mg+232Th

Abstract

Abstract.The production cross sections of the isotopes 252102, 253102, and 254102 were measured for the heavy ion fusion reactions of 22Ne + 236U and 26Mg + 232Th by using the kinematic separator VASSILISSA. The obtained excitation functions and the maximum production cross sections are compared with the ones for more asymmetric reactions leading to the same compound nucleus -'58102. The experimental cross sections and the results of statistical model calculations are compared and discussed.

Direct observation of first-chance fission ofNo258

“…These expectations are possibly at odds with the measurements of Ref. [2], in which the authors extracted a value of 0.8 for n tot , averaged over the first two steps only. In a previous attempt [5] to extract the first-chance fission probability, Loveland studied the evaporation residues from the 24,25,26 Mg + 232 Th reactions and found values of 0.058 and 0.065 for n tot for the first and second steps in the deexcitation.…”

“…For very heavy nuclei, frequently f n and n tot ≈ n f . The published cross sections for the production of superheavy elements 113-118 [1] using hot fusion reactions with 48 Ca beams, as well as somewhat older data of Andreyev [2] involving the production of 258 No via hot fusion in the Mg + Th reaction, may indicate the presence of unexpected nuclear effects or physics, as understanding these data require unusually large values of n f compared to expectations from systematic trends. Sikkeland et al [3] and Cherepanov et al [4] have parametrized the average behavior of n / f for the No isotopes as well as several other transcurium nuclei.…”

“…However, the present measurement technique differs from the earlier measurements of Refs. [2,5] in that we directly measure the neutrons emitted from the cooling compound system rather than measuring evaporation residue (EVR) cross sections. One advantage of this method is that the fission cross sections are many orders of magnitude larger than the EVR cross sections.…”

Spontaneous Fission

“…The additional SF halflives reported since then up until mid-1995 are given in Table 1 [Refs. [12][13][14][15][16][17][18][19][20][21][22][23], The half-lives for e-e (even Z-even Ν) nuclides are plotted in Fig. 1, and those for e-o (even Z-odd N), o-e (odd Z-even N) and o-o (odd Z-odd N) nuclides are plotted in Fig.…”

Enhancement and Suppression of Fusion in Reactions Forming Heavy Nuclei

“…• For these neutron-deficient Th nuclei, formed with heavy projectiles, the yield increases by a factor of 4 for each additional neutron in the final product. One example is 258 No, formed by reactions with 12 C [11], 16 O [12], 22 Ne and 26 Mg [13]. • Measurements for mass-asymmetric projectile-target combinations are lacking, whereas very many mass-symmetric combinations leading to Th compound nuclei have been measured.…”