Activation Cross Sections for 14.8-Mev Neutrons and Some New Radioactive Nuclides in the Rare Earth Region

R. G. Wille and R. W. Fink
Phys. Rev. 118, 242 – Published 1 April 1960
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Abstract

Activation cross sections on 27 stable nuclides of elements Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, and Lu were measured for 14.8±0.8-Mev neutrons. Highly enriched isotopes were used as targets in most cases, and in a few instances radiochemical separations were performed whenever it was necessary and possible in view of the product half-lives. The measured cross sections for (n, 2n) reactions were found to agree within an order of magnitude with predictions from statistical evaporation theory. However, experimental values of (n, p) and (n, α) cross sections generally appear to be larger than calculated from continuum theory of the compound nucleus. The cross sections show no significant effects due to the 82-neutron closed shell and, furthermore, the Levkovskii effect, which is quite striking in the low Z region, appears to be negligible for (n, p) and (n, α) reactions in the rare earth region. The (n, 2n) cross sections show little variation with mass number at constant Z, and they exhibit a decrease with increasing mass number at N=82.

Several previously unreported activities were observed; their half-lives, assignment, and gamma radiations are as follows: 12±3 min Pr148 from the Nd148(n, p) reaction; 0.5±0.1 min Sm157 from the Gd160(n, α) reaction, 0.57±0.01 Mev gamma; 7±1 min Tb163 from the Dy163(n, p) reaction, 0.18±0.05-Mev gamma; 3.3±0.5 min Ho168 from the Er168(n, p) reaction, 0.85±0.05-Mev gamma; 40±10 sec Ho170 from the Er170(n, p) reaction; 4.4±0.4 min Dy167 from the Er170(n, α) reaction; 2.0±0.5 min activity with gammas at 0.18±0.01, 0.25±0.01, and 0.36±0.01 Mev which may be Tm176, Er173, or possibly isomeric Yb177m from enriched Yb176 bombardments. Tentative assignment of a 5.5±0.5-min activity to Tm174 is suggested from bombardment of enriched Yb174.

  • Received 21 September 1959

DOI:https://doi.org/10.1103/PhysRev.118.242

©1960 American Physical Society

Authors & Affiliations

R. G. Wille* and R. W. Fink

  • Department of Chemistry, University of Arkansas, Fayetteville, Arkansas

  • *Phillips Petroleum Company predoctoral fellow, 1958-59.
  • Present address: The Gustaf Werner Institute for Nuclear Chemistry, University of Uppsala, Sweden.

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Vol. 118, Iss. 1 — April 1960

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