UC Berkeley

Part I discusses the study of a new nuclear reaction and chemical separation procedure for the production of ²⁴⁰Am. Thin ²⁴²Pu, ^natTi, and ^natNi targets were coincidently activated with protons from the 88-Inch Cyclotron, producing ²⁴⁰Am, ⁴⁸V, and ⁵⁷Ni, respectively. The radioactive decay of these isotopes was monitored using high-purity Ge gamma ray detectors in the weeks following irradiation. The excitation function for the ²⁴²Pu(p, 3n)²⁴⁰Am nuclear reaction was measured to be lower than theoretical predictions, but high enough to be the most viable nuclear reaction for the large-scale production of ²⁴⁰Am.

Details of the development of a chemical separation procedure for isolating ²⁴⁰Am from proton-irradiated ²⁴²Pu are discussed. The separation procedure, which includes two anion exchange columns and two extraction chromatography columns, was experimentally investi- gated using tracer-level ²⁴¹Am, ²³⁹Pu, and model proton-induced fission products ⁹⁵Zr, ⁹⁵Nb, ¹²⁵Sb, and ¹⁵²Eu. The separation procedure was shown to have an Am/Pu separation factor of >2×10⁷ and an Am yield of ∼70%. The separation procedure was found to purify the Am sample from >99.9% of Eu, Zr, Nb, and Sb. The procedure is well suited for the processing of ∼1 gram of proton-irradiated ²⁴²Pu to produce a neutron-induced fission target consisting of tens of nanograms of ²⁴⁰Am.

Part II describes the use of the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron for the study of the ²⁴²Pu(⁴⁸Ca,5n)²⁸⁵114 nuclear re- action. The new, neutron-deficient, superheavy element isotope ²⁸⁵114 was produced in ⁴⁸Ca irradiations of ²⁴²Pu targets at a center-of-target beam energy of 256 MeV (E^∗ = 50 MeV). The α decay of ²⁸⁵114 was followed by the sequential α decay of four daughter nuclides, ²⁸¹Cn, ²⁷⁷Ds, ²⁷³Hs, and ²⁶⁹Sg. ²⁶⁵Rf was observed to decay by spontaneous fission. The measured α-decay Q-values were compared with those from a macroscopic-microscopic nuclear mass model to give insight into superheavy element shell effects. The ²⁴²Pu(⁴⁸Ca,5n)²⁸⁵114 cross

section was 0.6_-0.2^+1.3 pb.