Decay Studies of Neutron-deficient Am, Cm, and Bk Nuclei Using an On-line Isotope Separator

Abstract

Spectroscopic studies of heavy and superheavy nuclei give usinformation on various nuclear properties in heavy element re-gion. Measured α-decay energies lead to the precise determina-tion of atomic masses which are one of the most essential quan-tities to define nuclear decay properties, fission and fusion prob-abilities, and shell stability in heavy nuclei. Gamma-ray spec-troscopy following α, β, and orbital-electron capture (EC) de-cays and fine structure of α-particle spectra reveal excited statesin daughter nuclei, single-particle energies, proton-neutron con-figurations, and nuclear deformation.Neutron-deficient Am, Cm, and Bk nuclei predominantly de-cay by EC, and their α-decay probabilities are very small. Thisproperty makes experimentalstudies for these nuclei difficult. Inorder to measure γ rays following the EC decay and very weakαtransitions, it is quite important to isolate the nuclei of interestfrom a large amount of other reaction products. The traditionalmethod to separate heavy nuclei is chemical separation owingto its high separation efficiency. Another efficient method is in-flight separation using recoil separators. However, these meth-ods are not so suitable to apply to the neutron-deficient Am,Cm, and Bk nuclei; their half-lives are in the order of a few min-utes, and their α-decay intensities are very small. In this work,we have studied EC and α decays of the neutron-deficient Amand Cm nuclei using the gas-jet coupled JAERI on-line isotopeseparator (ISOL)