M. Sakama

{alpha} decay of {sup 238}Cm and the new isotope {sup 237}Cm

Alpha decays of {sup 237}Cm and {sup 238}Cm have been studied using a gas-jet coupled on-line isotope separator. The new isotope {sup 237}Cm has been identified through the detection of 6656{+-}10 keV {alpha} particles. The {alpha} energy of {sup 238}Cm has been revised more precisely than the previous one. The {alpha} transition to the first excited 2{sup +} state in {sup 234}Pu has also been observed. It was found that the 2{sup +} energy in {sup 234}Pu is much higher than those in heavier Pu isotopes.

Spectroscopic studies of mass-separated heavy nuclei

EC and α decays of neutron-deficient nuclei 233–236Am have been studied using a gas-jet coupled on-line isotope separator. A proton orbital of the ground state of 235Am and neutron orbitals in 235Pu have been estimated from a decay scheme of 235Am. The 5− ground state and the 1− EC decaying isomer in 236Am and the configuration of two-quasiparticle states in 236Pu have been established. Qα values of 233,235,236Am have been determined from measured α-particle energies. It was found that evaluated Qα values were systematically overestimated by 100–200 keV in neutron-deficient Am nuclei.

Heavy element nuclear chemistry at JAERI

The present status of heavy element nuclear chemistry research at JAERI (Japan Atomic Energy Research Institute) is reviewed. Production of the transactinide nuclei 261Rf and 262Db via the reactions of 248Cm(18O,5n) and 248Cm(19F, 5n), respectively, at the JAERI tandem accelerator is reported. Study of the aqueous chemistry of Rf is being carried out with a newly developed rapid ion-exchange separation apparatus. Anion-exchange behavior of Rf in acidic solution is briefly discussed. Recent experimental results on decay studies of neutron-deficient actinide nuclei using the gas-jet coupled JAERI-ISOL are given. We also discuss characteristics of nuclear deformation properties at scission in symmetric and asymmetric fission of actinides. Prospects for studies in the near future are briefly considered.

Symmetric and asymmetric scission properties

Existence of two kinds of scission configurations associated with the symmetric and asymmetric fission modes is pointed out in the fission of actinides: elongated and compact configurations. Each symmetric and asymmetric scission property is discussed in terms of shape elongation evaluated from fragment total kinetic energy (TKE). It is found that the shape elongation associated with the asymmetric fission mode is nearly constant for a wide range of fissioning nuclei, while that with the symmetric one is also constant except for low-energy induced fission and spontaneous fission (SF) of heavy nuclei. Prom the systematic study of the scission properties, the bimodal fission observed in SF of the heavy actinides is interpreted as the presence of the two fission paths of the ordinary asymmetric mode and a strongly shell-influenced symmetric one.