G. M. Ter Akopian

Zero neutron emission in spontaneous fission of 252Cf: a form of cluster radioactivity

By using the triple gamma coincidence technique with 20 Ge detectors at the Holifield Laboratory in the spontaneous fission of 252Cf, neutronless fragmentations, like 104Mo-148Ba, 106Mo-146Ba, 108Mo-144Ba and 104Zr-148Ce, are experimentally observed directly for the first time. When zero neutron emission spontaneous fission occurs, essentially all the available energy goes into the total kinetic energy of the fragments (cold fission). This process is seen theoretically to be an extension of cluster radioactivity, which involves the emission of one light fragment like 14C, 20O, (24)Ne or 28Mg to nearly equal fragments. In the neutronless spontaneous fission reported here, double fine structures (i.e. decays to the excited states of both fragments) are observed experimentally in contrast to fine structure in only the heavy partner populated by the light partner in earlier cluster radioactivity work. Neutronless spontaneous fission is discussed in the framework of cluster radioactivity.

Investigation of 6He cluster structures

The +2n and t+t clustering of the 6He ground state were investigated by means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled to the MUST array. Experimental data for the transfer reaction were analyzed by a distorted wave Born approximation (DWBA) calculation, including the two neutrons and the triton transfer. The couplings to the 6He4He+2n breakup channels were taken into account with a polarization potential deduced from a coupled-discretized-continuum channels analysis of the 6He+1H elastic scattering measured at the same time. The influence on the calculations of the +t exit potential and of the triton sequential transfer is discussed. The final calculation gives a spectroscopic factor close to one for the +2n configuration as expected. The spectroscopic factor obtained for the t+t configuration is much smaller than the theoretical predictions.

Identification of the

From an experiment with Gammasphere and a 252C spontaneous fission source, two bands with signatures -i and +i are identified in 153Nd Also several new transitions in 149Nd are observed for the first time. The band with signature -i in 153Nd shows no back bending, similar to the one observed in 161Er. The signature splitting observed in the ground band of 153Nd is similar to the ones observed in N=93 isotones in this mass region. In 149Nd the new transitions are placed into a band with a proposed configuration of .

\nu_{\frac 32}-[521]

The relative {sup 4}He and {sup 5}He ternary fission yields were determined from a careful analysis of the energy distribution of {alpha} spectra from a new measurement with a {sup 252}Cf source and from published data on {sup 252}Cf and {sup 235}U(n,f). The kinetic energies of the {sup 5}He and {sup 4}He ternary particles were found to be approximately 11 and 16 MeV, respectively. {sup 5}He particles contribute 10-20 % to the total alpha yield with the remainder originating from {sup 4}He accompanied fission. (c) 2000 The American Physical Society.

Band in 153Nd and the γ-Transitions in 149Nd

The relative {sup 4}He and {sup 5}He ternary fission yields were determined from a careful analysis of the energy distribution of {alpha} spectra from a new measurement with a {sup 252}Cf source and from published data on {sup 252}Cf and {sup 235}U(n,f). The kinetic energies of the {sup 5}He and {sup 4}He ternary particles were found to be approximately 11 and 16 MeV, respectively. {sup 5}He particles contribute 10-20 % to the total alpha yield with the remainder originating from {sup 4}He accompanied fission. (c) 2000 The American Physical Society.

5Heternary fission yields of252Cfand235U(n,f)

High spin states in and have been investigated using - and - coincidence studies of spontaneous fission of . Alternating parity bands built on a 7/2-level are assigned up to spin I = (37/2) and I = (29/2) in and , respectively. Another possible octupole band based on multiplet with spin up to (29/2) also is observed in both nuclei. Cascades of enhanced E1 transitions and ratios indicate strong octupole correlations. Systematics of the , and multiplets and bands in N = 85 isotones are presented.