Role of Fragment Higher Static Deformations in the Cold Binary Fission of 252^{252}Cf

We study the binary cold fission of $^{252}$Cf in the frame of a cluster model where the fragments are born to their respective ground states and interact via a double-folded potential with deformation effects taken into account up to multipolarity $\lambda=4$. The preformation factors were neglected. In the case when the fragments are assumed to be spherical or with ground state quadrupole deformation, the $Q$-value principle dictates the occurence of a narrow region around the double magic $^{132}$Sn, like in the case of cluster radioactivity. When the hexadecupole deformation is turned on, an entire mass-region of cold fission in the range 138 - 156 for the heavy fragment arise, in agreement with the experimental observations. This fact suggests that in the above mentioned mass-region, contrary to the usual cluster radioactivity where the daughter nucleus is always a neutron/proton (or both) closed shell or nearly closed shell spherical nucleus, the clusterization mechanism seems to be strongly influenced by the hexadecupole deformations rather than the $Q$-value.Comment: 10 pages, 12 figure

Isovector soft dipole mode in 6Be

By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting alpha+p+p coincidences, an E_t spectrum of high statistics was obtained, containing approximately ~5x10^6 events. The spectrum provides detailed correlation information about the well-known 0^+ ground state of 6Be at E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by Delta L=1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the 6Li ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross section obtained in the measured energy range.Comment: 8 pages, 7 figure

5He ternary fission yields of 252Cf and 235U(n,f)

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

A new spontaneous fission mode for {sup 252}Cf: Hyperdeformation, cluster radioactivity, new levels

Direct measurements of yields and neutron multiplicities were made for Sr-Nd, Zr-Ce, Mo-Ba, Ru-Xe, and Pd-Te from {gamma}-ray coincidence studies in spontaneous fission of {sup 252}Cf. Strong enhancement of the 7-10 {nu} emission channels is seen in the Mo-Ba data. Unfolding the Mo-Ba data revealed a new fission mode associated with the enhanced {nu} yields with much lower total kinetic energy going by {sup 108}Mo-{sup 144}Ba, {sup 107}Mo- {sup 145}Ba, and/or {sup 106}Mo-{sup 146}Ba. Analysis indicates one or more of {sup 144,145,146}Ba are hyperdeformed with 3:1 axis ratio. Theoretical calculations predict a third minimum in the PES for {sup 252}Cf with {beta}{sub 2} {approximately} 0.9 and {beta}{sub 3} {approximately} 0.7. Zero neutron emission channels, a new form of cluster radioactivity, are seen in 8 and 7 correlated pairs in SF of {sup 252}Cf and {sup 242}Pu, respectively, with the odd-odd zero neutron channel yields strongly enhanced as predicted for cluster radioactivity. New level structures and isotopes include new octupole deformations, identical bands and other structures