The quasi-molecular stage of ternary fission

We developed a three-center phenomenological model,able to explain qualitatively the recently obtained experimental results concerning the quasimolecular stage of a light-particle accompanied fission process. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way,a new minimum of a short-lived molecular state appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments.The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the $^{10}$Be and $^{12}$C accompanied fission of $^{252}$Cf are roughly estimated to be the order of 1 ns, and 1 ms, respectively

Ternary configuration in the framework of inverse mean-field method

A static scission configuration in cold ternary fission has been considered in the framework of mean field approach. The inverse scattering method is applied to solve single-particle Schroedinger equation, instead of constrained selfconsistent Hartree-Fock equations. It is shown, that it is possible to simulate one-dimensional three-center system via inverse scattering method in the approximation of reflectless single-particle potentials.Comment: 8 pages, 1 figure, iopart.cls, to be published in Int.J.Mod.Phys.

The Quasi-Molecular Stage of Ternary Fission

We developed a three-center phenomenological model,able to explain qualitatively the recently obtained experimental results concerning the quasimolecular stage of a light-particle accompanied fission process. It was derived from the liquid drop model under the assumption that the aligned configuration, with the emitted particle between the light and heavy fragment, is reached by increasing continuously the separation distance, while the radii of the heavy fragment and of the light particle are kept constant. In such a way,a new minimum of a short-lived molecular state appears in the deformation energy at a separation distance very close to the touching point. This minimum allows the existence of a short-lived quasi-molecular state, decaying into the three final fragments.The influence of the shell effects is discussed. The half-lives of some quasimolecular states which could be formed in the $^{10}$Be and $^{12}$C accompanied fission of $^{252}$Cf are roughly estimated to be the order of 1 ns, and 1 ms, respectively.Comment: 12 pages, 6 epsf, uses ws-p8-50x6-00.cl

Kolektivne i jednočestične strukture u jezgrama bogatim neutronima

The neutron-rich nuclei of 104,106Mo, 139,141Ba, 139Xe, 115,117Ag and 133,135Te have been studied by using the spontaneous fission source of 252Cf with the Gammasphere array. In the present work, the collective and single particle structures in these neutron-rich nuclei have been reported. Gamma type vibrational bands in 104,106Mo, particle and hole states, including candidates for tilted rotor bands in 133,135Te and a 7/2[413] rotational band in both 115,117Ag have been observed. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba and 139Xe extend evidence for two opposite parity doublets characteristic of stable octupole deformation.Proučavali smo neutronima bogate jezgre 104,106Mo, 139,141Ba, 139Xe, 115,117Ag i 133,135Te pomoću izvora spontane fisije 252Cf, primjenom uređaja Gammasphere. Prikazujemo njihove kolektivne i jednočestične strukture. Opazili smo γ-vibracijske vrpce u 104,106Mo, čestična i šupljinska stanja, uključivši kandidate za nagnutu rotorsku vrpcu u 133,135Te i rotacijsku vrpcu 7/2[413] u 115,117Ag. Jezgre 135Te i 139Ba s N = 83 su izrazito različite zbog razlika u njihovim čestičnim i šupljinskim stanjima. Novi nivoi jezgara 141Ba i 139Xe daju dodatni dokaz za postojanje dvaju dubleta suprotne parnosti koji su karakteristični za stabilnu oktupolnu deformaciju

Kolektivne i jednočestične strukture u jezgrama bogatim neutronima

The neutron-rich nuclei of 104,106Mo, 139,141Ba, 139Xe, 115,117Ag and 133,135Te have been studied by using the spontaneous fission source of 252Cf with the Gammasphere array. In the present work, the collective and single particle structures in these neutron-rich nuclei have been reported. Gamma type vibrational bands in 104,106Mo, particle and hole states, including candidates for tilted rotor bands in 133,135Te and a 7/2[413] rotational band in both 115,117Ag have been observed. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba and 139Xe extend evidence for two opposite parity doublets characteristic of stable octupole deformation.Proučavali smo neutronima bogate jezgre 104,106Mo, 139,141Ba, 139Xe, 115,117Ag i 133,135Te pomoću izvora spontane fisije 252Cf, primjenom uređaja Gammasphere. Prikazujemo njihove kolektivne i jednočestične strukture. Opazili smo γ-vibracijske vrpce u 104,106Mo, čestična i šupljinska stanja, uključivši kandidate za nagnutu rotorsku vrpcu u 133,135Te i rotacijsku vrpcu 7/2[413] u 115,117Ag. Jezgre 135Te i 139Ba s N = 83 su izrazito različite zbog razlika u njihovim čestičnim i šupljinskim stanjima. Novi nivoi jezgara 141Ba i 139Xe daju dodatni dokaz za postojanje dvaju dubleta suprotne parnosti koji su karakteristični za stabilnu oktupolnu deformaciju

Subnanosecond lifetime measurements of excited states in nuclei far from stability

A system was developed to measure the lifetimes of nuclear states in the range of 0.05 to 1 nanosecond in nuclei far from stability. A Gerholm magnetic lens was placed on-line with the UNISOR mass separator to observe conversion electrons in coincidence with ..gamma.. rays detected in a plastic scintillator. With this system, the half-life of the 522 keV, O/sup +/ level in /sup 186/Hg was measured to be 155 +- 70 picoseconds. Improvements in this system should make possible on-line measurements of half-lives as short as approx. = 50 picoseconds. 12 references

Identification of new transitions and mass assignments of levels in 143−153^{143-153}Pr

The previously reported levels assigned to 151,152,153Pr have recently been called into question regarding their mass assignment. The above questioned level assignments are clarified by measuring g-transitions tagged with A and Z in an in-beam experiment in addition to the measurements from 252Cf spontaneous fission (SF) and establish new spectroscopic information from $N=84$ to $N=94$ in the Pr isotopic chain. The isotopic chain 143-153Pr has been studied from the spontaneous fission of 252Cf by using Gammasphere and also from the measurement of the prompt g-rays in coincidence with isotopically-identified fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced using 238U beams on a 9Be target at energies around the Coulomb barrier. The g-g-g-g data from 252Cf (SF) and those from the GANIL in-beam A- and Z-gated spectra were combined to unambiguously assign the various transitions and levels in 151,152,153Pr and other isotopes. New transitions and bands in 145,147,148,149,150Pr were identified by using g-g-g and g-g-g-g coincidences and A and Z gated g-g spectra. The transitions and levels previously assigned to 151,153Pr have been confirmed by the (A,Z) gated spectra. The transitions previously assigned to 152Pr are now assigned to 151Pr on the basis of the (A,Z) gated spectra. Two new bands with 20 new transitions in 152Pr and one new band with 7 new transitions in 153Pr are identified from the g-g-g-g coincidence spectra and the (A,Z) gated spectrum. In addition, new g-rays are also reported in 143-146Pr. New levels of 145,147-153Pr have been established, reliable mass assignments of the levels in 151,152,153Pr have been reported and new transitions have been identified in 143-146Pr showing the new avenues that are opened by combining the two experimental approaches.Comment: Accepted in Phys. Rev.