0000000000376760
AUTHOR
O. I. Osetrov
Neutron and fragment yields in proton-induced fission of 238U at intermediate energies
The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of 238 U at energies Ep ¼ 20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields ofneutron-rich fission products in the fission of 238 U by 25 MeV protons were measured using an ion guide-based isotope separator technique. The resul…
Peculiarities in fragment mass distribution in the 238U + 40Ar (243 MeV) reaction
A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of the 278110 composite system produced in the reaction 238U + 40Ar (243 MeV) at an initial excitation energy E * > 70 MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic nuclei (clusters). In the data there is also evidence for a new type of decay -- collinear cluster tripartition of an excited nucleus.
Fission product yields at intermediate energy
The results of experimental and theoretical studies of fission product yields in proton-induced fission of 238U are presented. The yields of neutron-rich Ni, Cu, Zn, Ga and Ge—isotopes were measured by 25 MeV protons and the ion guide-based isotope separator technique. The pre-neutron emission fragment mass distributions were measured by protons at energies Ep=20, 35, 50 and 60 MeV using time-of-flight method. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus. A model calculation of fission products yields for fission of 238U by protons and neutrons is presented which predicts the formation cross sections for neutr…
Pre- and post-scission neutron emission in the reaction180Hf(40Ar, fission) atE lab=216 MeV
Neutron and fission fragment spectra following the180Hf(40Ar,f) reaction atE lab=216MeV were measured. The following neutron total, pre- and post-scission multiplicities were extracted:M tot =7.2±1.3,M pre =2.7±0.9,M post =4.5±0.9. The average temperature parameters of the neutron spectra areT pre=(1.63±0.16) MeV andT post=(1.14±0.26)MeV. The mean total kinetic energy of the fission fragments is TKE=(166±10) MeV and the measured width is σTKE=17.3MeV. The width of the fragment mass distribution is σ A =18.3u. The same reaction was analyzed using a modified statistical code which includes nuclear dissipation effects and particle and γ-ray emission in the equilibrium compound nucleus state an…
Fine structure in fragment mass-energy distribution from 238U+40Ar (275 MeV)
Existence of a new feature in fragment mass-energy distribution is reported. Careful analysis of the data obtained in the reaction 238U + 40Ar (275 MeV) shows that small but statistically significant ripples visible already in the gross mass spectrum come from extended and regular 2D patterns in the TKE vs. mass matrix. Intensity distributions of these patterns coincide with the location of heavy clusters such as 78Ni, 108Mo, or 132Sn. Presumably, the observed patterns show the dominant trajectories in the elongation vs. mass-asymmetry space of the decaying system. This information, unknown in the past, can shed a new light even on the previously well-studied reactions.