121 research outputs found
An evaporation-based model of thermal neutron induced ternary fission of plutonium
Ternary fission probabilities for thermal neutron induced fission of
plutonium are analyzed within the framework of an evaporation-based model where
the complexity of time-varying potentials, associated with the neck collapse,
are included in a simplistic fashion. If the nuclear temperature at scission
and the fission-neck-collapse time are assumed to be ~1.2 MeV and ~10^-22 s,
respectively, then calculated relative probabilities of ternary-fission
light-charged-particle emission follow the trends seen in the experimental
data. The ability of this model to reproduce ternary fission probabilities
spanning seven orders of magnitude for a wide range of light-particle charges
and masses implies that ternary fission is caused by the coupling of an
evaporation-like process with the rapid re-arrangement of the nuclear fluid
following scission.Comment: 25 pages, 12 figures, accepted for publication in IJMP
Competition of fusion and quasi-fission in the reactions leading to production of the superheavy elements
The mechanism of fusion hindrance, an effect observed in the reactions of
cold, warm and hot fusion leading to production of the superheavy elements, is
investigated. A systematics of transfermium production cross sections is used
to determine fusion probabilities. Mechanism of fusion hindrance is described
as a competition of fusion and quasi-fission. Available evaporation residue
cross sections in the superheavy region are reproduced satisfactorily. Analysis
of the measured capture cross sections is performed and a sudden disappearance
of the capture cross sections is observed at low fusion probabilities. A
dependence of the fusion hindrance on the asymmetry of the projectile-target
system is investigated using the available data. The most promising pathways
for further experiments are suggested.Comment: 8 pages, 7 figures, talk presented at 7th International
School-Seminar on Heavy-Ion Physics, May 27 - June 1, 2002, Dubna, Russi
Manifestation of transient effects in fission induced by relativistic heavy-ion collisions
We examine the manifestation of transient effects in fission by analysing
experimental data where fission is induced by peripheral heavy-ion collisions
at relativistic energies. Available total nuclear fission cross sections of
238U at 1 A GeV on gold and uranium targets are compared with a
nuclear-reaction code, where transient effects in fission are modelled using
different approximations to the numerical time-dependent fission-decay width: a
new analytical description based on the solution of the Fokker-Planck equation
and two widely used but less realistic descriptions, a step function and an
exponential-like function. The experimental data are only reproduced when
transient effects are considered. The deduced value of the dissipation strength
depends strongly on the approximation applied for the time-dependent
fission-decay width and is estimated to be of the order of 2x10**21 s**(-1). A
careful analysis sheds severe doubts on the use of the exponential-like
in-growth function largely used in the past. Finally, we discuss which should
be the characteristics of experimental observables to be most sensitive to
transient effects in fissionComment: 18 pages, 2 figures, background information on
http://www-w2k.gsi.de/kschmidt
Mass measurements towards doubly magic Ni-78 : Hydrodynamics versus nuclear mass contribution in core-collapse supernovae
We report the first high-precision mass measurements of the neutron-rich nuclei Ni-74,Ni-75 and the clearly identified ground state of Cu-76, along with a more precise mass-excess value of Cu-78, performed with the double Penning trap JYFLTRAP at the Ion Guide Isotope Separator On-Line (IGISOL) facility. These new results lead to a quantitative estimation of the quenching for the N = 50 neutron shell gap. The impact of this shell quenching on core-collapse supernova dynamics is specifically tested using a dedicated statistical equilibrium approach that allows a variation of the mass model independent of the other microphysical inputs. We conclude that the impact of nuclear masses is strong when implemented using a fixed trajectory as in the previous studies, but the effect is substantially reduced when implemented self-consistently in the simulation. (C) 2022 The Authors. Published by Elsevier B.V.Peer reviewe
Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity
oai:ojs2.jnp.chitkara.edu.in:article/2This paper presents a journey within some open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable frame-work since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the dependence of viscosity on the temperature may change with the fissility of the composite system; iii) the opportunity to measure also observables in the evaporation residues channel translates into a larger set of effective constraints for the models
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