321 research outputs found
Exhaustion of Nucleation in a Closed System
We determine the distribution of cluster sizes that emerges from an initial
phase of homogeneous aggregation with conserved total particle density. The
physical ingredients behind the predictions are essentially classical:
Super-critical nuclei are created at the Zeldovich rate, and before the
depletion of monomers is significant, the characteristic cluster size is so
large that the clusters undergo diffusion limited growth. Mathematically, the
distribution of cluster sizes satisfies an advection PDE in "size-space".
During this creation phase, clusters are nucleated and then grow to a size much
larger than the critical size, so nucleation of super-critical clusters at the
Zeldovich rate is represented by an effective boundary condition at zero size.
The advection PDE subject to the effective boundary condition constitutes a
"creation signaling problem" for the evolving distribution of cluster sizes
during the creation era.
Dominant balance arguments applied to the advection signaling problem show
that the characteristic time and cluster size of the creation era are
exponentially large in the initial free-energy barrier against nucleation, G_*.
Specifically, the characteristic time is proportional to exp(2 G_*/ 5 k_B T)
and the characteristic number of monomers in a cluster is proportional to
exp(3G_*/5 k_B T). The exponentially large characteristic time and cluster size
give a-posteriori validation of the mathematical signaling problem. In a short
note, Marchenko obtained these exponentials and the numerical pre-factors, 2/5
and 3/5. Our work adds the actual solution of the kinetic model implied by
these scalings, and the basis for connection to subsequent stages of the
aggregation process after the creation era.Comment: Greatly shortened paper. Section on growth model removed. Added a
section analyzing the error in the solution of the integral equation. Added
reference
Effect of Coriolis Interaction on the Decay of Isotones with N = 149 and N = 153
© 2018, Allerton Press, Inc. The quasi-neutron structure of nuclei in two chains of odd isotones with N = 149 and N = 153:243,247Pu,245,249Cm,247,251Cf,249,253Fm,251,255No, and is considered. Single-particle energy spectra are calculated using the two center shell model (TCSM). Minimizing the potential energy with respect to the collective coordinates gives the ground state of the studied nucleos, which is subsequently used to describe low-lying quasi-neutron states. The K-mixing of the basis TCSM wave functions is considered by including the Coriolis correction in the total Hamiltonian of the system. The effect of level blocking is also considered in the calculations. The probabilities of the E2 transitions to the ground states and the corresponding lifetimes of the quasi-neutron levels are estimated
Application of the dinuclear system model to fission process
© 2016 Owned by the authors, published by EDP Sciences.A theoretical evaluation of the collective excitation spectra of nucleus at large deformations is possible within the framework of the dinuclear system model, which treats the wave function of the fissioning nucleus as a superposition of a mononucleus configuration and two-cluster configurations in a dynamical way, permitting exchange of nucleons between clusters. In this work the method of calculation of the potential energy and the collective spectrum of fissioning nucleus at scission point is presented. Combining the DNS model calculations and the statistical model of fission we calculate the mass, total kinetic energy, and angular distribution of fission fragments for the neutron-induced fission of 239Pu
Multi-step particle emission probabilities in superheavy nuclei at moderate excitation energies
The probabilities of -, -, and -evaporation channels in
excited superheavy nuclei were evaluated using the Monte Carlo method. The
calculations utilized microscopically determined nuclear level densities and
were compared with results obtained from the phenomenological Jackson formula.
Effective temperatures derived from the microscopic approach were incorporated
into the Jackson formula for different evaporation channels at low and moderate
excitation energies. Additionally, an analytical formula was introduced to
estimate the average kinetic energy of emitted particles in multi-step
processes.Comment: 10 pages, 3 figure
Entropies, level-density parameters, and fission probabilities along the triaxially- and axially-symmetric fission paths in Lv
We employ a statistical approach to investigate the influence of axial
asymmetry on the nuclear level density and entropy along the fission pathways
of a superheavy nucleus, explicitly focusing on the Lv isotope. These
pathways are determined within multidimensional deformation spaces. Our
analysis reveals a significant impact of triaxiality on entropy. Additionally,
suppressing shell effects can alter the fission scenario depending on the
available excitation energy. We derive the deformation-dependent level density
parameter, which plays a crucial role in estimating the survival probability of
a superheavy nucleus. Furthermore, we utilize a set of master equations to
obtain the time-dependent fission probabilities and calculate the ratio of
decay probabilities for both axial and triaxial paths.Comment: submitted to PR
- …