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

Formation of Heavy Neutron-Deficient Nuclides in 3He-Induced Reactions

Peer reviewe

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

CLIMATIC IMPLICATIONS OF THE FRESH WATER EXPANSION IN THE GREENLAND SEA AND THE NORTH ATLANTIC

In second part of XX century there are three valuable salinity anomalies in North Atlantic, so-called «The Great Salinity Anomaly» (GSA), which can be characterized as a large, near-surface pool of fresher water [31–33, 36, 37]. There are GSA’70s, GSA’80s and GSA’90s. Dickson [37] described this event as one of dramatic and prolonged changes in ocean’s climate in XX century. In this paper, we have shown genesis of GSA’70s connected with ice production in Arctic flaw leads. Formation of GSAs’ in 1980s and 1990s has, at least, two main reasons. First is fresh water pools and huge amounts of ice carried out fromArcticBasin. The second one is recirculation of previous salinity anomaly inSubarcticBasin. Phenomenological model of climate change formation in polar and subpolar zone of North Hemisphere is presented in the paper. Examination conditions of previous GSA’s appearance and analysis of valuable fresh water intrusions in North Atlantic allow us to conclude that conditions for GSA’2010s are formed already and started to propagate inNorth Atlantic. For the first time we described GSA during its appearance, not post factum. Thus, we are standing at the break point of relatively long cooling inArctic

Neutron-rich nuclei and fission: recent developments and future aspects

Production and studies of neutron-rich nuclei produced in fission are reviewed. Some recent experiments performed with the ISOL technique at the IGISOL and the ISOLDE facilities are reviewed. The manipulation of neutron-rich nuclei is discussed with a special focus on radioactive ion cooling and trapping techniques under construction worldwide. Perspectives of obtaining intense post accelerated beams of fission products are discussed. (50 refs)

Neck fragmentation in fission and quasifission of heavy and superheavy nuclei

The generalized approach is proposed for the ternary fission and the neck fragmentation of the dinuclear system formed in the heavy ion quasifission reactions. The light-charged-particles accompanied the fission and quasifission are the valuable probes for studies of the dynamics of the hyperdeformed nuclear configurations with neck. The developed model describes well the light-charged-particle emission probabilities and their mass distributions in the ternary fission of actinide nuclei. The model is also applied to analyze the double differential distributions of the protons and α-particles accompanied fragmentation in the reaction 86Kr + 206Pb at EKr = 500 and 600 MeV. It was found that the near scission emission multiplicities of α-particles are and 0.070 ± 0.005 at lower and higher energies, respectively. The neck emission of the protons was not detected

Advanced model for the prediction of the neutron-rich fission product yields

The consistent models for the description of the independent fission product formation cross sections in the spontaneous fission and in the neutron and proton induced fission at the energies up to 100 MeV is developed. This model is a combination of new version of the two-component exciton model and a time-dependent statistical model for fusion-fission process with inclusion of dynamical effects for accurate calculations of nucleon composition and excitation energy of the fissioning nucleus at the scission point. For each member of the compound nucleus ensemble at the scission point, the primary fission fragment characteristics: kinetic and excitation energies and their yields are calculated using the scission-point fission model with inclusion of the nuclear shell and pairing effects, and multimodal approach. The charge distribution of the primary fragment isobaric chains was considered as a result of the frozen quantal fluctuations of the isovector nuclear matter density at the scission point with the finite neck radius. Model parameters were obtained from the comparison of the predicted independent product fission yields with the experimental results and with the neutron-rich fission product data measured with a Penning trap at the Accelerator Laboratory of the University of Jyväskylä (JYFLTRAP)

КЛИМАТИЧЕСКИЕ ПОСЛЕДСТВИЯ ЭКСПАНСИИ ПРЕСНЫХ ВОД В ГРЕНЛАНДСКОЕ МОРЕ И СЕВЕРНУЮ АТЛАНТИКУ

In second part of XX century there are three valuable salinity anomalies in North Atlantic, so-called «The Great Salinity Anomaly» (GSA), which can be characterized as a large, near-surface pool of fresher water [31–33, 36, 37]. There are GSA’70s, GSA’80s and GSA’90s. Dickson [37] described this event as one of dramatic and prolonged changes in ocean’s climate in XX century. In this paper, we have shown genesis of GSA’70s connected with ice production in Arctic flaw leads. Formation of GSAs’ in 1980s and 1990s has, at least, two main reasons. First is fresh water pools and huge amounts of ice carried out fromArcticBasin. The second one is recirculation of previous salinity anomaly inSubarcticBasin. Phenomenological model of climate change formation in polar and subpolar zone of North Hemisphere is presented in the paper. Examination conditions of previous GSA’s appearance and analysis of valuable fresh water intrusions in North Atlantic allow us to conclude that conditions for GSA’2010s are formed already and started to propagate inNorth Atlantic. For the first time we described GSA during its appearance, not post factum. Thus, we are standing at the break point of relatively long cooling inArctic.Во второй половине ХХ в. в Северной Атлантике отмечено три значимых аномалии распреснения поверхностных вод. В иностранной литературе они получили собственное имя – Великая соленосная аномалия (ВСА) [31–33, 36, 37]. Выделяют ВСА-1970-х, ВСА-1980-х и ВСА-1990-х годов. Р. Диксон [37] описал это явление как одно из наиболее резко и продолжительно влияющих на изменения климата океана в ХХ в. По мнению авторов настоящей статьи, генезис ВСА-1970-х связан с ледопродуктивностью арктических заприпайных полыней. В этой статье даётся феноменологическая модель формирования климатических изменений в зоне полярных и умеренных широт Северного полушария, обусловленных периодическими выбросами в Северную Атлантику аномально больших объёмов распреснённых вод из Северного Ледовитого океана. Делается вывод, что в настоящий момент уже сформировалась ВСА-2010-х и началось её распространение в Северной Атлантике. Впервые аномалия описывается не постфактум, а в момент зарождения. Таким образом, мы стоим на пороге достаточно длительного периода похолодания