Search results for " Barrier"
showing 10 items of 540 documents
Shell effects in damped collisions ofSr88withYb176at the Coulomb barrier energy
2014
This work is a study of the influence of shell effects on the formation of binary fragments in damped collision. We have investigated binary reaction channels of the composite system with $Z=108$ produced in the reaction $^{88}\mathrm{Sr}$${+}^{176}$Yb at an energy slightly above the Bass barrier (${E}_{\text{c.m.}}/{E}_{\text{Bass}}=1.03$). Reaction products were detected by using the two-arm time-of-flight spectrometer CORSET at the K130 cyclotron of the Department of Physics, University of Jyv\"askyl\"a. The mass-energy distribution of primary binary fragments has been measured. For targetlike fragments heavier than 190 u, which correspond to a mass transfer as large as twenty nucleons o…
Correlated e+ e− peaks observed in heavy-ion collisions
1990
Abstract Three very narrow e + e − sum-energy peaks around 610, 750, and 810 keV have been observed in U+Th as well as in U+Ta collisions at beam energies around the Coulomb barrier. As no processes involving conventional atomic and nuclear physics were found to describe their origin, the data were in particular confronted with the hypothesis that the lines are due to the two-body decay of neutral objects in an e + e + pair. Although the 810 keV sum-energy line observed in U+Th is consistent with the prompt two-body e + e − decay of a neutral object if created nearly at rest in the heavy-ion center-of-mass system, the other lines require at least a considerably more complicated scenario if …
Influence of fusion barrier distributions on spin populations
2003
Abstract Heavy-ion fusion barrier distributions are now routinely obtained directly from experimental data. By measuring the total γ -ray multiplicity for the 58 Ni + 60 Ni system, which has a striking yet well understood barrier distribution, we show that some evidence of the barrier structures is present in the derived spin populations. In particular, very high spins can be populated at energies rather close to (and even below) the ‘nominal’ Coulomb barrier.
HOW MANY FUSION BARRIERS?
2004
Fusion barrier distributions for the 20 Ne + 112,116,118 Sn systems have been extracted from quasi-elastic scattering cross sections measured at the Warsaw HIL Cyclotron. Results are compared to coupled-channels calculations performed with the CCFULL code. The overall widths of the distributions are reproduced on taking account of the low-lying collective states of the target and projectile but some puzzling discrepancies in their shapes remain to be explained.
First Exploration of Neutron Shell Structure below Lead and beyond N=126
2020
The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical r process in producing nuclei heavier than A∼190. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in ^{207}Hg have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of ^{206}Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of ^{207}Hg marks a first step in improving our…
Asymmetric and symmetric fission of excited nuclei of Hg180,190 and Pb184,192,202 formed in the reactions with Ar36 and Ca40,48 ions
2021
Background: Observation of asymmetric fission of $^{180}\mathrm{Hg}$ has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region.Purpose: The study of asymmetric and symmetric fission modes of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei.Methods: Mass-energy distributions of fission fragments of $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$ formed in the $^{36}\mathrm{Ar}+^{144,154}\mathrm{Sm}$ and $^{40}\mathrm{Ca}+^{144}\mathrm{Sm}$ reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured $^{192,20…
Mean field methods in large amplitude nuclear collective motion
1984
The time dependent Hartree-Fock method (TDHF) is reviewed and its success and failure are discussed. It is demonstrated that TDHF is a semiclassical theory which is basically able to describe the time evolution of one-body operators, the energy loss in inclusive deep inelastic collisions, and fusion reactions above the Coulomb barrier. For genuine quantum mechanical processes as e.g. spontaneous fission, subbarrier fusion, phase shifts and the description of bound vibrations, the quantized adiabatic time dependent Hartree-Fock theory (quantized ATDHF) is suggested and reviewed. Realistic three-dimensional calculations for heavy ion systems of A1+A2<32 are presented. Applications to various …
Pair transfer processes probed at deep sub barrier energies
2011
Multinucleon transfer cross sections in the system 40 Ca+ 96 Zr have been measured at bombarding energies ranging from the Coulomb barrier to ~ 25% below. Target-like (lighter) recoils in inverse kinematics have been completely identif ed in A,Z and Q-value with the large solid angle magnetic spectrometer PRISMA. The experimental slopes of the neutron transfer probabilities at large internuclear separation are consistent with the values derived from the binding energies. A phenomenological interpretation of the transfer probabilities indicates the presence of enhanced values for the even number of neutron transfers.
Coulomb dissociation of 27P: A reaction of astrophysical interest
2011
The ground-state decay of 26Al(0+) (T 1/2=1.05× 106) has a shorter life-time than the Universe. The presence of this element in the Galaxy was measured via g-ray spectroscopy, showing that the nucleosynthesis of this element is an ongoing process in stars. The proton-capture reaction 26Si(p,γ) 27P competes with the production of 26Al(0+) by β-decay. Coulomb dissociation of 27P has been suggested as an indirect method to measure radiative-proton capture when the direct reaction is not feasible. Such an experiment was performed at GSI with a secondary 27P beam produced by fragmenting a 36Ar primary beam at 500 A MeV. Two main observables are preliminarily presented in this work: the reaction …
Enhancement of stability in randomly switching potential with metastable state
2004
The overdamped motion of a Brownian particle in randomly switching piece-wise metastable linear potential shows noise enhanced stability (NES): the noise stabilizes the metastable system and the system remains in this state for a longer time than in the absence of white noise. The mean first passage time (MFPT) has a maximum at a finite value of white noise intensity. The analytical expression of MFPT in terms of the white noise intensity, the parameters of the potential barrier, and of the dichotomous noise is derived. The conditions for the NES phenomenon and the parameter region where the effect can be observed are obtained. The mean first passage time behaviours as a function of the mea…