Emission Of Heavy Fragments Research Articles

Sequential binary decay of highly excited 40Ar*

The sequential statistical binary decay of the highly excited compound nucleus 40Ar* is described with an extended evaporation formalism implemented in a Monte-Carlo multi-step statistical model code. Asymmetric mass splittings involving nucleon emission up to symmetric binary ones are treated within the evaporation formalism, in a unified manner. Emission of heavy fragments in their ground and excited (particle-bound or unbound) states is considered. The evolution of the final mass distributions from 40Ar* is studied as a function of the initial excitation energy, in the range from 45 up to 405 MeV. The population of final states originating from the decay of intermediate mass fragments in particle-bound and particle-unbound states (side-feeding) is discussed. Results are compared with an alternative description in which the time-dependent decay process is described by rate equations for the generation of different fragment species.

Comparison between cross sections, saddle point and scission point barriers for the32S+24Mg reaction

One of the principal characteristics of nuclear multifragmentation is the emis- sion of complex fragments of intermediate mass. The statistical multifragmentation model has been used for many years to describe the distribution of these fragments. An extension of the statistical multifragmentation model to include partial widths and life- times for emission, interprets the fragmentation process as the near simultaneous limit of a series of sequential binary decays. In this extension, the expression describing inter- mediate mass fragment emission is almost identical to that of light particle emission. At lower temperatures, similar expressions have been shown to furnish a good description of very light intermediate mass fragment emission. However, this is usually not considered a good approximation to the emission of heavier fragments. These emissions seem to be determined by the characteristics of the system at the saddle-point and its subsequent dynamical evolution rather than by the scission point. Here, we compare the barriers and decay widths of these different formulations of intermediate fragment emission and analyze the extent to which they remain distinguishable at high excitation energy.

Time-scale analysis of three-fragment emission in the 12.7 GeV 4He + 197Au reaction

The time-scale for emission of three fragments ( Z ≥ 8) in the 12.7 GeV 4He + 197Au reaction has been studied using a sandwich configuration of the Makrofol polycarbonate track detector. In events with different multiplicity of heavy fragments ( Z > 20), the differences of the correlation functions for relative angle and relative velocity between pairs of fragments have been studied in order to determine the fragment emission-time scale. A sequential decay mechanism for the excited residual nuclei was found to be consistent with experimental data. It was determined that the fragment emission-time decreased with decreasing multiplicity of heavy fragments: from 1000 fm/c for events with two heavy fragments, through 300 fm/c for events with one heavy fragment, to 40 fm/c for events with no emission of heavy fragments.

Intermediate mass fragments and isospin dependence inSn124,Xe124+Sn124,Sn112reactions at28MeV∕nucleon

Intermediate mass fragment (Z>2) emission in Sn124,Xe124+Sn124,Sn112 reactions at 28MeV∕nucleon were studied using neutron ion multidetector for reaction oriented dynamics, a 4π charged particle detection system. A number of observables, such as isotopic yield distributions, energy spectra of light charged particles and intermediate mass fragments, isotopic and isobaric yield ratios, and average neutron to proton ratios are investigated. These observables show significant dependence on the isospin N∕Z of the reacting system. It is observed that the formation of neutron-rich clusters are correlated with the excess neutrons in the composite system and depends on the temperature of the emitting source. The origin of light particles and fragments was studied through observations of rapidity distribution as a function of collision violence. With increasing centrality, the heavier He6 isotope is found to be emitted closer to the midrapidity region than the lighter He3 isotope. The emission of heavy fragments from the midrapidity region becomes increasingly favorable for fragments with higher charge Z. The results suggest that the midrapidity region is not only neutron rich but also a rich source of heavy fragment (cluster) formation.7 MoreReceived 22 July 2003DOI:https://doi.org/10.1103/PhysRevC.68.054605©2003 American Physical Society

The INDRA detector at GANIL

Abstract One of the main goals of the current research in nuclear physics in the intermediate energy domain is to improve our knowledge about the properties of nuclear matter at high density and temperature. Of peculiar interest is the search for a “sudden multifragmentation” of the nuclei accompanied or not by a phase transition. This process is theoretically predicted during the expansion of the hot and compressed system formed in the early stage of nucleus-nucleus central collisions The de-excitation is characterized by the emission of alarge number of light charged particles (hydrogen or helium nuclei) and to a lesser extent by emission of heavy fragments. Experimentally, these studies require an event by event detection of all particles and fragments with precise measurements of their number, their size charge and mass), their spatial distributions and their energy. To satisfy these requirements, the community of physicists working on this subject at GANIL decided in 1989 to undertake the constructio...

Angular distribution of heavy fragments in 72 GeV Ar interactions with Cu

Within the framework of the study of the unusual behaviour of relativistic secondary particles formed in the interaction of 72 GeV 40 Ar within a 1 cm thick Cu target, the wide-angle emission of heavy fragments has been studied with CR-39 SSNTD. Within the laboratory-frame forward angular interval θ, with 5° < θ < 43°, we observed such heavy fragments with a frequency F = (0.2 ± 0.1)%, expressed as a fraction of the total primary Ar flux. Evidence is presented that these fragments are possibly ‘projectile fragments’ (PFs) within the charge range 6 ≤ Z < 18, and that they have relativistic energies. No attempt is made to interpret this possibly ‘new’ phenomenon. However, it is pointed out that these ‘wide-angle emitted’ heavy fragments cannot be related to any ‘unusual’ behaviour (observed at wide angles) by projectile fragments in other experiments, provided that these fragments have ‘normal’ reaction cross-sections.

8Li fragments associated with nuclear disintegration

This paper is a preliminary report on the emission of heavy fragments in nuclear disintegration. It is assumed that the probability of emission of a heavy fragment depends on the nuclear temperature (T) and the potential barrier (V) of the excited nucleus. It is the purpose of this investigation to study the dependence of the differential energy spectrum on the excitation energy. The data collected were from four stacks of Ilford G-5 emulsions, exposed to (a) a stopped pion beam; (b) 400 MeV proton beam; (c) (4÷5) GeV pion beam and (d) cosmic rays with an exposure in Texas, Magnetic latitude of 41° N, and on the Island of Guam at the magnetic equator. In this report emphasis will be placed on the emission of8Li as the heavy fragment. The results of the experiment indicate that for high excitation energy there is a collimation of lithium and beryllium fragments in the forward direction which may be explained on the basis of evaporation theory by assuming the fragment emission to take place during the flight of a highly excited nucleus. In the case of low excitation energy the angular distribution of8Li fragments is isotropic and the energy distribution indicates that the majority result from the absorption of aπ−-meson by a light nucleus.

Emission of Heavy Fragments in Nuclear Disintegrations

A phenomenological description is given of the processes which lead to the emission of energetic heavy fragments from cosmic-ray stars. The energy spectra, angular distribution, and relative frequency of the particles were determined, and a detailed comparison is made with the predictions from nuclear evaporation theory. A simple method for charge determination of the fragments is described. (auth)

Disintegration of Light Nuclei by -Meson Capture

o-stars in photographic plates are classified into those originated from heavy and light nuclei. The branching ratio of disintegration modes, the a-j ratio, and the energy distribution of emitted particles are measured for light stars. Foilowing characteristic features of light stars are ascertained; 1) the large prong number, 2) the large a-p ratio, 3) the low kinetic energy of emitted particles, and 4) the frequent emission of heavy fragments. The disintegration of 0 2 into two a-particles and a proton are studied in detail, and the possible emission of BeB nuclei is discussed. It turns out to be the main disintegration mode, that the rcst energy of o-meson is primarily shared among only a few member of nucleons and the residual part ramains in a similar to the excited levels appeared in low energy reactions.

Emission of heavy fragments in nuclear explosions

Observations have been made on the energetic nuclear fragments emitted in ‘giant’ cosmic-ray stars.The disintegrations were produced in the heavy nuclei of Ilford C2 and G5 emulsions exposed at high altitude. Methods are described for the identification of the fragments, both stable and unstable, with charges between three and ten units. It is found that fragment emission may be interpreted in terms of an asymmetric fission process, which is highly probable when the nuclear excitation energy becomes comparable with the binding energy. The average kinetic energies of the fragments are considerably greater than those to be expected from the Coulomb repulsion, a fact which may be explained in terms of specifically long-range nuclear forces. The fragments exhibit a peculiar tendency to be emitted in directions perpendicular to the incident star-producing particle.The mass of the emitted fragment does not depend appreciably on the size of star. At present there appears to be no comprehensive theoretical explanation of the precise mechanism of emission of such particles.