Production Of Heavy Fragments Research Articles

Production of heavy fragments in the fission mass region in 12C+U, Bi, Au and Ag reactions at 26.5 GeV

Formation of heavy fragments in the fission mass region in the interaction of 26.5 GeV C 12 with U, Bi, Au and Ag is studied using a sandwich configuration of the Makrofol polycarbonate track detector. Events in which at least one heavy fragment in the fission mass region is detected are analyzed. Fragments produced in these events are identified and an event-by-event model-free analysis is performed in order to separate different production mechanisms. We have identified the events produced in fission, deep spallation and fragmentation processes. The cross sections and experimental features are determined for these reaction mechanisms, and their variations as a function of the target mass have been investigated. The results show that in the interactions of C 12 with U the dominant process is fission, while in the interactions of C 12 with lighter target nuclei the dominant processes are deep spallation and fragmentation.

Heavy fragment production in [formula omitted] reactions at 0.65– [formula omitted

The processes of production of heavy fragments in the fission mass region in the interaction of 0.65, 1.74, 5.1, 8.8 and 12.7 GeV 4 He with 232 Th have been analyzed using the polycarbonate track detector Makrofol in the form of a sandwich. The decay channels ending with one, two, or more (three, four) fragments were detected. We have analyzed the events in which at least one heavy fragment ( Z>20) was registered. Fragments produced in the experiment were identified and an event-by-event model-free analysis was performed in order to separate different production mechanisms. We have identified the events produced in fission, deep spallation and fragmentation processes. The cross-sections and experimental features have been determined for the various reaction mechanisms, and their variation as a function of the incident energy has been investigated.

Disappearance of shell effects and persistence of an even-odd staggering in the fragment production in nuclear reactions at relativistic energies

The isotopic distributions of fragments produced in the spallation of uranium are strongly influenced by the fission of the excited prefragments, highly fissile nuclei. The competition between fission and evaporation around the doubly-magic nucleus Pb is discussed. The light fragments from Fe beam are produced with a strong enhancement of even-even nuclei compared to the odd-odd in the region of nuclei with equal number of neutrons and protons, N ∼ Z. This staggering in the production of light fragments is not observed in the production of heavy fragments, and is in contradiction with the basis of the statistical model of deexcitation of a hot nucleus. Pairing interaction as a function of the excitation energy and as a function of the isospin of the nucleus are questioned.

The influence of fission on the fragmentation of relativistic 208Pb and 238U projectiles in peripheral collisions

The projectile fragmentation in peripheral nuclear collisions was studied using ≈ 1 GeV·A of 208Pb and 238U from the SIS at GSI, impinging on a copper target. Lead and thallium isotopes from the fragmentation of 208Pb as well as uranium and protactinium isotopes from 238U, were selected by the fragment separator FRS. In contrast to the fragmentation of 208Pb, the cross sections for the production of heavy fragments from 238U are strongly reduced by fission. The measured isotopic yields may be explained quantitatively by calculations in the framework of the abrasion-ablation model, if fission is allowed to compete with particle evaporation in the deexcitation of the prefragments.

Interactions of 10.6 [formula omitted] gold nuclei in targets from 1H to 82Pb

The 10.6 GeV n gold beam from the AGS has been allowed to interact in a wide range of targets. The emerging fragments with charges between 80Hg and 57La have been identified. Preliminary values have been determined for the total cross sections for charge changing interactions, for the partial cross sections for the production of heavy fragments, and for the partial cross sections for charge pickup.

Heavy residue production in 215 MeV 16O+27Al reactions.

Mass, velocity, and angular distributions have been measured for heavy products and for light charged particles from the reaction 215 MeV $^{16}\mathrm{O}$${+}^{27}$Al. Coincidences between evaporation residues and light charged particles have also been measured. Statistical-model calculations, incorporating light-particle decay from either the compound nucleus or the composite nucleus formed in the direct emission of a beam velocity particle, cannot account for the observed cross sections or angular distributions of the heavy residues. More elaborate kinematic simulations, which include direct light-particle emission as observed in the light-particle inclusive data, also do not work. This supports the notion that heavy fragment production (A>4) would be needed to account for the residue distributions.

On the determination of reaction product parameters using polycarbonate track detector Makrofol

The improved Makrofol detection technique was applied in the study of intermediate mass and heavy fragment production in the interaction of 8.8 GeV alpha particles with gold nuclei. The limitations of the applied technique were discussed and the uncertainties of results obtained by the standard version of this technique were put forward. Fragments produced in the experiment were identified and an event by event model-free analysis was performed in order to separate different production mechanisms.

Complex fragment emission in the , 197Au reactions

Abstract Excitation functions have been measured for complex fragments with Z=3–15 emitted in collisions of E/A=60, 80 and 100 MeV 14 N ions with targets of natAg and 197Au. The results are analyzed in terms of a three-source model: projectile fragmentation, non-equilibrium emission from the composite system, and statistical decay of an equilibrated heavy residue. Enhanced heavy fragment production is found for reactions with the natAg target above E/A⩾60 MeV. Above E/A≅50 MeV the ratio of equilibrium to non-equilibrium cross sections is found to be nearly independent of bombarding energy. Fit-parameter systematics are presented.

Apparent temperature of fragments in the breakup of spectator residues.

Assuming the sequential decay of particle unstable primary fragments for light fragment production and the direct two body decay for heavy fragment production, we analyze the apparent temperature (the inverse logarithmic slope of kinetic energy distributions) of fragments in the breakup of spectator residues. Unlike other models it is independent of the projectile energy. Mass numbers obtained for the particle unstable primary fragments in the reactions of projectile proton and targets of Kr, Ag, and Xe are in the range 14-18.

“Mass scaling” phenomena in heavy fragment production in relativistic heavy ion collision

We point out the existence of “mass scaling” among different reaction channels in the inclusive nucleus production in high energy nucleus-nucleus collisions and discuss the reasons for its existence. The possible relationship between the inclusive cross sections and the existence-probability of clusters inside the nucleus is indicated.

Heavy fragment production through electropion excitation ofFe56

Heavy ejecta with charges ranging from $Z=3 \mathrm{to} 14$ have been observed following the collisions of 20 GeV electron with $^{56}\mathrm{Fe}$ nuclei. Crude charge and energy spectra of the fragments have been determined with track-etch detectors. For $Z\ensuremath{\le}8$, the source is found to be slowly moving ($\frac{v}{c}<0.004$) nuclear matter with a temperature of 13\ifmmode\pm\else\textpm\fi{}1 MeV, quite similar to that responsible for the evaporation of nuclei excited by high-energy protons. The total cross section for producing fragments with $Z=7 or 8 \mathrm{by} 20$ GeV electrons is about 700 times smaller than that for producing these fragments through collisions of 2 GeV protons with iron nuclei. The excitation mechanism is most likely that of electropion production, as evidenced by the similarity of calculated and measured cross sections. An additional, as yet unknown, mechanism is required to explain the observed production of fragments with $Z\ensuremath{\ge}12$, energy > 140 MeV, and cross section of the order ${10}^{\ensuremath{-}33}$-${10}^{\ensuremath{-}32}$ ${\mathrm{cm}}^{2}$.NUCLEAR REACTIONS $^{56}\mathrm{Fe}$($e$,$X$), $E=20$ GeV; Measured $\ensuremath{\sigma}({E}_{X},\ensuremath{\theta})$ for $X=\mathrm{L}\mathrm{i},\phantom{\rule{0ex}{0ex}}\mathrm{B}\mathrm{e},\phantom{\rule{0ex}{0ex}}\mathrm{B},\phantom{\rule{0ex}{0ex}}\mathrm{C},\phantom{\rule{0ex}{0ex}}\mathrm{N},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{O}$. Determined temperature and velocity of source of fragments.

Production of heavy fragments in interactions of high-energy protons with silver

A silver target was exposed to 14, 18 and 23 GeV protons. The values of the cross-sections for production of events with two and three fragments have been determined by the use of a polycarbonate detector. The results obtained show that these events are due to fission as well as to fragmentation and spallation.

Production of heavy fragments in the reaction O 16 + O 16

Heavy framents produced in the bombardment of an oxygen target with 10 MeV per amu (atomic mass unit) oxygen ions have been investigated with a proportional counter-CsI scintillator telescope. This arrangement permitted identification of the nuclear charge (species) of fragments from lithium through neon, as well as measurement of the energy spectra of each species. Several mechanisms would appear to contribute to the observed yields. Marked group structure, typical of direct pickup-type reactions, is evident at forward angles in the carbon and neon spectra. Groups are also seen in several cases which are suggestive of particle decay following simple transfer-type reactions. A smooth, broad distribution characteristic of several-body breakup occurs in all cases.