Abstract
We present a study of Gd+U collisions at 36 AMeV measured with the INDRA multidetector, permitting almost complete detection (over 80%) of all the reaction products. We show that events exist which correspond to the multifragmentation of a single system comprising the majority of the nucleons for a cross-section of 2.6 mbarn, by isolating reactions for which the emitted fragments have lost all memory of the entrance channel. Such reactions correspond to neither the most central collisions nor the most isotropic events (in the fragments' momentum space), and therefore cannot be correctly distinguished from the dominant binary deeply-inelastic collisions using these criteria. An initial comparison of the selected data with a statistical code indicates that fragments are formed in a dilute, compact system, undergoing a self-similar expansion corresponding to a collective energy of between 1 and 1.5 MeV. Comparison with the same type of events observed in Xe+Sn collisions at 32 AMeV reveals the existence of a scaling law for the multifragmentation of systems of different mass at the same excitation energy per nucleon: fragment Z distributions are identical while their multiplicity increases proportionally to the mass of the multi-fragmenting system. This observation is interpreted as an experimental signal that
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Frankland, John David
[1]
- Inst. de Physique Nucleaire, Paris-11 Univ., 91 - Orsay (France)
Citation Formats
Frankland, John David.
Study of very heavy systems by means of INDRA: First evidence for a volume effect in the nuclear multifragmentation process / Study of very heavy systems observed with INDRA: first evidence for a bulk effect in the nuclear multifragmentation process; Etude de systemes tres lourds observes avec INDRA: Premiere mise en evidence d'un effet de volume dans le processus de multifragmentation nucleaire.
France: N. p.,
1998.
Web.
Frankland, John David.
Study of very heavy systems by means of INDRA: First evidence for a volume effect in the nuclear multifragmentation process / Study of very heavy systems observed with INDRA: first evidence for a bulk effect in the nuclear multifragmentation process; Etude de systemes tres lourds observes avec INDRA: Premiere mise en evidence d'un effet de volume dans le processus de multifragmentation nucleaire.
France.
Frankland, John David.
1998.
"Study of very heavy systems by means of INDRA: First evidence for a volume effect in the nuclear multifragmentation process / Study of very heavy systems observed with INDRA: first evidence for a bulk effect in the nuclear multifragmentation process; Etude de systemes tres lourds observes avec INDRA: Premiere mise en evidence d'un effet de volume dans le processus de multifragmentation nucleaire."
France.
@misc{etde_690197,
title = {Study of very heavy systems by means of INDRA: First evidence for a volume effect in the nuclear multifragmentation process / Study of very heavy systems observed with INDRA: first evidence for a bulk effect in the nuclear multifragmentation process; Etude de systemes tres lourds observes avec INDRA: Premiere mise en evidence d'un effet de volume dans le processus de multifragmentation nucleaire}
author = {Frankland, John David}
abstractNote = {We present a study of Gd+U collisions at 36 AMeV measured with the INDRA multidetector, permitting almost complete detection (over 80%) of all the reaction products. We show that events exist which correspond to the multifragmentation of a single system comprising the majority of the nucleons for a cross-section of 2.6 mbarn, by isolating reactions for which the emitted fragments have lost all memory of the entrance channel. Such reactions correspond to neither the most central collisions nor the most isotropic events (in the fragments' momentum space), and therefore cannot be correctly distinguished from the dominant binary deeply-inelastic collisions using these criteria. An initial comparison of the selected data with a statistical code indicates that fragments are formed in a dilute, compact system, undergoing a self-similar expansion corresponding to a collective energy of between 1 and 1.5 MeV. Comparison with the same type of events observed in Xe+Sn collisions at 32 AMeV reveals the existence of a scaling law for the multifragmentation of systems of different mass at the same excitation energy per nucleon: fragment Z distributions are identical while their multiplicity increases proportionally to the mass of the multi-fragmenting system. This observation is interpreted as an experimental signal that this multifragmentation originates in a bulk instability of low-density nuclear matter (spinodal region). A complete semi-classical microscopic calculation for the two reactions, including the formation and multifragmentation by spinodal decomposition of very heavy, low-density systems, reproduces very well not only the experimental fragment multiplicities and Z distributions but also their mean kinetic energies, as well as the size distributions of the largest fragments. (author) [French] Nous presentons une etude des collisions Gd+U a 36 AMeV mesurees avec le multidetecteur indra qui permet une detection quasi-complete (superieure a 80%) de tous les produits des reactions. Nous mettons en evidence des evenements correspondant a la multifragmentation d'un systeme unique compose de la majorite des nucleons, pour une section efficace mesuree de 2.6 mbarn, en isolant des reactions pour lesquelles les fragments emis ont perdu toute memoire de la voie d'entree. Ces reactions ne correspondent ni aux collisions les plus centrales ni aux evenements les plus isotropes (dans l'espace des impulsions des fragments), et ne peuvent pas donc etre isolees correctement des collisions binaires profondement inelastiques dominantes a partir de ces criteres. Une premiere comparaison des donnees selectionnees avec un code statistique indiquent l'origine des fragments dans un systeme dilue a topologie compacte, avec une energie d'expansion auto-similaire de 1 a 1.5 AMeV. La comparaison avec des evenements du meme type observes dans les collisions Xe+Sn a 32 AMeV revele une loi d'echelle pour la multifragmentation de systemes de masses differentes a la meme energie d'excitation par nucleon: les distributions en Z des fragments sont identiques tandis que leurs multiplicites augmentent en proportion de la masse du systeme en multifragmentation. Cette observation est interpretee comme un signal experimental que cette multifragmentation trouve son origine dans une instabilite de volume de la matiere nucleaire a basse densite (instabilite spinodale). Un calcul microscopique semi-classique complet des deux reactions comprenant la formation et la multifragmentation par decomposition spinodale de systemes tres lourds a basse densite reproduit tres bien non seulement les multiplicites et les distributions en z experimentales des fragments mais aussi leurs energies cinetiques moyennes, ainsi que la distribution en taille des plus gros fragments.}
place = {France}
year = {1998}
month = {Dec}
}
title = {Study of very heavy systems by means of INDRA: First evidence for a volume effect in the nuclear multifragmentation process / Study of very heavy systems observed with INDRA: first evidence for a bulk effect in the nuclear multifragmentation process; Etude de systemes tres lourds observes avec INDRA: Premiere mise en evidence d'un effet de volume dans le processus de multifragmentation nucleaire}
author = {Frankland, John David}
abstractNote = {We present a study of Gd+U collisions at 36 AMeV measured with the INDRA multidetector, permitting almost complete detection (over 80%) of all the reaction products. We show that events exist which correspond to the multifragmentation of a single system comprising the majority of the nucleons for a cross-section of 2.6 mbarn, by isolating reactions for which the emitted fragments have lost all memory of the entrance channel. Such reactions correspond to neither the most central collisions nor the most isotropic events (in the fragments' momentum space), and therefore cannot be correctly distinguished from the dominant binary deeply-inelastic collisions using these criteria. An initial comparison of the selected data with a statistical code indicates that fragments are formed in a dilute, compact system, undergoing a self-similar expansion corresponding to a collective energy of between 1 and 1.5 MeV. Comparison with the same type of events observed in Xe+Sn collisions at 32 AMeV reveals the existence of a scaling law for the multifragmentation of systems of different mass at the same excitation energy per nucleon: fragment Z distributions are identical while their multiplicity increases proportionally to the mass of the multi-fragmenting system. This observation is interpreted as an experimental signal that this multifragmentation originates in a bulk instability of low-density nuclear matter (spinodal region). A complete semi-classical microscopic calculation for the two reactions, including the formation and multifragmentation by spinodal decomposition of very heavy, low-density systems, reproduces very well not only the experimental fragment multiplicities and Z distributions but also their mean kinetic energies, as well as the size distributions of the largest fragments. (author) [French] Nous presentons une etude des collisions Gd+U a 36 AMeV mesurees avec le multidetecteur indra qui permet une detection quasi-complete (superieure a 80%) de tous les produits des reactions. Nous mettons en evidence des evenements correspondant a la multifragmentation d'un systeme unique compose de la majorite des nucleons, pour une section efficace mesuree de 2.6 mbarn, en isolant des reactions pour lesquelles les fragments emis ont perdu toute memoire de la voie d'entree. Ces reactions ne correspondent ni aux collisions les plus centrales ni aux evenements les plus isotropes (dans l'espace des impulsions des fragments), et ne peuvent pas donc etre isolees correctement des collisions binaires profondement inelastiques dominantes a partir de ces criteres. Une premiere comparaison des donnees selectionnees avec un code statistique indiquent l'origine des fragments dans un systeme dilue a topologie compacte, avec une energie d'expansion auto-similaire de 1 a 1.5 AMeV. La comparaison avec des evenements du meme type observes dans les collisions Xe+Sn a 32 AMeV revele une loi d'echelle pour la multifragmentation de systemes de masses differentes a la meme energie d'excitation par nucleon: les distributions en Z des fragments sont identiques tandis que leurs multiplicites augmentent en proportion de la masse du systeme en multifragmentation. Cette observation est interpretee comme un signal experimental que cette multifragmentation trouve son origine dans une instabilite de volume de la matiere nucleaire a basse densite (instabilite spinodale). Un calcul microscopique semi-classique complet des deux reactions comprenant la formation et la multifragmentation par decomposition spinodale de systemes tres lourds a basse densite reproduit tres bien non seulement les multiplicites et les distributions en z experimentales des fragments mais aussi leurs energies cinetiques moyennes, ainsi que la distribution en taille des plus gros fragments.}
place = {France}
year = {1998}
month = {Dec}
}