Intermittency in nuclear multifragmentation at relativistic energy

Abstract

The charge distribution of nuclear fragments for the nonfissile events of ^^'U at 0.96A GeV in nuclear emulsion is fitted with a power law. The method of scaled factorial moments is used to study fluctuations in the nuclear fragmentations. An intermittent behavior is found in the data, but no clear evidence of critical phenomenon is observed in nuclear fragmentation.PACS numbers: 24.60.Ky The recent studies of intermittency 111 in particle and nuclear collisions have revealed a quite fruitful field of research, and in fact the study of fluctuations has led to interesting insights on physical phenomena. Moreover, the intermittency analysis in terms of scaled factorial moments in relation with percolation models has been shown to be relevant in the study of the nuclear multifragmentation process [2]. In nuclear collisions at lower bombarding energies (<\A GeV) particle production is strongly suppressed and nuclear breakup into fragments dominates. Fragment-size distributions exhibit similar features to those known in percolation models [3]. Thus heavy-ion collisions offer a unique opportunity to study new phases of nuclei. One phase is of a high-density high-temperature region around the quark-gluon plasma (hadron phase transition or a thermal transition at equilibrium). The other phase is the low-density moderatetemperature region near the liquid-gas phase transition, but not at equilibrium-a nonthermal process. One can study the transition by looking at the distribution in composition of the final products. Here we shall look at the nonthermal process.In 1984, we did an analysis of nuclear interactions produced [4] in emulsion from ^^^U projectile at 0.96A GeV, in which 51% of all the 894 interactions were due to lissionlike fragments with a cross section of a^ ==1755 ± 82 mb. Recently, considerable interest has centered around the idea of nuclear multifragmentation, so our interest in the present Letter is to analyze the remaining nonfissile events which broke up into multifragments. When a ^^^U ion passes through the emulsion detector, the interactions in this medium were recorded up to ~ 2.7 cm (corresponding to energy between 960 and 240), where various processes are competing which give rise to different charge spectra of the projectile fragments (PFs). The energy of the produced PFs is high enough to distinguish them easily from the target fragments [5]. In each event the charges of these projectile fragments were determined by a combination of different methods which included grain density, gap density, <5-ray counting, relative track widths, etc. [4]. For projectile fragments of heavy charges which stopped in the stack, we used relations between their thin down track length and the widths [6] which were developed from the data of standard stopping tracks by drawing the profile of their last (150-1000 pm) thin down track lengths with the help of a special Leitz ''discussion tube" and comparing them with the profiles of unknown tracks of different charges. A heavy fragment here is defined as a cluster w...

Effect of system size on the traditional signatures of critical behavior in projectile multifragmentation

“…Similar distribution fitted with a power law has also been reported in nuclear fragmentation of 238 U at 0.96 AGeV, 84 Kr at 1.25 AGeV, 84 Kr at 0.95 AGeV and 131 Xe at 1.22 AGeV in nuclear emulsion [16,19,23,[28][29][30].…”

“…The finite size effect thus lowers the critical point thereby resulting a possible change in the order of phase transition. A number of works [16][17][18][19][20][21][22][23][24][25][26][27], both theoretical and experimental, have been carried out to realize the role of size of the fragmenting nuclei on the traditional signatures of critical behavior and hence on nuclear MF process.…”

“…The connection between MF as decay mechanism of excited nuclei and a possible liquid-gas phase transition taking place in nuclear matter was initially motivated by the strong resemblance between vander-waals potential and nucleon-nucleon potential [4,5]. The presence of the power law in the mass yield distribution of the fragments along with the values of the exponents close to that of an ordinary fluid led Purdue [6] group to suggest that multifragmentation of nuclei might be analogous to a fluid undergoing a continuous phase transition from liquid to a gas.Although a considerable amount of work in understanding the statistical aspects of multifragmentation have been carried out by several groups [7][8][9][10][11][12][13][14][15][16][17][18][19], the mechanism of nuclear multifragmentation is not yet completely understood. One of the most complicated questions related to the liquid-gas phase transition in nuclear matter which is yet to be answered is the order of the phase transition.…”

Production of helium fragments in197Au-emulsion collisions at 10.6 A GeV

“…Using this technique, 1413 nuclear interactions were recorded by following a track length of 74.32 m. In each collision, the numbers of black tracks (Nb) , grey tracks (Ng), singly charged shower tracks (Ns) and projectile fragments (NpF) of charge Z> 2 were noted down [3]. The charges of the projectile fragments (PFs) were determined by the combination of several methods, for example, grain, gap, O-ray density or relative track width [4]. The helium nuclei can be easily distinguished from the singly charged particles due to their distinctive grain density in nuclear emulsion.…”

“…Each helium track was further followed at least by a distance of 2 cm from its formation point so as to get rid of any contamination due to grey tracks that might have proceeded in the forward direction. For the PFs with Z >__ 3, the other three methods of charge determination were employed [4]. In a data set of 1113 nuclear collisions, we were able to assign the charges to all the PFs emerged.…”