Multidetector study of primary projectilelike fragments in the reactionCa40+

Abstract

Properties of projectile fragments produced in peripheral and midperipheral collisions in the reaction Ca + ""Cu at 35 MeV/nucleon were investigated using the AMPHORA multidetector. A reconstruction of the primary projectilelike fragments enabled simultaneous determination of their excitation energy and angular momentum. These quantities are in good agreement with predictions of simple macroscopic and microscopic collision models. Partition of excitation energy between primary projectile and targetlike fragments is discussed. The multiplicity and charge distributions of the primary projectilelike fragment deexcitation products are fairly well reproduced by a statistical binary-decay model. PACS number(s): 25.70.Pq, 25.70.Mn I. INTR(ODUCTIQN Current understanding of projectilelike fragment (PLF) production in peripheral and midperipheral heavy ioncollisions at intermediate energies has been obtained mainly from inclusive or semiexclusive measurements, which have been used to test parametrized models of the production mechanism of the excited primary projectilelike fragments (PPLF's) and their subsequent decay [1 -6]. At low incident energies (below 15 MeV/nucleon) conversion of entrance channel kinetic energy and angular momentum into thermal and rotational energies of the primary projectile and targetlike fragments are thought to be dominated by a one-body mechanism [7,8]. At higher incident energies the Pauli principle becomes less eftective in suppressing nucleon-nucleon collisions and schematic microscopic models based on nucleon-nucleon collisions [9,10] have been quite successful in explaining total reaction cross sections and fragment yields, as well as PLF energy and angular distributions.Primary projectilelike fragments with excitation energies up to 6 -7 MeV/nucleon can be produced in very inelastic reactions at incident energies of the order of [30][31][32][33][34][35]11]. It is interesting to understand how the decay mechanism of such nuclei is infiuenced by temperature and rotation. At low excitation energies, the emitted light particles and projectile residues are well described by statistical evaporation models [12,13] based on the multistep Hauser-Feshbach formalism [14]. For higher excitation energies, such a Permanent address: IFUNAM, A.P. 20-364, Mexico 01000 DF, Mexico. formalism becomes inadequate, since the emission of intermediate mass fragments may compete significantly with light-particle emission [11]. Sequential binary statistical decay models [15] based on the transition-state formalism [16] are used to describe the deexcitation of such highly excited nuclei. At very high excitation energies, the time scale for particle emission may become comparable with typical equilibration times [17], and simultaneous multifragmentation mechanisms have been proposed [18,19]. The use of a multidetector in the experimental investigation provides a qualitative advance in the sense that, for completely exclusive measurements, it is possible (in favorable kinematic configurations) to separate projectilel...

Explosive multifragmentation in theS32+27Heuer1, Chabane2, Brandan3 et al. 1994Phys. Rev. CSelf Cite21070View full textAdd to dashboardCite

“…This finding is in sharp contrast with the work of Ref. [16] where an excellent description of charge and multiplicity distributions &om the decay of excited calciumlike nuclei is obtained (up to 6 -7 MeV/nucleon) with the same code. In Fig.…”

“…We have presented and discussed data for deep inelastic collisions in the 35 MeV/nucleon 4oCa+" tCu system in previous publications [15,16]. In this work we present results on central collisions for the S+ Al system at 37.5 MeV/nucleon.…”

“…The detector response was simulated with the filter code sIR [23]. The range of impact parameter associated with central collisions (and thus the range of angular momenta used in the GEMINI simulations) was obtained from a deep inelastic scattering calculation [24] which has been shown in previous work [16] to provide a reasonable description of the impact parameter dependence of energy and angular momentum dissipation. According to this calculation dissipation of all the available entrance channel kinetic energy occurs for impact parameters below 2.5 fm which implies angular momenta up to 45h.…”

Nuclear multifragmentation and phase transition for hot nuclei

“…system are attributed to the QP. Variants consist either in putting a low velocity cut for the lighter fragments [156,157], or in keeping only events with a compact fragment configuration in velocity space [74,158]. Then twice the light elements in the QP forward hemisphere are added.…”

New method for the discrimination of single-source events in heavy-ion collisions

“…Thus samples have been generated using the dbs ( [33] and references herein) event generator which falls into three steps. First, an entrance channel code simulates the pre-equilibrium emission (the numbers of protons n p , neutrons n n , and their mean kinetic energy T are treated as parameters).…”