Expansion time of hot nuclei produced by a relativistic deuteron beam
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ELEMENTARY PARTICLES AND FIELDS Experiment
Expansion Time of Hot Nuclei Produced by a Relativistic Deuteron Beam∗ V. A. Karnaukhov1), S. P. Avdeyev1)** , W. Karcz1), V. V. Kirakosyan1), P. A. Rukoyatkin1), V. I. Stegaylov1) , H. Oeschler2) , and A. S. Botvina3) Received December 3, 2014
Abstract—The multifragmentation time scale is measured for d(4.4 GeV) + Au collisions by the analysis of the relative angle correlation function for the intermediate-mass fragments. The experiment was performed with the FASA 4π setup installed at the external beam of the superconducting accelerator Nuclotron. A combined approach of intranuclear cascade prescription followed by the Statistical Model of Multifragmentation is used for the analysis of the data. Multifragmentation of a target spectator is measured to be 100 fm/c (CL > 99.5%) delayed in relation to the collision moment. The latter is fixed by the registration of the fast fragment with Z = 4, produced at the collision moment. DOI: 10.1134/S1063778815040079
1. MULTIFRAGMENTATION OF A TARGET SPECTATOR IN LIGHT RELATIVISTIC PROJECTILE COLLISIONS Multifragmentation is the main decay mode of hot nuclei when the excitation energy exceeds 4 MeV/nucleon. The process is copious emission of intermediate-mass fragments (IMF, 2 < Z < 20) and lighter nuclei. The multifragment emission is a real phase transition in finite nuclei [1–5]. An effective way to produce hot nuclei is reactions induced by relativistic light ions. The fragments are emitted by only one source—the slowly moving hot target spectator. It has been proved that there are two characteristic volumes of the fragmenting system [6, 7]. The first one, Vt , corresponds to the chemical freeze-out state when pre-fragments are formed (on top of barrier). The fragment yield depends on Vt , and it is estimated by comparison of the measured charge distribution with the calculated one: Vt = (2.6 ± 0.2)V0 . Figure 1 illustrates this comparison for d(4.4 GeV) + Au collisions. The second volume is reached by the hot nucleus after its “descent” from the top of the barrier to the scission point. It is the kinetic freeze-out volume, Vf . ∗
The text was submitted by the authors in English. Joint Institute for Nuclear Research, Dubna, Russia. 2) ¨ Kernphysik University of Technology, DarmInstitute fur stadt, Germany. 3) Frankfurt Institute for Advanced Studies Johann Wolfgang Goethe University, Frankfurt am Main, Germany. ** E-mail: [email protected] 1)
It was measured by comparing the kinetic energy spectra of the fragments with the calculated ones: Vf = (5.0 ± 0.5)V0 . The process of fragment emission is described in the combined model denoted as INC + Expansion + SMM. The fragment kinetic energy spectra are described by the technique of the multibody Coulomb trajectory calculations [8]. The reaction mechanism is composed of three steps. The first step is the energy deposition step, when energetic nucleons and pions are emitted and the nuclear remnant is excited. This step is considered using the intranuclear cascade model (INC). We use the D
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