Nuclear Fragment Emission in High-Energyp-Xe andp-Kr Collisions and a Description of Their Production Mechanism

Abstract

With the successful operation of the warm-gasjet facility 1 at Fermi National Accelerator Laboratory (FNAL) providing thin targets of heavy gases, it has become possible to employ electronic techniques to study the production characteristics of low-energy nuclear fragments at the highest available proton energies. In this paper we present data from Kr and Xe targets and discuss an interpretation in terms of a simple model for heavy-fragment emission. From comparisons of these data with previous light-fragment studies, there is evidence for a two-step process in/>-nucleus collisions; first, there is a simultaneous emission of a large number of nucleons (~20) which may coalesce into light fragments. The remaining excited nuclear remnant subsequently decays into heavy fragments via a quasitwo-body decay.This experiment was conducted in the internaltarget area of FNAL, Targets of 100 ng/cm 2 were created by injecting hydrogen-noble-gas mixtures through a de Laval nozzle into the circulating proton beam. The pressure pulse was maintained for 2.7 sec, coinciding with the acceleration time of the beam from 20 to 400 GeV/c, during which 10 18 protons/sec intersected the target. Fragments emerging from the p -nucleus collisions were detected by one of four AE-Eveto telescopes, each consisting of three surfacebarrier Si detectors. These telescopes were mounted symmetrically around the axis of the in-8 V. Canuto, J. Lodenquai, and M. Ruder man, Phys. Rev. D £, 2303 (1971); J, Lodenquai, V. Canuto, M. Ruderman, and S. Tsaruta, Astrophys. J. 190, 141 (1974).ternal-target magnetic spectrometer with a direct view of the gas jet. Data were taken at twelve approximately equally spaced intervals between 33° and 76° with respect to the proton beam. Target mixtures for the data reported here were 90% H 2 -10% Xe and 82% H 2 -18% Kr by partial pressures.Fragments were accepted which satisfied a AE •£• veto trigger within preset energy windows. Discriminator levels were optimized for fragments heavier than lithium with low kinetic energies (E < 120 MeV). Identification by AZ 2 , where A is the nucleon number and Z the charge, was determined through an empirical function of the energies deposited in the AE and E detectors. A typical spectrum indicating the presence of elements B to Si is shown in Fig. 1.A detailed analysis 2 of fragment energy spectra revealed no dependence upon beam momentum; thus, the data presented here are summed over beam momenta. Furthermore, the angular distributions evidenced only a weak correlation with emission angle. Laboratory kinetic energy distributions of B, N, Na, and Si from/>-Xe and />-Kr collisions are shown in Fig. 2. Multiplescattering corrections have been included. A slow variation of the slopes with fragment mass is apparent; similar spectra are observed from both krypton and xenon targets. To parametrize our data we used the formalism of Goldhaber 3 and Westfall etal., A which provides a simple de-We have studied the energy distributions of Li, and Si emerging from high-energy proton-xenon and...

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“…The EOS experiment was an outgrowth of earlier inclusive studies of MF in the interaction of Xe and Kr with high-energy protons [20][21][22][23][24][25][26] . In this work high precision counter techniques were used to obtain accurate information about the kinetic energy spectra of isotopically resolved nuclear fragments.…”

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