Onset of multifragment emission in heavy-ion collisions

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163

We have studied the fragmentation of Au projectiles interacting with targets of C, A1 and Cu at an incident energy of E/A = 600 MeV. The employed inverse kinematics allowed a nearly complete detection of projectile fragments with charge Z > 2. The recorded fragmentation events were sorted according to three observables, the multiplicity Mtp of light charged particles, the largest atomic number Zma x within an event, and a new observable, Zbound, representing the sum of the atomic numbers Z of all fragments with Z>__ 2. Using these observables, the impact parameter dependence of the fragmentation process was investigated. For all three targets, a maximum mean multiplicity of 3 to 4 intermediate mass fragments (IMFs) is observed. The corresponding impact parameters range from central collisions for the C target to increasingly peripheral collisions for the heavier targets. It is found that the correlation between the IMF multiplicity and Zbouna, extending from evaporation type processes (large Zbouna) to the total disassembly of the projectile (small Zbound) , is independent of the target nucleus. This universal behaviour may suggest an -at least partial -equilibration of the projectile fragment prior to its decay.

Section: Transition From Evaporation To Total Disassemblysupporting

confidence: 64%

Fragmentation of gold projectiles: From evaporation to total disassembly

Hubele

Kreutz

Adloff³

et al. 1991

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163

“…Other observations as, e.g. the monotonic correlation of r with the integrated cross section for fragment production at intermediate bombarding energies [21] are consistent with it. As a next step, it will be necessary to incorporate this dynamical condition into more complete models for the fragment decay of excited nuclei.…”

Section: Discussionsupporting

confidence: 72%

“…The strong correlation between the production cross section and the element distribution of the fragments, as apparent from Fig. 3, has been observed experimentally [21].…”

Section: A Schematic Model For Proton-nucleus Reactionsmentioning

confidence: 76%

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Systematics of the power law parameter and minimum angular momenta for fragment production

Trautmann

Milkau

Lynen

et al. 1993

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Abstract.The element yield distributions a(Z) of intermediate mass fragments from proton, helium, and heavy-ion induced reactions exhibit a universal behaviour as a function of the bombarding energy. The power law parameter ~, obtained from fits with a(Z)ocZ ~, falls monotonically with increasing projectile energy Ela b and reaches a saturation value ~-2.0 at Elab---2 GeV. It is suggested that the behaviour at low bombarding energies is caused by a dynamical hindrance of the fragment emission at low angular momentum. PACS: 25.40.Sc; 25.70.Gh; 25.70.Lm; 25.70.Mn; 25.70.Pq reactions on heavy targets. Our intention hereby is twofold. We first show that the r parameters describing inclusive cross sections exhibit a universal behaviour when plotted as a function of the total projectile energy. They decrease monotonically with increasing projectile energy until they assume a saturation value at several GeV and higher energies. We then search for possible explanations of this behaviour but limit ourselves to the lower bombarding energies. We recall experimental evidence for dynamic effect of angular momentum in fragment emission, and we show that the rise of z towards low bombarding energies may result from a dynamical hindrance of fragment emission at low angular momentum.

“…To get this type of information is the first natural step in approaching the phenomenon of multifragmentation. In previous measurements of this type, a measure of the excitation energy was derived from the source velocity [21,22] as in the present work, or from the multiplicity of charged particles [23,24] or from the number of protons in composite fragments [4] or from the energy balance with the projectile-like fragment [-25] and/or with preequilibrium particles [22,26,27]. The method of analysis used here resembles most closely to that of Bizard et al [22] who studied, however, a much heavier system at higher excitation energy.…”

Section: Discussionmentioning

confidence: 99%

Multifragmentation study on 30 AMeV32S+58Ni

Siwek¹,

Sourell

Budzanowski³

et al. 1995

Abstract. In a multidetector experiment on 26 or 30 AMeV 32S + 5SNi, up to four coincident heavier or intermediate-mass fragments were observed. One of these occasionally has the characteristics of a projectile-like fragment, up to three may be attributed to the decay of the heavy reaction product. Taking the velocity of the fragments as a measure of the heavy-product excitation energy, one finds evaporation, fission and multifragmentation to follow one another with rising excitation. Model simulations of sequential decay with up to two binary fissions and, alternatively, of simultaneous statistical multifragmentation were performed for comparison with experimental distributions of mass, velocity and (for events with three slow intermediate-mass fragments) relative azimuthal angle. Though in the three-fragment events indications of simultaneous multifragmentation are present, the sequential binary decay predominates. Evaporated protons and c~ particles detected in coincidence have a mean multiplicity growing with excitation energy, while the temperature governing the spectra has a plateau with a value of about 5.5 MeV.