Studies of fragment emission in light-ion-induced nuclear reactions
The formation and decay of hot nuclei can provide information about the limits of nuclear stability and the nuclear equation of state. A signature of these highly excited systems is the emission of intermediate-mass fragments (IMFs: 3 $\le$ Z $\sbsp{\sim}{<}$ 15). Several mechanisms for IMF forma...
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| Format: | Dissertation |
| Language: | English |
| Published: |
ProQuest Dissertations & Theses
01-01-1994
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| Online Access: | Get full text |
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| Summary: | The formation and decay of hot nuclei can provide information about the limits of nuclear stability and the nuclear equation of state. A signature of these highly excited systems is the emission of intermediate-mass fragments (IMFs: 3 $\le$ Z $\sbsp{\sim}{<}$ 15). Several mechanisms for IMF formation have been proposed, including emission from an equilibrated source, nonequilibrium emission from a composite system, and multifragmentation. Nonequilibrium IMF emission at very forward angles has been studied in the 200 MeV $\vec{\rm p}$+$\sp{\rm nat}$Ag reaction, using projectile polarization as a probe. Analyzing powers have been measured and are found to be consistent with zero, thus providing no evidence for a significant contribution from cluster knockout, or similar direct mechanisms. Isotope ratios were also measured and compared to the results of an accreting source calculation. The Indiana Silicon Sphere (ISiS), covering a solid angle of $\sim$74% of $4\pi ,$ was designed and built to study reactions induced by light-ion projectiles at intermediate bombarding energies. It consists of 162 detector telescopes with three elements: a gas-filled ionization chamber, a 500 $\mu\rm m$ passivated silicon detector, and a 2.8 cm CsI(Tl) crystal with photodiode readout. The first complete experiment using ISiS was performed in late 1993 at the Laboratoire National Saturne, Saclay, France. Two systems from this experiment have been studied: 4.8 GeV $\rm\sp3He$+$\sp{\rm nat}$Ag and $\rm\sp{197}Au.$ Multiplicity distributions for IMFs confirm multifragmentation; i.e., the observation of two or more IMFs in the final state. Rapidity plots and angular distributions indicate a nearly isotropic source, with a velocity of approximately 0.015c. Energy spectra, gated on increasing collision violence show broadening and shifting of the Coulomb peaks to lower energies and flattening of the spectra tails. This behavior has been predicted by a hybrid calculation, which uses the intranuclear cascade and expanding-evaporating source models. |
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| ISBN: | 9798208438374 |