Pre-equilibrium excitation of nuclei in ([rho], [alpha]) and ([rho], 3He) reactions induced by 120, 160 and 200 MeV protons

Arendse, Gillian John (1994)

Thesis (M. Sc.) -- University of Stellenbosch, 1994.

In title the [rho] and [alpha] are the Greek symbols and the 3 in 3He is in superscript.

Thesis

ENGLISH ABSTRACT: The study of pre-equilibrium reactions induced by medium-energy light ions have become of increasing importance in recent years as they represent the bulk of the measured spectrum. On a nuclear time scale these reactions are known to take place after a one-step process of exciting discrete states in the residual nucleus but long before the process whereby the projectile distributes its kinetic energy equally over all target nucleons to form a compound nucleus which decays statistically. In this work the systematic behaviour of the continuum of complex ejectiles was investigated as a function of incident proton energy and target mass. The continuum energy spectra for the reactions 27AI(p, X), 59Co(p,X), and 197 Au(p,X), with X=a and 3He, were measured using a five element detector telescope. Data were acquired at scattering angles between 10-100° at incident proton energies of 129 and 200 MeV, and at scattering angles between 20 - 140° for an incident proton energy of 160 MeV. Experimental angle-integrated cross sections were compared with calculated angle-integrated cross sections using the geometry dependent hybrid (GDH) model. The comparison between the experimental data and the calculations were used to quantitatively estimate the contribution of the evaporation process to the pre-equilibrium spectrum. The experimental angular distributions from the reaction (p,a) and (p,3 He) on 27 Al, 59Co, and 197 Au were compared with calculated angular distributions using the phenomenological parametrization of Kalbach. In general good agreement between the experimental data and the calculations were obtained. Minor discrepancies were observed with regard to target mass and incident proton energy dependence. It is believed that the characteristics of these discrepancies could provide guidance to the future attempts to develop a proper quantum mechanical description of the reaction mechanism of complex-ejectile production induced by energetic protons.

AFRIKAANSE OPSOMMING: Die ondersoek van voor-ewcwigs reaksies geïnduseer deur medium-energie ligte ione het oor die afgdope jare van toenemende belang geword aangesien dit 'n groot deel van die gemete spektrum uitmaak. Wat die tydskaal van die reaksies betref, vind dit plaas na 'n enkel proses waartydens diskrete toestande binne die reskern opgewek word, maar lank voor die projektiel al sy kinetiese energie oorgedra het aar die teiken-nukleone om sodoende 'n tussenkern te vorm wat statistics verval. In hierdie projek word die sistemariese gedrag van die kontinuum van komplekse deeltjies ondersoek in afhanklikheid van invalsenergie en teikenmassa. Energie spektra vir die reaksies 27Al(p, .Y.. ), 59Co(p, X) en 197Au(p, X), met X=a en 3He, is gemeet met behulp van 'n vyf element detektor teleskoop. Data is versamel by verstrooiings hoeke tussen 10 -_ 1600 vir invalsenergicë van 120 en 200 MeV, en vir verstrooiingshoeke tussen 20 - 1400 vir 'n invalscncrgi- van 160 M('V. Eksperimentele hock-geïntegreerde kanevlakke is vergelyk met berekende hoekgeïntegreerde kansvlakke wat verkry is met behulp van die geometries-afhanklike hibried ( GDH ) model. Die ooroenstemming tussen die eksperimentele data en die berekeninge is gebruik om 'n kwantitatiewe afskatting te maak van die bydrae van die verdampings-proses tot die gemete voor-ewewigs spektrum. Die eksperimentele hoekverdclings van die reaksies (p, Q) en (p,3 He) op 27Al, 59Co PIl 197Au was vergelyk met berekende hoekvcrdelings. afkomstig van die fenomcnologioso paramctrisering van Kalbach. Oor die algemeen is goeie ooreenstemming tussen die eksperimentele data en die berekende hoekverdelings gevind. C~~ringeafwykings tussen die eksperimentele data en die berekeninge kom nogt? M.1v1o~o\r afhangend, van invalsenorgie en teiken rnassa. Die aard van die sistem- I/.ti~~e·afwykings mag riglyne lewer tot die daarstelling van 'n kwantum meganiese beskrywing van di« reaksie meganismes betrokke by die produsering van «ornplcl-so deeltjies geïndus. ., . deur energieke protone.

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