Dissertation (PhD)--University of Stellenbosch, 2004. / 175 Leaves printed single pages, preliminary pages i-xiii and 147 numberd pages. Includes bibliography. List of figures, List of tables. / ENGLISH ABSTRACT: This study forms part of a larger investigation which has as a primary objective the development of a
comprehensive theoretical description of all the processes which contribute to the continuum in the
interaction of 12C and 16O with nuclei. Previous investigations of 12C and 16O induced reactions on
targets with mass close to A = 100 have shown that the experimental excitation functions and recoil
range distributions of heavy residues can be reproduced satisfactorily by means of a theoretical model
which takes relatively few dominant reaction mechanisms into account. These include the complete
fusion of the projectile with the target, the incomplete fusion of break-up α-type fragments (i.e. single
α particles, 8Be fragments and for the 16O induced reactions also 12C fragments) with the target and
single-nucleon transfer at incident energies above about 15 MeV/nucleon. The mean-field interaction
is mainly responsible for these interactions. The thermalization of the intermediate excited nuclei
produced in this first stage of the reaction is described by an intranuclear interaction cascade, during
which pre-equilibrium emission of particles and clusters may occur, followed by evaporation after
statistical equilibrium has been attained. The model also included the probability that break-up α
particles may escape with a large fraction of their initial energy after only a few interactions with
individual target nucleons following their initial incomplete fusion. The theory also predicted an
enhanced isobaric yield for residues with mass similar or near to that of the target.
The subsequent analysis of the emission spectra of intermediate mass fragments in these
reactions, however, indicated that two additional aspects need to be considered as well in order to
reproduce the experimental data. The first is that the projectile may lose a substantial amount of
energy in an initial-state interaction before breaking up, which can be described as a friction
dissipative process. The second is that several other incomplete fusion channels of “non-α-cluster”-
type fragments should also be included in a more complete description of these reactions as their
contributions are not negligible.
The present study has two main objectives. Firstly, to investigate the isobaric yield in the neartarget
mass region by measuring production cross sections for 103Pd, 103mRh and 103Ru. Previous
studies only provided data for 103Ag, which constitute only a few percent of the A = 103 isobaric yield.
The new data constitute more than 80% of the A = 103 isobaric yield, which provide experimental
confirmation of the enhanced isobaric yield in the near-target mass region. The second objective is to
perform extensive new calculations of the excitation functions and recoil ranges in order to investigate
the predictive power of the extended model in a priori calculations for the entire available data set. / AFRIKAANSE OPSOMMING: Hierdie studie maak deel uit van ‘n meer omvattende ondersoek wat as ‘n primêre doelwit die
beskrywing van al die bydraende prosesse tot die kontinuum in die interaksie van 12C en 16O met
kerne behels. In vorige ondersoeke van 12C en 16O geïnduseerde reaksies op skywe met massa naby
A = 100 kon die eksperimentele opwekkrommes van swaar reskerne en reikwydte distribusies van
terugslagkerne bevredigend gereproduseer word met behulp van ‘n teoretiese model wat slegs enkele
dominante reaksiemeganismes in berekening bring. Hierdie sluit in die volledige versmelting van die
projektiel met die skyfkern, die onvolledige versmelting van opbreek α-tipe fragmente (d.w.s. α-
deeltjies, 8Be fragmente, en in die geval van 16O geïnduseerde reaksies ook 12C fragmente) met die
skyfkern, en enkel-nukleon oordrag by invalsenergië wat hoër is as ongeveer 15 MeV/nukleon. Die
gemiddelde-veld interaksie is hoofsaaklik verantwoordelik vir bogenoemde reaksie meganismes. Die
oorgang na termiese ewewig van die opgewekte tussenkerne wat in hierdie eerste stadium van die
reaksie gevorm word, word beskryf deur ‘n intrakern interaksie kaskade wat gekenmerk word deur die
voorewewigs emissie van deeltjies en klonte van deeltjies, gevolg deur verdamping nadat statistiese
ewewig bereik is. Dié model sluit ook die waarskynlikheid in dat opbreek α-deeltjies kan ontsnap met
‘n betekenisvolle fraksie van hul aanvanklike energie na slegs enkele interaksies met individuele
skyfnukleone nadat hulle aanvanklik onvolledig versmelt het.
In latere studies van die emissiespektra van intermediêre massa fragmente in hierdie reaksies het
dit egter geblyk dat twee addisionele aspekte ook in berekening geneem moet word om die
eksperimentele data te reproduseer. Eerstens kan die projektiel ‘n substansiële hoeveelheid energie
verloor in ‘n aanvangstoestand interaksie voordat dit opbreek, wat beskryf kan word as ‘n wrywingdissipatiewe
proses. Tweedens kan verskeie ander onvolledige versmeltingskanale van fragmente met
‘n nié-α-karakter ook betekenisvol bydra en kan hulle dus nie verwaarloos word in ‘n meer volledige
beskrywing van hierdie reaksies nie.
Die huidige studie het twee hoofdoelwitte. Eerstens word die isobariese opbrengs in die nabyskyfgebied
ondersoek deur die produksie kansvlakke van 103Pd, 103mRh en 103Ru te meet. In vorige
studies is slegs data verkry vir 103Ag, wat net ‘n klein persentasie van die A = 103 isobariese opbrengs
verteenwoordig. Die nuwe data verteenwoordig meer as 80% van die A = 103 isobariese opbrengs,
wat eksperimetele bevestiging verleen dat ‘n verhoging in die isobariese opbrengs in die nabyskyfgebied
bestaan. Die tweede doelwit is om ‘n volledige stel nuwe a priori berekeninge te doen vir
al die opwekkrommes van reskerne en reikwydte distribusies van terugslagkerne wat tans beskikbaar
is om sodoende die voorspellings van die nuwe uitgebreide teoretiese model te toets.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/15939 |
| Date | 04 1900 |
| Creators | Buthelezi, E. Z.(Edith Zinhle) |
| Contributors | Cowley, A.A., Steyn, G.F., Van der Walt, T.N., University of Stellenbosch. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 162 leaves : ill. |
| Rights | University of Stellenbosch |
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