Thesis (MSc)--Stellenbosch University, 2016ENGLISH ABSTRACT :Relatively small changes to the overall shape of the photon strength function
such as the scissors or pygmy resonances can have a significant impact on reaction
rates. Reaction rates are important for modeling processes that take place
in astrophysical environments and nuclear reactors. Recent results indicate the
existence of a significant amount of scissors resonance strength in the photon
strength function for nuclei in the actinide region. In order to investigate the
extent and persistence of the scissors resonance strength towards lighter nuclei,
an experiment was performed utilizing the NaI(Tl) gamma-ray detector array
(CACTUS) and silicon particle telescopes (SiRi) at the cyclotron laboratory at
the University of Oslo. Particle-gamma coincidences from the 181Ta(d,p)182Ta
and 181Ta(d,d’)181Ta reactions were used to measure the nuclear level density
and photon strength function of the well-deformed 182Ta and 181Ta systems.
From these data (n,
) cross sections were calculated with the Talys reaction
code.
While there are possible bumps in the photon strength function of 181Ta that
may be due to the scissors resonance, it appears to be absent for 182Ta. These
results are discussed in the context of nuclear structure and other work done
in this and other mass regions.AFRIKAANSE OPSOMMING : Relatief klein veranderinge aan die algehele vorm van die foton krag funksie
soos die sk^er of dwerg resonansies kan beduidende invloed op reaksiesnelhede
h^e. Reaksiesnelhede is belangrik vir die modellering van prosesse wat plaasvind
in astrofisiese omgewings en kern reaktors. Onlangse resultate dui daarop
dat daar ’n beduidende bedrag sk^er resonansie krag in die foton krag funksie
vir kerne in die aktinied streek is. Ten einde die omvang en volharding van
die sk^er resonansie krag teenoor ligter kerne te bepaal, is ’n eksperiment uitgevoer
met behulp van die NaI(Tl) gammastraal-detektor matriks (CACTUS)
en silikon deeltjie teleskoop (SiRi) by die siklotron laboratorium aan die Universiteit
van Oslo. Deeltjie-gamma toevallighede van die 181Ta(d,p)182Ta en
181Ta(d,d’)181Ta reaksies is gebruik om die kern vlak digtheid en foton krag
funksie van die goed vervormde 182Ta en 181Ta stelsels te bepaal. Van hierdie
data is (n,
) dwarssnitte bereken met die Talys reaksie kode.
Hoewel daar moontlike bewyse vir die sk^er resonansie in die foton krag funksie
van 181Ta is, is dit afwesig in 182Ta. Hierdie resultate word bespreek in die
konteks van kernstruktuur en ander werk wat in hierdie en ander massa streke
gedoen is
