Coulomb excitation of the 2+ state in 14C and the quadrupole deformation of states in 194Pt

Thesis (PhD)--Stellenbosch University, 2019.ENGLISH ABSTRACT: The safe Coulomb excitation experiment of 14C and 194Pt which took place at Florida State University took advantage of the unique beam capabilities, the availability of highefficiency large volume LaBr3(Ce) detectors and the S3 double sided silicon strip detector. Using the advantageous experimental environment the B(E2: 2+1 ! 0+1 ) value of the firstexcited 2+1 state of 14C and the quadrupole deformation of states in 194Pt are investigated. B(E2: 2+1 ! 0+1 ) values of neutron-rich even-even C isotopes have been reported up to 20C and provide important information on the evolution of the underlying structural mechanism towards the drip line. They also provide critical constraints for theoretical models as is the case for the experimentally determined B(E2: 2+1 ! 0+1 ) value for 14C which exhibits persistent inconsistencies with that obtained from theoretical models. The B(E2: 2+1 ! 0+1 ) value in 14C cannot be reproduced by theoretical models making it indispensable to enhance our theoretical understanding of the C isotopic chain in general. The 2+1 state was not observed in the particle- data, which may indicate that 14C undergoes single-particle excitation and has a smaller B(E2: 2+1 ! 0+1 ) value than previously thought. The A 190 region is very interesting since it has oblate, prolate, -soft and spherical shaped nuclei. It is predicted that Pt evolves from prolate deformed 180186Pt to -soft 188Pt and triaxial 190Pt to oblate 192198Pt and finally to spherical 204Pt. From this work, the quadrupole deformation of the 0+1 , 2+1 , 4+1 , 2+2 , 4+2 states are successfully measured with increased accuracy. Additionally it is determined that 194Pt is triaxial oblate which supports the theoretical prediction of the shape evolution in Pt.AFRIKAANSE OPSOMMING: Die veilige Coulomb-eksitasie eksperiment van 14C en 194Pt aan die Florida State University het voordeel getrek uit die unieke vermoëns, die beskikbaarheid van hoë-doeltreffend groot volume LaBr3(Ce) detektors en die S3 silikon strook detektor. In die voordelige eksperimentele omgewing word ’n poging aangewend om die B(E2: 2+1 ! 0+1 ) van 14C te meet en die vierhoekige vervorming van vlakke in 194Pt. B(E2: 2+1 ! 0+1 ) waardes van neutronryke gelyke C isotope is aangemeld tot 20C en verskaf belangrike inligting oor die evolusie van die onderliggende strukturele meganisme teenoor die druplyn en kritiese beperkings vir teoretiese modelle. Die eksperimentele vasgestelde B(E2: 2+1 ! 0+1 ) waarde vir 14C vertoon egter volgehoue teenstrydighede met die waardes verkry uit teoretiese modelle. Die waarde van B(E2: 2+1 ! 0+1 ) in 14C kan nie gereproduseer word deur teoretiese modelle nie, wat dit onontbeerlik maak om ons teoretiese begrip van C isotopiese ketting in die algemeen te verbeter. Die 2+1 staat is nie waargeneem in die deeltjie- data nie, wat die moontlikheid uitwys van ’n enkel-deeltjie opwekking en ’n kleiner B(E2: 2+1 ! 0+1 ) waarde as verwag. Die A 190 streek is baie interessant aangesien dit afgeplatte, prolate, -sag en sferiese kerne bevat. Daar word voorspel dat Pt ontwikkel van die vervormde 180186Pt tot -sag 188Pt en triaksiaal 190Pt na afgeplatte 192198Pt tot uiteindelike spheriese 204Pt. Uit hierdie werk is die vierhoekige vervorming van die 0+1 , 2+1 , 4+1 , 2+2 , 4+2 state suksesvol gemeet met verhoogde akkuraatheid. Daarbenewens word dit vasgestel dat 194Pt triaksiaal afgeplat is wat die teoretiese voorspelling van Pt evolusie ondersteun.This research received financial assistance of the National Research Foundation (NRF) and the Professional Development Program (PDP).Doctora

Search for the scissors resonance in 182Ta

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