Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The study of α clustering is a well-established topic of research in nuclear physics. Recent
experimental evidence has revealed the first 2+ excitation of the Hoyle state in 12C, which is
known to have a strong α cluster structure. The idea of multi-particle α cluster structures
in light nuclear matter has received much attention from theoretical investigations of late.
This research has profound implications in the fields of both nuclear structure and nuclear
astrophysics.
The 20Ne nucleus is a good example for α clustering, since many of its states are known
to have α clustering structures. Few low spin states are known at high excitation energies
of this nucleus. It is predicted that this nucleus contains a 0+ 5-α cluster state, a so-called
‘Hoyle analogue state’, above its 5-α break-up threshold at Ex = 19.17 MeV.
This thesis presents a study of the 20Ne nucleus with the 22Ne(p,t)20Ne reaction at laboratory
angles θlab =(0◦, 7◦, 16◦, 27◦). The iThemba LABS K600 magnetic spectrometer
was employed with a beam of energy Elab = 60 MeV, incident upon a 22Ne gas target held
intact by Aramid foils. The aim was to search for low spin states in 20Ne at excitation
energies above Ex = 15 MeV, and, possibly, to find an indication of the 5-α cluster state.
Three narrow states were discovered at energies of Ex = 20.59 MeV, Ex = 21.16 MeV
and Ex = 21.80 MeV. Calculations performed with the isobaric multiplet mass equation
indicate that these states may be T = 2 isobaric analogue states of three known states
in 20O. However, shell-model calculations indicate that these states may also have T = 0
or T = 1 isospin values. There is also evidence of a new state at Ex = 17.67 MeV and,
possibly, of a collection of new states which could not be resolved at Ex = 18.84 MeV.
A tentative candidate for the desired 5-α cluster state was observed, but this will require
another measurement with cleaner background to be confirmed. / AFRIKAANSE OPSOMMING: Alfa bondelvorming is ’n gevestigde navorsingsonderwerp in kernfisika. Daar is onlangse
bewyse vir die ontdekking van die 2+ opwekking van die Hoyle toestand in 12C, wat ’n
erkende alfa bondelstruktuur het. Die idee van multi-alfa bondelstrukture in ligte kerne
het onlangs baie aandag geniet in teoretiese ondersoeke. Hierdie navorsing het besondere
implikasies vir kernstruktuur, sowel as vir kernastrofisika.
Die 20Ne kern bied ‘n ideale voorbeeld vir alfa bondelvorming aangesien dit bekend
is dat baie van die kern se toestande alfa bondelstrukture het. Min lae-spin toestande
is by ho¨e opwekenergie¨e bekend in hierdie kern. Daar word voorspel dat ’n 0+ 5-alfa
bondeltoestand, ’n sogenaamde ‘Hoyle analoogtoestand’, bo die drumpel vir 5-alfa verval
by Ex = 19.17 MeV bestaan.
Hierdie tesis beskryf ‘n studie van die 20Ne kern met die 22Ne(p,t)20Ne reaksie by laboratorium
hoeke van θlab =(0◦, 7◦, 16◦, 27◦). Die K600 magnetiese spektrometer van
iThemba LABS is gebruik met ‘n proton bundel, by ‘n energie van Elab = 60 MeV, wat op
‘n 22Ne gas teiken omhul met aramid foelies gerig is. Die doel was om lae-spin toestande
in 20Ne by opwekenergie¨e bo Ex = 15 MeV op te spoor, en om moontlik ook ‘n aanduiding
van die 5-alfa bondeltoestand te vind.
Drie smal toestande is by energie¨e van Ex = 20.59 MeV, Ex = 21.16 MeV en Ex =
21.80 MeV opgespoor. Berekeninge wat met die isobariese multiplet massa vergelyking
uitgevoer is, dui daarop dat hierdie toestande T = 2 isobariese analoogtoestande van drie
bekende toestande in 20O kan wees, hoewel skilmodel berekeninge ook T = 0 en T = 1
kandidate aandui. Daar is ook bewyse van ’n nuwe toestand by Ex = 17.67 MeV, en
moontlik van ’n versameling nuwe toestande rondom Ex = 18.84 MeV wat nie uitmekaar
geken kon word nie.
‘n Tentatiewe kandidaat vir die gesogte 5-alfa bondel toestand is waargeneem, maar
nog ‘n meting met ’n skoner agtergrond word vir bevestiging benodig.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86443 |
| Date | 04 1900 |
| Creators | Swartz, Jacobus Andreas |
| Contributors | Papka, Paul, Smit, Frederick David, Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 174 p. |
| Rights | Stellenbosch University |
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