Tesis doctoral de Francisco Gabriel Molina Palacios
This thesis covers an experimental study of the beta-decay of four tz=-1 nuclei. The main purpose of this work is to compare these four decays with the mirror process studied in the (3he,t) charge exchange (ce) reaction at rcnp in osaka, japan. the experimental work was carried out at two different laboratories, lisol at the centre de recherches du cyclotron crc in louvain-la-neuve, belgium and rising-frs at the gesellschaft f¿ur schwerionenforschung (gsi) in darmstadt, germany. The two facilities employ completely different methods of ion separation. The former uses the isol separation technique and the latter uses fragmentation reactions and in-flight separation. As we will see from the results, for nuclei with very short half-lives such as those studied in this thesis, the fragmentation method is in general more appropriate. with the analysis of the gsi experiment was possible to obtain very precise half-life values of the radioactive nuclei, 42ti, 46cr, 50fe and 54ni, using time correlations between the ion implanted in a dsssd si detector and the beta particles detected in the same detector. The 105 ge crystal rising detector array was used to measured °-rays associated with the decay of the implanted ion. The ground state feeding in the daughter nuclei was measured as well as the feeding to individual excited states. With the half-life value and the feedings to the different states in the daughter nucleus it is possible to obtain an absolute value for the gamow-teller transition strength b(gt). Assuming that the nuclear interaction is independent of the charge both beta decay and ce reactions must be analogue processes. Then a fair comparison of this principle can be done comparing the absolute b(gt) value obtained in beta decay experiment with the normalised b(gt) obtained in ce reactions. This comparison was done for the four nuclei studied and some differences were found. these differences cannot be interpreted as an isospin symmetry breaking but rather due to ambiguities in our understanding of the ce reaction mechanism. another interesting result from this experiment, is the absence of m1 transitions between the 1+ states in the daughter nuclei. This can be explained in terms of the isospin: the 0+ ground state, in the daughter nuclei, has isospin t=1, the 1+ states, in the daughter nuclei, have isospin t=0. In the m1 transitions of the type 1+(t=0) -> 0+(t=1) the strong isovector term predominates, and we can see those transitions. In the m1 transitions 1+(t=0) -> 1+(t=1) only the isoscalar term can contribute, which is around 20 times weaker than the isovector term, therefore below the sensitivity limits of our experiment. This corresponds to the so-called quasi-selection rule ofwarburton andweneser, and it has been observed to be valid for the first time for the fp-shell nuclei, in this work.
Datos académicos de la tesis doctoral «Beta decay of tz=-1 nuclei and comparison with charge exchange reaction experiments«
- Título de la tesis: Beta decay of tz=-1 nuclei and comparison with charge exchange reaction experiments
- Autor: Francisco Gabriel Molina Palacios
- Universidad: Universitat de valéncia (estudi general)
- Fecha de lectura de la tesis: 27/05/2011
Dirección y tribunal
- Director de la tesis
- Berta Rubio Barroso
- Tribunal
- Presidente del tribunal: william Gelletly
- alison Bruce (vocal)
- José roberto Morales peña (vocal)
- bertram Blank (vocal)