Date of Award

2-1-2022

Publication Type

Dissertation

Degree Name

Ph.D.

Department

Physics

Keywords

6He, 6Li+, Anisotropy, Beta, Decay, Helium

Supervisor

G.W.F. Drake

Supervisor

D. Xiao

Rights

info:eu-repo/semantics/openAccess

Abstract

According to the standard model the beta-decay of 6He is a pure Gamow-Teller transition. The aim of this thesis is to provide theoretical support in the search for new physics beyond the standard model by examining the angular distribution of beta particles following decay. The simple structure of 6He, along with its ability to under go beta-decay into 6Li+ makes it an ideal candidate for studying the weak force. Due to the sudden increase in nuclear charge from Z = 2 to Z = 3, and the recoil momentum of the daughter nucleus resulting from the emitted leptons, this decay causes an electronic rearrangement of the final 6Li+ atom. The method of calculation involves expanding the initial state of 6He in terms of a complete set of final states of 6Li+. Correlated nonrelativistic Hylleraas-like wave functions were used to create a pseudospectrum which span both the bound and continuum states of 6Li+. With the use of the sudden approximation, and the Taylor series expansion of the recoil momentum operator R = eiK.r, transition probabilities from an initial helium state to each of the final lithium ion pseudostates were calculated by applying Born's rule. Recoil terms up to the O(K2) were kept. Stieltjes imaging techniques were used to arrange the transition probabilities into bins according to the energy of each lithium pseudostate. The calculations were performed for the singlet 1S, triplet 2S, and triplet 2P (ML = 0 and ML = +/1) initial states of 6He and were compared with experimental results. These calculated charge state probability coeficients can be used by experimentalists to give a more accurate calculation of the correlation coeficient. Because the probability coeficients depend on ML, the angular distribution becomes anisotropic; their angular anisotropy was also calculated.

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