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Theory of Beta Decay

1963; Oxford University Press; Volume: 26; Linguagem: Inglês

10.1143/ptps.26.1

0375-9687

Masato Morita,

Neutrino Physics Research

m units of rn ' It c= 1, rn=electron mrrss.Here, p, E and Eo are the momentum, energy and maximum energy of electron, respectively.The Fermi matrix element ) 1 is energy independent.The F(Z, E) is called the Fermi function which comes from the correction to the emitted beta particle in nuclear Coulomb field.The spectrum above fitted the experimental data very well.Later the Fermi interaction was generalized to a linear combination of five relativistic invariants; scalar, vector, tensor, axial vector, and pseudoscalar (abbreviated S, V, 1: A and P, respectively).On the other hand, selection rules for spin and parity in the parent and daughter nuclei were known experimentally.In particular, there are two kinds of transitions with parity change No.They are called Fermi and Gamow-Teller transitions.Interaction V or S A or T Spin change 0 Parity change No 0, + 1 (except 0__,.0)No Transition Fermi Gam ow-Teller 'The remaining interaction is P which has an essential contribution only in the transition of no spin change but parity change.To find a correct comb~ nation out of five relativistic invariants was a central problem in 1950's.For this purpose, many nuclear recoil experiments were performed (see, Appendix A).In this period, the interaction for beta decay was once erroneously concluded to be a linear combination of scalar, tensor and pseudoscalar.In the late 1950's, one found, however, the true interaction to be vector and axial vector.The detour and success in finding the correct interaction are mainly based upon the development of counter technique.In January 1957, a revolutional finding was done on the parity nonconservation in beta decay.Lee and Yang were suspicious of parity conservation in weak interactions, and they proposed to test it, e. g., by measuring the asymmetry of beta-ray angular distribution from polarized nuclei (Le56).This experiment was immediately carried out by Wu and her collaborators in polarized Co 60 and the parity nonconservation was beautifully demonstrated (Wu57).Thus, (1/2) 112 6FPrM'frn) [Cv('frerM'frv) +C~('frervrs'frv)l, etc.After Wu's first experiment, various proposals for the parity experiments were put forward and performed.As a consequence, relations C~/Cv~ 1, etc., were established.In this connection the two-component neutrino theory was Downloaded from https://academic.oup.com/