Study of Weak Interactions with Delta-J = 0 Beta Decays.

The beta-gamma angular correlation for the decay of ^ {20}Na and ^{20} F to the 1.633 MeV state of ^{20 }Ne has been measured using a twenty-detector system of cylindrical symmetry. ^{20 }Na was produced by the ^{20 }Ne(p,n)^{20}Na reaction using the 19 MeV proton beam, and ^ {20}F was produced by the reaction ^{19}F(d,p)^{20 }F using SF_6 gas and 4 MeV deuterons. The activated gases were continuously transferred from the target cell into the source cell, in the center of the correlation apparatus, through a thin capillary. Two gamma detectors and sixteen beta detector telescopes allowed for the simultaneous measurements of beta -gamma coincidences at 0 ^circ, 25^circ , 45^circ, 65 ^circ, 90^circ , 115^circ, 135 ^circ, 155^circ and 180^circ and at their symmetric counterparts with respect to the 0 ^circ-180^circ direction. The beta- gamma correlation was also measured for the first-forbidden beta^- decay of ^{124}Sb, in order to confirm the computed attenuation in measured anisotropy caused by the finite geometry of the detectors and the source cell. The correlation function is denoted by W _+/-[theta_{beta -gamma}] = 1 + A[ p/E] costheta_{beta -gamma} + B_+/-[ E][ p/E]^2 cos ^2theta_{beta-gamma }. The +/- subscripts refer to electron or positron decay, p if the beta momentum, and E is the positron total energy. A arises from relativistic kinematics and can be calculable. The present result for ^{20}Na(beta, gamma) correlation is B_-[ E] = [-4.45+/-0.31 ] times 10 ^{-3} E + [1.87 +/- 0.42] times 10^{-4} E^2. The least squares fit to the energy dependence for ^{20}F was performed by assuming the quadratic energy dependence measured for ^ {20}Na and yielded B_+ [ E] = (0.08 +/- 0.14) times 10^ {-3} E + (1.87 +/- 0.44) times 10^ {-4} E^2. First and second class induced pseudotensor form factors (d_ {rm I} and d_{ rm II}) were evaluated by combining the linear energy dependences and yielded d_ {rm II}/Ac = -1.1+/-0.7 and d_{rm I}/Ac = 11.3 +/- 0.7. The 1977 Calaprice calculations for the value of the second forbidden axial vector form factor j_2 were used. Assuming the Calaprice prediction for j _2, j_3 could be deduced from the quadratic term of the energy dependence of the asymmetry. We obtained j_3 = -(19.5 +/- 3.0) times 10^{+4}. The beta-alpha angular correlation in allowed positron decay of ^{20}Na to the 7.415 MeV level of ^{20}Ne was measured using the same correlation apparatus with minor modifications. We obtained a lower limit for B_{beta -alpha};| B_{beta- alpha}[| E = 4.01 MeV) >= -(0.009 +/- 0.007). We conclude that the angular correlations in mass 20 may be in agreement with expectations based on conserved vector current theory. Our best value for second class axial currents, d_{rm II}/Ac = -1.1 +/- 0.7 is at the level of 10% of the weak magnetism term; however the statistical error given and the large uncertainty in j_2 derived from shell model wave functions preclude a more definite statement regarding the existence of second class currents.