Selected Citation

Decay of A35

Authors(s):O. C. Kistner, A. Schwarzschild, and B. M. Rustad Publication:Physical Review Publication Date:October 1, 1956 Publisher: American Physical Society Citation:Physical Review 104(1):154-158 Link:ResearchGate

The positron decay of A35 has been investigated with a magnetic lens beta-ray spectrometer and a NaI(Tl) scintillation spectrometer. A maximum beta-ray energy of 4.96+/-0.04 Mev was found, which is 0.5 Mev higher than the previous values determined by cloud-chamber measurements. The new value is in good agreement with the end point predicted from Coulomb energy considerations. Two weak gamma rays were found with energies of 0.19+/-0.04 and 1.73+/-0.04 Mev; both are in good agreement with reported levels in Cl35. Analysis of the complex beta spectrum shows that approximately 7% of the A35 decays to two excited states in Cl35. The ft value of the ground-state, mirror transition is 6200+/-400 seconds. From this ft value and the ft value of O14, the |sigma|2 for this transition was estimated to be less than 0.13; the e-nu angular correlation coefficients were calculated to be +0.96+/-0.04 and -0.93+/-0.09 for the V, T and S, T beta interactions, respectively. These coefficients are indistinguishable from those expected in the case of a pure Fermi transition, indicating that A35 would be very suitable for identifying the Fermi invariant in the beta-decay interaction by an angular correlation experiment.

The relatively small amount of Gamow-Teller component present in the decay of A35 will have very little effect on the results of an e-v angular correlation experiment for determining the Fermi invariant. The Gamow-Teller interaction has been shown to be predominantly tensor by e-v experiments on He6. On the assumption that there is no intermixing of the Fermi invariants, the angular correlation coefficient for a simple allowed transition is [equation] where the minus and plus signs apply to the cases of scalar and polar-vector for the Fermi interaction, respectively. This coefficient can be evaluated for the A35 ground state transition arms of the Fermi matrix elements and ft values for O14 and A35 by use of expression (1 ).

"The resulting values of X for the S,'1 lower beta groups before the results could be compared and V,T admixtures are [2 equations]. These quantities are indistinguishable from the case of a pure Fermi transition, which would yield values of either —1 for the scalar invariant or +1 for the vector invariant. The A35 mirror transition is, therefore, considerably more favorable for a recoil experiment than was previously indicated by the values, X8, z = —0.36 and Xv, z=0.68, calculated from the old ft value of 3400 seconds. An experimental measurement of X for A", however, would have to be corrected for the weak lower beta groups before the results could be compared with the above predictions.


ACKNOWLEDGMENTS We thank Dr. O. Kofoed-Hansen for his advice and assistance in the experiments. We are grateful to Professor W. W. Havens, Jr., and Professor C. S. Wu for their encouragement and many helpful suggestions.