H. E. Swanson

Beta decays ofNe18andNe19and their relation to parity mixing inF18andF19

We have studied transitions weakly fed in the ..beta../sup +/ decays of /sup 18/Ne and /sup 19/Ne. The /sup 18/Ne activity was produced by bombarding natural O/sub 2/ gas with 12.0 MeV /sup 3/He ions. ..gamma..-ray groups with energies of 659, 1042, 1081, and 1700 keV were observed with relative intensities of 1.72 +- 0.05, 100.0, (2.89 +- 0.26) x 10/sup -2/, and 0.687 +- 0.013, respectively. These intensities correspond to relative branching ratios of 100.0, (2.70 +- 0.36) x 10/sup -2/, and 2.45 +- 0.05 for ..beta../sup +/ transitions to the 1042, 1081, and 1700 keV levels, respectively. Normalizing to previous data we obtain ft values of 1247 +- 11, 2971 +- 87, (1.03 +- 0.14) x 10/sup 7/, and (3.00 +- 0.10) x 10/sup 4/ sec for the transitions to the ground state, 1042, 1081, and 1700 keV levels, respectively. The difference in excitation energies of the 0/sup -/ and 0/sup +/ states is found to be 39.20 +- 0.11 keV. The /sup 19/Ne activity was produced by bombarding SF/sub 6/ gas by 6.4 MeV protons. A branching ratio of (1.20 +- 0.20) x 10/sup -4/ was obtained for the transition to the 110 keV level which correspondsmorexa0» to an ft value of (1.15 +- 0.19) x 10/sup 7/ sec. Transitions to the 1554 keV level were observed in a 9.2% Ge(Li) detector operated in the singles mode. A branching ratio of (2.34 +- 0.30) x 10/sup -5/ was obtained which corresponds to an ft value of (5.01 +- 0.47) x 10/sup 5/ sec. The /sup 18/Ne(0/sup +/;1)..-->.. /sup 18/F(1081 keV 0/sup -/;0) and /sup 19/Ne(1/2/sup +/; 1/2)..-->../sup 19/F (110 keV 1/2/sup -/; 1/2) first-forbidden ..beta../sup +/ branches are analogs of the previously measured parity mixing of the 1042 keV (0/sup +/;1) and 1081 (0/sup -/;1) keV levels of /sup 18/F and of the ground ((1/2)/sup +/;(1/2)) and 110 keV ((1/2)/sup -/;(1/2)) levels of /sup 19/F, respectively.«xa0less

Parity mixing in 21Ne; evidence for weak neutral currents in nuclei

The parity nonconserving circular polarization of γ-rays from the 2.789 → 0.0 MeV transition in ^(21)Ne is found to be (0.8 ± 1.4) × 10^(−3), which corresponds to a parity mixing matrix element │〈H_W〉│ = 0.009 ± 0.016 eV between the two members of the 2.8 MeV doublet. This matrix element can be combined with parity mixing matrix elements measured in ^(18)F and ^(19)F to predict isoscalar and isovector weak nucleon-nucleon coupling constants in excellent agreement with theoretical “best” values obtained in a Weinberg-Salam model calculation.

Beta decays of Ne-18 and Ne-19 and their relation to parity mixing in F-18 and F-19

We have studied transitions weakly fed in the ..beta../sup +/ decays of /sup 18/Ne and /sup 19/Ne. The /sup 18/Ne activity was produced by bombarding natural O/sub 2/ gas with 12.0 MeV /sup 3/He ions. ..gamma..-ray groups with energies of 659, 1042, 1081, and 1700 keV were observed with relative intensities of 1.72 +- 0.05, 100.0, (2.89 +- 0.26) x 10/sup -2/, and 0.687 +- 0.013, respectively. These intensities correspond to relative branching ratios of 100.0, (2.70 +- 0.36) x 10/sup -2/, and 2.45 +- 0.05 for ..beta../sup +/ transitions to the 1042, 1081, and 1700 keV levels, respectively. Normalizing to previous data we obtain ft values of 1247 +- 11, 2971 +- 87, (1.03 +- 0.14) x 10/sup 7/, and (3.00 +- 0.10) x 10/sup 4/ sec for the transitions to the ground state, 1042, 1081, and 1700 keV levels, respectively. The difference in excitation energies of the 0/sup -/ and 0/sup +/ states is found to be 39.20 +- 0.11 keV. The /sup 19/Ne activity was produced by bombarding SF/sub 6/ gas by 6.4 MeV protons. A branching ratio of (1.20 +- 0.20) x 10/sup -4/ was obtained for the transition to the 110 keV level which correspondsmorexa0» to an ft value of (1.15 +- 0.19) x 10/sup 7/ sec. Transitions to the 1554 keV level were observed in a 9.2% Ge(Li) detector operated in the singles mode. A branching ratio of (2.34 +- 0.30) x 10/sup -5/ was obtained which corresponds to an ft value of (5.01 +- 0.47) x 10/sup 5/ sec. The /sup 18/Ne(0/sup +/;1)..-->.. /sup 18/F(1081 keV 0/sup -/;0) and /sup 19/Ne(1/2/sup +/; 1/2)..-->../sup 19/F (110 keV 1/2/sup -/; 1/2) first-forbidden ..beta../sup +/ branches are analogs of the previously measured parity mixing of the 1042 keV (0/sup +/;1) and 1081 (0/sup -/;1) keV levels of /sup 18/F and of the ground ((1/2)/sup +/;(1/2)) and 110 keV ((1/2)/sup -/;(1/2)) levels of /sup 19/F, respectively.«xa0less

1/2/sup +/. -->. 1/2/sup -/ beta decay of /sup 19/Ne and the parity nonconserving NN force

A branching ratio of (1.20 +- 0.20) x 10/sup -4/ is obtained for the ..beta../sup +/ decay of /sup 19/Ne to the 110 keV 1/2/sup -/ level of /sup 19/F. This transition (presumably dominated by the ..delta..J/sup ..pi../ = 0/sup -/ axial charge operator) provides a crucial test of wavefunctions used in interpreting the parity mixing of the ground and 110 keV levels of /sup 19/F. These wavefunctions, which yield a parity mixing larger than that observed experimentally, also predict too large a ..beta../sup +/ decay rate.