Evidence for isovector parity mixing in the 11.264 MeV 1+ T = 1 state in 20Ne
Fifield LK., Catford WN., Chew SH., Garman EF., Pringle DM., Allen KW., Lowe J.
A search has been carried out for the 1+ T = 1 level at 11.264 MeV in 20Ne formed as a parity-forbidden resonance in the 16O(α,γ)20Ne reaction. The yield of 11.26 MeV γ-rays was measured as a function of α-particle energy over an interval of 8 keV centred on the expected resonance energy of the 1+ T = 1 level. An energy and intensity standard was provided by the nearby 1- T = 1 resonance at an excitation energy of 11.275 MeV in 20Ne. A significant improvement in the fit to the measured yield curve was obtained by including a sharp resonance at the expected energy of the 1+ T = 1 level. From the analysis it is concluded that the 1+ T = 1 level has been observed with 90% confidence. The resonance strength extracted from the fit implies a parity-forbidden a-particle width of 42(+-20)× 10-6 eV for the 1+ T = 1 level. The corresponding parity non-conserving matrix element linking the 1+ T = 1 level with the 1+ T = 0 state at 11.23 MeV therefore lies within the, range 0.8 eV ≤ 〈VPNCΔT = 1〉 ≤ 2.6 eV. © 1983.