The relative polarization of positrons emitted in pure Fermi ${(}^{14}$O) and Gamow-Teller ${(}^{10}$C) decays has been measured using a new technique based on time-resolved positronium decay. The result ${\mathit{P}}_{\mathrm{GT}}$/${\mathit{P}}_{\mathrm{F}}$=0.9996±0.0037 provides constraints on possible right-handed and scalar-tensor current admixtures to the weak interaction of -4<ζδ×${10}^4$<7 and ‖(${\mathit{C}}_{\mathit{S}}$/${\mathit{C}}_{\mathit{V}}$)-(${\mathit{C}}_{\mathit{T}}$/${\mathit{C}}_{\mathit{A}}$)‖=(1±9)×${10}^{\mathrm{-}3}$ (90% C.L.), respectively.

• Received 21 May 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.3249