Beta-neutrino angular correlation in the decay of $\chem{{}^{14}O}$

The positrons and coincident gamma-rays following the pure Fermi $0^+ \rightarrow 0^+$ branch of $\beta^+$-decay in $\chem{{}^{14}O}$ were measured. The Doppler shift of the $\gamma$-quantum observed is sensitive to the beta-neutrino correlation coefficient, which is unity ($\alpha=1$) in the absence of scalar coupling. The interatomic interaction of recoiling daughters was noticed, which has prevented to obtain an improved result for scalar coupling despite of the excellent statistical accuracy of the measurement. At the same time, it was shown that the method described can be used as a very sensitive and flexible tool to probe the interatomic interactions in matter at the hundred eV energy level. Perspectives in this direction as well as the future angular-correlation experiments aimed to search for scalar coupling in beta-decay are discussed