Search for Superscreening effect in Superconductor

4 pages, 3 figures, Expérience au GANIL avec SPIRAL/EXOGAMThe decay of $^{19}$O($\beta^-$) and $^{19}$Ne($\beta^+$) implanted in niobium in its superconducting and metallic phase was measured using purified radioactive beams produced by the SPIRAL/GANIL facility. Half-lives and branching ratios measured in the two phases are consistent within one-sigma error bar. This measurement casts strong doubts on the predicted strong electron screening in superconductor, the so-called superscreening. The measured difference in screening potential energy is 110(90) eV for $^{19}$Ne and 400(320) eV for $^{19}$O. Precise determinations of the half-lives were obtained for $^{19}$O: 26.476(9)~s and $^{19}$Ne: 17.254(5)~s