The probability of non-radiative decay of the 3d level in muonic 237Np

The X-ray spectrum of muonic 237 Np has been investigated with stopped muons in a NpO 2 target, containing about 10 g of 237 Np. The probability of the radiationless muonic 3d→1s transition in 237 Np , (9±4)% , was obtained by comparing the relative intensities of the main muonic X-ray transitions in singles and coincidence spectra. The coincidences were gated by the 2p→1s transitions.