Measurement of the electron capture probabilities of 55Fe with a metallic magnetic calorimeter

The ratios of the electron capture probabilities PK, PL and PM of 55Fe have been measured with a metallic magnetic calorimeter, a specific type of cryogenic detector. The 55Fe source was enclosed in the detector absorber, whose dimensions were chosen such that the detection efficiency for Mn K X-rays was larger than 99.99%. Since all electrons and photons emitted by the source are absorbed in the detector, the detection efficiency is virtually 100% for K, L and M captures. The energy threshold was low enough to allow for clear separation of the M captures (~ 80 eV) from noise. The capture probability ratios were translated to capture probabilities using the recommended value for the probability of the undetected N captures. The resulting values are in agreement both with the recommended values of PK, PL and PM and with the experimental data of Pengra and coworkers.