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

The ratios of the electron capture probabilities P_K, P_L and P_M 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 (~ 80eV) 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 P_K, P_L and P_M and with the experimental data of Pengra and coworkers.