Determination of L-X ray absolute emission intensities of 238Pu, 244Cm, 237Np and 233Pa radionuclides using a metallic magnetic calorimeter

Energy dispersive photon spectrometry is a common analysis technique to quantify radionuclides present in a sample, the analysis is based on the knowledge of the photon emission intensities specific to each radionuclide. Among them, actinides have in general intense emission of L X-rays during the decay. However, their emission intensities are not well known and not detailed in the nuclear and atomic data tables due to the complexity of their spectra that cannot be resolved by conventional semiconductor spectrometers. Using a dedicated high energy resolution cryogenic detector, based on metallic magnetic calorimeter sensor technology, the L X-ray spectra of the decays of Pu-238(alpha) -> U-234, Cm-244(alpha) -> Pu-240, Np-237(alpha) -> Pa-233 and Pa-233(beta(-)) -> U-233 were measured with an energy resolution between 23 eV and 43 eV (full width at half maximum) given access to an unprecedented level of detail. Moreover, the detector was conceived to provide a quasi-constant efficiency in the energy range of the L X-rays, minimizing the uncertainty for relative L X-ray emission intensities. Prior to the measurements, the full energy peak efficiency was carefully characterized, which enabled the determination of absolute emission intensities, with an uncertainty of the order of 1%. Some corrections had to be introduced using Monte Carlo simulations, in particular to take into account the surface activity inhomogeneities of the sources. Total and group L X-ray emission intensities are compared with the available data and with the recommended values. In addition, nearly 30 individual L X-ray intensities are presented.