First intercomparison of ²⁴¹Am activity measurements using primary methods including magnetic micro-calorimetrers

Low-temperature detectors, such as Magnetic Micro-calorimeters (MMCs), exhibit several characteristics that make them strong candidates for primary activity standardization of various radionuclides. As a relatively new technique, however, many aspects of MMC-based measurements still require validation. For this purpose, ²⁴¹Am was selected to conduct an intercomparison of activity measurements between MMCs and other well-established conventional methods. The alpha-particle emitter ²⁴¹Am is well-suited to such comparisons, as it can be standardized with low uncertainty using a variety of techniques, including defined solid angle counting, coincidence counting, ionization chambers, and liquid scintillation counting (LSC). A key challenge in this context is the preparation of sources compatible with both MMCs and traditional standardization methods. An ²⁴¹Am source was prepared by electro-precipitation in a specially designed geometry compatible with both multi-channel MMC spectrometry and conventional methods. This source was measured by four metrology institutes - LNE-LNHB, CIEMAT, CHUV, and PTB - using different primary methods. Subsequently, the original source was divided into 21 secondary sources, which were integrated into 11 absorbers of a multi-channel MMC spectrometer for the final activity determination. Activity measurements using MMCs will be presented, along with the results of the intercomparison between different laboratories and techniques. The reported uncertainties are relatively high, in the range of a few percent, due to the rather low activity of the source and a potential loss of activity during the exercise. However, this first intercomparison provides insights and opportunities for improvement, which will be implemented in the future.