Considerations for massic activity determination by Decay Energy Spectrometry (DES) using cryogenic Transition Edge...

Decay Energy Spectrometry (DES) using cryogenic Transition Edge Sensors (TES) is a promising technique for activity standardization due to its 4π geometry, high absorption efficiency, high energy resolution, and low background. This enables DES to identify and quantify radionuclides, including impurities that are difficult to quantify simultaneously by other methods, without the need for chemical separations. For DES to be used as a primary standardization method, it is necessary to ensure accurate deposition of microgram amounts of source solution and to eliminate bias from pulse pileup or pulse shape variability. To address these challenges, we have developed new methods for DES sample preparation, TES chip design, and data analysis. We present massic activity and isotopic ratio results for ²⁴³Am sources with ²⁴¹Am impurity, live-timing with extending dead time and pileup exclusion, and correction of systematic errors due to data acquisition challenges unique to DES. We show that after these considerations are made, relative combined standard uncertainties below 1% are achievable. The ²⁴³Am massic activity determined by DES agrees well with the value determined by liquid scintillation (LS) counting, with the ratio of the two values and its combined uncertainty A_DES/A_LS=1.000±0.005.