Measurement of 227 Ac impurity in 225 Ac using decay energy spectroscopy

• Published in: Applied radiation and isotopes 2021-06, Vol.172, p.109693, Article 109693
• Main Authors: Tollefson, A D, Smith, C M, Carpenter, M H, Croce, M P, Fassbender, M E, Koehler, K E, Lilley, L M, O'Brien, E M, Schmidt, D R, Stein, B W, Ullom, J N, Yoho, M D, Mercer, D J
• Format: Article
• Language: English
• ISSN: 0969-8043; 1872-9800
• DOI: 10.1016/j.apradiso.2021.109693

Ac is a valuable medical radionuclide for targeted α therapy, but Ac is an undesirable byproduct of an accelerator-based synthesis method under investigation. Sufficient detector sensitivity is critical for quantifying the trace impurity of Ac, with the Ac/ Ac activity ratio predicted to be approximately 0.15% by end-of-bombardment (EOB). Superconducting transition edge sensor (TES) microcalorimeters offer high resolution energy spectroscopy using the normal-to-superconducting phase transition to measure small changes in temperature. By embedding Ac production samples in a gold foil thermally coupled to a TES microcalorimeter we can measure the decay energies of the radionuclides embedded with high resolution and 100% detection efficiency. This technique, known as decay energy spectroscopy (DES), collapses several peaks from α decays into single Q-value peaks. In practice there are more complex factors in the interpretation of data using DES, which we will discuss herein. Using this technique we measured the EOB Ac impurity to be (0.142 ± 0.005)% for a single production sample. This demonstration has shown that DES is a useful tool for quantitative measurements of complicated spectra.