Spectrometric analysis and internal dose assessment in lung counting for reactor-grade Pu compounds

Internal contamination with plutonium (Pu) isotopes represents one critical exposure scenario in nuclear fuel cycle facilities. Lung counting is commonly employed as the initial individual monitoring method following inhalation of Pu. Due to the low detection sensitivity for characteristic X-rays emitted by Pu isotopes, the γ-ray emitted by coexisting 241Am is typically used as a surrogate for measurement. However, it is essential to establish clear procedures applicable in cases of severe internal exposure. In this study, key challenges associated with lung counting and dose assessment were examined, focusing on an inhalation event of reactor-grade Pu compounds containing 238Pu to 242Pu. These challenges included: complex spectral peak analysis; increased minimum detectable activity for Pu isotopes due to interference from 241Am; and evaluation of the minimum assessable dose considering Pu isotopic composition. Based on these considerations, procedures from lung counting to internal dose assessment were refined to support emergency response.