Internal dose assessment of 148 Gd using isotope ratios of gamma-emitting 146 Gd or 153 Gd in accidently released spallation target particles

The pure alpha emitter Gd may have a significant radiological impact in terms of internal dose to exposed humans in case of accidental releases from a spallation source using a tungsten target, such as the one to be used in the European Spallation Source (ESS). In this work we aim to present an approach to indirectly estimate the whole-body burden of Gd and the associated committed effective dose in exposed humans, by means of high-resolution gamma spectrometry of the gamma-emitting radiogadolinium isotopes Gd and Gd that are accompanied by Gd generated from the operation of the tungsten target. Theoretical minimum detectable whole-body activity (MDA) and associated internal doses from Gd are calculated using a combination of existing biokinetic models and recent computer simulation studies on the generated isotope ratios of Gd/ Gd and Gd/ Gd in the ESS target. Of the two gamma-emitting gadolinium isotopes, Gd is initially the most sensitive indicator of the presence of Gd if whole-body counting is performed within a month after the release, using the twin photo peaks of Gd centered at 115.4 keV (MDA