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

• The pure alpha emitter Gd-148 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-148 and the associated committed effective dose in exposed humans, by means of high-resolution gamma spectrometry of the gamma-emitting radiogadolinium isotopes Gd-146 and Gd-153 that are accompanied by Gd-148 generated from the operation of the tungsten target. Theoretical minimum detectable whole-body activity (MDA) and associated internal doses from Gd-148 are calculated using a combination of existing biokinetic models and recent computer simulation studies on the generated isotope ratios of Gd-146/Gd-148 and Gd-153/Gd-148 in the ESS target. Of the two gamma-emitting gadolinium isotopes, Gd-146 is initially the most sensitive indicator of the presence of Gd-148 if whole-body counting is performed within a month after the release, using the twin photo peaks of Gd-146 centered at 115.4 keV (MDA<1 Bq for ingested Gd-148, and<25 Bq for inhaled Gd-148). The corresponding minimum detectable committed effective doses will be less than 1 mu Sv for ingested Gd-148, but substantially higher for inhaled Gd-148 (up to 0.3 mSv), depending on operation time of the target prior to the release. However, a few months after an atmospheric release, Gd-153 becomes a much more sensitive indicator of body burdens of Gd-148, with a minimum detectable committed effective doses ranging from 18 to 77 mu Sv for chronic ingestion and between 0.65 to 2.7 mSv for acute inhalation in connection to the release. The main issue with this indirect method for Gd-148 internal dose estimation, is whether the primary photon peaks from (146) and Gd-153 can be detected undisturbed. Preliminary simulations show that nuclides such as Ta-182 may potentially create perturbations that could impair this evaluation method, and which impact needs to be further studied in future safety assessments of accidental target releases.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

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