Speaker
Description
Activated water is a significant radiation source in DT fusion-oriented research environments, where neutron-activated cooling and auxiliary water systems can produce mixed-energy gamma fields that complicate measurement and dose assessment. Separating low- and high-energy dose contributions is still challenging. In this work, incremental lead shielding is applied as a controlled, energy-selective perturbation: the low-energy component is preferentially filtered, while multi-MeV photons are affected comparatively weakly. The resulting spectral changes are used to probe dose formation in the KATANA activated-water field.
Lead shielding can strongly alter spectra near activated water because emissions span ≈200 keV to ≈7 MeV. We investigate the influence of incremental lead shielding on the gamma-ray spectrum from the KATANA facility at the TRIGA Mark II reactor (Jožef Stefan Institute, Slovenia). Gamma spectra were acquired with a coaxial HPGe detector positioned at a fixed distance of 200 cm from the outer observation snail under steady reactor power of 30 kW. To assess the influence of source strength and transport conditions, measurements were repeated for two water-flow settings (0.25 L/s and 0.67 L/s). For each flow rate, lead thickness in the detector line of sight was varied from 0 mm (unshielded reference) to 10 mm, while detector placement and acquisition settings were kept unchanged.
The observed changes are dominated by the strongly energy-dependent attenuation in lead. The 197 keV peak is suppressed rapidly: 2 mm of lead reduces the net peak area by ~65%, and at 4 mm the line is practically indistinguishable from local background under the present geometry and counting statistics. In contrast, the 6129 keV peak remains clearly observable even at 10 mm, demonstrating spectral hardening. While the higher flow rate increases overall count rate, the relative suppression pattern is governed primarily by photon energy: low-energy diagnostic lines are removed quickly, whereas very high-energy features persist.