ABSTRACT
This paper presents the investigation carried out by CEA List and ArcelorMittal R&D in order to assess the potential of linac-based neutron activation analysis to detect and quantify copper in scrap metal. Performances are evaluated using MCNP6 and then validated experimentally using a 6 MeV linac coupled with heavy water. It is shown that (γ, n) reaction cross-sections for deuterium are likely to be undervalued in ENDF/B-VII and suggested that photoneutron production algorithms in Monte Carlo codes should be reexamined.
ABSTRACT
When new materials appear as potential alternatives for radiation detection, several criteria have to be fulfilled. The one presented herein is the response variation to large irradiation doses of neutron/gamma discriminating plastic scintillators. Thus, several samples were exposed to high gamma doses reaching 10 kGy. They were characterized in terms of gamma spectrometry and fast neutron/gamma discrimination, prior to and after irradiation. Results show an unexpected increase of the figure of merit (FoM), which is the numerical value for n/γ discrimination performances. An in-depth investigation evaluates the physicochemical impact of such large doses within the material. The characterization includes photophysics, radiation/matter interaction and chemical analyses (EPR, 1H NMR, fluorescence spectroscopy and HRMS).
ABSTRACT
The scope of this work was to develop a synthetic single crystal diamond dosimeter (SCDD-Pro) for accurate relative dose measurements of clinical proton beams in water. Monte Carlo simulations were carried out based on the MCNPX code in order to investigate and reduce the dose curve perturbation caused by the SCDD-Pro. In particular, various diamond thicknesses were simulated to evaluate the influence of the active volume thickness (e AV) as well as the influence of the addition of a front silver resin (250 µm in thickness in front of the diamond crystal) on depth-dose curves. The simulations indicated that the diamond crystal alone, with a small e AV of just 5 µm, already affects the dose at Bragg peak position (Bragg peak dose) by more than 2% with respect to the Bragg peak dose deposited in water. The optimal design that resulted from the Monte Carlo simulations consists of a diamond crystal of 1 mm in width and 150 µm in thickness with the front silver resin, enclosed by a water-equivalent packaging. This design leads to a deviation between the Bragg peak dose from the full detector modeling and the Bragg peak dose deposited in water of less than 1.2%. Based on those optimizations, an SCDD-Pro prototype was built and evaluated in broad passive scattering proton beams. The experimental evaluation led to probed SCDD-Pro repeatability, dose rate dependence and linearity, that were better than 0.2%, 0.4% (in the 1.0-5.5 Gy min-1 range) and 0.4% (for dose higher than 0.05 Gy), respectively. The depth-dose curves in the 90-160 MeV energy range, measured with the SCDD-Pro without applying any correction, were in good agreement with those measured using a commercial IBA PPC05 plane-parallel ionization chamber, differing by less than 1.6%. The experimental results confirmed that this SCDD-Pro is suitable for measurements with standard electrometers and that the depth-dose curve perturbation is negligible, with no energy dependence and no significant dose rate dependence.
