The use of portable equipment for the activity concentration index determination of building materials: Methodology and first results

Abstract

The legislation concerning the natural radioactivity in building materials will be ratified in the near future; expected 2015. It will then be required to assess the activity concentration index for each building material applied for dwellings or buildings such as offices or workshops. Therefore it is expected that a large number of building material analyses will have to be performed. NuTeC applies easy to operate portable equipment in order to assess the activity concentration index (ACI) in building materials. The goal is to provide an easy to operate and low-cost alternative to the standard laboratory analyses with HPGe spectrometry and 21 days equilibrium delay. A LaBr(Ce) scintillation probe which provides a 3% energy resolution and high light output is applied to obtain the spectral data. The data acquisition is a one-touch operation and runs for 12 hours; e.g. overnight. The net peak areas are determined via custom set-up Genie algorithms and the efficiency of the complete measurement setup is calculated via commercially available software. In order to calculate the ACI the activity concentrations of 226-Ra; 232-Th and 40-K must be determined. The 226-Ra part of the ACI calculation allows for different approaches. Since the improved LaBr(Ce) resolution with respect to NaI(Tl); it is possible to assess the activity concentration of 226-Ra at 186 keV. The obtained 226-Ra activity concentration can be accepted without correcting for natural occurring uranium to provide a “safe overestimation” of the ACI. Otherwise, it can be corrected for the uranium concentration. A third option is to calculate the 226-Ra activity concentration via its daughters 214-Pb and 214-Bi. Because most building materials are relatively high density, the radon exhalation coefficient is of limited importance and may be neglected for high density building materials – not for porous materials. The first results of our measurement method will be presented and compared to standard laboratory analysis with respect to secular equilibrium (radon exhalation) and using HPGe spectrometry. First results indicate an appreciable estimation of the ACI via the portable equipment.