In-Situ Measurements And Analysis Of Naturally Occurring Radioactive Materials

The measurement and quantification of naturally occurring radioactive materials (NORM) is an important element of workplace radioprotection in key industries such as oil and gas production, heavy metals mining and refining, coal burning waste, and water treatment. Monitoring of NORM content in home building materials is another challenge for human safety in the prevention of chronic dose uptake. Materials are classified NORM in case they contain significant amounts of the decay chains of U-238 (Ra-226 as a long lived daughter), U-235 or Th-232 or the primordial nuclide K-40. Due to the decay of the radionuclides, gamma rays with a signature in the energy range from 45 keV up to 2615 keV are emitted. The most accurate method to measure NORM in a sample is to use a high resolution spectrometric instrument such as a germanium detector in a well-shielded laboratory environment. The shield is used to prevent background with the same signature from the building material of the laboratory. There are occasions in which one is required to assay samples in the field. These in situ field applications may require performing measurements with reduced (or no) background shielding conditions, or involve the use of medium resolution spectrometric instruments such as LaBr3 or NaI detectors. In-situ analyses such as these have increased complexity. The reduced shielding enforces the subtraction of NORM events produced from the environment but the sample material and container can also shield the detector against this background thus biasing the measured results if not appropriately accounted. The use of medium resolution detectors has additional complications that the multiplicity of gamma-rays from NORM materials is such that most of the gamma-rays are interfering and thus require a very careful quantitative analysis. In this presentation, we will discuss the details of the NORM source term both in the environment and what could potentially be in the sample. We will also discuss the potential consequences if the NORM daughter products are not in secular equilibrium, and present procedures and guidelines for measuring and analyzing NORM samples in situ with both high and medium resolution spectrometry devices.