RADIATION TESTING
registration of activity has been reduced, with values for naturally occurring radionuclides outlined in
them.
MEASUREMENT OF NORM To determine the levels of radiation present in a material, samples must be analysed by a specialised radiochemical laboratory. The measurements can then be used to estimate the risk to human health and the environment, or for determining the correct waste repository. Before the radioactivity can be quantitatively
measured, the sample must be prepared for analysis. There are many ways to do this, depending on the aim of the investigation. For concrete cores or slabs where the penetration depth of the radioactive contamination needs to be known, a diamond precision saw can be used to accurately cut samples to within 0.1mm. These slices are then analysed to obtain a penetration profile of the radioactive contamination. On the other hand, if an average radioactivity
concentration is required, a ball mill can be used to reduce and homogenise soil and other solid samples. Representative sub-samples, which reduce the possibility of radioactive hot spots, can then be produced using sample splitting equipment. Softer materials, like roofing felts or clothing, use flail mills to break down the sample. Once the samples have been prepared for analysis,
a range of techniques can be applied to identify and quantify the nature of the radioactivity. These techniques can be broadly divided into three classes: gamma spectrometry, beta counting and alpha spectrometry. Gamma spectrometry is widely used to determine a
range of radionuclides from the NORM decay series. While the analysis itself is non-destructive, precise measurements require the sample material to be ground. Gamma is very often used as an initial scan to determine the requirement for the other analyses. Alpha spectrometry is widely used to determine
specific alpha emitting radionuclides, like uranium or thorium. Radiochemical separation is required to isolate the actinides and to be able to measure the alpha particles, which are otherwise absorbed in the sample itself. A total actinide isolation can be carried out as well, giving semi-quantitative information of alpha emitters potentially present in the materials. Beta counting techniques can be used to produce a
total figure for all alpha and beta particle emitting radionuclides (“gross alpha activity” and “gross beta activity”, respectively). However, they can also be used to determine specific, beta emitting radionuclides, like Pb-210 and Bi-210. The latter requires a radiochemical separation. Examples of such techniques are gas-proportional counting and liquid scintillation counting. NORM analysis has the potential to detect low
levels of radiation, down to 0.1Bq/kg. In determining the level of radiation within the materials, it is possible to compare the limits against the regulations in place to verify compliance and ensure the correct procedures are in place.
16 /// Environmental Engineering /// September 2018
❱❱ Sample grinding is necessary to gain precise measurements. A number of techniques are available depending on the nature of the material under examination
WHEN TO TEST FOR NORM NORM analysis to determine levels of radiation is very important for the process industries in several sectors. Ore smelting, fertiliser production and scrap metal processing are common industrial activities that require NORM analysis support to determine compliance with the relevant regulations. In oil and gas, maintenance of the oil and gas production plants, pipelines and storage facilities will become an increasing focus for NORM analysis in decommissioning and dismantling of rigs and distribution networks. Metal ores often contain uranium, radium and
thorium. In mining, when extracting and processing these metal ores, concentrations of the radionuclides become elevated. For example, when smelting separates the metal from the ore, the waste that is produced in the form of ore tailings or smelting slag often contains elevated levels of uranium. It is therefore important that NORM analysis takes place, to ensure levels are below a set limit. Equally, in large quantities, the storage of these metal ores can require NORM analysis to ensure safe handling and minimal exposure to the radiation sources. Scrap metals have the potential to be
‘ NORM
analysis can support and contain risk through understanding radioactivity levels and implementing appropriate measures
’
contaminated with radioactive materials. If metals are being passed into the scrap metal chain from one of the processes listed above, for example, or from countries where the regulations and controls are less stringent, cross-contamination can occur and lead to undetected radioactive exposure; NORM analysis prevents this. With phosphate, commonly used as a constituent
in fertiliser, production of fertiliser results in elevated levels of radioactivity in the material itself and the product, as well as the process waste. Transport or storage of phosphate ores can also lead to radionuclide contamination; NORM analysis can support and contain the risk through understanding radioactivity levels and implementing appropriate measures to control the risk of radioactive exposure. Through analysing NORM and detecting the
radioactive levels within the material, appropriate and sufficient protection can be put in place to ensure safe handling and regulatory compliance. EE
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