Radioactivity Analysis

Detection, identification, and quantification of the specific radionuclide responsible for the presence of ionizing radiation is very often required. Identification of the radionu-clide facilitates the design of systems to safely and economically handle radioactive materials. Many different types of instruments, ranging in price from several thousand to several hundred thousand dollars, are available. Field measuring devices are often used to detect and approximate the amount of radiation present. Identification and quantification is usually performed in a controlled laboratory area, equipped to minimize background interference and gross contamination, and to ensure personnel safety.

Radiological analysis must be done using good laboratory practices and sound scientific judgement (Knoll 1989). Many measurements are done at extremely low levels (NCRP 1976), and poor laboratory technique often leads to erroneous conclusions (NCRP 1978). The laboratory area dedicated to radiological analysis is often called the counting room. The gross alpha-beta measurement is the most frequently run analysis. This relatively inexpensive analysis screens samples to determine if more elaborate analysis for specific radionuclides is required. Specific ra-dionuclide analyses are usually done if dose estimates are desired, if long-term trends are being established, or if regulatory requirements are mandated. Analyses of specific radionuclides are usually more expensive and require greater expertise to interpret the results. These analyses are based on accurately measuring the half-life or the energy of the radiation emitted. Chemicals are often separated prior to instrumental analysis to eliminate potential interferences or to concentrate the radionuclide of interest. Gamma-emitting materials can be identified and quantified quickly with little or no sample preparation by using gamma ray spectroscopy.

A sample representing the area or situation under analysis must be obtained. Survey instruments can be effective in obtaining a proper sample. Liquid and solid samples are very amenable to analysis by gamma ray spectroscopy. Air samples can be collected using continuous samplers. Airgrab samples can be taken directly into evacuated scintillation cells if alpha emitters are being monitored.

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