8 Applied Radiation Measurements

The radiation detection systems employed in radioanalytical chemistry laboratories have changed considerably over the past sixty years, with significant improvement realized since the early 1980s. Advancements in the areas of material science, electronics, and computer technology have contributed to the development of more sensitive, reliable, and user-friendly laboratory instruments. The four primary radiation measurement systems considered to be necessary for the modern radionuclide measurement laboratory are gas-flow proportional counters, liquid scintillation (LS) counters, Si alpha-particle spectrometer systems, and Ge gamma-ray spectrometer systems. These four systems are the tools used to identify and measure most forms of nuclear radiation. Some operating parameters can be considered in common for all these detectors, notably detection efficiency and the radiation background. Additional parameters pertain only to detectors with associated spectrometers. These parameters concern the radiation energy peaks that identify and quantify radionuclides, and include energy calibration, energy resolution, peak-to-Compton ratio, and peak shape. Each of the detection instruments has a specialized field of application. The gasflow proportional counter is the laboratory workhorse for measuring radionuclides that emit alpha and beta particles in samples before radionuclide separation and then again in the purified fractions. The LS counter also measures radionuclides that emit alpha and beta particles and is particularly useful for measuring low-energy beta particles. The alpha-particle spectrometer is applied for purified samples to measure radioisotopes, notably of the heavy elements, that emit alpha particles. The gamma-ray spectrometer is the laborsaving device for measuring photon-emitting radionuclides, in most cases without chemical separation. Many ingenious applications of these detectors go beyond such specialization so that their use can be a matter of matching sample characteristics, radiation types, the radionuclide of interest and associated impurities, required sensitivity, and convenience in sample preparation, or even analyst preference. Various other detection systems and instrumental techniques that are mentioned at the end of