32: Radiochemical Methods
- Page ID
- 333385
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Radiochemical methods of analysis take advantage of the instability of some elemental isotopes, which decay through the release of alpha particles, beta particles, gamma rays, and/or X-rays, often provide for a selective analysis for one analyte in a complex mixture of other species without the need for a prior separation. In this chapter we review the basics of radioactive decay and its direct application to samples, and two additional methods of importance: neutron activation and isotope dilution.
- 32.1: Radioactive Isotopes
- Atoms that have the same number of protons but a different number of neutrons are isotopes. Although an element’s different isotopes have the same chemical properties, their nuclear properties are not identical. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, disintegrate spontaneously, emitting radioactive decay particles as they transform into a more stable form.
- 32.2: Instrumentation
- Alpha particles, beta particles, gamma rays, and X-rays are measured by using the particle’s energy to produce an amplified pulse of electrical current in a detector. These pulses are counted to give the rate of disintegration. There are three common types of detectors: gas-filled detectors, scintillation counters, and semiconductor detectors.
- 32.3: Neutron Activation Methods
- Few analytes are naturally radioactive. For many analytes, however, we can induce radioactivity by irradiating the sample with neutrons in a process called neutron activation analysis (NAA). The radioactive element formed by neutron activation decays to a stable isotope by emitting a gamma ray, and, possibly, other nuclear particles.
- 32.4: Isotope Dilution Methods
- In isotope dilution, an external source of analyte is prepared in a radioactive form with a known activity. We add a known mass of the tracer to a portion of sample that contains an unknown mass of analyte. Analyzing for the total amount of analyte and amount of activity allows us to determine the amount of analyte in the original sample.
Thumbnail: Visual representation of alpha decay. (Public Domain; Inductiveload via Wikipedia)