Radiochemical Methods of Analysis

Radiochemical Methods of Analysis

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol A/zE, where E is the ele- ment’s atomic symbol, Z is the element’s atomic number (which is the number of protons), and A is the element’s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most impor- tant difference between isotopes is their stability. The nuclear configuration of a sta- ble isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form.

The most important types of radioactive particles are alpha particles, beta parti- cles, gamma rays, and X-rays. An alpha particle, which is symbolized as α, is equiv- alent to a helium nucleus, ⁴₂He. Thus, emission of an alpha particle results in a new isotope whose atomic number and atomic mass number are, respectively, 2 and 4 less than that for the unstable parent isotope

Beta particles, β, come in two forms. A negatron, ⁰_-1β is equivalent to an electron, and is produced when a neutron is converted to a proton, increasing the atomic number by 1.

Converting a proton to a neutron results in the emission of a positron, .

Emission of an alpha or beta particle often produces an isotope in an unstable, high-energy state. This excess energy is released as a gamma ray, γ, or an X-ray. Gamma ray and X-ray emission may also occur without the release of alpha or beta particles.

Although similar to chemical kinetic methods of analysis, radiochemical meth- ods are best classified as nuclear kinetic methods. In this section we review the ki- netics of radioactive decay and examine several quantitative and characterization applications.