Beckman's Biogamma Radioimmuno Analyzer was introduced in 1973. Radioimmunoassay (RIA) is a technique for measuring the antigen concentration. Known quantities of radioactive (labeled or “hot”) antigens and antibodies are mixed, then non-radioactive (unlabeled or “cold”) antigens are added at varying concentrations; the labeled and unlabeled antigens compete to bind to the antibodies. The bound and unbound antigens are separated, and the radioactivity of the unbound samples determines the concentration.