Activation analysis with solid state detectors

Most of the radioisotopes used as isotopic labels in activation analysis decay with beta (positron and negatron) radiations and/or gamma rays. By convention, beta-emitting radionuclides are usually measured by gas-filled or gas-flow proportional counters or Geiger counters. Sometimes, liquid scintillation counters are used to complete a beta-ray measurement. The more conventional method for gamma-ray measurements involves the use of a gamma-ray spectrometer equipped with either a scintillation or solid-state detector. Stevenson (918) discusses the characteristics of radioactive decay and gives details on the methods and instruments used to detect emitted radiations. 

There are several potential sources of radioactive materials that can contaminate water (see Chapter 4, Section 4.14). Radioactive contamination of water is normally detected by measurements of gross P activity and gross a activity, a procedure that is simpler than detecting individual isotopes. The measurement is made from a sample formed by evaporating water to a very thin layer on a small pan, which is then inserted inside an internal proportional counter. This setup is necessary because P particles can penetrate only very thin detector windows, and a particles have essentially no penetrating power. More detailed information can be obtained for radionuclides that anit y-rays by the use of gamma spectrum analysis. This technique employs solid-state detectors to resolve rather closely spaced y peaks characteristic of specific isotopes in the sample s spectra. In conjunction with multichannel spectrometric data analysis, it is possible to determine a number of radionuclides in the same sample without chemical separation. This method requires minimal sample preparation. 

---