Environmental Monitoring
One aspect of environmental monitoring which has been highlighted in recent years concerns the
detection, identification and determination of radioactive substances. A high proportion of
radionuclides emit gamma radiation, thus high-resolution gamma-ray spectrometry is a valuable tool for
their detection and measurement. Typically, a semiconductor detector with a multichannel pulse height
analyser will be used. Identification will be by peak energy and quantitative analysis by peak area.
Figure 10.18 shows the spectrum of an environmental sample which contains both naturally occurring
and artificial radionuclides. Alpha and beta emitters such as Sr-90, and some of the transuranic
elements, also frequently need to be determined. An initial survey for the presence of alpha and beta
emitters is conveniently and efficiently carried out using photographic imaging by films selectively
responding to the different types of radiation. A technique known as differential autoradiographic
imaging (DAI) employs these films in combination with phosphor screens in a so-called 'sandwich
assembly'. Figure 10.19 illustrates the use of this technique in the examination of a soil sample
contaminated in the Chernobyl accident. A peculiar advantage of this approach is that it not only
demonstrates the presence of the radionuclides but also their distribution as 'hot particles'. Where
accurate measurements are also needed, separation and concentration of the radioactive material is a
prior requisite. This is accomplished by the use of techniques such as precipitation, solvent extraction,
ion-exchange and, where alpha counting is used for transuranic elements, electrodeposition.
Figure 10.18
γ-Ray spectrum of a sediment sample from Lake Baikal in Eastern Siberia, showing
peaks for Ra-226, Tl-108 and Ac-228 from the uranium decay series, fission
products, Cs-137 and Co-60, and naturally occurring K-40.
(Courtesy of L. Chevallereau, Kingston University)