## RADIOCHEMISTRY 1 The Nucleus and Radioactivity 1.1 The nucleus Atomic nuclei consist of positively charged protons an~ uncharged neutrons, particles which are collectively known as nucleons. Nucleons interact with one another through a short range attractive force, and it is this force which holds the nucleus together. Protons also interact with one another through a long range (inverse square law) repulsive force. Nuclear stability depends to a first approximation on the combination of the short range attractive forces and the longer range repulsive forces within the nucleus. As neutrons contribute mainly attractive forces to this sum, there is a sense in which the neutrons can be regard• ed as keeping the nucleus together. As the number of protons in the nucleus (the atomic number, Z) increases, so more neutrons are required to prevent the nucleus breaking apart under the strain of proton-proton repulsions. Atoms are now known with atomic numbers up to about 108. For all of these elements a range of isotopes has been made or discovered, that is nuclei with a given number of protons but differing numbers of neutrons. The majority of these isotopes of the elements-or nuclides-are observed to be unstable with respect to other nuclides, and spontaneous transformations of these isotopes to more stable nuclides are seen. These spontaneous transformations are called radioactive decay, and a nuclide which undergoes radioactive decay is referred to as a radionuclide or a radioisotope. Nuclides are most commonly referred to by the elemental symbol preceded by the mass number,A, for example, 12 C, 16 0, and 238 U. Figure 1.1 shows many of the known nuclides arranged to show the number of protons and the number of neutrons in the nucleus. Those nuclides which are stable and do not undergo radioactive decay are shown in black squares, the others-the radionuclides-are shown in white squares. Clearly the stable nuclides lie in a relatively narrow band which extends from hydrogen, 1 H, at the bottom left of the diagram, to bismuth, 209 Bi, well up in the right hand portion of Figure 1.1. The radionuclides are unstable, and this generally means that the total energy content of the nucleus is greater than that of the nearest stable nuclide. There 'Y LT. s.f. Front Matter....Pages i-viii The Nucleus and Radioactivity....Pages 1-11 Sources of Radioisotopes....Pages 12-19 Detection and Measurement of Radioactivity....Pages 20-35 Statistics of Counting....Pages 36-44 Liquid Scintillation Counting....Pages 45-60 γ Spectrometry....Pages 61-75 Radiochromatography....Pages 76-88 Some Radioanalytical Techniques....Pages 89-98 The Preparation of Labelled Compounds....Pages 99-111 Purity, Stability and Storage of Labelled Compounds....Pages 112-121 Health and Safety Aspects....Pages 122-134 Back Matter....Pages 135-145
