ASSAY OF RADIOACTIVITY 



using coincidence circuitry, even the 0-018 MeV /3-particles given by tritium 

 iiave been recorded successfully with liquid scintillators. 



CHOICE OF EQUIPMENT FOR TRACER EXPERIMENTS 



It should by now be clear that the equipment needed for a tracer experiment 

 is determined partly by the nature of the experiment and partly by the 

 characteristics of the isotope concerned. When working with an isotope 

 giving strong ^-radiation a wide choice of measuring techniques is avail- 

 able. Geiger or proportional counter tubes will probably be the most 

 convenient detecting devices, and samples can be counted in either solid 

 or liquid form with roughly the same sensitivity. It is also possible to 

 devise methods for measuring the amount of radioactivity in living tissues, 

 both isolated and in vivo. For isotopes giving weaker /5-radiation, the 

 sensitivity of liquid counters and of measurements in vivo is apt to become 

 excessively small, but if a y-ray is also emitted, as for example in the case 

 of ^^^I, scintillation counting of the y-radiation is likely to be the most 

 efficient technique to use. The choice of counting methods only becomes 

 really seriously circumscribed for those isotopes (e.g. ^H, ^^C, ^^S) which 

 emit weak /9-radiation without any accompanying y-radiation, and in 

 experiments where maximum sensitivity is essential. Johnston^^ has given 

 a useful account of the relative merits of the various gas chamber and 

 liquid scintillator techniques for very low-level /9-counting. 



REFERENCES 



^ Kamen, M. D. Isotopic tracers in biology, 3rd ed. New York; Academic Press. 



1957 

 ^ Sacks, J. Isotopic tracers in biochemistry and physiology, 1st ed. New York; 



McGraw-Hill. 1953 

 ^ Sacks, J. Tracer techniques : stable and radioactive isotopes. In Physical 



techniques in biological research. Vol. 2, ed. by G. Oster and A. W. Pollister. 



New York; Academic Press. 1956 

 ^ SiRi, W. E. Isotopic tracers and nuclear radiations, 1st ed. New York; McGraw- 

 Hill. 1949 

 ^ WfflTEHOUSE, W. J. and Putnam, J. L. Radioactive isotopes Oxford University 



Press. 1953 

 ^ Taylor, D. The measurement of radio isotopes London; Methuen. 1951 

 ^ Sharpe, J. Nuclear radiation detectors London; Methuen. 1955 

 ^ DoNiACH, I., Howard, Alma and Pelc, S. R. Progress in Biophysics Vol. 3. 



London; Pergamon Press. 1953 

 ^ Boyd, G. A. Autoradiography in biology and medicine New York; Academic 



Press. 1955 

 ^" Rossi, B. B. and Staub, H. H. Ionization chambers and counters, 1st ed. New 



York; McGraw-Hill. 1949 

 ^^ Wilkinson, D. H. Ionization chambers and counters Cambridge University 



Press. 1950 

 12 Cook, R. H. and Keynes, R. D. /. sci. Instrum. 30 (1953) 141 

 " Keynes, R. D. /. Physiol. 114 (1951) 119 

 1^ Veall, N. Brit. J. Radiol. 21 (1948) 347 

 15 Johnston, W. H. Science \1A (1956) 801 

 i« Farley, F. J. M. J. sci. Instrum. 31 (1954) 241 



Arnold, J. R. Science 119 (1954) 155 



442 



