work is shown in Table 14.5. The key factors in the decision are often based on safety,
the type of detection to be used, the sensitivity required (see section 14.4.2) and the
cost. For example^33 P may be chosen for work with DNA because it has high enough
energy to be detected easily, it is safer than^32 P and its half-life is short enough to give
high specific activity but long enough to be convenient to use.Table 14.5The relative merits of commonly used radioisotopes
Isotope Advantages Disadvantages
(^3) H Relative safety Low efficiency of detection
High specific activity possible Isotope exchange with environment
Wide choice of positions in organic
compounds
Isotope effect
Very high resolution in autoradiography
(^14) C Relative safety Low specific activity
Wide choice of labelling position
in organic compounds
Good resolution in autoradiography
(^35) S High specific activity Short half-life
Good resolution in autoradiography Relatively long biological half-life
(^33) P High specific activity Lower specific activity than (^32) P
Good resolution in autoradiography Less sensitive than^32 P
Less hazardous than^32 P Cost
(^32) P Ease of detection Short half-life affects costs and
experimental design
High specific activity
Short half-life simplifies disposal Highbenergy so external radiation
hazard
Cˇerenkov counting Poor resolution in autoradiography
(^125) I Ease of detection High penetration of radiation
High specific activity
Good for labelling proteins
(^131) I Ease of detection High penetration of radiation
High specific activity Short half-life
576 Radioisotope techniques