MORE ABOUT NUCLEAR RADIATIONRadionuclides and radioisotopes
The term radionuclidemeans an atom which undergoes radioactive decay; such an
atom is said to be (radioactively) unstable. Isotopes which are radioactive are called
radioisotopes.
There are 365 different nuclides in nature. Of these, 55 are radionuclides. In addi-
tion, there are hundreds of radionuclides which have been artificially manufactured,
mainly by smashing nuclei together at very high speed in giant devices called particle
accelerators. For example, in 1937, technetium (Tc) was made by firing deuterium
atoms at molybdenum (Mo) atoms:
42(^96) Mo
1
(^2) H
43
(^97) Tc +
0
(^1) n
Elements with atomic numbers greater than that of uranium (92) are known as
transuranium elements. They do not occur naturally and have all been made in
particle accelerators or in nuclear reactors.
Table 21.2 shows the half-lives and the mode of decay of selected radionuclides.
21.2
401
Fig. 21.2Penetrating powers of nuclear radiation.
Table 21.2Data on selected radionuclides
Nuclide Main type of Half-life
radiation emitted
137
55 Cs , 30.17 years
(^146) C 5730 years
131
53 I , 8.04 days
(^22688) Ra , 1600 years
60
27 Co , 5.27 years
(^24195) Am , 432 years
90
38 Sr 28 years
(^3215) P 14.3 days
40
19 K , 1.25^10
(^9) years
(^23892) U 4.46 109 years
235
92 U^ 7.04^10
(^8) years
(^31) H (tritium, T) 12.26 years
222
86 Rn^ , 3.82 days
(^3516) S 87.2 days
239
94 Pu^ , 2.41^10
(^4) years
Alpha particles
Beta particles
Gamma rays
and neutrons
Aluminium Lead or thick
concrete