From Handbook of Nuclear Chemistry: Basics of Nuclear Science, Volume 1
S.Nagy
Department of Nuclear Chemistry, E tv s Lor nd University, Budapest, Hungary
SUMMARY
After giving a phenomenological and then a statistical interpretation of the exponential law, we discuss the various combinations of individual decay processes as well as the cases of equilibrium and non-equilibrium. Half-life systematics of the different decay modes detailed in Chapters 2 and 4 of this Volume are also summarized.
At present there are over 3000 known nuclides (see the Appendix in Volume 2 on the Table of the Nuclides ), 265 of which are stable, while the rest, i.e. more than 90% of them, are radioactive. The chemical applications of the specific isotopes of chemical elements are mostly connected with the latter group, as well as with quite a number of metastable nuclear isomers, making the kinetics of radioactive decay an important chapter of nuclear chemistry.
1. THE EXPONENTIAL LAW OF DECAY
1.1 Phenomenological approach
The most fundamental quantity of radioactive decay is the activity A meaning the number of atoms decaying in the specimen per time.
Historical units of activity. The formerly used unit of radioactivity the curie (Ci) was introduced in 1930. One curie was originally defined as the disintegration rate of 1 gram of pure 226Ra. Radium was chosen as a reference because of its then importance among radioactive elements. However it was rather disturbing that the value of the unit had to be changed from time to time as more accurate data were obtained for the decay of radium. Finally the...
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