The Unstable Atom
Radiation comes from atoms, the basic building blocks of matter. Most atoms are stable; a carbon-12 atom, for example, remains a carbon-12 atom forever, and an oxygen-16 atom remains an oxygen-16 atom forever, but certain atoms eventually disintegrate into a totally new atom. These atoms are said to be 'unstable' or 'radioactive'. An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change towards a more stable form. This is called 'radioactive decay'. When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles. One can describe the emissions as gamma, beta and alpha radiation. Apart from the normal measures of mass and volume, the amount of radioactive material is given in curie (Ci), a measure which enables us to compare the typical radioactivity of some natural and other materials.
| Radioactivity of Some Natural and Other Materials | |
|---|---|
| 1 adult human (2.7 X 10-9 Ci/kg) | 1.89 X 10-7 Ci |
| 2.2 lbs. of coffee | 2.70 X 10-8 Ci |
| 2.2 lbs. of super phosphate fertilizer | 1.35 X 10-7 Ci |
| The air in a 1076 sq. foot Australian home (radon) | 8.12 X 10-8 Ci |
| The air in many 1076 sq. foot European homes (radon) | 8.12 X 10-7 Ci |
| 1 household smoke detector (with americium) | 8.12 X 10-7 Ci |
| Radioisotope for medical diagnosis | 1.89 X 103 Ci |
| Radioisotope source for medical therapy | 2702.7 Ci |
| 2.2 lbs. of 50-year old vitrified high-level nuclear waste | 270.27 Ci |
| 1 luminous Exit sign (1970s) | 27.027 Ci |
| 2.2 lbs. of uranium | 675.68 X 106 Ci |
| 2.2 lbs. of uranium ore (Canadian, 15%) | 675.68 X 106 Ci |
| 2.2 lbs. of uranium ore (Australian, 0.3%) | 13.51 X 106 Ci |
| 2.2 lbs. of low-level radioactive waste | 27.03 X 106 Ci |
| 2.2 lbs. of coal ash | 5.41 X 10-8 Ci |
| 2.2 lbs. of granite | 2.70 X 10-8 Ci |
Though the intrinsic radioactivity is the same, the radiation dose received by someone handling a kilogram of high grade uranium ore will be much greater than for the same exposure to a kilogram of separated uranium, since the ore contains a number of short-lived decay products.