What if the elapsed time is not an exact number of half-lives? We can still calculate the amount of material we have left, but the equation is more complicated. Most experts agree that while it is foolhardy to expect absolutely no exposure to radioactivity, we can and should minimize exposure to excess radioactivity. However, carbon is the element that makes up the backbone of most living molecules, making carbon-14 more likely to be present around important molecules, such as proteins and DNA molecules. Potassium-40 also decays with about 10 times more energy than carbon-14, making each decay potentially more problematic. There is more potassium-40 in the body than carbon-14, and it has a much longer half-life. There is debate about which radioactive element is more problematic. Potassium and carbon are two elements that we absolutely cannot live without, so unless we can remove all the radioactive isotopes of these elements, there is no way to escape at least some radioactivity. Most of the radioactivity in the human body comes from potassium-40 and carbon-14.
The average human body experiences about 8,000 radioactive decays/s. This sequence of events is illustrated in Figure 15.1 “Radioactive Decay”. After another 12.3 y-now a total of 36.9 y-another half of the remaining tritium will have decayed, leaving 12.5 g. After another 12.3 y-making a total of 24.6 y-another half of the remaining tritium will have decayed, leaving 25.0 g of tritium.
After 12.3 y, half of the sample will have decayed from hydrogen-3 to helium-3 by emitting a beta particle, so that only 50.0 g of the original tritium remains. Suppose we have 100.0 g of tritium (a radioactive isotope of hydrogen). The half-life of a specific radioactive isotope is constant it is unaffected by conditions and is independent of the initial amount of that isotope.Ĭonsider the following example.
An interesting and useful aspect of radioactive decay is half-life, which is the amount of time it takes for one-half of a radioactive isotope to decay. As time passes, less and less of the radioactive isotope will be present, and the level of radioactivity decreases. Some isotopes are stable indefinitely, while others are radioactive and decay through a characteristic form of emission.
Whether or not a given isotope is radioactive is a characteristic of that particular isotope.
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