It thus enables a comparison to be made between values of aircraft of different types and ages using a common denominator. As of this writing, the largest atom ever detected has atomic number 118, mass number 293, and a half-life of 120 ns.Sometimes also known as half-time – is a standard industry appraisal term to indicate that no value adjustment has been made for the actual maintenance status of the aircraft. The longest-lived isotope of lawrencium, 262Lr, has a half-life of 3.6 h, while the shortest-lived isotope of lawrencium, 252Lr, has a half-life of 0.36 s. On the other hand, some nuclei have extremely short half-lives, presenting challenges to the scientists who study them. Uranium-238, the most common isotope of uranium, has a half-life of about 4.5 × 10 9 y, while thorium-232 has a half-life of 14 × 10 9 y. A half-life of 432 y may seem long to us, but it is not very long as half-lives go. In that time, americium-241, which has a half-life of about 432 y, loses less than 4% of its radioactivity. The expected working life of an ionization-type smoke detector (described in the opening essay) is about 10 years. Occasionally, however, the daughter element is also radioactive, so its radioactivity must also be considered. In fact, it is the time required for half-not all-of the element to decay radioactively. Many people think that the half-life of a radioactive element represents the amount of time an element is radioactive. Looking Closer: Half-Lives of Radioactive Elements This sequence of events is illustrated in Figure 11.1 "Radioactive Decay". After another 12.3 y-now a total of 36.9 y-another half of the remaining 3H will have decayed, leaving 12.5 g of 3H. After another 12.3 y-making a total of 24.6 y-another half of the remaining 3H will have decayed, leaving 25.0 g of 3H. After 12.3 y, half of the sample will have decayed to 3He by emitting a beta particle, so that only 50.0 g of the original 3H remains. Suppose we have 100.0 g of 3H (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. of a radioactive isotope is the amount of time it takes for one-half of the radioactive isotope to decay. The half-life The amount of time it takes for one-half of a radioactive isotope to decay. An interesting and useful aspect of radioactive decay is half-life. 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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