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Uses of Nuclear Radiation |
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The most common and accepted method of 'absolute geologic dating' (establishment of actual age) is based on the natural radioactivity of certain minerals found in rocks. As the rate of radioactive decay of any particular isotope is known, the age of a specimen can be worked out from the ratio of the remaining isotope and its decay product.
Geologists use this method to date igneous rock samples. If you look carefully at the half-lives of isotopes in the Uranium series you appreciate that the Uranium has a much longer half-life than any of the others. See the Uranium decay series(4N+2). So, by comparing the proportion of Uranium in the rock to the proportion of Lead produced by its decay you can work out how many half-lives it has been decaying. Then by using the
half-life of Uranium you can work out the time involved.
Carbon dating measures the remaining amount of the radioactive isotope carbon-14 in organic matter. It can be used to date specimens as old as 35,000 years. During its lifetime a biological entity (plant or animal) takes an active part in the carbon cycle and it contains the same proportion of the isotope as the atmosphere does (about one ten millionth of the carbon is carbon-14). The death of an organism terminates the incorporation of this isotope into the fabric of the entity. From the time of death onwards the proportion of carbon-14 decreases as it decays into nitrogen.
By calculating the ratio of C-14 to total carbon in a sample of the artefact it is possible to work out its age. The half-life of carbon-14 is 5,600 years. E.g.
  Tracers in Industry
Some smoke detectors contain a small amount of Americium-241, an alpha emitter (and low energy gamma emitter) with a half life of 460 years. It consists of an ionisation chamber linked to a simple electronic alarm circuit The Americium ionises the air between the plates, causing a current to flow. Smoke entering the detector blocks some of the alpha particles, lowering the current, and triggering the alarm.
All radium dial watches should be disposed of properly. Above is a demonstration of the radioactivity from a radium-containing 1950's Timex watch dial, using Geiger counter. They also use tritium, see emergency exit signs above.
Medical ApplicationsNuclear radiation is used in two ways in medicine: - as a tracer (also see PET scans) - Radioactive isotopes and radioactively labeled molecules are used as tracers to identify abnormal bodily processes. This is possible because some natural elements tend to concentrate in certain parts of the body: iodine in the thyroid, phosphorus in the bones, potassium in the muscles. When a patient is injected with a radioactive element, a special camera can take pictures of the internal workings of the organ. - as a medical treatment for cancer (radiotherapy)
LOJ
(February 2001)
- revised February 2003
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Tracers
in industry - detecting leaks in pipes 
Gamma rays kill bacteria. Therefore irradiating food or surgical instruments is a good way of ensuring they are sterile. The gamma rays penetrate packaging, so the food or instrument can be sealed and then sterilised so that re-contamination cannot occur. 
Automatic control over the thickness of paper in paper mills can be obtained by passing beta radiation through the paper and monitoring the count rate. An isotope with a long half-life is used so that the count-rate hardly changes with time. Electrical circuitry is then set up to ensure that a constant rate is maintained. If the rate is too low the rollers automatically move closer to each other (making the paper thinner) and vice versa. 
The Apollo Moon missions used a radioisotope thermal generator (RTG). The NASA designation for the devices that powered the Apollo Lunar Surface Experiments Package (ALSEP) for missions 12, 14, 15, 16, and 17 was SNAP-27 (Systems for Nuclear Auxiliary Power model number 27). The energy source for this device was a rod of plutonium-238 weighing approximately 2.5 kilograms and providing a thermal power of approximately 1250W. Plutonium-238 is a non-fissile isotope of plutonium that decays by alpha particle emission with essentially zero associated gamma emissions. 
Smoke Detectors 
Many camping lantern mantles used to contain thorium (alpha emitter with a long half-life see 
During a fire, it's necessary to make sure that emergency exit signs remain illuminated, even if the power goes out. Some signs have a battery-powered light. Others have used tritium, a beta-emitting isotope of hydrogen, with a half-life of 12.3 years. 
Vaseline Glass is a particular color of yellow-green glass that is made by adding 2% Uranium Dioxide to the ingredients when the glass formula is made. The addition of the Uranium Dioxide makes the glass color yellow-gr
Radium was painted on the hands of clocks, so they would glow in the dark. The radium was painted by women, who had the bad habit of licking the brush tips to form them, ingesting the radium. This resulted in illness. See the MIT research document: 
