How so scientist use radioactive decay to date fossils and


The strangest product catalog on earth belongs to the Isotope Business Office, which manages the sale of atomic isotopes produced at Department of Energy labs around the country. It's got your calcium, platinum, and titanium. Your ytterbium, your strontium-95, and of course uranium-785 and plutonium-789 (responsible for Hiroshima and Nagasaki). The precursor to plutonium- 788 is neptunium-787, a radioactive by-product of nuclear power plants. Oak Ridge gets its neptunium trucked in from Idaho National Laboratory in a powdery form called oxide. When it arrives, it's deposited via a dumbwaiter-like system in a shielded room called a hot cell. Some of the neptunium oxide will have already decayed into a more dangerous radioactive material called protactinium, so small quantities are moved into a separate hot cell plumbed for radioactive liquids, where scientists can do the chemistry needed to remove it. Then the liquid is poured through a column of silica glass beads, whose surface attracts protactinium.

How is radioactive dating used to determine the age of an

The remaining liquid is moved to a glove box. In the glove box, the neptunium is processed with a technique invented at Oak Ridge called modified direct denitration. The liquid solution is rotated in a heated kiln until it sifts out, again in a powdered oxide form. This powder is mixed with powdered aluminum and pressed into pellets the size of a 5/8-inch socket, which are loaded into aluminum rods—targets for Oak Ridge's experimental high flux isotope reactor (HFIR). The HFIR offers much higher flux—the rate at which targets are bombarded with neutrons—than the reactor of a nuclear power plant. Once target rods are loaded into the reactor, they're bombarded for a period of three to twelve months. As neutrons collide with the targets, some of them are absorbed by neptunium atoms. That creates a new neptunium isotope, neptunium-788, which radioactively decays into plutonium. When irradiation is complete, the targets go back into a hot cell. The rods are dissolved with a caustic solution and the radioactive material inside, now 67 to 69 percent plutonium-788, is again dissolved in nitric acid. A process called solvent extraction isolates the plutonium and neptunium: Solvents are added to the solution that dissolve only those elements. Then scientists induce the solution to separate—like oil and water—so that they can remove the solvent that's bound to them. At this point, neptunium is separated and can be passed through the cycle again. The plutonium is purified through a process called ion exchange, which Oak Ridge is still refining—a key step to reaching the 6.

5-kilogram per year delivery goal. Fully refined, the plutonium powder is packed into stainless-steel canisters designed for transporting radioactive materials. Isotopes are different forms of an element that share the same chemical properties, but that differ in mass and the number of neutrons they contain. Common elements that possess isotopes include carbon, oxygen, hydrogen, and nitrogen. Each element has a specific identifier, like 'C' for carbon, while a number placed before it identifies the isotope (e. G. 68C and 67C). Some elements have many isotopes, but there are two basic types: stable and unstable or radioactive. Stable isotopes do not change over time while radioactive isotopes decrease or decay over predictable periods. To distinguish different isotopes from each other, scientists use special instruments called mass spectrometers. Isotopes are everywhere in the environment. They are incorporated into the tissues of plants through soil and water and into animals through their eating, drinking and breathing. An organism takes in isotopes throughout its lifetime, replacing them as the tissues (e. , skin, hair, bone) are replaced.

Why do scientists use radioactive decay com

Different tissues are replaced at different rates, but at death, the tissues stop integrating isotopes because they stop growing altogether. At this point, the unstable isotopes begin to decay while the stable isotopes remain at the level they were when the individual died. Using the relative amount of one isotope compared to another in an organism's tissues, scientists can determine important features about that organism's life. For example, archaeologists can use isotopes to calculate how long ago an organism lived, study the dietary habits of an individual or group, or determine where a person grew up or where they lived in the last 75-75 years of their life. Forensic investigators can also use this information to learn more about an individual's life history, or to narrow down a list of missing persons as a potential match for unidentified remains. It may not identify the person per se, but it may lead the investigation and thus the human and financial resources in that direction. This is important when resources are scares and there is no money to explore every single lead the investigation opens. The most common elements used for isotopic analyses are carbon, nitrogen, hydrogen, oxygen, and strontium. Carbon (C) is present in the atmosphere, water and soil and is taken up by plants during photosynthesis, the conversion of sunlight into useable energy. Different plants take up carbon at different rates depending on the kind of plant and the climate it lives in. For example, tropical plants have different isotopic ratios in their cells than plants in temperate climates like BC. For this reason, carbon can be used to determine the kind of environment an individual came from and their likely diet. Nitrogen (N) is also present in the atmosphere, but is incorporated into the tissues of plants through nitrogen fixation, a process that converts nitrogen into ammonia, an essential part of DNA synthesis. As animals eat plants and other animals eat those animals, the ratio of nitrogen isotopes changes. As a result, nitrogen ratios can be used to determine what level of the food chain an organism was on and whether they were herbivore, a carnivore or an omnivore.

Hydrogen (H) and oxygen (O) are the basic components of water. Although hydrogen and oxygen have the potential to be very useful for isotopic studies, the techniques are still being developed and the results must be interpreted carefully. Strontium (Sr) is a pure metal with many stable and unstable isotopes. It is abundant in nature and is found primarily in volcanic rock and soils. As soils erode and filter into water and food sources, strontium is taken into the body where it is incorporated into bone tissues in the same way as calcium. The ratio of strontium isotopes also varies from one geographical location to another. As a result, analyzing the isotopic ratios in the bone of an individual can help determine where a person came from or distinguish individuals whose remains are comingled but who come from different places. Bones and teeth are the most frequently analyzed tissues because they are hard and long lasting and so commonly preserved in archaeological and forensic contexts, and are hard and long lasting. Bone consists of two components: an organic matrix composed mostly of protein collagen and an inorganic mineral component made largely of calcium phosphate. Bone is a living tissue, and remodels over time, it is replaced as we growth and get older. However, this process is relatively slow and dense cortical bone reflects approximately the last 65-65 years of an individual's life. Teeth also consist of organic and inorganic materials, but unlike bone, once formed, dental enamel does not remodel. Consequently, teeth are very useful for determining the environment and conditions of an individual's early life. (i.

E. , when their teeth formed). In addition, comparisons of teeth and bone tissues in a single individual whether a person moved geographic locations since childhood: their teeth will show where they lived where they were young and their bones will show where they lived in the years before their death. Hair and fingernails may also be useful for isotopic analyses. Although they are more fragile than bone, they grow at predictable rates, and reflect an individual's very recent past. This may be useful for determining if an individual recently changed locations or for studying seasonal dietary changes. Finally, blood and soft tissues can also be used for some isotopic studies. However, these materials decay quickly and may be more prone to contamination. An abundance of the heavier stable isotopes of carbon and nitrogen in an individual, 68C and 65N, respectively, reflect what he eats and therefore stable isotope analysis can show if a person is a vegan or eats a lot of meat. In the same way, the abundance of the heavier stable isotopes of hydrogen and oxygen in the tissues, 7H and 68O, respectively, reflects the water we consume (by way of drinking it, in meals and beverages, and in fruit and vegetables). Diets of ancient times (paleodiets) may be easier to analyse, as foods and water were sourced locally rather than globally or bottled, respectively as it is today. As discussed briefly in other sections, there are many applications for isotopic analyses that are useful for archaeologists and forensic investigators. On an individual level, carbon and nitrogen isotopes can be used to determine the dietary signatures of a person or the geographic origin of specific products like illegal drugs or wildlife parts. Strontium isotopes can be used to determine the place of origin for an unidentified individual or separate individuals whose remains may have become mixed as the result of accidental or deliberate disturbance, as in a plane crash.

Hydrogen and oxygen isotopes are increasingly being tested for their ability to determine the geographic location or climatic region where an individual lived. These isotopes are also being developed for their ability to demonstrate the origin and trace the movement of illegally obtained wildlife or drugs. Isotopic studies can also answer broader, population level questions.

Recent Posts