Stable and unstable nuclei - Radioactivity - Physics - FuseSchool

Scientists look at half-life decay rates of radioactive isotopes to estimate when a particular atom might decay. A useful application of half-lives is radioactive dating. This has to do with figuring out the age of ancient things. It might take a millisecond, or it might take a century. But if you have a large enough sample, a pattern begins to emerge. It takes a certain amount of time for half the atoms in a sample to decay. It then takes the same amount of time for half the remaining radioactive atoms to decay, and the same amount of time for half of those remaining radioactive atoms to decay, and so on.Comparing the disintegrations per minute per gram of carbon from an archaeological sample with those from a recently living sample enables scientists to estimate the age of the artifact, as illustrated in Example A plot of the specific activity of 14 C versus age for a number of archaeological samples shows an inverse linear relationship between 14 C content a log scale and age a linear scale.

Inthe remains of an apparently prehistoric man were found in a melting glacier in the Italian Alps. Analysis of the 14 C content of samples of wood from his tools gave a decay rate of 8.

How long ago did the man die? It is believed that humans first arrived in the Western Hemisphere during the last Ice Age, presumably by traveling over an exposed land bridge between Siberia and Alaska.

Archaeologists have estimated that this occurred about 11, yr ago, but some argue that recent discoveries in several sites in North and South America suggest a much earlier arrival.

Analysis of a sample of charcoal from a fire in one such site gave a 14 C decay rate of 0. What is the approximate age of the sample? The half-life of a reaction is the time required for the reactant concentration to decrease to one-half its initial value.

Radioactive decay reactions are first-order reactions. The rate of decay, or activity, of a sample of a radioactive substance is the decrease in the number of radioactive nuclei per unit time. Skills to Develop To know how to use half-lives to describe the rates of first-order reactions. Subtract the remaining concentration from the initial concentration. Then divide by the initial concentration, multiplying the fraction by to obtain the percent completion.

What is the half-life for the reaction under these conditions? If a flask that originally contains 0. Answer a 4.

# Radioactive dating and half life

Radioactive Decay Rates Radioactivity, or radioactive decay, is the emission of a particle or a photon that results from the spontaneous decomposition of the unstable nucleus of an atom. Note Radioactive decay is a first-order process. Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.

Note that this does not mean that the ratios are the same everywhere on earth. It merely means that the ratios are the same in the particular magma from which the test sample was later taken. As strontium forms, its ratio to strontium will increase.

Strontium is a stable element that does not undergo radioactive change. In addition, it is not formed as the result of a radioactive decay process. The amount of strontium in a given mineral sample will not change.

It turns out to be a straight line with a slope of The corresponding half lives for each plotted point are marked on the line and identified. It can be readily seen from the plots that when this procedure is followed with different amounts of Rb87 in different mineralsif the plotted half life points are connected, a straight line going through the origin is produced.

These lines are called "isochrons". The steeper the slope of the isochron, the more half lives it represents. When the fraction of rubidium is plotted against the fraction of strontium for a number of different minerals from the same magma an isochron is obtained. If the points lie on a straight line, this indicates that the data is consistent and probably accurate.

## Nuclear Chemistry: Half-Lives and Radioactive Dating

An example of this can be found in Strahler, Fig However, if strontium 87 was present in the mineral when it was first formed from molten magma, that amount will be shown by an intercept of the isochron lines on the y-axis, as shown in Fig Thus it is possible to correct for strontium initially present.

Comparing figures The age of the sample can be obtained by choosing the origin at the y intercept.

In Fig Note that the amounts of rubidium 87 and strontium 87 are given as ratios to an inert isotope, strontium However, in calculating the ratio of Rb87 to Sr87, we can use a simple analytical geometry solution to the plotted data. Again referring to Fig. Since the half-life of Rb87 is Therefore: log. When properly carried out, radioactive dating test procedures have shown consistent and close agreement among the various methods.

If the same result is obtained sample after sample, using different test procedures based on different decay sequences, and carried out by different laboratories, that is a pretty good indication that the age determinations are accurate.

Of course, test procedures, like anything else, can be screwed up. Mistakes can be made at the time a procedure is first being developed. Creationists seize upon any isolated reports of improperly run tests and try to categorize them as representing general shortcomings of the test procedure. Exposure to sunlight or heat releases these charges, effectively "bleaching" the sample and resetting the clock to zero.

The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried. Stimulating these mineral grains using either light optically stimulated luminescence or infrared stimulated luminescence dating or heat thermoluminescence dating causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.

These methods can be used to date the age of a sediment layer, as layers deposited on top would prevent the grains from being "bleached" and reset by sunlight. Pottery shards can be dated to the last time they experienced significant heat, generally when they were fired in a kiln.

Absolute radiometric dating requires a measurable fraction of parent nucleus to remain in the sample rock. For rocks dating back to the beginning of the solar system, this requires extremely long-lived parent isotopes, making measurement of such rocks' exact ages imprecise. To be able to distinguish the relative ages of rocks from such old material, and to get a better time resolution than that available from long-lived isotopes, short-lived isotopes that are no longer present in the rock can be used.

Debunking the creationist radioactive dating argument. Creationists also attack radioactive dating with the argument that half-lives were different in the past. The isotope 14C is radioactive, and beta-decays with a half-life of 5, years. This means that in 5, years, only half of the 14C will remain, and after 11, .

At the beginning of the solar system, there were several relatively short-lived radionuclides like 26 Al, 60 Fe, 53 Mn, and I present within the solar nebula. These radionuclides—possibly produced by the explosion of a supernova—are extinct today, but their decay products can be detected in very old material, such as that which constitutes meteorites.

By measuring the decay products of extinct radionuclides with a mass spectrometer and using isochronplots, it is possible to determine relative ages of different events in the early history of the solar system. Dating methods based on extinct radionuclides can also be calibrated with the U-Pb method to give absolute ages. Thus both the approximate age and a high time resolution can be obtained. Generally a shorter half-life leads to a higher time resolution at the expense of timescale.

Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes. Learn about half-life and how it is . The best-known techniques for radioactive dating are radiocarbon dating, potassium-argon dating and uranium-lead dating. After one half-life has elapsed, one. Unstable nuclei undergo spontaneous radioactive decay. Thus the half-life of a reaction is the time required for the reactant concentration to.

The iodine-xenon chronometer [32] is an isochron technique. Samples are exposed to neutrons in a nuclear reactor.

This converts the only stable isotope of iodine I into Xe via neutron capture followed by beta decay of I. After irradiation, samples are heated in a series of steps and the xenon isotopic signature of the gas evolved in each step is analysed.

Samples of a meteorite called Shallowater are usually included in the irradiation to monitor the conversion efficiency from I to Xe.

This in turn corresponds to a difference in age of closure in the early solar system. Another example of short-lived extinct radionuclide dating is the 26 Al — 26 Mg chronometer, which can be used to estimate the relative ages of chondrules. The 26 Al — 26 Mg chronometer gives an estimate of the time period for formation of primitive meteorites of only a few million years 1.

From Wikipedia, the free encyclopedia. A technique used to date materials such as rocks or carbon.

Main article: Closure temperature. Main article: Uranium—lead dating. Main article: Samarium—neodymium dating. Main article: Potassium—argon dating. Main article: Rubidium—strontium dating. Main article: Uranium—thorium dating.

Scientists look at half-life decay rates of radioactive isotopes to estimate when a particular atom might decay. A useful application of half-lives is radioactive. Explain radioactive half-life and its role in radiometric dating; Calculate radioactive half-life and solve problems associated with radiometric dating. Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate.

Main article: Radiocarbon dating. Main article: fission track dating. Main article: Luminescence dating. Earth sciences portal Geophysics portal Physics portal.

Part II. The disintegration products of uranium".

American Journal of Science. In Roth, Etienne; Poty, Bernard eds. Nuclear Methods of Dating. Springer Netherlands. Annual Review of Nuclear Science. Bibcode : Natur. Earth and Planetary Science Letters. Brent The age of the earth. Stanford, Calif. Radiogenic isotope geology 2nd ed.

Cambridge: Cambridge Univ. Principles and applications of geochemistry: a comprehensive textbook for geology students 2nd ed. Using geochemical data: evaluation, presentation, interpretation. Harlow : Longman. Precambrian Research. Bibcode : PreR. Cornell University.

Nuclear Half Life: Intro and ExplanationUnited States Geological Survey. Kramers June Hanson; M. Martin; S. Bowring; H. Jelsma; P. Dirks Journal of African Earth Sciences. Bibcode : JAfES. Vetter; Donald W. Davis Chemical Geology.

Bibcode : ChGeo. South African Journal of Geology. Wilson; R.

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