what is radioisotopic dating?
414512
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. \nA formula to calculate how old a sample is by carbon-14 dating is: \n\n\nt = [ ln (Nf/No) / (-0.693) ] x t1/2 \nwhere ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years). \n\nSo, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: \n\n\nt = [ ln (0.10) / (-0.693) ] x 5,700 years \nt = [ (-2.303) / (-0.693) ] x 5,700 years \n\nt = [ 3.323 ] x 5,700 years \n\nt = 18,940 years old \n\nBecause the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old. However, the principle of carbon-14 dating applies to other isotopes as well. Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years. Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).
707906
Just look up carbon 14 dating in applied anthropology, archaeology.
419931
Rather than radioactive element, let's call it a radioactive isotope.  Why?  Because a radioactive element can decay and still be the same element but have fewer neutrons.  As other posters sort of explained, if an isotope is radioactive then half of it should become something else in the specific half life time.  It could still be the same element, or it might be a lighter element.  Read the link about carbon dating and you might understand how this is useful.
874077
You have asked this question in different forms elsewhere -- I am not sure what you mean by "period and sign dating" here so I will assume you mean dating of fossil remains in general.\n\nMy most detailed answer is located in response to this question:\n\nhttp://answers.yahoo.com/question/index;_ylt=AlreU4PXgsD7aQCLe3GmF4Psy6IX?qid=20061115131041AAnjMF1\n\nTo sum up:\n\nThe world's carbon consists mainly of the Carbon-12 and Carbon-13 isotopes, which are not radioactive and are therefore stable, and a small amount of Carbon-14 which is a radioactive isotope of Carbon and is not stable (it decays over time, turning into stable Nitrogen at a very regular and slow rate).\n\nThe rate at which Carbon-14 decays into Nitrogen and the rate at which new Carbon-14 is created by the action of solar radiation on the upper atmosphere are essentially identical.  This, the ratio of Carbon-14 to Carbon-12 on the earth is fairly stable as a whole.\n\nLiving things take in carbon as part of their life cycle.  As long as they are alive, carbon is coming into and going out of their systems continuously, so it is being maintained at essentially the same ratio of Carbon-14 to Carbon-12 as the world at large.\n\nWhen something dies, the intake of carbon stops.  As the radioactive carbon-14 breaks down into Nitrogen, it is not replaced with new Carbon-14.  In time essentially ALL of the Carbon-14 will decay into Nitrogen, but until then the ratio of Carbon-14 to Carbon-12 (Carbon-14 divided by Carbon-12) will give a fairly accurate representation of how long the thing has been dead, assuming it has not been contaminated with fresh Carbon.\n\nSince geological dating is mainly concerned with rocks, there are 2 things preventing carbon-14 from being used:  (1) the rocks were not living things taking in carbon from their surroundings, so we can't say WHAT their original ratio of Carbon-14 divided by Carbon-12 was, and (2) rocks are so old that even if they HAD started with the normal ratio of Carbon-14 to Carbon-12, all of that Carbon-14 would have long since decayed into Nitrogen -- there would not be enough left to be able to measure it.
294065
You may mean this.  If not post again.\n\nhttp://wwwrcamnl.wr.usgs.gov/isoig/period/ar_iig.html\n\nhttp://www.csudh.edu/oliver/smt310-handouts/dating/dating.htm
915684
Very roughly:  by comparing the ratio between a radioisotope and its "daughter product", and with the knowledge of the radioisotope's half-life, calculate the amount of time needed for the observed ratio to develop.\n\nIn short, if there is a 50-50 split between the radioisotope and its daughter product, one half-life has passed.
570720
The age of a fossil may be specified in both relative terms (how old it is in relation to other fossils or rock units) and in absolute terms (approximately how many years old it is). One principle of relative dating is called superposition, which holds that in any one place, the lower rock layers (and fossils in them) are older than higher ones, unless there is evidence that the layers have been overturned. This is logical, since the lower sediments would have been deposited first. A related concept is correlation, whereby rock layers (strata) are compared with others in another location on the basis of their mineral composition, fossil content, and other features. When a rock unit or series closely matches those of another area, they are said to be correlated and considered to be of similar age. Correlations are especially reliable when they include index fossils, which are fossils with a limited age range. Good index fossils are easily recognized and widely distributed around the world, so that they aid both local and international correlations.\n\nAbsolute dating complements relative dating by providing a specific (not necessarily precise) chronological age for a given specimen, such as "50 million years before present." In recent years reliable forms of absolute dating became available through the development of radiometric dating methods. These methods are based on the known, regular decay of certain radioactive elements (isotopes) into other isotopes or "daughter products." By measuring the amount of "parent" and "daughter" products in a rock sample, its approximate age may be calculated.\n\nMany people have heard of the Carbon 14 method and assume that fossils are dated by it. Actually, in most cases the C-14 method is useful only on organic material less than about 50,000 years old, which includes many human remains and artifacts, but excludes most fossils. Absolute dating of fossils requires other dating methods such as the potassium-argon or rubidium-strontium methods, which involve isotopes with slower decay rates (longer "half-lives"). Such isotopes are rare in fossils themselves, but may occur in surrounding or adjoining rock layers, yielding an approximate age for the fossil-bearing unit. Using the principles discussed above, scientists also can deduce the approximate age of other layers correlated with the same formation, as well as an approximate age for layers above and below the formation (which would be somewhat younger and older respectively).\n\nThe terms "above" and "below" in this context are used in a relative or stratigraphic sense; that is, they are based on the positions of the units relative to each other (or correlated units), rather than their height above sea level. The branch of geology that deals with the correlation of rock layers is known as stratigraphy (or biostratigraphy when focusing on the fossils within the layers), and is an important tool of paleontologists.
34307
Carbon 14 Dating measures the amount of the Carbon-14 isotope in carbon-based life forms. The decay of the carbon-14 isotope is known and predictable, so the amount remaining in the material tells how old the item is, with a little degree of error.\n\nOrganic material must be used, though. I do not think true fossils can be dated this way, because all the organic material is gone. (I could be wrong on this.)\n\nI think fossils are aged by the location of the fossil within the surrounding rocks, and the approximate time that the layers, or strata, of rocks were formed.
89157
radioactivity is the decay of an atom by emmision of radiation. Biotechnology is the use of biology to improve something, be it health or living conditions etc.
496873
Sorry this is so long, but I have to first fix some misinformation given in other people's answers.  Specifically, carbon-14 (a.k.a. C14, carbon dating, or radiocarbon dating) is useful for dating a lot of things, but *not* fossils!  Instead, other forms of radiometric dating are used for fossils.  \n\nThe 'half-life' is a measure of how fast the process of radioactive decay causes one type of atom to decay into another type.  For example carbon-14 (C14) decays into nitrogen-14 (N14) with a half-life of 5,730 years.  This means that if you have a bone with 1 gram of C14, then after 5,730 years, 0.5 grams will have decayed to N14, leaving 0.5 grams of C14.  After another 5,730 years only 0.25 grams would remain.  And so on.\n\nNow, 5,730 years is not very long in geologic terms.  This means that after 50,000 years or so, the amount of C14 left is so small that it is practically unmeasurable.  It's for this reason that C14 dating is not much good for fossil dating, as most fossils are *much* older than 50,000 years.\n\n[Aside:  There's another reason carbon-14 dating is not useful for fossils.  It's only useful for dating once-living matter (bones, wood, teeth, shells, cloth, paper, etc.) that was incorporating carbon into its body while it lived ... either a plant that was once breathing CO2, or an animal that was eating things that contained carbon (like plants or other animals).  A fossil is not once-living matter.  It is rock that has filled in the impression left by a dead organism.  So fossils themselves may contain very little carbon of any type.]\n\nBut there are other atoms with a *much* longer half-life.  For example potassium-40 (K40) decays into argon-40 (Ar40) with a half-life of 1.26 *billion* years.  So when a rock is created by a volcano, it contains only K40 (as argon is a gas, so any Ar40 present at the time the rock forms escapes from the molten rock before it cools).  But over millions of years this K40 decays to Ar40, which remains trapped in the rock.  So a geologist can dig up a rock from a layer of strata, melt it down, and measure the amount of molten K40 and gaseous Ar40 that is released.  By the ratio of K40 to Ar40 in the rock, the geologist can calculate the age of the rock, in millions of years.  The geologist then also knows the age of anything else that was encased in the same layer of strata as the rock ... such as a fossil.\n\nCarbon-14 dating and potassium-argon dating are two forms of what are called 'radiometric dating'.  Other examples are uranium-lead dating (half-life of 700 million years), and rubidium-strontium dating (half-life of 50 billion years ... which is *very* long, considering that the earth is only 4.5 billion years old).
508155
Write the word 'radioactivity' in www.google.com.Then collect watever information u need.
443590
Check this site: http://www.et.byu.edu/~adw45/Carbon%20Dating.htm\nIt's an undergrad paper that won "undergrad paper of the year" according to the website.  Second paragraph states, "...carbon dating can only be use to date geologically young, 35k - 50k years, carbon containing substances..."\n\nWikipedia's article on carbon dating says "The current maximum radiocarbon age limit lies in the range between 58,000 and 62,000 years. This limit is encountered when the radioactivity of the residual 14C in a sample is too low to be distinguished from the background radiation."
1066565
Although some of the answers you have received are accurate they aren’t exactly succinct or to the point.\nYou haven’t however said what age the kids are you need to explain it to, please forgive me if this explanation seems too simplistic.\nThe theory of radioactive dating works along these lines.\n\n1. SOME ELEMENTS “DECAY” (CHANGE) FROM ONE THING TO ANOTHER, e.g. from Potassium to Argon or from one isotope to another e.g. C14 to C12\n2. THIS RATE OF CHANGE IS KNOWN, the speed at which it changes is known as the half life, i.e. how long before half of the total has changed\n3. A COMPARISON IS MADE i.e. you work out how much there was and how much has changed\n4. THE AGE IS CALCULATED. Once you know how much has decayed you can compare the amounts on well-known charts e.g. if you know halve the amount of C14 has changed to C12 then the sample is 5730 years old.\n\nIt is considered accurate because the rate of radioactive decay is absolute, measurable and observable. It has been tested numerous times and can be experimented on. The same results can be achieved and repeated by numerous people at many different labs. On the whole the decayed products (e.g. C12 etc.) are not found naturally. The original material is created at the time the sample is formed or moved (e.g. when the plant, animal grew).\n\nHowever the problems are\n1. In order to calculate the percentage of element changed you have to know how much there was. Sometimes the sample can have some of the original material removed or more of the original material can be added, e.g. new living fungi can grow and die on a log hundreds of years after the log was originally felled and buried.( this would give a younger date)\n2. The resulting product can be removed or further altered e.g. Argon from potassium can escape as it is a gas ( this would give you a later date because it would seem not as much or the argon had been formed)\n3. This time clock can be reset due to outside influences. A fire can reset the amount of C14/C12 because the carbon from the fire is different from the carbon formed in the living thing (e.g. the problems with dating the shroud of Turin)\n\nThis of coarse assumes that the equipment used is accurate and that no contamination was added e.g. someone touching or sneezing on the sample.\n\nOn the whole though in theory the method should be extremely accurate. Given perfect samples, good laboratory practice and accurate measurements the results seem impressive. This shouldn’t automatically however be taken for granted.\n\nThe final thing to remember though is that there is no other way of giving empirical, measurable dates on extremely ancient rocks or artefacts.
594617
try:  Yahoo search / video / isotopes
1167196
Radioactive Decay Equation\n\nA(t) = [Ao] [e(-?t/T)]\n\nUse this equation to determine the activity of a\nradioactive material at any given period of time.\nA(t) = the number of radioactive atoms at time (t)\nAo = the number of radioactive atoms at time zero (originally)\ne = base of the natural log\n? = a constant (0.693)\nt = the number of days of decay\nT = the half-life in days of the radioactive material of interest
626812
Are you talking of naturally occuring Radio isotopes like Carbon-14 or the synthesized ones like Cobalt-60 or krypton:\n\nAnyway, I will try!\n\n1. Carbon Dating: Living things absorb a certain amount of carbon-14 as long as they are living. When they die the Carbon-14 starts to decay at a half-life of 5730 yrs, by measuring the amount of the residue Carbon-14,the time since their death can be determined.\n\n2. In medicine:Positron emission Tomography PET uses radio isotopes to collect a tracer on brain activity including cerebral metabolism and oxygen use, while Nuclear magnetic Resonance is used to collect images of tissues that a more precise than CAT scans\n\n3. In industry, cobalt 60 is used to detect flaws in steel as thick as 6 inches, by picking up beta and gamma radiation on a photographic film emitted after radiating a cobalt wire.\n\n4.Nuclear Power production:Water heated due to radioactive decay produces steam to turn turbines that turn massive electric generators!\n\n5.Least desirable use: Nuclear weapons use the chain reaction properties to unleash megajoules of destructive energy!
168747
In radioactivity, it is the time taken for half of the nuclei in a given sample to decay (either by alpha or beta decay).  These vary form radioisotope to another.  For example Carbon-14 has a half life of 5700 years.  This means that if I have 1 gram of carbon-14, 5,700 years from now I will end up with 0.5grams (the rest would have become Nitrogen with beta decay).  If another 5,700 years pass I end up with 0.25g (!) and not 0g as common sense would indicate.  Each time a half life passes HALF the nuclei decay!In fact 'activity' decreases as time passes.\nAs said this time interval varies a lot.  The half life of Uranium-238 is 4,470,000,000 years, while that of thorium-230 is only 75,380 years.  Other half lives are quite short.  E.g. Iodine-131 has a half life of just 8 days and Sodium-24 has a half life of just 15 hours!