wat is meant by a half-life of a radioactive isotope?
930232
the time it takes for half of the material to decay
372960
Well, it could be a date with Mick Jagger (from the Rolling Stones) or more likely it is using the various isotopes of elements found in a sample of stone to estimate its age. Say a stone was found with 50% of its original uranium in it. Uranium has a half life of 4.5 billion years so the stone would have passed one half life and would have an age of 4.5 billion years.  If only 25% of the original uranium were left, then 2 half lives or 9.0 billion years would have passed since the stone was created.
636669
suppose u have 100gm of a radioactive material with half life as 5 yrs. after 5 yrs the amount will be 50gms as half of it has decayed in 5 yrs.In next 5 yrs it will reduce to 25 gms and so on . As the radioactive material decays to half of its initial amount so it is called half life of that material.
292520
The law of radioactive decay makes a prediction how the number of the not decayed nuclei of a given radioactive substance decreases in time. The red circles of this simulation symbolize 1000 atomic nuclei of a radioactive substance whose half-life period (T) amounts to 20 seconds. The diagram in the lower part of the applet represents the fraction of the not yet decayed nuclei (N/N0) at a given time t, predicted by the following law:\n\nN   =   N0 ·   2-t/T\n\nN .... number of the not decayed nuclei\nN0 ... number of the initially existing nuclei\nt .... time\nT .... half-life period\n\n\nAs soon as the applet is started with the green button, the atomic nuclei begin to "decay" (change of color from red to black). You can stop and continue the simulation by using the button "Pause / Resume". In this case a blue point for the time and the fraction of the not yet decayed nuclei is drawn into the diagram. (Note that these points often don't lie exactly on the curve!) If you want to restore the initial state, you have to click on the "Reset" button.\n\nIt is possible to give the probability that a single atomic nucleus will "survive" during a given interval. This probability amounts to 50 % for one half-life period. In an interval twice as long (2 T) the nucleus survives only with a 25 % probability (half of 50 %), in an interval of three half-life periods (3 T) only with 12,5 % (half of 25 %) and so on.\n\nYou can't, however, predict the time at which a given atomic nucleus will decay. For example, even if the probability of a decay within the next second is 99 %, it is nevertheless possible (but improbable) that the nucleus decays after millions of years.
608949
cant answer secifically, but you should be able to back calculte taking elements present today and using the half lives as your main variable.
206512
it depends on how long you have been taking them and the mg of the pill. the half life in your body is 3.8 hours. this means that in 3.8 hours one-half of it has metabolized out of your system, over the next 3.8 hours one-half of what is left in your system after the first 3.8 hours is gone and so on and so on until you reach zero.
247742
The half time for decay of C14 is about the same as the biblically calculated age of the earth by change.\nThe decay time is constant and the age grows.\nThe margin is a couple of years, depending on the measured time. The longer you count the more precise the result.
393448
half-life is how long an item remains radioactive and has nothing to do with the lifespan of that item.
470977
Certain radioactive isotopes have such short half-lives that they almost completely decay into daughter isotopes in less than 10 seconds or even less than 1 second. Look it up on Wikipedia.
1106952
There are 24 isotopes of potassium (atomic number 19), ranging in atomic mass from 32 to 54 amu.\n\nThe most abundant isotope, K39 (which comprises 93.26% of all potassium known), is stable, as is the next most abundant isotope, K41 (6.73%).  So the stable isotopes make up 99.99% of all the potassium in the world.\n\nOne other stable isotope, K32, is present in vanishingly small portions. \n\nHowever, that remaining 0.01% consists of the other 21 known isotopes, all of which are radioactive to some degree:\n\nK33 has a half-life less than 25 nanoseconds.\nK34 has a half-life less than 40 nanoseconds.\nK35 is a positron/gamma emitter with a half-life  of 0.19 seconds.\nK36 is a positron/gamma emitter with a half-life of 0.342 seconds.\nK37 is a positron/gamma emitter with a half-life of 1.23 seconds.\nK38m is a positron emitter with a half-life of 0.924 seconds.\nK38 is a positron/gamma emitter with a half-life of 7.63 minutes.\nK39 is stable.\nK40 is 0.01% of the total, and is a beta/gamma emitter with a half-life of 1.26x10^9 years.\nK41 is stable.\nK42 is a beta/gamma emitter with a half-life of 12.36 hours.\nK43 is a beta/gamma emitter with a half-life of 22.3 hours.\nK44 is a beta/gamma emitter with a half-life of 22.1 minutes.\nK45 is a beta/gamma emitter with a half-life of 17.8 minutes.\nK46 is a beta/gamma emitter with a half-life of  1.8 minutes.\nK47 is a beta/gamma emitter with a half-life of 17.5 seconds.\nK48 is a beta/gamma emitter with a half-life of 6.8 seconds.\nK49 is a beta/gamma emitter with a half-life of 1.26 seconds.\nK50 is a beta emitter with a half-life of 0.472 seconds.\nK51 is a beta emitter with a half-life of 0.365 seconds.\nK52 is a beta emitter with a half-life of 0.105 seconds.\nK53 is a beta emitter with a half-life of 30 milliseconds.\nK54 is a beta emitter with a half-life of 10 milliseconds.
240255
The definition of the half-life is the amount of time for half the substance to react.  \n\nWhen the last molecule (or atom) reacts, the reaction is complete.  One might argue that the half-life ends when the reaction ends.  However, for many reactions, the half-life is independent of the amount of that substance (a good example is  nuclear fission), so you could argue since the half-life doesn't change, it doesn't end.  This is really a matter of semantics.
745292
the definition of 1/2 life is that 1/2 of the material will be left after that amount of time.\n100 g to start, 50 g after 1 half life.\n25 g after 2 half lives.\n\nb) 60 yrs is 2 half lives.  see ans to part A)\nc) 25 g will be left after 60 yrs.  See answer to part A)\n-->
176116
A halflife is a form of time constant for characterizing exponential trends with a decay rate of 1/2. Another common time constant decay rate is 1/e.
212309
The half-lives will vary depending on the isotope.  Go to the library and look them up in "The Handbook of Chemistry and Physics" in the reference section.
926537
The decay is of the form N(t)/N0 = e^-t/h, where h is a constant.  When t = HL (half life time) N(t)/N0 = .5  therefore N(HL)/N0 = .5 = e^-HL/h.  Take the natural log of both sides to get ln(.5) = -HL/h, so h = HL/ln(2).  Therefore the formula for decay is \n\nN(t)/N0 = e^-t*ln(2)/HL\n\nYou want to find tx such that N(t)/N0 = 100/10^6 = 10^-4.  That means 10^-4 = e^-tx*ln(2)/HL.  Again, taking log (base 10) of both sides gives you -4 = log(e^-tx*ln(2)/HL) or[ -tx*ln(2)/HL]*ln(10).  The time tx is then 4*HL*ln(10)/ln(2).  This comes out 74,411years
628925
That is the law of hughe numbers.\nAbout the decay of individual nucleus you can predicht nothing.\nHowever about a measurable amount of isotope you can give its half life time.
311743
Certain substances have a radioactive halflife.  That means it takes a certain amount of time for that substance to decay so far.  Carbon dating is the process of observing the decay of the carbon present in an object to determine its age.\n\nLike any scientific property, there is always error.  The equation and theory models very close to reality but never exactly.  And there are so many other things that could've assisted in the decay which result in incorrect data.\n\nWhich is why whenever you want to make a scientific claim about certain fossils containing carbon for example, you will take many samples from various objects within a certain layer of the soil, then take the average age of them all, giving a rough estimate of the age of that particular layer of soil.\n\nIs carbon dating perfect?  No.  No scientific method is without errors.  But if done intelligently it can give reliable statistics about the age of objects.\n\nMost of the people who are wholly against carbon dating point out errors and flaws with it that any reasonable scientist is fully aware of and they pretend that it's a profound problem which invalidates the whole process.  The majority of Carbon Dating critics are coming from the religious front, who oppose it because it disproves their beliefs.\n\nUltimately though, if done by a careful scientist with lots of samples, then averaged, carbon dating is generally reliable.