RADIOACTIVE HALFLIFE
Tuesday, January 26, 2010
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The activity of different radioisotopes falls at different rates. Some radioisotopes take only a few seconds for nearly all the unstable nuclei to decay. Others take days, weeks, months, years and even billions of years to decay. To compare the activity of different radioisotopes we talk about the half-life of a radioisotope. The original term, dating to 1907, was "half-life period", which was later shortened to "half-life" sometime in the early 1950s.
Definition:
The half-life of a radioisotope is the time it takes to disintegrate to half its initial mass.
The half-life period of a radioactive isotope is the same irrespective of its initial mass.
half-life. This is an exponential decay process that steadily decreases the proportion of the remaining isotope by 50% every half life. Hence after two half-lives have passed only 25% of the isotope will be present, and so forth.
| Number of half-life | Fraction remaining | Percentage remaining |
| 0 1 2 3 4 5 6 7 … n | 1/1 ½ ¼ 1/8 1/16 1/32 1/64 1/128 … 1/(2n) | 100 50 25 12.5 6.25 3.125 1.563 0.781 … 100/(2n) |
Example (1)
The picture below shows how long it takes Phosphrous-32 to decay into Sulphur-32.You can see that, after every 14 days, half of the unstable nuclei of the Phosphrous-32 atoms decay into stable Sulphur-32 atoms. We say the half-life of Phosphrous-32 is 14 days.
Example (2)
The first picture shows a sample of Carbon-14 at 0 years. The second picture shows the sample of Carbon-14 after 5730 years.
This shows that it takes 5730 years for half of the unstable nuclei of Carbon-14 atoms in the sample to decay into stable Nitrogen atoms. So we say that the half-life of Carbon-14 is 5730 years.
A number of experiments have shown that decay rates of naturally-occurring radioisotopes are, to a high degree of precision, unaffected by external conditions 
such as temperature, pressure, the chemical environment and electric, magnetic or gravitational fields.
posted by Lekshmi @ 3:10 PM,
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