Difference between revisions of "Half-life"
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'''Half-life''' is the time it takes for half of the original sample of a [[radioactive]] [[isotope]] to decay.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref> If the [[exponential decay]] of a radioisotope is expressed as <math>A = A_0 e^{-(t-t_0)/\tau}</math>, then the half-life is equal to <math>\tau</math> ln 2. Knowing these decay rates is important for dating, such as with [[carbon|carbon-14]]. | '''Half-life''' is the time it takes for half of the original sample of a [[radioactive]] [[isotope]] to decay.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref> If the [[exponential decay]] of a radioisotope is expressed as <math>A = A_0 e^{-(t-t_0)/\tau}</math>, then the half-life is equal to <math>\tau</math> ln 2. Knowing these decay rates is important for dating, such as with [[carbon|carbon-14]]. | ||
| − | It should be noted that the measurement of half-life is based on ''recent'' observations, and the numbers that follow from radioactive dating based on nuclear decay extrapolate from this assumption. For example, if a sample of biological material has 1/4 of the Carbon-14 relative to the rate a similar biological material has, ''constant'' half-life extrapolation dates this sample as two half-lifes old (in the order of 11,000 years). | + | It should be noted that the measurement of half-life is based on ''recent'' observations, and the numbers that follow from radioactive dating based on nuclear decay extrapolate from this assumption. For example, if a sample of biological material has 1/4 of the Carbon-14 relative to the rate a similar biological material has, ''constant'' half-life extrapolation dates this sample as two half-lifes old (in the order of 11,000 years). The creationist blog Answers In Genesis suggests that half-life varies over time<ref>[http://www.answersingenesis.org/articles/am/v1/n1/creation-research Raising the Bar on Creation Research - by Don DeYoung, Ph.D.]</ref>. |
An analogy for this extrapolation would be taking the population growth of Germany today (a negative rate), extrapolating backwards, and concluding that there were 100 billion germans during the time of the fall of the Roman Empire. | An analogy for this extrapolation would be taking the population growth of Germany today (a negative rate), extrapolating backwards, and concluding that there were 100 billion germans during the time of the fall of the Roman Empire. | ||
Revision as of 15:16, March 7, 2010
Half-life is the time it takes for half of the original sample of a radioactive isotope to decay.[1] If the exponential decay of a radioisotope is expressed as , then the half-life is equal to ln 2. Knowing these decay rates is important for dating, such as with carbon-14.
It should be noted that the measurement of half-life is based on recent observations, and the numbers that follow from radioactive dating based on nuclear decay extrapolate from this assumption. For example, if a sample of biological material has 1/4 of the Carbon-14 relative to the rate a similar biological material has, constant half-life extrapolation dates this sample as two half-lifes old (in the order of 11,000 years). The creationist blog Answers In Genesis suggests that half-life varies over time[2].
An analogy for this extrapolation would be taking the population growth of Germany today (a negative rate), extrapolating backwards, and concluding that there were 100 billion germans during the time of the fall of the Roman Empire.
References
- ↑ Wile, Dr. Jay L. Exploring Creation With Physical Science. Apologia Educational Ministries, Inc. 1999, 2000
- ↑ Raising the Bar on Creation Research - by Don DeYoung, Ph.D.