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If Radium has a half life of 1600 years what does that mean It means that every 1600 years half of the radium will decay. By using this Site you agree to the following Terms and Conditions. Half life is the rate at which a radioactive substance decays.
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#What does half life mean professional
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#What does half life mean update
For example, using a Bayesian approach, if we have a poor prior, and little information to update to a posterior, the poor prior cannot be modified accurately to provide a good posterior and the Bayesian estimate can be way off. Half lives range from millionths of a second for highly radioactive fission. In 14 more days, half of that remaining half will decay, and so on. If a radioisotope has a half-life of 14 days, half of its atoms will have decayed within 14 days. (More trials contribute to our improved state of knowledge, but in general other factors also contribute.)įor cases with significant state of knowledge (epistemic) uncertainty, we have insufficient information to use the probability measure of uncertainty, even in a Bayesian sense. The half-life is the amount of time it takes for a given isotope to lose half of its radioactivity. Our uncertainty is reduced as we perform more trials or improve our state of knowledge the confidence interval is reduced and the subjective probability distribution is "narrowed". For example: The half-life of Ambien is about 2 hours. Half-life is used to estimate how long it takes for a drug to be removed from your body. Using the Bayesian approach we can treat the classical $P_O$ as a random variable and express the uncertainty in $P_O$ as a subjective probability distribution for $P_O$ based on our imperfect state of knowledge. What does half-life mean give one example by The half-life of a drug is the time taken for the plasma concentration of a drug to reduce to half its original value. Using classical statistical inference this uncertainty can be expressed as a confidence interval for $P_O$. See the text Bayesian Reliability Analysis by Martz and Waller for information on the Bayesian approach.įor the more general case where we have limited information (trials for the classical case or state of knowledge for the Bayesian case) we have uncertainty in the probability. With sufficient information, the classical objective probability $P_O$ and the Bayesian subjective probability $P_S$ for the event are the same: one value with no uncertainty. For a large body of information we know the updated $P_S$ with no essentially uncertainty. For a very large $N$, observing $N(E)$, we know $P_O$ with essentially no uncertainty.įor the Bayesian approach, we assume a prior value for the event, $P_S$, and update it to a more accurate estimate for $P_S$, called the posterior, as we gather more information. This probability is the same using either a classical (objective or frequency) approach, or a Bayesian (subjective) approach.įor the classical approach, the probability of event $E$ is $P_O = lim_$ where $N$ is the number of independent trials and $N(E)$ is the number of times event $E$ occurs. We have sufficient information from observing the decay of a very large number of identical radionuclides to claim we know the decay rate, hence the probability of decay, with no uncertainty.
In general, a pesticide will break down to 50 of the original amount after a single half-life. This occurs as it dissipates or breaks down in the environment. The following is a little more discussion of the good comment by Karonen on the response. A half-life is the time it takes for a certain amount of a pesticide to be reduced by half.
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