(4 points) One method for calculating the half-life of radioisotopes consists of
ID: 1658555 • Letter: #
Question
(4 points) One method for calculating the half-life of radioisotopes consists of measuring the activity of a radioisotope at given intervals and relating the decrease in activity over time to the exponential decay law to determine the decay constant and ultimately the half-life. However, for long-lived radioisotopes, this method is not possible on meaningful time scales for people. For an isotope such as 238U (which has a half-life of 4.468×109 y), how can the half-life be calculated?
(4 points) One method for calculating the half-life of radioisotopes consists of measuring the activity of a radioisotope at given intervals and relating the decrease in activity over time to the exponential decay law to determine the decay constant and ultimately the half-life. However, for long-lived radioisotopes, this method is not possible on meaningful time scales for people. For an isotope such as 238U (which has a half-life of 4.468x10 y), how can the half-life be calculated?Explanation / Answer
For very long lived radioisotopes, one method to determine the half life is to isolate very pure form of the radionuclide and measure its activity over period of time. For example, if we isolate 5 mg of pure 238UO2, it has 4.41 mg of 238 U. The uranium decays 100 pc of the time by alpha decay and when deposited in a thin foil we can measure a count of 16.9 curie per second. This gives us the activity, and by knowing the initial amount of radionuclide one can know lambda
A = No*lambda
and half life is related to lambda as under
t1/2 = ln(2)/lambda
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