ED-1. Tests on a particular radioisotope reveal a decay rate of 570 C/M (counts per minute). Two hours later, the decay rate is 222 C/M. Determine the half life for this isotope.

ED-2. ED-1. Tests on a another radioisotope reveal a decay rate of 570 C/M (counts per minute). Exactly four years later, the decay rate is 470 C/M. Determine the half life for this isotope.

ED-3 During the course of a twelve hour period, the decay rate of an isotope has decreased to 10% of its original value. What is the half life of the isotope?

ED-4. It has been reported by reliable sources that a radioactive sample is fundamentally non-existent after it has gone through ten half-lives. a) What fraction of the original amount of an isotope is still present after ten half-lives? b) If the number of atoms in the original sample were Avogadro’s number, how many atoms would be left after ten half lives? Is this number significant in terms of our ability to measure small quantities of matter?

ED-5. An isotope is known to have a half-life of 12.0 days. How much of a sample will be left after 5 days? After 15 days? After 32 days?

ED-6. The half-life of francium-221 is 4.80 min. How long will it take for the rate of decay for a particular sample to be reduced to 1% of its original value?

ED-7. U238 has a half-life of 4.5 x 10*9 yrs and decays by alpha emission. a) What is the decay constant for U238? b) What mass of U238 is required for an activity of 1 Curie? (Note that 1 Ci = 3.7 x 10*10 disintegrations/sec.) How many a particles are emitted by 1 g of uranium?

ED-8. The unstable isotope K40 is used to date rock samples and has a half-life of
2.4 x 108 yrs. How many decays per second (this unit is the Becquerel = Bq) occur from a sample of K40 whose mass is 2 x 10-6 g?

dN/dt = - lambda N

ln(N/N0) = - lambda N

N = No e*-lambda t = No 1/e*lambda t

T1/2 = .693/lambda

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last edited 12/29/05