91Ó°ÊÓ

Strontium-90 has a half-life of 28 years. If a \(1.00\)-mg sample was stored for 112 years, what mass of Sr-90 would remain?

Strontium-90 has a half-life of 28 years. If a sample was tested in 1980 and found to be emitting 240 counts/min, in what year would the same sample be found to be emitting 30 counts/min? How much of the original Sr-90 would be left?

Potassium-40 has a half-life of \(1.25 \times 10^{9}\) years. How many months will it take for one-half of a \(25.0-g\) sample to disappear?

List three devices used for radiation detection and explain their operation.

Many home smoke detectors use americunium-241 as a radiation source. In the smoke detector, \({ }^{241}\) Am emits alpha particles. These alpha particles are detected by the detector unless smoke particles block their passage. Thus, as long as there are no smoke particles, the detector gets a continuous stream of alpha particles hitting it; smoke causes a disruption in this stream and activates the alarm. Write out the nuclear equation for the decay of \({ }^{241}\) Am by alpha emission.

The curie is equal to \(3.7 \times 10^{10}\) disintegration/sec, and the becquerel is equivalent to just 1 disintegration/sec. Suppose a hospital has a 150 -g radioactive source with an activity of \(1.24 \mathrm{Ci}\). What is its activity in becquerels?

Potassium-42 is used to locate brain tumors. Its half-life is \(12.5\) hours. Starting with \(15.4 \mathrm{mg}\), what fraction will remain after 100 hours? If it was necessary to have at least \(1 \mu \mathrm{g}\) for a particular procedure, could you hold the original sample for 200 hours before using it?