3 (a) - Radioactive isotopes used in cancer therapy have an "expiration date". For example, a widely used one is 60^Co, which as soon as it is produced in a nuclear reactor has an activity of 5000 Ci, but when its activity drops below 3500 Ci it is considered too weak for treatment. Imagine that you work in a hospital where one of the 60^Co fonts was produced on February 1, 2022. Can this font still be used on August 1, 2024? (Note: The half-life of the 60^Co isotope is 5271 years.)
( ) Yes
( ) No
3 (b) A source of a certain isotope with a half-life of 20s is produced at time t=0s. For this source, we can say that after 20s half of the isotopes present in the source will decay and in 40s all will decay.
( ) Real
( ) False
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