1. what is meant by half-life?

the time for a radioactive sample to reduce to half of its radioactivity.
the time for half of a radioactive sample to decay into new substances.
the time for a radioactive sample to reduce to half of its original mass.
the time for half of a radioactive sample to lose its radioactivity.

4. the isotope uranium-232 has a half-life of 68.9 years. how long will it take for 60% (n/n0 = 0.60) of the original sample to decay?

5.8 years
50.8 years
93.5 years
407 years

5. the isotope barium-133 has a half-life of 10.51 years. of a 10 kg sample, how much will remain after 50 years?

0.37kg
4.53kg
8.64kg
270kg
6. a piece of bone from a horse found in an archaeological site is dated using carbon-14 dating. it is found that the bone has 78% of the carbon-14 that it would have when the horse was alive. approximately how long ago did the horse die?

900 years ago
2,000 years ago
14,100 years ago
35,800 years ago
7. at an physics research facility 0.0027 kg of a new isotope is made in an atomic collider. after 6 seconds, 0.00147 kg remain. what is the half-life of the isotope?

0.25 seconds
5.26 seconds
6.84 seconds
500 seconds