Question

1. A rock from Australia was found to contain 0.435 g of Pb−206to every 1.00 g of U−238.

Assuming that the rock did not contain any Pb−206 at the time of its formation, how old is the rock?

Express your answer using two significant figures.

2. Plutonium-236 is an alpha emitter with a half-life of 2.86 years. How long will it take for the 1.00 mg sample of Pu−236 to decay to 0.180 mg ?

3.

a)You are using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the reading of 400. counts has diminished to 100. counts after 82.8 minutes , what is the half-life of this substance?

b) An unknown radioactive substance has a half-life of 3.20 hours . If 30.7 g of the substance is currently present, what mass A0 was present 8.00 hours ago?

c)Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 33.0 % of an Am-241 sample to decay?

d)A fossil was analyzed and determined to have a carbon-14 level that is 40 % that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil?