Question

In the parts that follow, use the following abbreviations for time:

Measure of time	Units of time
minutes	min
hours	h
days	d
years	yr

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 93.0 minutes , what is the half-life of this substance? Express your answer with the appropriate units.

t(1/2) = ______

b) An unknown radioactive substance has a half-life of 3.20 hours . If 17.1 g of the substance is currently present, what mass A0 was present 8.00 hours ago? Express your answer with the appropriate units.

A(0) = ______

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 40.0 % of an Am-241 sample to decay? Express your answer with the appropriate units.

t = ______

d) A fossil was analyzed and determined to have a carbon-14 level that is 50 % that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil? Express your answer with the appropriate units.

t = ______