Part A. You are using a Geiger counter to measure the activity of a radioactive
ID: 757743 • Letter: P
Question
Part 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. m counts after 93.1minutes , what is the half-life of this substance? Express your answer with the appropriate units. t_1/2 = _____ Part B. An unknown radioactive substance has a half-life of 3.20hours . If 37.0g of the substance is currently present, what mass A_0 was present 8.00 hours ago? Express your answer with the appropriate units. A_0 = _______ Part C Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 m years. How long will it take in years for 43.0% of an Am-241 sample to decay? Express your answer with the appropriate units. t = ________Explanation / Answer
Assumption:: radioactive decay is itself not radioactive - i.e. that the material decays to a stable isotope in one transition. The half life is the time taken for the mass of radioactive material present to fall to half of its initial value. The time given (61.9mins - I assume this is supposed to be mins) is two half lives, since in this period the rate of counts falls to 1/4 of its initial value. The half life is therefore 61.9/2 = 30.95min Answer