Question

Review | Constants Periodic Table In the parts that follow, use the following abbreviations for time If a substance is radioactive, this means that the nucleus is unstable and will therefore decay by any number of processes (alpha decay, beta decay, etc.). The decay of radioactive elements follows first-order kinetics. Therefore, the rate of decay can be described by the same integrated rate equations and half-life equations that are used to describe the rate of first-order chemical reactions: Measure of time Units of time minutes min hours h days d At In Αρ =-kt years ут and ti/2 = 0.693 k 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. counts after 72.4 minutes, what is the half-life of this substance? Express your answer with the appropriate units. where Ao is the initial amount or activity, At is the amount or activity at time t, and k is the rate constant. By manipulation of these equations (substituting 0.693/t1/2 for k in the integrated rate equation), we can arrive at the following formula fraction remaining = A = (0.5)" where n is the number of half-lives. The equation relating the number of half-lives to time t is View Available Hint(s) μΑ ? n= t1/2 ti/2 = Value Units where t1/2 is the length of one half-life