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Unformatted text preview: Introductory Lab: Poisson Statistics Experiments in Modern Physics (P451) In this experiment we will explore the statistics of random events in physical measurements. The random events used in this study will be pulses from a scintillation detector exposed to a radioactive source. We will practice generating and fitting histograms and discuss both the 2 and maximum likelihood methods of estimating fit parameters. This experiment is adapted from a similar one at MIT [1]. Additional information about scintillation counters and Poisson statistics is available in Refs. [2, 3] and should be reviewed before beginning work on the lab. Introduction A sequence of independent random events is one in which the occurrence of any event has no effect on the occurrence of any other. One example is simple radioactive decay such as the emission of 663 keV photons by a sample of 137 Cs. In contrast, the fissions of nuclei in a critical mass of 235 U are correlated events in a chain reaction in which the outcome of each event, the number of neutrons released, affects the outcome of subsequent events. A continuous random process is said to be steady state with mean rate if lim T X T = , (1) where X is the number of events accumulated in time T . How can one judge whether a certain process does, indeed, have a rate that is steady on time scales of the experiment itself? The only way is to make repeated measurements of the number of counts x i in time intervals t i and determine whether there is a trend in the successive values of...
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This document was uploaded on 01/20/2012.
 Fall '09

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