Although our sources aren't very active, it is best to develop good safety habits concerning radioactivity. Use tongs when handling the sources. Make sure that the souces are kept in a shielded location. Also, lead is very bad for your health, wash your hands after touching the lead.

In the sciences we often use the Gaussian distribution (this is also known as the "Normal" distribution). However, not all natural processes follow this distribution. Radioactivity is governed by the Poisson distribution. In fact, the Poisson will apply to any situation where you are measuring a number of events with an average rate where the events are independent.

The fuction describing the Poisson distribution has two variables, λ and k. λ is the expected (average) number of events that would occur in the given time period, and k is the number of events we are interested in seeing. In other words, if λ was equal to 5 and k was equal to seven, the Poisson fuction would give us the probabilty of seeing 7 events when the average number is only five.

Mathematically:
P(λ,k) = (1/k!) (e^-λ) (λ^k)

In terms of the numbers we used before, this reduces to:
P(5,7) = (1/5040) (e^-5) (5⁷) = 0.1044

In other words, 10.44% of the trials will have seven events.
A chart for five expected events is given below:

Today's lab will consist of taking many data points. Get a beta emitter and position it so that a few (0-4) counts are detected per second. Proceed to take 1500 one-second measurements. Plots these results and compare them to the Poisson prediction. Note that the final value of lambda will be known only after the experiment has been completed.

In addition, keep a running total of counts for each 20 trials (in other words, not only should you be taking data in one-second intervals, also record for twenty-second intervals). Compare these results to Poisson, but also to what a Gaussian distribution would predict. Note that with large numbers, the Poisson (and most other distributions) should roughly converge to Gaussian. Come to class with a formula that will generate a Gaussian curve based upon the mean and standard deviation that you will determine from your data.

It is worth spending a few minutes with your lab partners discussing how data collection will work in this lab. Partners who do this well finish in a much shorter time than others. Also, this lab is typically done in groups of three. A careful assignment of roles can be critical.