Physics307L:People/Mondragon/Notebook/071003
Poisson distribution
This is an exercise in dealing with data that tends to fall into a Poisson distribution
Lab equipment and setup
The scintillator and PMT are one unit. It looks like a large flashlight. The scintillator is a large Thallium doped Sodium Iodide crystal in the wider end of the detector device. What the scintilator does is emit a pulse of ultraviolet light every time it absorbs high energy electromagnetic or particle radiation. Read more about scintillators and scintillation. The burst of UV light has an energy roughly proportional to the energy of whatever radiation the scintilator absorbed, but this isn't important in this experiment.
The PMT is on the other end of the detector. Read about Photomultiplier tubes. The PMT will produce a current roughly proportional to the energy of the ultraviolet light falling on its photocathode. How proportional and by what proportion aren't of much importance here either, since we are using the device to count events, not to measure their energy. The PMT needs a high voltage power source to turn the pulses of light hitting its photocathode into currents, usually in the range of 1000V to 2000V. Increased voltage usually corresponds to increased sensitivity. The point of this exercise is to find what the probability of distribution function of an unlikely event looks like, so throughout the experiment, use a voltage of 1000V. To further decrease the number of events detected, keep the detector in a cavity formed by lead brick
final graph
Shows the Probability distribution function as is drifts from a Poisson distribution of a rarely occuring event to the more familiar Gaussian
