# AP Statistics Curriculum 2007 Limits Norm2Poisson

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[[Image: SOCR_Activities_ExploreDistributions_Christou_figure11.jpg|600px]]
[[Image: SOCR_Activities_ExploreDistributions_Christou_figure11.jpg|600px]]

### Applications: Positron Emission Tomography

The physics of positron emission tomography (PET) provides evidence that the Poisson distribution model may be used to study the process of radioactive decay using positron emission. As tracer isotopes decay, they give off positively charged electrons which collide with negatively charged electrons the result of which (by the law of preservation of energy) is one or a pair of photons emitted at the annihilation point in space and detected by photo-multiplying tubes surrounding the imaged object (e.g., a human body part like the brain). The (large) number of arrivals at each detector is a Poisson process, which can be approximated by Normal distribution, as described above. This figure shows the schematics of the PET imaging technique.