Positron Annihilation with Sodium-22 (Na-22)

Detecting positrons (e⁺) is easy with the cosmic ray detector setup. Well, actually we do not detect the positron itself, but the gamma rays (gamma radiation) when it annihilates with an electron (e^-) of surrounding matter.

The gamma's are emitted in opposite directions (180 degrees), so our setup is very well suited. In the illustration on the right you see one positron emitted by the Sodium-22 (Na-22) disc source, which hits an electron and annihilates by emitting 2 gamma rays (511 keV signature) in opposite directions (180 degrees).

Sodium-22 (Na-22) is well suited, because it emits good amounts of positrons (radioactive beta⁺ decay).
Since the system is also exposed to atmospheric muons, take some measurements without the positron source inbetween. You then know the "idle-count-rate" - place the test disc between the two detectors and compare the new count rate to the average value you got when it was "idle".

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