Neutrons from a source under the bed are directed upwards toward the body of a subject lying on the bed. Gammas emitted by the subject are counted by detectors alongside the bed.

Neutrons interact with elements, such as nitrogen, and cause them to give off characteristic gamma rays. The gammas are produced immediately, and stop appearing as soon as the neutron source is removed. This is why the system is called a prompt gamma system.

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[Prompt gamma technique] ]theory] [process] [schematic]
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