Transcript ykleeShtalk.ppt

Gamma Rays
•Definition: Photons with high energy (>0.01 MeV) emitted during
nuclear transitions
•Fusion: Nuclei fuse together
•2H + 1H
3He
+ gamma ray
•Fission: Split nucleus by collision with high speed neutron
•238U + n
239U+
gamma ray
•Gamma Decay: Nucleus decays from unstable energy state to
lower, more stable energy state
Gamma Rays
•Interaction with matter:
•Photoelectric Effect:
•Energy of gamma ray totally transferred to orbiting
electron and ejects electron from atom
•Compton Scattering:
•Part of energy of gamma ray transferred to orbiting
electron, ejects electron from atom and remaining energy
leaves as new lower energy gamma ray
•Pair Production:
•Energy of gamma ray converted into mass of electronpositron pair, excess energy appears as kinetic energy of
pair and recoiling nucleus.
Detecting Gamma Rays
•Scintillation Detectors:
•Composed of a scintillating crystal optically coupled to a
photomultiplier tube
•Crystal usually doped with an impurity
•most commonly used is NaI(Tl)
•Gamma ray interacts with crystal, emitted electron excites
activator, which decays by emitting a visible photon
Detecting Gamma Rays
• Scintillation Detectors