- Fast neutrons are thermalized.
- Thermal neutron capture by 6Li
- Alpha particle and Tritium atom produced
- Triton excites Ce 3+ ion.
- Ce 3+ fluoresces and visible photons transmitted through fiber to PMT.
The bulk composition of the high soda glass incorporates large weight fractions of both 6Li and Ce. How does the scintillating glass fiber technology work? The physics of the interaction begin with moderation of the neutrons. The 6Li atom has a large cross-section for thermal neutrons. Thermalization can occur anywhere from the neutron source, typically Pu atoms, to the detector. A good neutron moderator to maximize Thermalization before the neutron reaches the glass fiber usually surrounds the sensors.
Once a neutron is incident on the fibers, there is nearly 50% efficiency for its interaction within the glass. A 6Li atom absorbs the thermal neutron and the reaction products include a Tritium ion and an alpha particle. Although the range of alpha particles is small, there is a high probability that the alpha particle will interact with a Ce atom in the glass causing one of its electrons to be raised to an excited state. The de-excitation of the Ce atom’s electron to a ground state results in the emission of visible light, a fluorescence event.
The light is guided down the fiber until its interacts with one of the sensors photo-multiplier tubes. Scintillation can also result from gamma rays that produce energetic photoelectrons in the glass.