The scintillation in organic scintillators is due to the transitions between energy levels in a single molecule. These scintillators avoid the need for a regular crystal lattice structure. In organic scintillator molecules, the energy spacing the vibrational modes is 0.15eV and between the levels S0 and S1 is 3eV. Excitation of molecule from the ground state to the higher states occurs when energy is stored in the scintillator by a charged particle. Phosphorescence is emitted when the molecule is transferred from the S1 state to the T1 state.
A bulk solvent is added to the organic scintillant at small concentrations and the mixture is exposed to ionizing radiation. Light is emitted when the energy absorbed by the solvent is transferred to the scintillant.
Liquid scintillation counting is one of the challenging applications of organic scintillators in the field of nuclear medicine. In this technique, the scintillator used is a liquid dissolved with the radioactive sample to be assayed. The activity of low energy β-emitting radionuclides like 14C and 3H can be measured using this method.
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