scintillation counter
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Introduction
An instrument used to quantify radioactivity.
Principle
When gamma rays or ionizing particles are absorbed by a scintillator, a pulse of visible or near UV light is emitted. The light is then detected by a photomultiplier tube either directly or internally through a reflecting optic fiber.
- used to detect gamma-radiation
- NaI crystal with 1% thallium are used
- gamma rays excite iodine
- UV emission results from relaxation of excited iodine
- thallium absorbs UV radiation
- visible or near UV emission results from relaxation of excited thallium
Liquid scintillation
- used to detect beta particles
- a sample is suspended in a solution of 'cocktail' consisting of:
- a solvent such as toluene
- a primary scintillator such as 2,5-diphenyloxazole (PPO)
- a secondary scintillation such as 2,2'-p-phenylenebis- (5-phenyloxazole) or POPOP
- beta particles from the radioactive sample ionize the primary scintillator
- the secondary scintillator absorbs photons emitted by the primary scintillator & re-emits then at a longer wavelength
- the secondary scintillator facilitates more efficient energy transmission from the beta particles (i.e. reduces quenching)
More general terms
Additional terms
References
- ↑ Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 70