Scintillation Counter

From Anvita Health Wiki

Contents 1 Introduction 2 Principle 3 More General Terms 4 Additional Terms 5 References

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.
  
• Crystal scintillation:

• 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 seconday 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

• laboratory instrument

Additional Terms

• scintillator

References

Clinical Diagnosis & Management by Laboratory Methods, 19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1996, pg 70

scintillation counter