1. Radioactivity B. Sc. -III Feb. -2017 Dr. Wagh G. S. M. Sc. M. Phil. Ph
Radioactivity B.Sc. -III Feb Dr. Wagh G.S. M. Sc. M. Phil. Ph. D.

2. Detection and Measurement of Nuclear Radiation 1
Detection and Measurement of Nuclear Radiation 1. Scintillation Detectors 2. Geiger Muller (G.M.) Counter
CANBERRA; Scintillation Detectors
A gamma ray interacting with a scintillator produces a pulse of light, which is
converted to an electric pulse by a photomultiplier tube. The photomultiplier
consists of a photocathode, a focusing electrode and 10 or more dynodes
that multiply the number of electrons striking them several times each. The
anode and dynodes are biased by a chain of resistors typically located in a
plug-on tube base assembly. Complete assemblies including scintillator and
photomultiplier tube are commercially availabl.
The properties of scintillation material required for good detectors are
transparency, availability in large size, and large light output proportional to
gamma ray energy. Relatively few materials have good properties for
detectors. Thallium activated NaI and CsI crystals are commonly used, as
well as a wide variety of plastics. NaI is the dominant material for gamma
detection because it provides good gamma ray resolution and is economical.
However, plastics have much faster pulse light decay and find use in timing
applications, even though they often offer little or no energy resolution.

3. Scintillators Emit light when irradiated Can be promptly (<10-8s)
fluorescence
delayed (>10-8s)
phosphorescence
Can be
liquid
solid
gas
organic
inorganic

8. Cutaway diagram of solid-fluor scintillation detector
Photocathode
Scintillation
event
Photomultiplier tube
Gamma ray
Dynodes
Photoelectrons
Fluor crystal NaI (Tl)
Reflector housing

10. Advantages 1. Scintillation Counter simple to operate 2
Advantages 1.Scintillation Counter simple to operate 2.High sensitivity to all ionizing radiation 3.for alpha and used in gamma ray spectrometer 4.Fast counting rate

19. Disadvantages: 1. Gamma radiation can not be detected 2
Disadvantages: 1.Gamma radiation can not be detected 2.Counter is slow 3. For alpha and Beta voltage used is different hence separate G.M. is required

20. Thanks