Use of Scintillator for Gamma Rays

[m-i-t-o]

Hi all, i want to ask use of scintillator. Actually what i studied that to convert highly energetic gamma rays, to visible photon we use scintillator before p.m. tube, so that photoelectric effect can occur and we get photo-electrons.
But when gamma rays interact with matter in three different ways, i.e. photo-electric effect, compton effect, pair production. Since we are getting photoelectric effect then why we need to convert it to visible photon and allow directly to incident on p.m. tube?
THANKS

 

[malawi_glenn]

We want to measure the photons electronically, and this you do by a PM tube.

But you can't mount the PM tubes everywhere on the scinitillating material, so you build *light gates* which are transparent and works as optical fibres, to lead the light into optical fibres to the PM tubes where the photons are recorded electronically.

And why you need visible light? -well do you know of any optical fibres for microwavelengths or X-rays, you tell me :-)

So you use scinitillating material which emits in the visible part of spectra, where optical fibres etc exists.