Ludlum Model 3 with scintillation detectors

Building the biggest scintillation detector

Fortunately I was able to get my hands on a gigantic NaI(Tl) detector. The crystal inside is 3″ by 8″ which is 76mm in diameter and 203mm in length. It weights about six kilograms (12 pounds). The crystal is made by Bicron and I bought it from Albuquerque, New Mexico.

My small 2″ x 2″ detector reads at about 5.000 CPM at backround levels. This big crystal is expected to generate more than 30.000 CPM in the same conditions.

As a PMT I will be using the well known Philips XP3312.

Philips XP3312 Photomultiplier tube
Philips Photons XP3312 Photomultipliers

The default breakout PCB had to be desoldered with a little effort. Paint thinner proved to be effective in removing the red coating on the PCB. Many think this is is a voltage divider, but it is actually not. Thers is only a filtering circuit and male headers to take the voltage divider. Most likely the signal is fed through the coaxial output.

The scintillator coupled to the PMT
Finished probe with Ludlum Mod 3 and one of my other probes as comparison