Info about probe

[Zagros]

Hello I recently purchased this probe for few pounds on eBay:
[broken link removed - Steven]

Anyone can give me infos about it?
Thank you

[iRad]

Nice find, an odd one for sure. It appears to be a 3" diameter NaI(Tl) crystal with WELL in center and probably a 1-1/8" PMT (maybe a Hamamatsu R6095 or similar) attached to the side of the crystal (D style coupling with a section of rounded part of the crystal flattened for PMT attachment). Of course the voltage divider is on-board, some testing may give approximate resistance. Although the pictures are a bit blurry, it's appears to be setup for simple single coax connection, maybe a LIMO connector. Very cool detector...

[Zagros]

The label reports:
Quartz& Silice Holland BV

Harshaw scintillation Crystal

12SF3M/1.1B-X3.

[iRad]

Of course... The model number gave me all sorts of information about its configuration.
A user here named Luuk used to work for Harshaw, and now Scionix Holland. He may know more about the detector and its design use.

[luuk]

Hi Zagros,
I can tell you that the detector is built around 1991/1992 so almost 30 years old, there are several hundreds of these detector build in that time.
The crystal is 3” in diameter the thickness is only 3mm and the hole is around 28mm, there is a lightguide mounted to connect the 1” pmt that is mounted under an angle with the crystal.
There is a single connection vd mounted on the pmt so it can only work on Positive high voltage!
If remember well the connector is a pet type.
I remember well it was used in the British army, use as bomb detectors when mounted on a stick they were used e.g. to detect under a car.
But not sure what exactly they expect to detect with it.
Hope this info help you a little.
Luuk

[iRad]

I figured you would know more... :)

[Zagros]

Hi Luuk I ‘ve had no doubt you were the only guy that could gave me info.
3mm thickness : this is the reason I cannot obtain a spectrum of cs137!
The detector is working : it give good cps response also with weak sources.
But if the Crystal is so thin: what’ the center hole for?

[luuk]

Hi Zagros,
Well it slowly pops up in my memory again, it has been a long time ago and I do forget things.
It was used with a radioactive source mounted in the center of the detector the source was collimated so that the radiation went 180 Degrees away from the detector .
Then the detector detected the backscattering from material in front of the detector when “hidden” material e.g. an explosive such as Semtex or other “plastic” explosives they contain lots of hydrogen that will give a different backscattering signal then when there is no hidden material.
It is a well known technic also used to detected drugs hidden in e.g. car doors.
Not sure what energy of source they used that I cannot remember, sorry!
Luuk