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The DT-590 Plutonium Probe is part of a military PDR-56F
RADIAC set and is available as a separate part from time to time, and from Lee Frank @ Surplusstuff.
RADIAC set and is available as a separate part from time to time, and from Lee Frank @ Surplusstuff.
The scintillator crystal that comes in the '590A is a very thin one, made
for low energy X-Rays only, as from Pu-239. Since we don't have a lot of
need for a Plutonium detector in these parts, it was decided to make this sturdily made probe into
a more or less standard medium and high energy detector.
As the project developed, it became obvious that this probe case and PMT could be used with a multitude of different crystals, for testing
and actual radiation detection use.
As mentioned, the original crystal is only 1/8" thick at most, but there is
room for at least a 2" long crystal if the small un-needed circuit board is first
removed from the housing. Rewiring the base to a standard 950+ single coax
feed like we use on all our probes was easy, and a BNC was added to the rear
cap, once the handle fitting there was removed on the lathe ( a hacksaw will suffice). Removing the original RADIAC
room for at least a 2" long crystal if the small un-needed circuit board is first
removed from the housing. Rewiring the base to a standard 950+ single coax
feed like we use on all our probes was easy, and a BNC was added to the rear
cap, once the handle fitting there was removed on the lathe ( a hacksaw will suffice). Removing the original RADIAC
electrical connections left a hole on the side, which was covered with a small metal plate attached with black epoxy. Be sure to use a light tight cover here.
Inside the original probe is a circuit board which contains preamplification and energy discrimination functions that we do not need.
By removing the circuit board, space is made for different thickness crystals with the original total overall length retained by the use of blank spacer plates in its place.
Also on the lathe we turned the square block of plastic scintillator into a cylindrical shape, being
careful not to scar up the polished ends. Turning the scintillator plastic
on a lathe is very similar to any Plexiglas type product, you just have to
use a sharp tool, and keep the speed low so friction doesn't melt the
plastic and mess up your work.
Once the final shape was achieved, the thing went together just as if it had
been designed that way from the beginning.
The front cap already had a metal screen "window" so I decided to add a nice
Zinc Sulfide alpha screen at the very front of the plastic, hoping that the
light generated by it would go through the plastic Gamma scintillator as if
it were a light pipe. Works just fine. A thin Mylar light shield is
installed just behind the metal screen. This crystal now provides
alpha-beta-gamma-X-Ray detection like the expensive ones being sold on ePay, at less than $100 USD investment.
I might add that this article was first published 5 or 6 years ago, being the very first "Universal Probe" anywhere.
Basically I wanted to report the project to stimulate ideas for others who may have one of these "X-Ray Probes".
Not only is it an excellent working probe, it makes a great test bed for experimental work with various crystals.
Since the original project, all sorts of crystals have been used in this rig including the super dense BGO and BaF2.
References:
PMT Data Sheet:
Original PC Card-
Layout:
Schematic:
Original Probe Mechanical Drawing:
Radiac Set AN/PDR 56F Manual:
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