Scintillation Counters and Multichannel Analyzers (MCAs)

The Precision Radiation Instrument (PRI) Model 111B “Deluxe Scintillator” was one of the earliest commercial NaI survey meters and, like most of the company’s instruments, it employed an eye-catching chromed finish.  The PRI 111B’s main specifications are:

Detector:      1.5” x 1”NaI crystal.

Range:          0 – 0.025, 0 – 0.05, 0 – 0.25, 0 – 0.5, 0 – 2.5 and 0 – 5 mR/h

Batteries:      four 1.5 volt flashlight batteries, two 22.5 volt batteries and two 67.5 volt

Price:            $495.00 new in 1954, $300 to $500 on eBay in 2005

 

 

Restoring a Precision Radiation Instrument (PRI) Model 111B “Deluxe Scintillator”

David Prutchi’s Mod of the DT-590A/PDR-56 “X-Ray” Probe into a Scintillation Counter and MCA Probe

◄  The Radiac Set, AN/PDR-56 is a portable scintillation type instrument used for detection of alpha contamination. The system includes a large and small interchangeable probe with a probe extension. The AN/PDR-65/65A system measures gamma intensities to 10,000  cGy/hr; and records cumulative doses to 9,999 cGy/hr.  I do not have the Am-141 checksource.

◄  The AN/PDR-56 has been replaced by the AN/PDR-77, which resulted in many new scintillation probes to be placed in the surplus market.

In addition to emitting 5.1 MeV alpha particles, the element Plutonium-239 also emits gamma rays in the energy range of 14 to 21 keV. Because these gamma rays are more penetrating than the alpha particles, they travel further in matter and air and can be detected at further distances from the ground. The “x-ray” probe for the AN/PDR-56 uses a CaF2(Eu) scintillator/photomultiplier combination to detect the 14-21 keV gammas from Pu-239. The photomultiplier tube fits into a tube socket with a voltage divider network to supply the dynode voltages. A mu-metal shield surrounds the phototube to protect it from gain changes due to stray magnetic fields or from changes in orientation with respect to the earth’s magnetic field. The x-ray probe is an assembly which includes the amplifier-discriminator circuits integral to the phototube scintillator housing. The discriminator is a single channel analyzer adjusted to detect Pu-239 gamma rays.

 

CLICK HERE for the complete maintenance manual (including schematics) for the PDR-56

◄  Coming soon:  Modifying the DT-590A/PDR-56 “X-Ray” Probe into a Scintillation Counter and MCA Probe

David Prutchi’s Scintillation Crystal / PMT Evaluation Setup

David Prutchi’s Home-Brewed Multichannel Analyzer (MCA)

◄  Current state of my PIC-based portable MCA.  The pulse processing and peak-detection circuit is shown at the bottom.  A PIC applications development board is my breadboard platform.  Spectra are displayed on a Scott Edwards Electronics graphics LCD.  I’ll post schematics when the system is debugged.  Keep an eye on this page!

David Prutchi’s Mod of the CD V-700 Survey Meter for Scintillator Operation

◄  My “CDV-700 Pro” can be connected  either to a 900V Geiger Mueller tube or to a 900V or 1200V photomultiplier-based scintillation probe. The CDV-700 Pro has an internal preamplifier which makes it possible to detect low-amplitude pulses related to low-energy gamma interactions with the scintillation crystal.

 

CLICK HERE to go to my CD V-700 mods page

◄  In my home-brew scintillation probe, a surplus 8” long x 2” dia NaI(Tl) crystal is coupled to a Photonis XP2102 photomultiplier tube. The complete assembly is wrapped in optical-black cloth and placed inside a thick cardboard tube closed using PVC caps. CLICK HERE for Schematic [PDF], CLICK HERE [3MB PDF] for detailed instructions.

CLICK HERE for pictures of my restored PRI 111-B

CLICK HERE for PRI 111B repair by Allyn Goshy's

CLICK HERE for a source of NaI(Tl) crystals - Contact Dr. Ival Toepke at Radiation Sensors.  They do sell to hobbyists.

CLICK HERE for instructions on replacing the batteries using a DC/DC converter

CLICK HERE for the schematic diagram for the PRI 111B

CLICK HERE for data on the type 6199 end-viewing, 1 1/2 inch diameter, 10-stage photomultiplier tube used in the PRI-111B

CLICK HERE for a source of PMT replacements:  Sphere Research Corporation

CLICK HERE for data on the CK526 pentode tube

CLICK HERE for data on the 6007 radiation-cooled pentode tube

CLICK HERE for data on the 5841 gas regulator tube

© 2005 David Prutchi.  All rights reserved.

◄  My 1” disc check sources (from top right, clockwise): 10uCi Cs-137, PMI checksource, 0.1uCi Sr-90, 1uCi Ba-133, 1uCi Eu-152, 1uCi Co-60.  Center: a GeoElectronics thorium mantle.  These are all legal to have without a license!

Radioactive Sources