An assortment of Radiacs

Tom Jennings, 1997
revised, 6 Feb 2000

'Radiac', or sometimes 'radiacmeter', is the generic word for radiation detection and measurement equipment, in the context of human hazard avoidance. Pocket dosimeters, hand-held, permanently-fixed, mobile and other devices are included.

I have no idea how I ended up collecting this stuff. Some of it is intrinsically interesting, some I bought to pilfer for parts (the Canadian Admiral survey meters, for instance) but once under way, I started rounding out the pile.

Pocket dosimeters

There are a number of different types of portable "pocket" dosimeters: the electrometer type, described below; portable ionization chambers, film badges, and activated glass dosimeters, such as the DT-60 described further on. Only the pocket electrometer is direct-reading, eg. dosage readable without external equipment. Very generally speaking, professionals get direct reading dosimeters, and everyone else gets film badges, etc.

The dosimeters shown below are tiny electrometers, a compact version of the ones you might remember from grade-school science; two extremely thin leafs of metal, which when charged with static electricity, repel each other and swing apart.

A pocket electrometer dosimeter uses single a 5 micron diameter quartz fiber plated with metal, on a tiny pivot, instead of two thin leafs. Inside is an equally tiny chart, calibrated (generally) in Roentgens; by holding the bottom of the dosimeter up to a bright light peering through the built-in microscope in the top you can see the fiber's current position over the chart.

Inside it works as follows: the dosimeter is first charged with an external high-voltage source (see photos 2, 3, 4, 5), which serves the same purpose as charging the school electrometer with a wool-rubbed rod; this causes the fiber to swing away; the charge is adjusted to make the fiber swing to "zero" on the calibrated chart.

Radiation (gamma rays) passing through the electrometer -- and presumably the human wearer -- dissipates some of that charge, which causes the fiber to swing back to its resting state. As more charge is dissipated by gamma energy, the more the fiber swings to the right end of the chart, indicating higher and higher dosage. (It measures accumulated dosage, since a long exposure to a weak gamma source measures the same as a brief exposure to a stronger source -- both remove the same amount of charge from the fiber.)

Pocket electrometer dosimeters in the current form have been in use at least since the late 40's. The original design was by Dr. F.R. Shonka of the Argonne National Laboratory. Here's a schematic of the innards, taken from Radiological Defense, vol. IV.

Photo 1, L to R: U.S. Civil Defense issue, Bendix #CD V-74, 0-200R, circa 1965; Civil Defense, Landsverk CD V-138, unusual 0-200 mR, ca. 1965; commercial radiacmeter, 0-200R, used at Lockheed(?), Mil. Spec. IM-93A/UD, Landsverk 4596-PP-61, date unknown; Canadian civil defense ("E.M.O.") CCD-200, 0-200R, made by Landsverk, early 60's; military issue radiacmeter IM-143/PD, date unknown, calibrated 0-600R (ouch!).

I routinely use the milliroentgen-range dosimeter in my radiation projects.

Civil Defense pocket electrometer dosimeter charger

This is more or less representative of the standard charger for pocket electrometer dosimeters, containing a transistorized high voltage source to charge the electrometer. These were in use in the early 60's.

All pocket electrometer dosimeters work in the following manner: The charging end of the dosimeter is pressed firmly onto the contact on the upper left corner of the charger. The contact is made of transparent plastic with a metal electrode in the center. Pressing down turns the charger on, and a lamp illuminates the electrometer microscope so that the operator can turn the knob on the charger, adjusting the charge placed on the electrometer to cause the fiber to swing to the "0" position.

Photo 2

Various pocket electrometer dosimeter chargers

These are physically and electrically similar to photo 2, probably all copying some original military contract or design. They differ only in the slightest details. See photo 2 for details of operation.

Photo 3, clockwise, from upper left: Canadian civil defense, Mil. Spec. PP5120/PD, made by Canadian Admiral, early 60's vintage (serviced June 66); commercial, Bendix #906-2, ca. early 60's; commercial, Landsverk Model L-136, s/n 112, early 60's.

I use a PP5120/PD to charge my milliroentgen dosimeter.

Antique pocket electrometer dosimeter charger

This Keleket Charging Unit Model K-125, s/n 237, uses an obsolete high-voltage battery instead of a transistor oscillator, though the principle of operation is the same as the others; it dates from the late 40's. This low serial-number model is probably quite old.

Photo 4

Military field electrometer dosimeter charger

Shown with its web belt carrying case, this incredibly rugged non-electronic charger contains a piezoelectric crystal and a mirrored light pipe. The dosimeter is pressed onto the charger's electrode with one hand, and the "X"-shaped knob is turned with the other, while pointing at the sun for a light source with another hand, while peering into the dosimeter. Turning the knob flexes the crystal which generates pulses of voltage to charge the dosimeter. While in principle easy to operate, it requires impressive gymnastics to actually pull off, and the light source better be full sunlight as the light pipe is not exactly efficient. Whew. But it requires no batteries, good for when you're living in a bombed-out basement, chewing dead rats and waiting for it to be safe to come out.

Photo 5

Pocket dosimeter, DT-60/PD

These are very inexpensive dosimeters worn pinned to clothing, consisting of a piece of lithium-doped glass, inside a plastic and lead container. Gamma radiation impinging on the glass "activates" certain components of the glass, which then glow extremely faintly when later illuminated with ultraviolet light; this faint glow is read by a 'Radiac Computer-Indicator', CP-95A/PD. The DT-60's have the advantage (sic) that unlike pocket electrometer dosimeters, the wearer cannot read their exposure, since it requires a CP-95A.

Photo 6, L to R: DT-60A/PD, an ordinary safety pin passes through a hole on the protrusion on the side; the square of activated glass in the lower screw-on case; the lead shield with a hole in the top half of the case.

DT-60's were made at least by Corning Glass Works and Polaroid Corp, in 1951. They are not mentioned in AFSWP 'RADIOLOGICAL DEFENSE' dated Jan 1950; I believe they were deployed first by the Navy in 1954.

NOTE: I have cornered the free world's supply of DT-60's, new wrapped in original wrapping paper, and can supply a copy of the manufacturers data sheet; willing to trade for...?

CP-95A/PD, Radiac Computer-Indicator, reads DT-60's

I do not have a CP-95A/PD Radiac Computer-Indicator, but I do have the instruction book, approval date 10 June 55; a scan of a bad photo from it is shown below. It consists of a light-tight chamber containing a UV lamp, photomultiplier tube, associated electronics (tubes) and batteries necessary to read the DT-60's.

NOTE 6 Feb 2000: I now have a CP-95, complete, but with leaky capacitors. I'll eventually get it working and put a photo here. Don't hold your breath though.

Photo 6a

U.S. Civil Defense survey meter ("geiger counter") and accessories.

This is the legendary geiger counter, issued in one form or another to Civil Defense authorities in the 50's and 60's. This is a relatively recent model, late 60's. It is transistorized (quaint word, meaning originally designed for vaccuum tube circuitry). Not spectacularly accurate, but a decent go/no-go checker.

Photo 10, clockwise, from upper left: A pocket dosimeter, described in photo 1; hang-off-the-side accessory loudspeaker for the survey meter; the dosimeter charger described in photo 2; incredibly uncomfortable headphones; the survey meter itself, with the Geiger/Mueller tube unsnapped from the handle; the Geiger/Mueller tube on its cable, with the beta-particle window open.

The survey meter also has a tiny Cesium-137 source fastened to the side for 'calibration' (eg. checking), sufficiently small to be safe to humans unless ingested or fastened to reproductive organs for extended periods.

Radiation dosage calculator

This cheerful device is a circular slide rule, a nomograph used to calculate safe dosage, based upon bomb yield, time since blast, distance, etc. It has different disks for land and sea conditions. I believe it to be Canadian military. I can't imagine this thing was more than a comfort talisman, 'cause if the commander says march, I'm sure the troops just marched, period, wearing their DT-60's. It is optimistically labelled "Radiac Calculator No. 1" (there are more?), made by BRL, Weymouth, England, ref. no. 6665-99-911-0060. It comes with a lovely plastic case in de rigeur kahki vinyl.

Photo 8

U.S. military high-range gamma counter

This scary device is simply a higher-range geiger counter in a very rugged case with a heavy duty protective canvas case, strap, and vinyl window. With a range of 0-500R/hr, I wouldn't want to be its operator in the field.

Photo 11

Photo 13: Proportional counter tube. Actually, I have two of these. They are both hand-made, steel tubes with glass seal and brass hardware, with an India inked paper label. The older of the two reads 'Mark 17 Model 13, Type N, No. V423. METALLURGICAL LAB. University of Chicago, DATE 8/26/46'. The Metallurgical Laboratory was the euphemistic name of Fermi's then-secret wartime lab, where the first uranium pile was built. This counter tube very possibly was made by the same people, since it's dated less than four years after the pile went critical, and about 14 months after the Trinity test. On some PBS documentary on the Manhattan Project, there was a rack of these exact tubes sitting on Fermi's desk!

Photo 13

The other counter tube, not shown above, is labelled 'Mark 17, Model 13, Type N, No. V225, INSTRUMENT DIVISION Argonne National Lab. DATE usa 62308'; the encoded date is somewhat inscrutable, but if '6' means 1946, '2308' may be 23 Aug. The tube was enclosed with an ancient characteristic plot of the same mark/model/number tube, dated in pencil 1949. [NOTE: A reader tells me the date code is likely a military format of YYDDD (eg. the code above means day 308 of year 62). But this isn't a military instrument; though ANL's works is mostly of military interest it's a lab, and this tube is definitely lab-made. There's the circumstantial evidence of it being in the same box with the unambiguously dated tube (further above), but it's too odd that it is physically identical, and has the 1949 graph plot attached. So the mystery remains.]

Funny enough the older tube still operates OK, even though some crud now rattles around inside.

Canadian civil defense survey meter

A very nice survey meter, of 60's design. Exact date is unknown, though it was serviced in 1973. It contains two Geiger/Mueller tubes, one for each range (high/low) and a nice cast aluminum case. They're modern enough to be quite usable today, assuming of course you have anything to measure (though if you are serious, you should buy a modern survey meter such as the Radalert.

Photo 14 "Low Range Survey Meter", Model CCD 100-10, made by Canadian Admiral Corp. Ltd., s/n 623. Range: 1-100mR/hr, .1-10R/hr.

Radiac Set AN/PDR-39A

An early hand-held survey meter. The size of a large lunch pail, it contains a half-dozen batteries of now-bizarre voltages (67-1/2V, 45V, etc, common in the late 50's/early 60's in portable radios) powering a vaccuum tube survey meter and a large-volume (2"x4"x5") ionization chamber. In fair shape, I haven't cleaned this one up or tried to operate it, and due to the battery problem, likely never will. It once contained a tiny radioactive calibration source, probably removed when decommissioned.

These were probably deployed for many years; though this is the only one I've seen, they are common in science-fiction and Civil Defense films. The design is quite nice, other than the overall bulk.

Photo 15 Radiac Set AN/PDR-39A, U.S. Army Signal Corps, s/n 2848. Range: 1-50,000 mR/hr, in 5 decades.

LASL Model 201 Integrating Dosimeter

This is a stationary, as opposed to portable, dosimeter, intended to be mounted in equipment or room. Of unknown vintage, likely 60's, of no particular import other than the incredibly cool LASLdecal: white and blue oval, an Erlenmyer flask with vapors drifting out towards a mushroom cloud with the silhouette of a bomber superimposed, and the still-current graphic of a gamma photon dislodging nuclear particles in black over the flask. Text reads: 'Los Alamos Scientific Laboratory J-11' the latter is the project title. I believe the J section was the bomb group -- excuse me, 'explosive-driven metal systems' group.

Photo 17

Photo 19, showing decal

Radiac Set AN/PDR-63

A reasonably modern radiac kit, containing a survey meter head, two detectors, headphones, etc in a foam-lined carrying case, complete with technical manual. It was last calibrated 24 May 1994, and the Navy Approval Date is 2 Apr 71. It was made by Nucor Corp, Denville NJ. The components are shown with their web-belt pouches removed.

Photo 21, AN/PDR-63 case

Photo 22, AN/PDR-63 components, clockwise from top left: more excruciating headphones; IM-226 Radiac Meter; IM-507 Low-Range detector with attached detector tube.

Photo 23, AN/PDR-63 components, clockwise from lower left: IM-508 High-Range Detector; PP-6597 Battery Charger; technical manual.

Plastic scintillator/PMT assembly

I don't know why this should be here, but questions like that will come to no good. This is one of two surplus gamma detection/spectroscopy detectors I'm using to build a 2-dimensional gamma telescope. It looks like hell because I light-sealed the welded seams with black paint.

Photo 24 Inside is a 5"x6" plastic scintillator (type unknown) with a generic RCA photomultiplier tube stuck to one end. Plastic should be OK for this application since I'm only interested in detecting the presence of high-energy (MeV) gamma photons. Or so I hope.

Boron-line Neutron Counter tube

An old, never-used, proportional counter tube used to detect neutrons. The inside of the tube is coated with boron, which generates secondary electrons when struck with neutrons. Since replaced with more efficient designs.

Photo 25, 10-B lined Neutron Counter made for AEC by General Electric, Contract #AT-(30-1)-419. tested "OK" on 27 Apr 1955.

Photo 26: NE-102 scintillation plastic

Actually fairly interesting stuff, this is pretty ordinary-looking plastic that 'scintillates' -- gives off energy in the visible range when its molecules are excited with higher energies, such as X-ray or gamma photons. It's interesting because you can see a faint violet glow inside the water-clear plastic, in bright sunlight -- though oddly, it photographs as faintly yellow, as shown here, which may be an artifact of the film processor.

Photo 26

IM-179 pocket survey meter

Of shockingly poor quality, this AF-contracted pocket survey meter is very simple -- one READ button, one TEST BUTTON, and a logarithmic scale reading .02 to 200 R/hr. Unfortunately it takes odd, unknown batteries.

The legend on the front reads: "GREEN: Travel permissible. [.02-2R/hr] AMBER: 8-10 Hours exposure permitted [2-20R/hr] RED: Take cover. Check reading every 6 hours until in green [20-200R/hr]."

Photo 27 IM-179, s/n B6755, made by Nucor (Nuclear Corp. of America), Denville NJ. AF Contract #AF 41(608)-35976.

Radalert 'Nuclear Radiation Monitor' aka survey meter

A very lovely, modern, pocket survey meter. I bought this new from Real Goods Trading Co. Inc for around $400. I use it for live-monitoring my radiation lab as well as checking surplus equipment for unpleasant surprises, and for checking environmental stuff. It has an LCD display, counts/minute and total-count modes, and an alert mode that beeps upon reaching a level set by trimpot switches. It also produces an LS TTL pulse output and accepts external power.

Photo 28 Radalert survey meter, made by International Medcom, Sebastapol CA (707)-823-7207.