FAQ - Test sources from hamfests and surplus.

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Richard Hull
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FAQ - Test sources from hamfests and surplus.

Post by Richard Hull » Tue Apr 05, 2011 3:08 pm

We have long discussed old military meters and aircraft instruments as a source of radium for gamma spec calibration and general radiation instrument testing. Based on what I have experienced recently, these are great rarities now. While they can still be found, it is only the most trained eye that scores a win on one of these. Radium, for the gamma ray spectroscopist is an ideal source having many gamma peaks due to its many daughter products. These peaks span a huge range from ~75kev up to nearly 3mev. Frankly, If I were limited to just once source for calibration and testing it would be radium. The peaks rise rapidly from the base line. Mere seconds are needed to home in on and calibrate the MCA on a favorite line.

A particularly strong U ore specimen will stand in as a substitute source for radium, albeit a bit slower in responding to pump up the needed lines. U ore is not found at hamfests, however and the following is a series of tips on sleuthing out the few remaining radium sources to be found surplus.

Radium coated dials in military instrumentation hit their peak use in WWII. This continued into the Korean war, but just did not make it much farther along the time line than that. WWI saw the first use of radium in aircraft instruments as well as army and navy time pieces and compasses. This WWI stuff is very collectable and you will not see much of this older material.

The typical instrument that you will encounter at a favorable price will be WWII radio and aircraft panel meters. These include RF ammeters, S-meters, tuning meters, amp and volt meters. These are rarely over 4-inches in diameter and most often 3-inches or smaller. The occasional oil pressure gauge or amp-meter from a large truck or jeep will be found. However, most hamfest sales are due to radio amateurs and the collected materials will most often represent something a radio amateur would use when there were real amateurs who built their own ham gear.

Most of these old builder boys are now "silent keys". The usual "Ra dial" find, now, is to be had at tables that denote "silent key estate sale to benefit the wife of W4TAP". Some younger pal of his has cleaned out the old boy's basement or shack to help the wife get the junk out and sell what he can for her benefit. His pay is "first pickins" for free or a small donation. I have had most of my recent luck at such sales tables.

The real goal is the old battered cardboard box under the table that is full of meters too strange to make the upper part of the table's meter display.

Another superlative Ra source are old aircraft toggle switches! These have "bat handles" that are glass tipped with radium underneath the glass. These switches are instantly recognized as they are not the normal, "hole and nut" mounted type. They present as a dull gray zinc or cadmium coated, rectangular metal block attached to a flat mounting plate with two female threaded screw holes. The toggle's glass tip will have a white or brownish tip.

Aircraft flight operations instruments are loaded with Ra! Among the best of these are oil pressure gauges, BDHI indicators, airspeed indicators, altimeters, turn-and-bank indicators, temperature gauges, engine rpm gauges, etc. The most incredible of these is the turn-and-bank indicators made by Bendix during WWII. These contain a monsterous load of Ra! Note, however, that all aircraft instruments are now rare and very collectable, and command collector prices. "War bird" restorers are scooping these up now and paying big money for them. What was a $10.00 old turn-and-bank in a 1993 hamfest is now a $100.00 collectable to many at antique shops.

Seeing at sight....................

Seeing at sight is an art form. Look for the following on all suspected instruments as an indicator of a "hot" item.

1. A slathered on, raised paint
2. The paint is now brown, tan or cream colored
3. The paint, when carefully examined obliquely, will appear granular or as a micro fine "sand" composite.
4. Sometimes the painted mass appears "splotchy" or lumpily discolored.
5. Instruments that have military date stamps on their bodies prior to 1954 preferably before 1950. Classic meters and instruments often have a red orange anchor or triangle with date code on the rear body.

Not radioactive, leave 'em behind.........

1. Slathered on paint that is vivid yellow or a bright, clean, yellow green. Note* many toggle switches, noted above, have greenish tipped bat handles that are not radium.
2. Instruments obviously from modern jets. (air speed over 400 knots. Turbine RPM, etc.)
3. Instruments that have mil. date stamps on them after 1955.

While all the above relates to military instruments, there are hundreds of civilian alarm clocks and time pieces extant that were manufactured with Ra dials into the mid to late 1960's! By the late 50's the radium content in all such items was reduced to save money, (reduce cost), and a true green phorphor was used that was also phosphorescent. Thus, on civilian times pieces you can be readily deceived into buying a non-radioactive 1970's Westclox "baby ben" that looks exactly like the "hot" baby ben from 1962. In this case, it is best to have a GM counter with you.

I have just relayed my 30 years of experience to you guys just about the time that the desireable instruments are disappearing. I wish you all luck. Enjoy the hunt.


Never, ever open a meter or instrument! Never, ever scrape off or disturb the dial paint!! Use the meters "as is" and keep them fully sealed. The gamma rays of interest will whistle through the face glass with ease.

For the "Nervous Nellies", a single instrument that is hermetically sealed by the Navy or Airforce is safe to keep indoors, but if you are paranoid, as nervous nellies a wont to be, put it in a poly sealed baggy or in a large jar with a lid for storage.

For the bold and OCD driven who seek to collect a number of these items for collector value, resale, etc. I would suggest not storing the instruments in your home or living space, due to radon build-up. I prefer to place the few that I have in a medium sized 50 caliber, US ammo can with its superlative rubber gasket and positve latch, then store this can in an out building not attached to the house. These cans are found at gun shows and surplus stores for about $5.00 each and are worth $100.00 for what value and service they provide.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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