[Test-Equipment] Radioactive Tube Stamp (was: re: Nixie project)

[Richard Knoppow]

----- Original Message ----- 
From: <k4pf at juno.com>
To: <test-equipment at mailman.qth.net>
Sent: Saturday, July 03, 2010 7:52 AM
Subject: [Test-Equipment] Radioactive Tube Stamp (was: re: 
Nixie project)


>
>> Dave Harmon" <k6xyz at sbcglobal.net> wrote
>> I remember buying a used 30L-1 and the 811A tubes
> had a 'radio-active' stamp on them.
> I got rid of them quick.
> Don't need an environmental cleanup in the shack!
> I've never seen any other 811A's with that stamp.
> At AT&T we used some other quick firing tubes with that 
> stamp
> and we were careful not to break one of them.
>
>
>
> Hi, Dave
>
> That tube manufacturer was just being extra-cautious
> in his labeling.  All thoriated tungsten filament tubes
> such as the 811A, 572B or 3-500Z are mildly radioactive,
> due to the thorium present in the filament.
> The thorium reduces the work function of the filament
> surface, making it a more efficient electron emitter.
>
> 73,
> Ed Knobloch
>
     There are a lot of tubes with thoriated tungsten 
filaments, I think most of the Eimac triode and tetrode 
transmitting tubes have them.
     Thorium was used in some types of optical glass 
especially for aerial photography lenses during WW-2. Some 
of these had enough radiation to cause "browning" of the 
glass over a period of many years. Thorium lends some 
desirable optical qualities to the glass but it was 
discontinued after the degree of radiation was discovered. 
Some sources claim that the thorium was an accidental 
ingredient, included as an impurity particularly to 
lanthanum, but that is not the case: thorium was delibrately 
used and is included in the formulas shown in the patents 
issued to the National Bureau of Standards, where rare-earth 
optical glass was developed. Even some high-performance 
lenses for domestic rather than military use contained some 
thorium elements. I don't know what the radiation levels of 
these lenses are but I understand that the decay products of 
thorium may be more hazardous than the thorium.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com