Re: Thoriated Tungsten vs Pure

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• Subject: Re: Thoriated Tungsten vs Pure
• From: "Edward V. Phillips" <ed-at-alumni.caltech.edu>
• Date: Sat, 28 Sep 1996 15:21:59 -0700 (PDT)

Thoriated tungsten is used for tube filaments because it hnas
has much higher emission at lower temperatures than pure tungsten,
hence lasts much longer.  Effect was discovered accidently in the
early 1920's.  Thorium was originally added to light bulb filaments
"to make them easier to draw through the wire dies" (per RCA
Vaccum Tube Design Manual, circa 1940).
Can't prove it, but suspect the radioactivity is barely detectable,
and certainly not a health hazard.
Ed Phillips

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