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On Mar 8, 2021, at 10:05 PM, Ed Breya via groups.io <edbreya@...> wrote:

?Steve said: "Thoriated magnesium was even used in the Apollo program..."

Huh, I have never heard of that before. What did thoriating do for the Mg?

Ed

On 09 March 2021 at 18:11 stevenhorii <sonodocsch@...> wrote:


Thoriated magnesium was even used in the Apollo program. The frames of the
computers (CM and LM) and some of the other electronics were made using it.
NASA did a study of the radiation from these components and determined that
given the duration of the lunar missions, it would not be a risk. The
radiation exposure from the Van Allen belts would be higher. NASA designed
the trajectories to minimize time passing through the belts and to pass
through (or near) the less energetic area of them. I was visiting the
Kansas Cosmosphere when they received a Titan I for their collection. It
was in segments. The body segments were all stamped with "Thoriated
magnesium" so the government determined at some point to warn people.

Beryllium is very interesting stuff. Again, the Apollo spacecraft used a
lot of it. Most of the structure of the optical assemblies (sextant and
telescope in the CM, alignment telescope in the LM) were made of beryllium
because of the light weight and high rigidity. The inertial measurement
unit had a beryllium stable member into which the gyros and accelerometers
were bolted. The mirrors in the sextant and LM telescope were also made of
beryllium. It was nickel plated, then aluminized for the reflective
surfaces. A company called Speedring made most of these parts - they had
the facility to machine beryllium without causing berylliosis among the
workers (or the people in neighboring areas!)

Beryllium is not toxic in the same way that say, arsenic is toxic. What it
does is to cause a severe allergic reaction in the lungs which leads to
severe chronic lung disease. If enough dust is breathed in, there is a form
of acute beryllium toxicity which produces a chemical pneumonia. If you get
a sliver of beryllium, you develop a localized allergic reaction to it. So
it is poisonous in the sense that it will kill you but not like cyanide or
other toxins that immediately affect your metabolism.

I don't know when they started making beryllium oxide parts pink, but the
manufacturers did. The early BeO parts were white and looked like aluminum
oxide. Dust from those would also be toxic. I once contacted a surplus
seller because they had insulators listed in their catalog. The photo
showed them to be pink and they were designed as heat conductor/insulators
for high-power transistors. I warned them that these were made of BeO and
at the least, they should warn purchasers about them. They pulled them from
the catalog. I also was in a scrap yard and they had these huge tubes -
maybe 12 feet long and 6 inches in diameter - that were all white ceramic.
They had a tag that said they were beryllium oxide. I've no idea what they
were for. I'd never seen any BeO parts that large. I warned the surplus
dealer about them - he didn't know. But he knew of someone who would buy
them as beryllium scrap so he did not do his usual thing with stuff he
could not identify and smash or cut it up.

I don't recall seeing any BeO insulators in Tek stuff. I think there were
some silicone ones or in early stuff, mica ones. I am pretty sure that the
500-series scopes with the ceramic terminal strips used aluminum oxide or
porcelain for them. Maybe someone in this group knows. I doubt they were
beryllium oxide.

As a radiologist, I've seen chest x-rays of people with berylliosis and
also asbestosis. The Philadelphia Navy Yard had a lot of people exposed to
asbestos and there were a couple of aerospace companies that used beryllium
parts, but I don't know that they machined the parts in-house. Both are
very nasty diseases.

Steve Horii





On Mon, Mar 8, 2021 at 7:45 PM Ed Breya via groups.io <edbreya=
[email protected]> wrote:

Steve, you may be thinking of beryllium alloyed with magnesium. Many
structural and precision mechanical parts were made with Be in the old
days, for light weight and strength. Be particles can be highly toxic if
inhaled. Same with things containing it, like the alloys and BeO ceramics.
It's still used today, but only where essential, like Be X-ray tube windows
(transparent), and BeO for very high thermal conductivity - although newer,
better, less toxic things have emerged, offering more choices in critical
thermal applications. If you have any microwave gear, you may find it
interesting that the tiny YIG spheres in YTOs and such, are typically
mounted on tiny BeO rods.

As far as I recall, the only things in electronics with thorium are
thoriated-tungsten in high power and other special tubes, and TIG welding
electrodes. The old lantern mantles with Th do indeed make handy sources,
but need proper safe handling.

I think the common indirectly heated tubes we normally see use a nickel
cathode sleeve with zirconia and maybe barium coating. The tungsten heater
wire inside is similarly coated for insulation, but also forms a rectifier
from it to the cathode, so the H-K bias voltage and leakage is a
consideration for operation.

Ed

I have a fair number of items with asset tags from SRI, Lawrence Livermore, Ampex, Nasa, etc.? I really hate tags all over front panels, and usually remove them, but will leave them if they are interesting.? It's also interesting to see the variation in marking- from crude etching to fabric tags, decals and aluminum plates.
-Dave
On Monday, March 8, 2021, 07:12:28 PM PST, Sean Turner <[email protected]> wrote:
I have a lot of interesting property tags on stuff, from all over. Naval Underwater Systems Center (doesn't exist anymore, absorbed into something else), LANL, Sandia, Boeing, IBM, Bendix Kansas City Division, Eitel-McCullough (aka Eimac, a Type CA plug in), and probably more I can't remember,

It's interesting to ponder what the gear did in it's prior life for sure...

Sean

Unbroken, the vacuum tubes with thoriated cathodes would not be a problem.
The government made things worse by having them smashed. But the government
also sold off Bomarc Missile surplus years ago without warning that the
structural parts were thoriated magnesium. A scrap metal dealer supposedly
died after cutting the missile chassis apart with a grinder. However,
though I heard this story from a couple of scrap metal dealers, one also
mentioned that he was also a heavy smoker so any inhaled thoriated
magnesium dust or radon was not likely the main cause of his undoing.

WW II aircraft instruments with radium-painted dials were also sold off as
surplus. Many of the WW II sextants also had radium paint around the bubble
chambers for a "backup" if the electric illumination failed. These sextants
and aircraft instruments still turn up. People make the mistake of thinking
that if the instrument face does not glow in the dark that it is safe. It
is not. The radium is still plenty radioactive - the phosphor mixed with it
quits glowing (oxidation?) I buy a lot of surplus electronics and I keep a
survey meter around to check things.

Ionization smoke detectors have small amounts of 241Americium, but about 1
microcurie. Not particularly hazardous and they can apparently either be
simply thrown in the trash or (if your county has one) a disposal facility.
So far as I know, they are not handled like radioactive waste.

I don't know of any radiation hazard from Tek scopes. I suspect that any
x-rays produced by the beam and the faceplates are minimal.

Steve Horii

Chuck is absolutely right. The amount of thorium in a cathode is vanishingly small — it is used to lower the work function at the surface of the tungsten, and is typically present in concentrations measured below tenths of a percent, if memory serves.

It is relevant to note that tungsten cathodes are not used in CRTs (nor in modern receiving tubes). Those, as far as I know, are all indirectly heated. No thorium. They use cathodes of barium/strontium oxide.

Lantern mantles of old were full of thorium. Those were great for testing Geiger counters. Modern mantles are thorium free. I did not know this until I told a friend he could test his ionization detector with a mantle. He was disappointed.

—罢辞尘