In article ,
"Martin H. Eastburn" wrote:

Not so sure - as it is a high Alpha emitter - used in Vacuum tubes for
massive currents -
with a very long lifetime. TH 232 is close to the famous U 238 isolated by
1 element called Protactinium.
By the way - U is an alpha source also.

The half-life of Thorium is something like ten billion years, so the
radiation is very dilute -- every so often, a thorium nucleus goes POP.


The Alpha emitters can cause eye damage. You state it was all a mental illness.
I think that was bad science running rough shod over victims. Just like
agent orange and .....

I don't know how one would achieve eye damage with thorium-bearing
glass. I suppose one could hold the lens against one's eye for a
million years. But the thorium-bearing lenses were typically used only
within the optical system, because this glass was too easily scratched.

Cosmic rays are by far the larger radiation source. If one flys from LA
to NYC, being above most of the atmosphere and its shielding, one gets a
100 milliREM dose, about the same as from a dental X-Ray.

Fear of radiation from thorium-bearing glass lenses in an optical
instrument is therefore a mental issue.


The real danger was that people grinding lenses from thorium-bearing
glass for a living would ingest a lot of the dust, and would be
irradiated from within. Even that danger wasn't very large, as the dust
passes right through largely unaffected. But there are many reasons to
avoid ingesting glass dust.

Lens grinding is always done wet (using water), which already controls
the dust. One can still use thorium-bearing glass, but the required
manufacturing safety precautions and swarf disposal regulations are such
that people use other kinds of glass these days, kinds of glass that
were not available back when. I don't know if one can still buy the
thorium-bearing glass in the West. The Russians probably still make it.


Joe Gwinn



Martin

Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH & Endowment Member
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member


Joseph Gwinn wrote:
In article ,
xray wrote:


On Wed, 22 Mar 2006 20:03:09 -0600, "Martin H. Eastburn"
wrote:


The Captains and near - would be able to see better
with the radioactive lenses.

Any logical explanation for why radioactive glass (I presume thats where
the radioactivity was) would be better optically? Seems odd. The
radioactivity can't matter by itself can it?


Thorium oxide based glasses have a very different combination of
refractive index and dispersion than other glasses available at the
time, allowing better correction of optical abberations.

Thorium is only very slightly radioactive, and the health problems were
psychosomatic, not physical, for users of the resulting optical systems.
Manufacturers had to be more careful, as they were exposed to the dust
resulting from grinding lenses.

Joe Gwinn

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