[LargeFormat] Re: radioactive glass

[philip Lambert]

I found this on the net:
About radio-active optics....  XX wrote:
>
>>I was recently informed that Aero Ektar lenses are radioactive
>>to the tune of 1 Mr per hour. Is this significant? If so, why would
>>the lenses be radioactive?
>
>  They contain some Thorium glass which is slightly radioactive.
>Someone here once reported actually detecting this with a radiation
>counter. It is not supposed to radiate any significant level.
>  The Thorium glass is also supposed to be a little unstable,
>yellowing a little with age. This is meaningless in an aerial lens
>which is typically used with a yellow filter anyway.
>  The Thorium glass had some desirable characteristic for getting the
>optical performance wanted from these lenses and they were not
>intended to have a long lifetime. However, there are a lot of Aero
>Ektars around and they seem to be holding up just fine:-)


Thorium is easily detectable with a 'beta' counter.  I work in a nuclear
power plant and made the mistake of taking a 'newer' 35 F2.0 leica summicron
into the power block last winter.  Everything coming out of the power block
is scanned for radiation and the assumption is if it is radioactive it was
dosed in the power block.  It almost went to a rad waste dump.  However with
a lot of work I was able to convince them the radioactivity was fixed and a
product of manufacture (some articles from the Leica historical magazine
helped).

IMHO (and the people whose job is to protect me from radiation on a daily
basis) the level was inconsequetional.  Somewhere on the order of less them
n1 Mr. per hour (or 1/1000 of a rem).  If you have a lens putting out 1 rem
an hour you better find the number for the NRC and call them immediately.
Sounds like Chernobyl.


The lens illustrations were missing from my email; did anybody get them
intact? If you want an informal test put the lens overnight on a sheet of
5x4 film in a light-tight black plastic wrapper. If on development the film
has been fogged by the lens there is probably a good case for investigating
its radioactivity level. In the meantime don't carry it in your pocket. I
did think it was lanthanum glass that was radioactive.  My luminous watch is
said to be radioactive.  Does it matter?
Philip