The very underestimated problem of RADIOACTIVE lenses

[Creteil78]

On 12/3/2019 at 9:43 AM, unclean said:

Hello Folks, 

Just thought I'd spice up the talk and point out that although Thorium is only an alpha emitter, its "daughter" products are beta emitters, which require a bit more shielding than paper. 

So, when 232 Thorium decays, releases an alpha, and becomes 228 Radium (HL 5.7 years), which throws off an electron (-beta particle) to 228 Actinium. That lasts just over 6 hours and throws another -beta particle to a lighter version Thorium--228 Thorium (HL 1.9 yr). Next, you loose another alpha and create 224 Radium in 3.5 days, which you create something a bit nasty, 220 Radon (HL 55 seconds) then another alpha particle and 216 Polonium (HL .14 sec). Losing another alpha, you come to 212 Lead (HL 10.6 hr). Throwing another -b particle, you come to 212 Bismuth (HL 60 min), where the decay takes two different paths. 64% of the time--it throws a -b particle and you get 212 Polonium (HL 3 * 10^-7 seconds) and immediately heads to 208 Lead. 36% Lose an a particle and head to Thallium for ~3 minutes and then throw off another -b particle becoming 208 Lead, which is stable. This liberates 42 MeV per completed decay chain for one atom of Thorium. This is happening constantly. 

It's admittedly not a monster amount of MeV, however, it doesn't happen one at a time. The main problem is likely the discoloration of the Thorium doped lens element. I just don't like the idea that this wasn't revealed to us till later. I've seen stories of newer lenses still being doped with Thorium (something I'm planning on working on) well past the early 70's. 

Take this info for what you will. Just remember Thorium is not just an alpha emitter. 

 

 

Yep. Indeed. It's not only an alpha emitter

and there is not only Thorium, also Lanthanium or something like that

[John Matthews]

I've already heavily researched this, but could someone tell me is the a Konica Hexanon AR 57mm f/1.2 made in March of 1973 with a serial number of 75088XX-ish would have thorium? Does anyone have a lens with a later serial number they KNOW has thorium either by discoloration or having tested with a Geiger meter?

I'm not worried about it, just curious. I'm having trouble finding precise information on the topic. I find that anything Konica is difficult to find.

[John Matthews]

40 minutes ago, John Matthews said:

I've already heavily researched this, but could someone tell me is the a Konica Hexanon AR 57mm f/1.2 made in March of 1973 with a serial number of 75088XX-ish would have thorium? Does anyone have a lens with a later serial number they KNOW has thorium either by discoloration or having tested with a Geiger meter?

I'm not worried about it, just curious. I'm having trouble finding precise information on the topic. I find that anything Konica is difficult to find.

Never mind. I finally found one with a serial number 7511105 with significant yellowing according to the seller. That would mean one with a serial number lower would definitely have it too. I'm still not sure when it stopped. I'm fairly sure they made this lens into the 80s and they wouldn't have done it then. It's so easy to blow time on things like this.

[zlfan]

On 4/26/2014 at 6:18 AM, Andrew Reid said:

10 μSv is the dose everyone just got from background radiation in the last 24hrs.

 

So 1 hour of cuddling the rear element of your radioactive lens = 1 normal day living on earth.

 

Just after Fukushima I went to Japan.

 

People there over the entire year had a 1,052 μSv dose of radiation based on Tokyo's readings.

 

That is still only 2% of what the US allows workers to receive per year at work!

 

Source: http://www.blacksmithinstitute.org/blog/radiation-101-what-is-it-how-much-is-dangerous-and-how-does-fukushima-compare-to-chernobyl/

 

So say you spent 5 hours shooting with your radioactive lens per day, EVERY DAY of the year. That is still only 1825 Î¼Sv exposure and still under 5% of the total limit which is considered 'safe' by the US authorities.

I guess those friends of op want op to donate his lenses to them.

think about it. the vintage cameras and the lenses are luxury goods, sold to rich people. rich people care about their health more than poor men. 

lol.