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 Post subject: Detecting Lab-Irradited Gemstones
PostPosted: Thu Nov 22, 2012 4:35 am 
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How to check if the stone has been irradiated by human? Can we just rely on Geiger counter? Then where can we get "radiation data sheet" in un-irradiated gems and irradiated gems as a comparison and to make conclusion?

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 Post subject: Re: Detecting Lab-Irradited Gemstones
PostPosted: Thu Nov 22, 2012 2:19 pm 
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Just buying a Geiger counter will do very little for you. A Geiger counter detects radioactivity. Just because a stone was irradiated does not make it become radioactive although this does happen in some cases.

Radiation is "added" by neutron activation when a stone is treated in a nuclear reactor and exposed to neutron flux. Some of the neutrons crash into the nuclei and generate unstable species which are then radioactive and decay with the emission of radiation. It can happen to a lesser extent from electron beam radiation when electrons make it into a nucleus and convert protons into neutrons again affecting the stability of the nucleus
(Dr. Brian?)

If the emission is alpha emission the Geiger counter is not very good at measuring it even if you use a thin window Geiger tube. An alpha counter is needed. These are pretty rare birds.

For beta and gamma emitters a scintillation detector and gamma spectrometer is a better choice because it can also give you some identification info on the emitting nuclides. A gamma spectrometer can also be hooked up to a Geiger tube. It is a more sophisticated piece of electronics to collect and analyze the data the Geiger tube or scintiillation detector puts out. Google Geiger Counter ,, Scintillation Detector,, and Gamma Spectrometer,, and MultiChannel Analyzer for more detailed explanations.

All this only tells you what the stone is doing now. You have to , by virtue of knowledge and experience know what to make of this information. The main area of use would be to tell you whether irradiated Topaz had been allowed to "cool down" long enough. It won't tell you the history of the stone. It won't tell you if its color was modified in an gamma ray beam (Cobalt 60 radiation) which does not make the stone radioactive.

There are many stones which are radioactive , above the background level in their natural state because of the presence of naturally occurring unstable isotopes of thorium and uranium and probably many others. Zircon is the best known of these.

There are some stigmata of radiation treatment that can be detected with UV VIS spectroscopy notably some radiation damage lines in diamond. To see information on that subject go to Martin Haske's website http://www.adamasgem.org/sas2000.html


http://en.wikipedia.org/wiki/Gemstone_irradiation
This page has a good bibliography of the papers on the subject. The Ashbaugh paper is the most recent and comprehensive of the ones I have looked at.

http://www.nrc.gov/reading-rm/doc-colle ... tones.html

https://www.google.com/search?source=ig ... 7iCqSvUSYk


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 Post subject: Re: Detecting Lab-Irradited Gemstones
PostPosted: Sat Nov 24, 2012 6:24 am 
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Nice reply, G4, very interesting. Thank you!

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~~~Lennie~~~


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 Post subject: Re: Detecting Lab-Irradited Gemstones
PostPosted: Sun Dec 09, 2012 4:37 am 
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http://pbadupws.nrc.gov/docs/ML0721/ML072140766.pdf


http://www.gammaspectacular.com/

This company sells a Gamma Ray spectrometer that will work with your smart phone. If a gemmologist wanted to have radiation detection capability this would be better than the old civil defense Geiger counters that are floating around out there. Just the thing for detecting hot topaz, zircon or gold recycled from the radiation therapy seed department. Or other hot things.


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