What's wrong with this NaI(Tl) crystal?

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9a3daa
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What's wrong with this NaI(Tl) crystal?

Post by 9a3daa »

It's 2"x2" NaI(Tl) 8D8 type by Harshaw
I want to use NaI(Tl) crystal as a gamma spectrometry, but I do not know if I'll be able to use - because crystal it is not clear - has tiny fractals as frosting fractals.
Moisture is not entered since it is evident that the crystal is not turning yellow, crystal is white but at the front window is full of fractals - I do not see that it's transparent - it is blurry!

Can you give me a advice - Will I be able to use the crystal to gamma spectroscopy or do I have to buy a new one?

Thank you
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George Dowell
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Re: What's wrong with this NaI(Tl) crystal?

Post by George Dowell »

My advice is to mount it to a PMT with good quality optical coupling compound, a high current dynode string, a stable HV supply- and test the FWHM for quality. Crystals that look perfect to the eye sometimes don't pass, others you would never think, give good results.
Good for amateur work anyway.

Use a PMT that is larger than the crystal for best performance.

George Dowell
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Steven Sesselmann
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Re: What's wrong with this NaI(Tl) crystal?

Post by Steven Sesselmann »

Arni,

A good new crystal should be water clear, id it is foggy or yellowed, it has probably absorbed some moisture. The crystal is essentially a solid block of salt, and as such it it hygroscopic, and will absorb moisture like a sponge. This is why it is packaged in an aluminum container with a glass window and a seal.

As George says, give it a try, it will probably give work, but I doubt it will be much good for Spectrometry.

Steven

PS: Have you seen my new web site?

http://www.beeresearch.com.au
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
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9a3daa
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Re: What's wrong with this NaI(Tl) crystal?

Post by 9a3daa »

Thank you all. I will try to test the crystal.

Steven Sesselmann - good web site!
and I'll buy your GS-1100A - but now I have no money - sorry
Or if you're going to have some "Used" GS-1100A that it is cheaper - if we can arrange?
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9a3daa
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Re: What's wrong with this NaI(Tl) crystal?

Post by 9a3daa »

Another beautiful 2"x2" NaI(Tl) crystal that is not yellow and blurry, but it has fractals :/
It works, but not for gamma spectroscopy.
Nobody can not convince me that it is moisture.
No. This is not to damage from moisture. My crystal is not yellow.
But it is transparent clear, but it has fractals. I think it's from mechanical or thermal shock.
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Richard Hull
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Re: What's wrong with this NaI(Tl) crystal?

Post by Richard Hull »

If it is not a water issue, it could well be a result of separation of the optical coupling gel from the glass sealed cover. This could be caused by crystal shrinkage or improper handling at some point. It is certainly, as you note, never going to work for spectro work.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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