Repairing Old NaI(Tl) Crystals

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Steven Sesselmann
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Repairing Old NaI(Tl) Crystals

Post by Steven Sesselmann » 30 Apr 2016, 19:20

Hi Guys,

I came across this letter on ReasearchGate, it talks about repairing NaI crystals damaged by moisture, by immersing the crystals in solvents. Might be interesting to some of you.

I should point out here that NaI(Tl) crystals contain Thallium which is very toxic, so this is something to consider carefully before cutting open an old detector.

https://www.researchgate.net/publicatio ... l_Crystals

Luuk might have some input here, as a professional in this area.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | beejewel.com.au |

stamasd
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Re: Repairing Old NaI(Tl) Crystals

Post by stamasd » 30 Oct 2017, 20:44

Do you happen to have somewhere the actual article referenced above? The link is to a page that allows one to request access to the article. I did that about 10 days ago and nothing happened since.
Real name: Silviu Tamasdan

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Steven Sesselmann
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Re: Repairing Old NaI(Tl) Crystals

Post by Steven Sesselmann » 31 Oct 2017, 08:58

Silviu,

I will send you a PM with a link..

I would also like to know what the proper way of disposing of old damaged NaI(Tl) crystals. Is it too toxic to dispose of in the household waste? Luuk might be able to answer this too.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | beejewel.com.au |

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Re: Repairing Old NaI(Tl) Crystals

Post by stamasd » 31 Oct 2017, 09:57

Well from the paper it appears that the content of thallium in NaI(Tl) is about 200ppm - I had actually tried looking that up previously and I never found a figure for the doping ratio, this paper is the first I see that mentions it. For a huge 1kg crystal, that would be about 200mg of thallium. Finding toxicology data on thallium wasn't as straight forward as I expected, the best I could find is that the LD50 by oral route is 0.9 to 9.4mg/kg in humans. That is a very wide range as LD50 goes. Taking the lowest value of 0.9, that means that for a person of 100kg (approximately my size) a dose of 90mg has a 50% chance of killing them. So the 200mg contained in 1Kg of NaI(Tl) if administered to 2 persons my size has the statistical probability of killing one of them.
Hope that puts things in perspective.
Also, thallium has an antidote (Prussian blue aka ferric ferrocyanide) and all the calculations above are made without taking into account any of the 2 being administered the antidote.
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Steven Sesselmann
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Re: Repairing Old NaI(Tl) Crystals

Post by Steven Sesselmann » 31 Oct 2017, 11:50

Yes, I think it's unlikely that anyone would ingest half a kg of Sodium iodide, and if they did, it's likely that the salt would be more toxic than the Thallium. That said, I think its sensible to use rubber gloves and keep the stuff safe from other people and children who might not know what it is. I once broke a Sodium Iodide crystal in my lathe, and immediately cleaned it up, but when I went back to use the lathe a week later it had rusted all over.

Here is an old post with images: http://www.fusor.net/board/viewtopic.php?f=13&t=6259
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | beejewel.com.au |

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Re: Repairing Old NaI(Tl) Crystals

Post by stamasd » 01 Nov 2017, 23:11

I'm not surprised that NaI is so corrosive. Not only is it hygroscopic meaning it will suck moisture from the air and keep it stuck in place where the tiny crystals are, but also it can get oxidized very easily in air generating in place small amounts of elemental iodine which will attack iron readily. If you make a solution of NaI and leave it exposed to air you will see that after a while from completely transparent and clear it takes a yellowish-brownish hue from the iodine generated by oxidation.
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Re: Repairing Old NaI(Tl) Crystals

Post by maher5198 » 12 May 2019, 06:07

I would think long and hard before opening an NaI casing. Make a glove box with drying agent in it to work in or work in a clear trash bag with drying agent. I tried to use a solvent to clean the cloudy outside hydrate on a 50's era crystal from a Victoreen model. The acetone dissolved 50% of a large crystal faster than I could snatch it out. I recommend gloves, dry atmosphere and only wet the crystal with a solvent dampened cloth. You can probably skip the solvent and just use abrasives and then polish just like it's soft acrylic. If you are trying to recover a totally hydrated crystal by solvent recovery and subsequent recrystalization just forget it unless you already have a lab.

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