Re: Thallium Activated Xtals and Neutron Dse Rate Measurements

[John_Sukosky@dom.com]

Mike Malaxos wrote:

> What is the toxicity of Thallium activated NaI.  A detector was cut open
> with a hand saw. Is a trace amount absorbed through the skin of the hands
> liable to be hazardous.

We just had some NaI(Tl) detectors refurbished by Bicron (www.bicron.com).
Here's an excerpt from the operating manual they sent back with the detectors:

IMPORTANT NOTE ON THE SAFE HANDLING OF NAI(TL) CRYSTAL MATERIAL

A sodium iodide [NaI(Tl)] crystal is activated by the addition of a very low
concentration of thallium iodide (TlI).  Several years ago we asked our law
firm to give us an opinion whether this product should be treated as a
hazardous material for labeling purposes.  A quote from their response dated
November 29, 1984 follows.  "We have examined the Dangerous Goods Regulations
promulgated by the U. S. Department of Transportation, Research and Special
Programs Administration, Materials Transportation Bureau.  It is our opinion,
based upon our review of these materials, that your products containing sodium
iodide crystals with traces of thallium iodide are not considered hazardous or
poisonous."

However, thallium iodide as a pure chemical is toxic.  One of our suppliers
tells us that amounts of more that 1 gram per person can cause death.  Another
supplier states the LD-50 is 28 milligrams per kilogram body weight.  On a more
practical basis, there is the personnel hazard that exists from a damaged, and
possibly leaking, crystal container.  A thallium-activated sodium iodide
crystal on average is 99.8% sodium iodide and 0.2% thallium iodide. The weight
of a 2-inch diameter by 0.25 inch thick NaI(Tl) crystal is 47.24 grams
including 0.094 grams of TlI.  Casual contact with the small fraction of this
material which might leak from a damaged container is not a serious hazard.

If a container is damaged, handle with disposable rubber gloves.  Dispose of
the detector materials according to local and federal regulations at an
approved site.


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