EUKITT for watertight embedding of Scintillatir (NaI)

[scientificfun]

Hi-

what about making a thin layer of EUKITT (MMA resin solution) an a NaI scintillator to protect it from humidity? And how to couple it in general to the PMT without hard to get greases...? Imersion oil suited? (from microscopy)

Kind regards

[Richard Hull]

In general, you will never get your hands on a naked piece of NaI:Tl optical crystal. They are all manufactured in hermetically seal environments. (aluminum can with an glass end window. There is never a need to handle or link a naked chemical crystal to a PMT.

Any number of silicone compounds can link the glass to glass optical contact.

Richard Hull

[scientificfun]

Hi Richard-

thaks for the answer. But if the crystals are always sealed- why then the problem with them absorbing moist and degrading? (getting cloudy...) Because the seal is broken? If so- then "reseal" it with EUKITT? I got a really big PMT with scintillator but it was unscrewed- i.e. surface of the pmt and scintillator were not connected anymore- scintillator still water clear. So I can expect it to be sealed somehow on the surface anyways- what I see on the side of the pmt is not the "naked" crystal?

Thanks again

[Carl Willis]

As Richard said, there is typically a glass end window that provides a hermetic barrier on the PMT side. The exception to this is if you have an integrated assembly where the crystal is directly abutting the PMT, but these do not come in conveniently detachable arrangements. Exposed NaI turns bright yellow and blotchy within minutes or hours due to humidity in virtually any climate on earth. Punctures to the metal housing or cracked epoxy near the window will result in localized blooms of yellow on the crystal. The epoxy or housing can be repaired with new epoxy to hold off further degradation of the crystal, but what damage it has already sustained cannot be repaired.

-Carl

[UG!]

i once had such a sealed assembly that had turned yellow and cloudy. i removed the crystal (carefully avoiding contact with the perculior extremely hydrophobic white powder that serounded the thing) and put it in a vacuum chamber in the hope i could remove some of the absorbed watter. in this i failed, despite leeving it in the pumped down chamber for some months. on removal (i suppose it was a slightly more humid day than average) the crystal instantly started to deliquess in my (gloved) hands. i gave up at that point. i still have its desolved remains lurking in a flask somewhere.

Oliver