Issue with 1.5" NaI:Tl detector DOA.

Post by **Conor Whyte** » 29 Jul 2024, 14:51

About a month ago I received a package from a well known ebay vendor, a 1.5" refurbed Hamamatsu R980 based NaI:Tl (Bicron branded)detector that was "tested as new". This past Friday I finally got around to desoldering the voltage divider with a brand new Hakko FR301 desoldering gun and put a new one on. The cap was put back on the unit and sealed it up as I have done with other units. No counts on my Bicron Surveyor M at 900V. I took it off the
HV and examined the tube looking down on the side of it, and noticed the side of the tube has a fractured wall which has resulted in a loss of vacuum.
I am more than a little annoyed at this result. Looks like UPS has done it yet again... This is the third item I have ordered that they have completely destroyed during shipping. UPS stands for oops ?
I have received a refund but I am now wondering if it is possible to salvage the crystal from it?
Has anyone here mastered the art of crystal salvaging from refurb units? please let me know.

YouTube · Post by **Sesselmann** » 29 Jul 2024, 16:55

Conor,

If this is one of those sealed Bicron detectors, the PMT might be glued onto he crystal, meaning the crystal is not separately encapsulated therefore mist likely glued into the housing.

If you post a picture someone here will know how they are constructed.

Steven

PS: Sorry about your misfortune..

Post by **Conor Whyte** » 29 Jul 2024, 17:02

Thanks, sure I will post a picture sometime in the next few hours.

Post by **Conor Whyte** » 30 Jul 2024, 06:24

Pictures of the PMT are below

Post by **Conor Whyte** » 30 Jul 2024, 06:28

Wire used here is stranded Silicone rated for 3Kvdc. tube is wired for + input.

YouTube · Post by **Sesselmann** » 30 Jul 2024, 11:35

Conor,

It looks like the PMT is set into the tube with epoxy, I don't like your chances....

If it was DOA when you received it from the seller, it is the sellers responsibility, but as you have modified the detector and specifically applied heat to desolder the board, it might be difficult to prove what happened..

Best of luck..

Steven

Post by **iRad** » 30 Jul 2024, 13:01

Hi Connor - Was the detector already opened when the seller sold it to you? Did they also claim "Resolution: excellent 6.9% FWHM @ 662 keV". I don't know how a seller can sell detectors "tested as new" when they sell them in the condition you described. Why bother opening the detector just to sell it "opened"? Sounds fishy... Sounds to me like they opened the detector to mod themselves, then realized there was an issue. So, they decided just to sell it as working condition and claim it was the buyer that broke it during their own mod attempt. Or blame UPS should the buyer complain. I've shipped hundreds of these by UPS and USPS without breakage. Were there obvious signs of package distress? While it's possible it broke in shipping, it seems more likely it was broken by the seller when they initially opened it up.

And yes, Steven is correct. The PMT is permanently epoxied to the crystal. While it is "possible" to salvage the crystal, it is difficult and not worth the effort considering the cost of replacement. Luuk had demonstrated the process of salvaging such a crystal in the past, and I have done so successfully myself, but do not recommend it... unless you just have to that is...

Post by **Conor Whyte** » 31 Jul 2024, 05:42

Yes, to your answer Tom. The amount paid was refunded so all is good. The vendor in question didn't hesitate with giving a refund. There was evidence on the box that it had been knocked around a bit in transit. The wrapping job was also very poorly done as well. The end cap had come off during transport and was banging around inside the box ( I left that part out), so that alone could be why the side of the PMT was cracked.

At any rate I learned a lesson here.

Post by **iRad** » 31 Jul 2024, 06:39

Connor - Glad you at least were able to get a refund, as well as end up with the broken detector to try and salvage.

I think maybe you were hoping to replace the original PMT. While possible, there is an easier option to still utilize the detector without trying to remove the crystal or original PMT from the housing. However, it leaves the detector only good as a nice counting detector, which is not necessarily a bad thing to have as a spare...

It is possible to "gently" break off the glass at the back of the PMT and pull the guts out, making sure all loose glass and metal debris from inside the old PMT tube are out. Be sure what is left of the old PMT tube is clean inside, being careful of handling the broken glass and debris. Then it's possible to fit a 1.25-inch (or smaller) PMT inside, using a clear epoxy to anchor its face against the inside face of the old PMT (new PMT fitted inside the old one).

This method works great and at least makes the crystal and detector housing salvageable for a good counting detector. Still very useful for counting applications, or for general survey or field use. I'm sure there are a few others with similar broken detectors out there that can benefit from this salvage tip. And it is a lot easier than trying to salvage the epoxied in place crystal itself.

(I ADDED SOME PICTURES IN THE FOLLOWING POST...)

Oh... and it helps to use a low-profile PMT, or you may have to make a new longer end-cap.