Gamma Spectrometry Forum

Hi Guys,
Do you want to see some nice pictures of a strange effect in a pmt!
If interested please read the pdf.
Luuk

Cool effect indeed, but I'm guessing only finding 2 such samples over your many years is a good thing in this instance. :)

Luuk,

Very interesting, I assume the glass envelope has had a small leak, so the pressure inside is too high.

Maybe with a spectrometer you can identify the fill gas?

Steven

Hi Steven,
Yes, there is a small leak somewhere so the “gas” is Nitrogen (actually air) that gives this particular color.
The pmt that I wrote about 7 years ago, I tested it last year again and still gave the same “light show” so for some reason the leak closed.
If not the vacuum was lost a long time ago, and the cathode would have been gone.
Luuk

Hi Tom,
Yes it is really rare that this happens, so don't worry your pmt's are all good I expect!
Luuk

If you solder something directly to the pins of a PMT, microcracks can appear in the glass and air can slowly penetrate. Never solder directly to a PMT.

Peter - I've actually never seen that happen and have soldered directly to the pins of thousands of PMTs. Perhaps it is possible by using excessive heat and/or poor soldering technique, or excessive stressing of the pins with certain especially fragile PMTs, but it is not something to usually worry about. Of course, a socket is nice if the PMT accepts one and the detector or project calls for one. More often than not, a socketed PMT may not be the best solution. Custom circuit boards are also used often and soldered directly to the PMT pins. Also note that quite a few PMTs that accept sockets have the base itself soldered directly to the PMT pins. Just my observations... All said, it's always best to treat the pins of an expensive PMT as gently as possible.

I doubt that is what happened with the PMT Luuk is demonstrating in his post. With only 2 such samples in his many years of work with them, then it is not much to worry about, I'm sure.