Old photomultiplier tubes, worthwhile or waste of time? - Page 1
Forum section: electronics / projects

author: thomastheo
author_rank: Regular Contributor
timestamp: March 10, 2017, 08:41:37 pm
content: Hi folks!I just bought four new-old-stock Philips/Amperex xp2202b type photomultiplier tubes for next to nothing. They're old though, manufacture date seems to be 1984. Otherwise still in original box and wrappers, so prime condition given their age, and the photocathode seems in good condition. My question is, would it be worth the trouble to design a dynode voltage divider and supply for these puppies, or are they a lost cause due to things like helium ingress or other forms of aging over the 30+ years that they've been sitting around in dusty university closets? Anyone here with experience involving PMTs, aging and failure modes who would care to chime in and give me their 2 cents? Mind you, i'm just messing about here, no mission-critical shenanigans, just a scintillation detector, possibly two working in tandem as a coincidence/muon detector.Thanks!Th.

author: daqq
author_rank: Super Contributor
timestamp: March 10, 2017, 08:51:03 pm
content: I think that they will probably be fine - vacuum tubes that are stored reasonably well will stay functional for a long time.

author: thomastheo
author_rank: Regular Contributor
timestamp: March 10, 2017, 09:18:49 pm
content: I hope you're right, these seem to be really nice tubes. They have little individual test certificates with dark current, cathode voltages and everything. There's even a unique serial number embossed on a little plate and welded to the structure inside the envelope of each tubeI wish to learn more about the aging/failure modes of these tubes, but it's hard to find specific information. You can buy loads of old scintillation probes online, and people seem to still use them with success, so I guess they will still operate, but I also read about helium ingress and deteriorating performance, so I am unsure, hence the request.I wish silicon photomultipliers were more affordable, but as it stands they're still out of my reach for tinkering at a price above 100 dollars for single quantities. The 2 inch window on these tubes is nice though, for easy coupling to a larger scintillator.

author: MagicSmoker
author_rank: Super Contributor
timestamp: March 10, 2017, 10:08:04 pm
content: Hamamatsu has a really nice book in PDF format on photomultiplier tubes. It's 300+ pages long and fairly comprehensive, as I recall. A quick search of Google shows it is still available so you might want to check it out.

author: thomastheo
author_rank: Regular Contributor
timestamp: March 10, 2017, 10:35:58 pm
content: Quote from: MagicSmoker on March 10, 2017, 10:08:04 pmSuper, thank you! There's a lot of useful information in there. Most notably related to my original question, it seems that the composition of the glass envelope is crucial when it comes to susceptibility of a photomultiplier tube to helium ingress from normal environmental conditions or otherwise. The tubes I have are thankfully made of lime glass, which is, I have found explained elsewhere, the least helium-permeable material, as opposed to say, fused quartz used in UV sensitive tubes. It seems that given the storage conditions, helium ingress is not something I should be overly worried about.For anyone reading this who is interested, the handbook mentioned can be found here:http://www.hamamatsu.com/resources/pdf/etd/PMT_handbook_v3aE.pdfA comparison of helium permeability between different envelope materials can be found here:http://www.et-enterprises.com/files/file/technical-information/rp101_effect%20of%20exposure%20to%20helium%20on%20photomultiplier%20performance%20and%20lifetime.pdf

author: tecman
author_rank: Frequent Contributor
timestamp: March 11, 2017, 01:22:25 am
content: PMs, if not abused, have a very long life. NIB will stay "fresh" for decades. They are very sensitive photon detectors, needing only some resistors, a few caps and a low current HV supply. Still widely used today.paul