Kind friends

This is to inquire whether unpowered PMTs (Photo Multiplier Tubes) are subject to damage or degradation corollary to intense or continuous illumination (of their photocathodes)? While I am (too) well aware of the liability to, and mechanism of, damage attendant to strong illumination of powered devices -- There seems to be no consensus as regards sequelae of acute or chronic illumination of unpowered tubes.

While, inasmuch as my query concerns only unpowered devices, it may seem that I am merely inquiring after the 'photostability' of the photocathode material -- One hesitates to assume...

Many, many advance thanks for any assistance, thoughts or feedback of any kind!

Best regards
HP

 

Your concerns appear to be well-founded. See page 254 of the pdf file (book page number 239) at the link below.

psec.uchicago.edu/links/pmt_handbook_complete.pdf

 

You should not expose a P.M tube to light as it will strip the cathodes!

 

Your concerns appear to be well-founded. See page 254 of the pdf file (book page number 239) at the link below.

psec.uchicago.edu/links/pmt_handbook_complete.pdf

Many thanks for your response and citation of the highly informative text!

Re: the referenced .PDF -- While I see discussion of deleterious effects corollary to ambient storage temperature, pressure, humidity, ionizing radiation and --yikes!-- He permeation?! (who would have have thought?) -- I'm not seeing monitions in regards to illumination (or 'light storage') of unpowered PMTs?

You should not expose a P.M tube to light as it will strip the cathodes!

Thanks! -- As a point of curiosity, what is the mechanism of photo-induced PK degradation in unpowered tubes?

Many thanks and very best regards
HP

 

Kind friends

This is to inquire whether unpowered PMTs (Photo Multiplier Tubes) are subject to damage or degradation corollary to intense or continuous illumination (of their photocathodes)? While I am (too) well aware of the liability to, and mechanism of, damage attendant to strong illumination of powered devices -- There seems to be no consensus as regards sequelae of acute or chronic illumination of unpowered tubes.

While, inasmuch as my query concerns only unpowered devices, it may seem that I am merely inquiring after the 'photostability' of the photocathode material -- One hesitates to assume...

Many, many advance thanks for any assistance, thoughts or feedback of any kind!

Best regards
HP

We always stored them in black lined boxes (black felt or flat black painted cardboard) and kept them in the refrigerator, if not used for a long time. (to reduce the inevitable outgassing.....not sure how much it helped...but my old school mentor had us do this).

 

It looks like there is some validity to the refrigerator bit after all:

https://www.hamamatsu.com/resources/pdf/etd/PMT_handbook_v3aE-Chapter13.pdf

 

I received training (short period) for repairing an instrument including them. Amongst the several reccomendations for the handling, it was to keep them in the original box all the time and not do anything else than installing, calibrating and closing the covers once done. Other than cost, extreme
sensitivity and high cost, no other particular reasons were given.

EDIT/

The fridge part took me in surprise.

/EDIT

 

Lemme tell ya! -- It's this helium permeation 'business' that's got me 'bummed'! -- Am I to take the charts seriously, it seems Ca. 20 years represents the maximum shelf-life for even all glass PMTs!? --- One wonders why other glass-envelope vacuum tubes aren't subject to 'He fouling'? I, for instance, have several 60+ YO video camera tubes featuring wall-thickness on a par with that of the PMTs - and yet exhibiting flawless performance?

Many thanks and very best regards
HP

 

Lemme tell ya! -- It's this helium permeation 'business' that's got me 'bummed'! -- Am I to take the charts seriously, it seems Ca. 20 years represents the maximum shelf-life for even all glass PMTs!? --- One wonders why other glass-envelope vacuum tubes aren't subject to 'He fouling'? I, for instance, have several 60+ YO video camera tubes featuring wall-thickness on a par with that of the PMTs - and yet exhibiting flawless performance?

Many thanks and very best regards
HP

I believe PMTs have a higher vacuum than CRTs. Also, since CRTs have a hot filament, the gettering action continues....you don't have a getter in a PMT, I believe.

 

since CRTs have a hot filament, the gettering action continues....you don't have a getter in a PMT, I believe.

Aye! That would explain it! -- Thanks! -- But how does one 'getter' an inert element (He)?- Some manner of adsorption perhaps? -- À la H2 on finely divided Pt?

Very best regards
HP

 

@Hypatia's Protege It's true that you can fix helium saturated tubes by storing at less than <1um pressure for a few weeks but you have to do it b4 ion current damage happens!

 

Aye! That would explain it! -- Thanks! -- But how does one 'getter' an inert element (He)?- Some manner of adsorption perhaps? -- À la H2 on finely divided Pt?

Very best regards
HP

There are no better materials for He.