So what would be a good photo diode to replace a PMT in a scintilation counter setup?

unter setup?

If you need single photon detection - or anything close to it - you'd need to go for a

The paper by Cova et al that Wikipedia references is pretty good.

-- Bill Sloman, Nijmegen

setup?

APD, but the nice thing about a PMT is the relatively huge sensitive area.

John

setup?

You could try using a Geiger-mode APD if you have enough counts, but the SNR will suffer very badly unless you can do a lot of clever coincidence counting. The problem is that APDs have about six orders of magnitude worse dark count rates than PMTs of the same area, and they're a factor of 10 slower.

PMTs are amazing.

Cheers

Phil Hobbs

On a sunny day (Sun, 7 Nov 2010 11:55:28 -0800 (PST)) it happened Bill Sloman wrote in :

Thank you I will read that.

On a sunny day (Sun, 07 Nov 2010 15:26:20 -0500) it happened Phil Hobbs wrote in :

counter setup?

Been doing nuclear physics all day, sort of catch up, been some years. Anyways I found some manufacturer of PMTs has stopped, so that made me wonder, also some other publications mentioned photo diodes. Thank you for the help.

counter setup?

Photonis used to manufacture most of the small-vendor PMTs (Burle, EEV, Philips, etc.) but their PMT operation shut down in June of last year, iirc. Hamamatsu is now about the only game in town.

PMTs have a much shorter shelf life than other tubes (about 5 years or so) due to caesium migrating around inside and probably other surface effects, and to helium getting through the glass. Quartz and metal envelope PMTs are much better for helium resistance--in a helium atmosphere, the old soda-lime glass units would die in an hour.

Cheers

Phil Hobbs

Jan, if your'e looking for a one off PMT see if you can find what tube Hamamatsu sell for use in oxygen analysers. I can't recall how much they were but they are something that is replaced in O2 analysers every now and again so they may be a bit cheaper due to volume sold.

On a sunny day (Sun, 07 Nov 2010 15:46:10 -0500) it happened Phil Hobbs wrote in :

counter setup?

APDs sound great, I have been less lucky finding one, look at this: ftp://panteltje.com/pub/APD_no_go.gif Mouser.com was one of the few who list them, but I cannot buy them, see the pop-up window that pops up when you click 'restricted availability'. I wonder why the Netherlands has restricted sales. Makes me wonder why the f*ck we should buy that Joint Strike Fighter. I will vote Eurofighter.

It gets wierder each day, the US complains about low exports, can you imagine. Altera asked me to update my email info, but I cannot, as the Netherlands is no longer listed in the pull-down menu on my personal config page. Maybe the maps got lost? LOL

Never mind I found some PMTs on ebay in Europe. J.L. is right, much bigger window. Those APDs will likely need some optics, and lenses reduce sensitivity. But I sure would have liked to try some.

counter setup?

wonder,

pop-up

no longer listed in the pull-down menu

APDs stink for most things. There are some applications, particularly in the 1 pA to 100 nA photocurrent range, where there are too many photoelectrons do photon counting but not enough to get near the shot noise with a PIN diode. In that range the dark current doesn't bite you so hard, and it's nice to have the durability.

APD gain is also horribly temperature-dependent, so it's much harder to get any stability that way.

Cheers

Phil Hobbs

counter setup?

wonder,

pop-up

no longer listed in the pull-down menu

How about an LED that squirts a tiny bit of square-wave-pseudo-random light into the APD. A phase-sensitive detector digs that out of the noise and tweaks the HV to servo gain. (There are industrial control systems that do that, squirt a little extra noise into an actuator and analyze the process output, to continuously derive the plant transfer function.)

Adding a crude temperature feed-forward would refine things a bit.

John