Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: Photomultiplier
Date: Oct 04, 6:37 am
Poster: Mark Harriss

On Oct 04, 6:37 am, Mark Harriss wrote:

>The PMT is not damaged if no voltage is applied. However, PMT's have a noise floor and once placed in total darkness and powered up they will be noisey for a few days as the materials inside release the odd photon or two as the various materials "calm down" in the dark. Much of this info is in the RCA Photomultiplier handbook.

Thats some interesting background on how the tube functions when new. I have checked out the local market and about all i can find over here are the RCA-931A's which look nicely antique. I can get them cheaply but whether they would be up to the task is another thing

>I had beautiful Hamamatsu S-11 response PMTs for sale that were absolutely perfect for nuclear apps with full preamps, sockets and wired dynode strings (see former post here offering them for sale). They sold out quickly as folks gobbled them up.
>Remember, the tube is just the first step. a very special socket is needed and divider resistor strings and an ultra fast preamp. Then you will need a discriminator and pulse amp combo outside of that. Oh, also a source of about 800-1500 volts and usually a bipolar +/- 15 volt supply. (both very well regulated and noise free.
>Richard Hull

I suppose the power supply would have to be noise free... I have used the LM317-HV three terminal regulator to build a floating 1000V regulator , that had about 60 dB or so of hum noise rejection if i remember rightly.

I was going to have a fet buffer and feed a comparator for discrimination and then some new super duper low noise op amp for the output.

Just how fast a slew rate are we looking at??.