Andrew Smallshaw wrote:> Oliver Betz <obetz@despammed.com> wrote: > >> My calc above should demonstrate that 1pA is 6 million electrons >> per second. Hard to measure this "current" with 100MHz bandwith. > > In isolation, that's actually quite doable. Electron multipliers > can easily detect individual electrons. I've used them in the past > in the form of photomultipliers. 100MHz is quite fast but ISTR > seeing PMTs with quoted sub-nanosecond response times. If PMTs > can work at those kind of speeds then plain electron multipliers > must also be able to work at those speeds.FYI we have been detecting single electrons with photo-multipliers for at least the past 60 years. I can personally vouch for about 55 of them. I fail to see how you can describe the action of a single electron in terms of frequency. I consider that a frequency requires a wave, which in turn requires a large multiplicity of point-style objects to simulate. -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section.
Hardware handholding
Started by ●November 3, 2008
Reply by ●November 5, 20082008-11-05
Reply by ●November 5, 20082008-11-05
In article <49122965.B3C039CB@yahoo.com>, cbfalconer@yahoo.com says...> Andrew Smallshaw wrote: > > Oliver Betz <obetz@despammed.com> wrote: > > > >> My calc above should demonstrate that 1pA is 6 million electrons > >> per second. Hard to measure this "current" with 100MHz bandwith. > > > > In isolation, that's actually quite doable. Electron multipliers > > can easily detect individual electrons. I've used them in the past > > in the form of photomultipliers. 100MHz is quite fast but ISTR > > seeing PMTs with quoted sub-nanosecond response times. If PMTs > > can work at those kind of speeds then plain electron multipliers > > must also be able to work at those speeds. > > FYI we have been detecting single electrons with photo-multipliers > for at least the past 60 years. I can personally vouch for about > 55 of them. > > I fail to see how you can describe the action of a single electron > in terms of frequency. I consider that a frequency requires a > wave, which in turn requires a large multiplicity of point-style > objects to simulate.To be pedantic some form of repetitive occurance, even signalling with lights using Morse Code has 'burst frequency', but the code patterns are not exactly waves in themselves. The light is (depending on whether you view the photons at that time as a wave or a particle....). -- Paul Carpenter | paul@pcserviceselectronics.co.uk <http://www.pcserviceselectronics.co.uk/> PC Services <http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font <http://www.gnuh8.org.uk/> GNU H8 - compiler & Renesas H8/H8S/H8 Tiny <http://www.badweb.org.uk/> For those web sites you hate
Reply by ●November 6, 20082008-11-06
On 2008-11-05, CBFalconer <cbfalconer@yahoo.com> wrote:> Andrew Smallshaw wrote: >> Oliver Betz <obetz@despammed.com> wrote: >> >>> My calc above should demonstrate that 1pA is 6 million electrons >>> per second. Hard to measure this "current" with 100MHz bandwith. >> >> In isolation, that's actually quite doable. Electron multipliers >> can easily detect individual electrons. I've used them in the past >> in the form of photomultipliers. 100MHz is quite fast but ISTR >> seeing PMTs with quoted sub-nanosecond response times. If PMTs >> can work at those kind of speeds then plain electron multipliers >> must also be able to work at those speeds. > > FYI we have been detecting single electrons with photo-multipliers > for at least the past 60 years. I can personally vouch for about > 55 of them. > > I fail to see how you can describe the action of a single electron > in terms of frequency. I consider that a frequency requires a > wave, which in turn requires a large multiplicity of point-style > objects to simulate.I wasn't referring to the frequency of an electron, wave/particle duality or any other area of theoretical physics, but to the the mechanics of actually counting the electrons and recording when they arrive. The current from a PMT isn't sharply defined - it has a definite rise and fall time just like anything else. While the tube itself is asynchronous in operation the same is probably not true of the surrounding circuitry. To keep that circuitry simple you want to interpret the PMT output as a simple binary signal - is there a photon/electron there or not - and the response time of the tube should be short compared to the sampling frequency to reduce the effects of what happens when an individual pulse straddles a clock transition. -- Andrew Smallshaw andrews@sdf.lonestar.org
