Michel Jullian wrote. > > > From: "Frederick Sparber" <[EMAIL PROTECTED]> > Sent: Friday, April 14, 2006 1:27 PM > > > The S1 (Cs-CsO- on Ag) Photoemissive surface is the one with the > > photon peaks at ~ 330 and ~ 800 nanometers with a threshold of about 1254 > > nm (1.0 eV IR) > > Cr YAG Laser? > > > > http://ssd-rd.web.cern.ch/ssd-rd/Pad_HPD/Principle/photocathodes.htm > > > > 0.1 eV electrons have a velocity v = (0.1* 2*1.6e-19/9.1e-31)^1/2 = > > 1.875e5 meters/sec! > > Checked/agreed. That's 10.66 µs for a 2m flight, quite a comfortable thing > to measure. > But you don't want these"volunteers". :-) > > > Electron space charge will act as a "velocity filter" that allows the > > higher energy electrons > > out, > > Agreed, thats' a good thing since we are only interested in the fastest > electrons: they are the only one whose initial velocity we know for sure. > It lets the "volunteers" that you don't want to measure, wrt Repulsed Electrons. > > > but if there is a repulsive gravity force F(gr) = m*g = = 9.1e-31*9.8 > > = 8.9e-30 newtons on an electron > > and the restraining electric field (E volts/meter) > > force F(e) = E*q = 1.6e-19 newtons at E = 1.0 volt/meter, there is a > > problem. :-) > > What, which restraining electric field, where ??? > Space Charge builds up due to the Image Charge around an electron emitter, thus creating a restraining electric field. In Thermionic Converters it's neutralized with cesium or potassium ions. > > > Sounds like a Faraday cup approach, Michel. > > A Faraday saucer actually (not a joke this time, the positive collecting > plate wouldn't be hollow) > Agreed. A one or two meter evacuated (vertical height) tube with some cesium at the bottom surface and a pulsed LED light source at the top near the Faraday Saucer collection electrode etc.. > > >> Time of flight would be time between laser flash and power supply current > >> pulse wouldn't it? > >> > > Yes. But the ~ 5 microseconds/meter 0.1 eV electrons get there ahead of > > the S = 0.5 * a* t^2 ~ = 3.0e-10 meters gravity repelled electrons > > traveled. > > Please explain. > Use the GSU "Free Fall" calculator, except down might be up. > > > OTOH. if you light pulse it and wait for the "slowpokes" ? > > No, as I said we wouldn't know their initial velocity. > It doesn't really matter, as these GSU calculators show for Free Fall (the same as an upward Repulsive Force) vs Vertical Trajectory for those electrons that get past Image Charge and Space Charge, say you reject any times less than 0.45 seconds the negative distance will be minus 0.94725 meters with a "launch speed" of 0.1 meters/sec.
http://hyperphysics.phy-astr.gsu.edu/Hbase/traj.html#tra3 IOW, neglect the high velocity stuff (easy to do electronically) and look for detection after at least 0.3 seconds delay. Fred > Michel > >
