mathman said:
Electron shield - anything solid, especially (but not necessarily) metal.
Nuclear (fission) propelled airplane - there was a project in the 1960's to develop such an airplane (I did some peripheral work in the area), but the engineering problems related to safety, etc. were too big to be overcome. Nuclear fusion reactors have been under study for over forty years: until something is developed, the use for airplanes is too far in the future.
Electrons as weapons - don't know, but it seems unlikely, since they are readily stopped. Lasers make better high tech weapons.
Electrons as weapons? Well, here's an idea...
If someone was to develop one, this is what I imagine it being like. It would consist of a photomultiplier tube, into which a laser of unspecified intesnity is fired, coupled to a chamber containing any material that would, in some configuration, induce electron-positron pair production from the photons. The resulting electrons and positrons would, by drift momentum, enter a mass-spectrometer like device coupled to the end of the "Bremmstrahlung Chamber" (as it might be called), and there the electrons and positrons would be diverted into opposing tubes, collimated and accelerated by magnetic guidance into tight, focused beams. The positron beam would be directed down a long barrel, almost like a miniature linear accelerator, until they would exit the barrel and hurtle towards their target at nearly the speed of light.
The electrons, on the other hand, could travel down a much shorter tube into a confinement vessel, like a giant, shielded capacitor of sorts, for holding until they become needed.
As long as the target (tank, personnel, aircraft, etc.) remains within range, the positrons will be deposited on its armor sufficiently to annihilate with electrons on its outer surface, slowly stripping the target of electrons and irradiating it with gamma ray photons. The target not only gets irradiated (possibly exposing any crew inside to lethal doses of gamma radiation), but also builds up a progressively more massive positive charge (provided it is sufficiently insulated from the ground, or provided the positron beam is of sufficient strength to rapidly strip the target of electrons) due to the lack of electrons and overabundance of protons.
As if this step wasn't nasty enough, here's the kicker...
The electrons stored in the weapon's electron chamber, or capacitor, are suddenly, either by switch or by disabling a magnetic containment field, deposited all at once on a bulbous probe positioned over the barrel where the positrons were fired from. I imagine it would look something like a giant Van de Graff. At this moment, if the range to the target has closed sufficiently, and the negative charge now released onto the bulb is sufficiently large (as well as the positive charge on the target), the electrons will leap across to the target in the form of artificial lightning! This effect could further damage the target by burning its surface or electrocuting the crew inside.
You could call it "Thor's Hammer"...
Gee, I'm glad not a lot of other people think like I do... here's to weapons I hope never to ever see developed, much less fired!
Fortunately, I think such a weapon would be hampered by design problems, and most likely the air would absorb most of the positrons before they reach any target. In any case, there's no guarantee that any target could get close enough for a bolt of "artificial lightning" to ever hit it. And of course, there's always the element of putting the attacking crew in more danger from their own weapon misfiring than the target could ever be in. All in all, this idea would probably never work out. Thank goodness...