Digital positronics

This is in computer:storage because that's one of several applications.

Certain radionuclides exhibit positive beta decay. They emit positrons when decaying into another element. One of the most stable of these seems to be potassium forty, with a half-life over an aeon, though others exist with much shorter half-lives. These can be used as sources of positrons.

Now, suppose you have an evacuated chamber like a cathode ray tube with a lump of potassium forty, or maybe carbon eleven, at one end. Using an electric field, you steer the beam of positrons into a side compartment where it collides with some kind of dense matter, releasing gamma rays as they annihilate the electrons in it. These gamma rays are then used to generate electricity which powers the whole thing. At the other end of the chamber is a further screen with which the positrons collide, producing gamma rays. This is scanned with a second electrical field like a CRT monitor, and the "display" is fed back into the first set of electrical coild. If this field is then switched on and off, it can store digital information like a Williams tube. That's the storage bit.

Also, you have smaller, triode-like devices. These are evacuated chambers with a positron source and two compartments, the beam of positrons being steered in a similar way to the memory tube, with a similar detector at the other end. This is functionally similar to a transistor or valve, and can therefore be used to build logic gates.

Finally, the Williams tube-style device can be adapted for use as a raster-scan display by covering the front with phosphor, placing a mirror in the appropriate position and providing lead shielding to protect the viewer from the gamma rays.

The result of all this is that a digital computer can be built out of positronic devices, as in Asimov. It would be rather radioactive and the devices might fail quite quickly due to the gradual decay of the positron sources and the production of argon thirty-nine, but it would have the advantage of being self-powering. No external source of energy would be needed for it. It would just sit there working until it wore out. Argon thirty-nine is fairly stable and decays by negative beta emission, so that wouldn't mess it up.

Possible applications would be automatic space probes and robots mining other planets and moons.

Of course, this could all be done with ordinary beta emitters, but it wouldn't have the SF cachet of positrons.

I know this is somewhat WICTTISITMWIBNIIWR, but it does actually have an advantage.