As we have seen, solar cells are able to convert the kinetic energy of
charged nuclear particles directly into electricity, but a simpler and
more straightforward way of doing this exists. This involves direct use
of the flow of charged particles as current.
The _nuclear battery_ shown in Figure 13 performs this trick. A central
rod is coated with an electron-emitting radioisotope (a beta-emitter;
say, strontium-90). The high-velocity electrons emitted by the
radioisotope cross the gap between the cylinders and are collected by a
simple metallic sleeve and sent to the load. Simple, but why don’t space
charge effects prevent the electrons from crossing the gap as they do in
the thermionic converter? The answer lies in the fact that the nuclear
electrons have a million times more kinetic energy than those boiled off
the thermionic converter’s emitter surface. Consequently, they are too
powerful to be stopped by any space charge in the narrow gap.
Nuclear batteries are simple and rugged. They generate only microamperes
of current at 10,000 to 100,000 volts.
[Illustration: Figure 13 A NUCLEAR BATTERY
_The nuclear battery depends upon the emission of charged particles
from a surface coated with a radioisotope. The particles are
collected on another surface._]
ENERGY OUT
INSULATOR
LAYER OF BETA-EMITTING RADIOISOTOPE
VACUUM