pickens writes "Nuclear batteries that produce energy from the decay of radioisotopes are an attractive proposition for many applications because the isotopes that power them can provide a useful amount of current for hundreds of years at power densities a million times as high as standard batteries. Nuclear batteries have been used for military and aerospace applications for years, their large size has limited their general usage. But now a research team at the University of Missouri has developed a nuclear battery the size of a penny that could be used to power micro- and nano-electromechanical systems. The researchers' innovation is not only in the battery's size, but also that the batteries use a liquid semiconductor rather than a solid semiconductor. 'The critical part of using a radioactive battery is that when you harvest the energy, part of the radiation energy can damage the lattice structure of the solid semiconductor,' says Jae Wan Kwon. 'By using a liquid semiconductor, we believe we can minimize that problem.' The batteries are safe under normal operating conditions. 'People hear the word "nuclear" and think of something very dangerous,' says Kwon. 'However, nuclear power sources have already been safely powering a variety of devices, such as pacemakers, space satellites, and underwater systems.'"