The shape of things to comeBatteries included: Day of radioactive batteries nears

Is it possible to invent a better mouse trap — or battery? Good question, too, since the military and law enforcement always need more batteries and better batteries, especially as both rely more and more on power-guzzling hi-tech gear. The ever-restless Defense Advanced Projects Research Agency (DARPA) is funding a project to develop betavoltaic batteries, that is, cells which generate current from radioactive materials that emit electrons (these are also known as beta emitters). Betavoltaic cells work like photovoltaic cells, which are, in essence, semiconducting diodes. In a photovoltaic cell, when a photon strikes the diode junction, it frees an electron, causing a current to flow. In betavoltaic cells, an electron from the radioactive source does the job instead of a photon.

The New Scientist’s Justin Mullins writes that the trouble is that diode junctions are two dimensional and so only offer a limited surface area for beta electrons to hit. Here comes DARPA: It is funding a team at Cornell University to come up with a way of increasing the surface area of betavoltaic cells. The Cornell team figures that the latest techniques for carving silicon makes it possible to create 3D diode junctions, resembling pillars, on top of a silicon carbide substrate. The design consists of a silicon carbide substrate with several diode junction columns. The spaces in between are then filled with a radioactive beta emitter such as tritiated water (in which hydrogen is replaced by its radioactive isotope tritium), and the device is sealed.

The team speculates that such batteries would generate enough power to run something like a pacemaker for twenty years. This type of battery should be safe since beta particles are relatively low energy and can be easily shielded.

-VCs and other interested investors: Read the full betavoltaic batteries patent application.