Betavoltaic batteries

The increasingly high-tech US military always needs better batteries. So its research branch, the Defense Advanced Projects Research Agency (DARPA) based in Virginia, US, is funding a project to develop betavoltaic batteries – cells that generate current from radioactive materials that emit electrons (so-called beta emitters).

Betavoltaic cells work rather like photovoltaic cells, which are essentially 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 trouble is that diode junctions are two dimensional and so only offer a limited surface area for beta electrons to hit.

DARPA has funded a team at Cornell University in, New York, US, to come up with a way of increasing the surface area of betavoltaic cells. The Cornell team reckons 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, like a miniature version of the Parthenon. 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 20 years. This type of battery should be safe since beta particles are relatively low energy and can be easily shielded.

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