Diamond gammavoltaic devices

A gammavoltaic device (sometimes referred to as a radioluminescent battery) is a device which converts gamma rays into electricity. They work similarly to standard photovoltaic (PV) solar cells, but the photons have ten-thousand to one-million times more energy, and are thus are far more likely to damage a Si-based PV device, or more likely still, to simply pass straight through. Diamond, whilst it carries its own challenges as a material, is a good candidate for gammavoltaic devices because it is very resistant to radiation damage.

Gammavoltaic device
An example of a gammavoltaic device in development at Arkenlight
(a company spun out from the Bristol Diamond Group by Tom Scott and Neil Fox).

The development of diamond gammavoltaics is motivated by the potential for some real-world applications. Currently, diamond-based dosimeters for high dose-rate environments require high-bias voltages, around 300 V – 500 V, to operate effectively. This may be fine for short investigations where cables can be laid, but there is an interest in creating sensor packages that stay in place for decades in locations without easy cable access, such as nuclear-waste repositories, accident sites, and retrofitting fission reactors. In these situations, a gammavoltaic sensor might be used instead. Rather than supplying a high voltage continuously, a sensor package with a long-life battery would only have to detect the generation of a small current from the gammavoltaic detector to know a gamma dose was being delivered. It would then wirelessly transmit a reading to the monitoring base. There is even a possibility, further down the line, that sensor packages may be self-powered by the gammavoltaic device, negating the need for a battery. However, this application would likely have to await the development of much more radiation-hard electronics, or MEMS-based sensors, for continuous irradiation to not destroy the rest of the sensor package.

Dr Robbie Mackenzie is currently funded by STFC for a project called TREASURγ to develop and prove that such devices work as expected.

Gammavoltaic device IV curve
The current-voltage behaviour of a diamond gammavoltaic device being irradiated with ~ 1 kGy/h (air kerma) of Cs-137 gamma rays (662 keV). The points are fitted with the model from the equivalent circuit shown on the right. Inset: the portion of the curve where power is being produced (i.e. P= IV is negative).

Example papers