Nuclear batteries are pretty simple devices that are conceptually rather similar to photovoltaic (PV) solar, just using the radiation from a radioisotope rather than solar radiation. It’s also possible to make your own nuclear battery, with [Double M Innovations] putting together a version that uses standard PV cells combined with small tritium vials as radiation source.
The PV cells are the amorphous type, rated for 2.4 V, which means that they’re not too fussy about the exact wavelength at the cost of some general efficiency. You generally find these on solar-powered calculators for this reason. Meanwhile the tritium vials have an inner coating of phosphor so they glow. With a couple of these vials sandwiched in between two amorphous cells you thus have technically something that you could call a ‘nuclear battery’.
With an approximately 12 year half-life, tritium isn’t amazingly radioactive and thus the glow from the phosphor is also not really visible in daylight. With this DIY battery wrapped up in aluminium foil to cover it up fully, it does appear to generate some current in the nanoamp range, with a single-cell and series voltage of about 0.5 V.
A 170 VAC-rated capacitor is connected to collect some current over time, with just under 3 V measured after a night of charging. In how far the power comes from the phosphor and how much from sources like thermal radiation is hard to say in this setup. However, if you can match up the PV cell’s bandgap a bit more with the radiation source, you should be able to pull at least a few mW from a DIY nuclear battery, as seen with commercial examples.
This isn’t the first time we’ve seen this particular trick. A few years ago, a similar setup was used to power a handheld game, as long as you don’t mind waiting a few months for it to charge.