In Scifi there is often the issue that all the fancy technology like Mechas and Lasguns need a lot of energy. Chemical sources are limited by volumetric and regular power density. Batteries and capacitors even more so. Compact fusion, fission and antimatter devices produce problemeic amounts of waste heat, are insanely complex and dangerous. Using tanks with power plants which regularly recharge their robot swarms or just have constant power cords to them is interesting and feasible, but I'm interested in alternative solutions.
Alpha and Beta-Voltaic devices turn particle radiation directly into electricity. This should help a lot with the wast heat and issues of huge generators. This question from Physics SE deals with the question why we are ten using them currently outside of low power and long term operations. This list of issues is from an answer.
- Power produced is non-adjustable. The battery produces power at nearly constant rate (slowly decaying with time). It cannot be increased and if not consumed (or stored) the power is lost.
- Low power density. 63Ni for instance produces ~5 W/kg (and kg here is just mass of radioactive material, the actual battery would be at least order of magnitude heavier). There are, of course isotopes with power densities much higher but they encounter other problems.
- Semiconductor damage. If we try to increase power by using isotopes with higher decay energies we find that the high energy electrons damage semiconductors, reducing service life of batteries to times much shorter than isotope halflife. Alpha particles, especially, damage the p-n junctions, so even though (for instance) 238Pu produces 0.55 W/g of alpha radiation, it is mainly used in the thermoelectric schemes rather than in direct energy converters.
- Gamma radiation. Many isotopes has gamma emission as a secondary mode of decay. Since this type of radiation is difficult to shield, this means that the selection of isotopes usable for batteries is limited only to pure beta emitters.
- Bremsstrahlung. Electrons braking produces this type of radiation, that had to be shielded. Again, this limits our selection of isotopes to those with relatively low decay energies.
- Low volume of production / Economics. Many isotopes cost too much to be practical in wide array of applications. This is partly explained by low volume of production and partly by production process which will be costly at all volumes because it requires energy consuming isotope separation and special facilities for working with radioactive materials. For instance, tritium (one of the materials for betavoltaics) costs about $30 000 per gram and its world annual production is 400 g (from wikipedia).
- Safety / Regulations / Perception: 63 grams of 63Ni constitute more than 3500 curie of radioactivity, which would definitely require regulations for handling and probably would not be allowed inside a single unit for unrestricted civilian use. We know that when properly used betavoltaics are safe. But what about im-proper use / improper disposal / potential for abuse? At any rate, current perception of nuclear power by general public is not that good, so marketing nuclear batteries will present certain challenge.
The answer mentions that advancements in technology could help with these issues. So, these are the advancements concerning this technology in my setting.
Pick the right isotope for the mission. Story wise this is an amazing source of tension. Furthermore carrying chargeable units to get energy boosts for certain applications later in the mission is a solution. In the beginning of the mission the device is far above is normal energy needs.
"There are, of course isotopes with power densities much higher but they encounter other problems." This is great. What are these other problems? Can they be dealt with? Especially isotopes with half-life's of hours, days and weeks are interesting for many applications.
As I'm more interested in high powered short lived applications, this isn't a big issue. In case it matters, maintenence and redundant systems are the answer.
& 5. Advanced bio and nanotechnology made radiation damage much less relevant. Its an annoyance, nothing more.
Fusion economy makes the energy cost of manufacturing appropriate isotopes much more acceptable.
Critics of nuclear power may discuss their issues with my Gundam's main death ray.
So are there any other issues preventing Alpha and Beta-Voltaics from being used form everthing from weapon power celks to synthsects and Mechas?