Ever heard of Wigner energy? It caused the worst nuclear disaster in British history. That's because it works much better in fiction than in reality.
Nuclear fission can cause energy to store up in ordinary material, until it suddenly explodes. This is what happened in 1957, when one of the piles at the Windscale nuclear facility in England caught fire (a "pile" is a large stack of alternating layers of graphite and uranium). The uranium atoms split, sending out both energy and neutrons. The neutrons split other uranium atoms, and keep the reaction going. Graphite slows down neutrons.
The Wigner Effect and the Windscale Facility
The slowing down process isn't as simple as it sounds. It isn't even as simple as people thought it to be in 1950, when the piles were built. As neutrons fly out through the graphite, they cause breaks in its lattice structure. Atoms are displaced, and in turn displace other atoms. Sometimes the original break in the structure can cause a massive amount of secondary breaks in a process called a displacement cascade. This breaking and displacement is called the Wigner effect.
While some atoms come to rest firmly where they should, re-forming the lattice structure, others stop in odd places. These atoms have a large amount of potential energy ready to be released. Imagine a car crashing into the side of a building and leaving one wall on the point of buckling, or a ball rolling just up to the edge of a cliff and teetering on the precipice. This is called Wigner energy. A little jolt, and it can be set free.
Today, nuclear facilities regularly plan these little jolts. The graphite -—or any other material meant to catch neutrons — is regularly heated to the point where the energy is released and the structure realigns in a process called annealing. The people at the Windscale facility attempted to use annealing to release the energy, but they weren't set up for the task. The Wigner effect had only recently been explored. Its importance came to light in 1952, after the pile had already been built.
It was during one of the annealing periods that the facility caught fire. The staff at the facility was pushing it beyond its specified limits and had the pile's heat sensors incorrectly positioned. They believed that the pile was cooling, when in fact it was over-heating in places far away from the sensors. Eventually, the pile caught fire. The fire took days to put out, and spread some radioactive material across Europe.
The Wigner Bomb in Science Fiction
Graphite is a relatively easily annealed substance. You can shoot it full of neutrons for a while, then heat it up to 250 degrees Celsius, and it will put itself right again. In theory, though, nearly any solid substance could be shot full of Wigner energy. The first step would be putting it next to some neutron-emitting substance for a while. It could be a natural source of radiation, or it could be human-made. With the material primed, it would be an incredible weapon. To set it off, simply walk it up next to whatever needs exploding, and give it a jolt.
There are plenty of advantages to a Wigner bomb... at least as an idea. It's infinitely customizable. Different substances would be capable of storing different amounts of energy, and releasing that energy in different ways. One substance could store a small amount of energy and heat up only to a point where the objects around it ignited, making it perfect for arson. Another substance could let a small amount of energy out quickly, making a light, small bomb. Another could be a building-leveler of a bomb.
Most importantly, the bombs would be undetectable. They're nothing more than lumps of an inert substance. They have no special chemicals or ignition devices. The only thing that makes them different from any other substance are tiny internal flaws that have stored up a lot of energy.
As for flaws? Well, that's why Wigner bombs would only work in fiction. In order to prime them you'd need access to radioactive material for extended periods of time. There no real way of checking to see how much they'll explode, other than doing experiments over and over until you could chart out an explosion pattern for each substance. And, as all they need is a jolt, which sometimes can come from within, they could go off at any time. Totally unworkable in reality.
But if you want your space rebel to blow up a Death Star in your short story, this may be the fictional device for you.