Xenothium is an extremely rare and dangerous compound. It is very unstable and thus quite volatile, but this instability makes it highly suitable as a high-output power source. However, Xenothium appears to not be radioactive, since several characters were seen handling it without the protection of a radiation suit. This suggests that the Xenothium's molecular structure gradually breaks down, releasing energy, in a process similar to radioactive decay, though more in a chemical rather than energetic way. Still, Xenothium is considered an extremely hazardous material; the only safe way to dispose of it apppears to let it decay naturally.
The most prominent use Xenothium has seen in the series is as the power source of the Red X suit and the disintegrator cannon designed by Professor Chang.