Instead, X-ray lasers rely on the speed of various reactions to create the population inversion. When heated beyond a certain energy level, electrons dissociate from their atoms entirely, producing a gas of nuclei and electrons known as a plasma. Plasma is a gas, and its energy causes it to adiabatically expand according to the ideal gas law. As it does, its temperature drops, eventually reaching a point where the electrons can reconnect to nuclei. The cooling process causes the bulk of the plasma to reach this temperature at roughly the same time. Once reconnected to nuclei, the electrons lose energy through the normal process of releasing photons. Although rapid, this release process is slower than the reconnection process. This results in a brief period where there are a large number of atoms with the electrons in the high-energy just-reconnected state, causing a population inversion.