"Neutron blankets" Deuterium and tritium fusion generates neutrons. The substitution of deuterium atoms for hydrogen atoms thus reduces scattering noise. Its isotope deuterium, or heavy hydrogen, contains a proton and a neutron. Fusion boosting is achieved by introducing tritium and deuterium gas. The cycle is a combination of endothermic and exothermic neutronic reactions involving lithium and deuterium/tritium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. A very prominent example is hydrogen and its isotope deuterium. Light nuclei like deuterium and lithium can combine in nuclear fusion. These two clouds of gas contain no elements heavier than hydrogen and deuterium. Water enriched in molecules that include deuterium instead of protium is called heavy water. The easiest to fuse are deuterium and tritium. Deuterated chloroform is an isotopologue of chloroform with a single deuterium atom. This group consists of deuterium and helium-3. However, forming helium-4 requires the intermediate step of forming deuterium. For deuterium and tritium, the ratios are about 1/3670 and 1/5497 respectively.