A key part of the secondary in a fusion bomb is lithium-6-deuteride. When irradiated with high-energy neutrons, Li-6 creates tritium, which mixes with the deuterium in the same mixture and fuses at a relatively low temperature. Russian weapon designers have reported (1993) that red mercury was the Soviet codename for lithium-6, which has an affinity for mercury and tends to acquire a red colour due to mercuric impurities during its separation process.
