In March 1996, a group of scientists at Lawrence Livermore National Laboratory reported that they had serendipitously produced the first identifiably metallic hydrogen for about a microsecond at temperatures of thousands of kelvins, pressures of over , and densities of approximately . The team did not expect to produce metallic hydrogen, as it was not using solid hydrogen, thought to be necessary, and was working at temperatures above those specified by metallization theory. Previous studies in which solid hydrogen was compressed inside diamond anvils to pressures of up to , did not confirm detectable metallization. The team had sought simply to measure the less extreme electrical conductivity changes they expected. The researchers used a 1960s-era light-gas gun, originally employed in guided missile studies, to shoot an impactor plate into a sealed container containing a half-millimeter thick sample of liquid hydrogen. The liquid hydrogen was in contact with wires leading to a device measuring electrical resistance. The scientists found that, as pressure rose to , the electronic energy band gap, a measure of electrical resistance, fell to almost zero. The band gap of hydrogen in its uncompressed state is about , making it an insulator but, as the pressure increases significantly, the band gap gradually fell to . Because the thermal energy of the fluid (the temperature became about  due to compression of the sample) was above , the hydrogen might be considered metallic.