Solar neutrino research. View of the structure housing the GALLEX experiment. Located under 1400 metres of rock in the Gran Sasso Laboratory, Italy, GALLEX is looking for neutrinos created by nuclear fusion reactions in the interior of the Sun. GALLEX consists of a tank containing 54 tonnes of gallium trichloride. Solar neutrinos interact with the atoms of gallium and give rise to a radioactive isotope of germanium. This process creates about one atom of germanium a day. Every 3 weeks the germanium atoms are chemically extracted and counted. GALLEX hopes to resolve the missing solar neutrino" problem."