Hydrogen and deuterium cold and ultracold neutron sources at the PNPI research reactor in Gatchina

St. Petersburg Nuclear Physics Institute (PNPI) is located in Gatchina, Russia, has a 16 MW WWR-M reactor. The reactor has been operating since 1959 and since the middle of the 1970s the cold and ultracold neutron production has been in progress there. As intended, this program has increased substantially the experimental capabilities of the reactor as an instrument for fundamental physics research. It has allowed us to make progress in the investigations which require an extremely high neutron beam intensity such as the search for neutron electric dipole moment, neutron lifetime and correlation constants measurements, the search for P-odd effects in interactions with cold neutrons and so on. Having started with a simple cold beryllium UCN converter, we went on to use the most efficient moderators such as liquid hydrogen and deuterium, recently solid deuterium. Some new approaches were developed in designing cold sources, which resulted in our medium power reactor becoming competitive with high flux reactors. (author)