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At present, the possible existence of a sterile neutrino having a significantly smaller cross section of interaction with a substance than, for example, electronic antineutrinos from a reactor is being widely discussed. It has been suggested that, due to reactor antineutrino transition into a sterile state, one can observe both the oscillation effect at short distances (5–15 m) from the reactor and a deficiency of the reactor antineutrino flux at large distances. We have investigated the possibility of performing experiments in search for reactor antineutrino oscillations into a sterile state on research reactors. A model experiment has been carried out on a 16-MW WWR-M reactor at the Petersburg Nuclear Physics Institute with a view to implementing a full-scale experiment using a 100-MW SM-3 reactor at the Research Institute of Atomic Reactors (RIAR). Background conditions of these experiments have been studied for both reactors. It is concluded that the implementation of a full-scale Neutrino-4 experiment on the SM-3 reactor at the RIAR is possible.

An experiment on search for neutron–antineutron oscillations is proposed based on the storage of ultracold neutrons (UCNs) in a material trap. The main factors influencing sensitivity of the experiment are the trap size and the amount of UCNs trapped. A high-intensity UCN source will be created at the WWR-M reactor of Petersburg Nuclear Physics Institute, which must provide an UCN density two to three orders of magnitude higher than that in the existing sources. The results of simulations of the experiment for detecting neutron–antineutron oscillations with the new source show that the sensitivity can be increased by ~20–80 times compared to existing depending on the model of neutron reflection from walls.

Placing polycrystalline bismuth filter in front of an ultracold neutron (UCN) source with superfluid helium at 1 K is shown to be effective. The use of this filter ensures a 30-fold decrease (down to 0.5 W) in the level of heat load in the UCN source, while reducing by 30% the flux of neutrons with 9-A wavelength (which are converted into UCNs). The phenomenon of small-angle scattering on polycrystalline bismuth has been studied and shown to be insignificant. Cooling of the filter to liquid nitrogen temperature increases the transmission of 9-A neutrons by only 8%; hence, creation of this cooling system is inexpedient. A project of a technological complex designed for the UCN source at the PIK reactor is presented, which ensures the removal of 1-W heat load from the UCN source with superfluid helium at a 1-K temperature level.

The “Neutrino-4” experiment for the 100-MW SM-3 reactor has been developed with the aim of testing the reactor antineutrino anomaly at Petersburg Nuclear Physics Institute. The advantages of this reactor for studying the antineutrino anomaly are (i) a low background level and (ii) small dimensions (35 × 42 × 42 cm) of the active zone. Operation of a position-sensitive antineutrino detector comprising five working sections and moving so as to cover a region of distances within 6–13 m from the active zone has been simulated by the Monte-Carlo method. The range of experimental sensitivity with respect to the oscillation parameters Δm 2 and sin22θ is determined, which will make it possible to confirm the hypothesis of antineutrino oscillations into a sterile state.

The project of ultracold neutron sources at the PIK reactor with superfluid helium as a moderator is presented. The rate of producing ultracold neutrons in superfluid helium is 100 cm−3 s−1 at neutron flux density Φ(λ = 9 A) = 109 cm−2 s−1 A−1. At a moderator temperature of 1 K within the experimental volume of 351, the density of ultracold neutrons may be equal to 1.3 × 103 cm−3, which is two orders of magnitude exceeds that the currently existing ultracold neutron sources.

The design of a multichannel system of stabilization of the magnetic resonance of ultracold neutrons in a multichamber spectrometer developed in the search for the electric dipole moment (EDM) of the neutron is briefly described. The results of tests on a prototype of this system are presented, which show the possibility of ensuring the stability of resonance lines that is equivalent to a magnetic field variation not exceeding ∼30 fT over a 100-s period of EDM measurements.

The design of a quantum magnetometer on cesium vapor is described. The device is intended for stabilization of the neutron resonance in experiments devoted to the search for the electric dipole moment (EDM) of neutron. The choice of this magnetometer type is justified and its potential sensitivity is estimated.

The design of a permanent-magnet trap for ultracold neutron (UCN) storage is described. This trap excludes neutron collisions with the walls and, hence, eliminates anomalous losses. Used in the experiments on the neutron lifetime determination such UCN traps remove the main systematic error related to the anomalous neutron losses on the walls.