A. N. Strepetov

New Experiment on the Observation of the Effect of Accelerating Matter in Neutron Optics

The results of a new experiment on the observation of the effect of accelerating matter in neutron optics are reported. It has been shown that the velocity of neutrons periodically varies when they pass through a harmonically moving refractive sample. The idea of the experiment is based on time focusing, i.e., on the fact that the periodic modulation of the velocity of neutrons leads to the oscillation of the flux density at the observation point. The magnitude of the effect is in reasonable agreement with the theoretical predictions. The experiment has been carried out with ultracold neutrons and a change of ±1 cm/s has been detected in the neutron velocity.

A Quantum Time Lens for Ultracold Neutrons

The possibility of creating a time lens, an analogue of the zone plate in X-ray optics, for ultracold neutrons is experimentally demonstrated. The neutron energy was changed by means of a purely quantum effect: the phase modulation of a neutron wave at a variable modulation frequency. The modulator was a phase grating with variable spatial period moving across the neutron beam.

Effect of accelerating matter in neutron optics

The results of an experiment on the observation of a new neutron-optical effect are reported. It has been experimentally shown that the energy of a neutron passing through a refracting sample moving with acceleration changes. The magnitude of the effect is in qualitative agreement with theoretical predictions. The experiment was carried out with ultracold neutrons and the energy transform is equal to ±2 × 10−10 eV.

Neutron Diffraction at a Moving Grating as a Nonstationary Quantum Phenomenon

The observation of the discrete energy spectrum in a new experiment on the diffraction of ultracold neutrons at a moving phase grating is reported. The results are in quantitative agreement with theoretical predictions and can be treated as additional evidence of the validity of the plane-wave representation of the initial neutron state.

Spectrometer for new gravitational experiment with UCN

Abstract We describe an experimental installation for a new test of the weak equivalence principle for neutron. The device is a sensitive gravitational spectrometer for ultracold neutrons allowing to precisely compare the gain in kinetic energy of free falling neutrons to quanta of energy ℏ Ω transferred to the neutron via a non stationary device, i.e. a quantum modulator. The results of first test experiments indicate a collection rate allowing measurements of the factor of equivalence γ with a statistical uncertainty in the order of 5×10 −3 per day. A number of systematic effects were found, which partially can be easily corrected. For the elimination of others more detailed investigations and analysis are needed. Some possibilities to improve the device are also discussed.

Accelerating medium effect as a general wave phenomenon

Already at the end of the last century theory predicted that the wave number and frequency of any wave will change when passing an accelerating refractive medium. The effect was calculated both for electromagnetic and neutron waves. As a refractive index may be introduced for waves of any nature one can speak about a very general Accelerating Medium Effect. As far as we know this effect has not yet been observed for light. Here we report on a neutron-optics experiments performed with ultra-cold neutrons where this effect has been demonstrated for the first time ever. The maximum energy transform in the experiment was ± (2÷6) ×10−10 eV which agrees with theory within less than 10%. Possibilities for future investigations of the Accelerating Medium effect will be discussed.

Flexible polyvinyl chloride neutron guides for transporting ultracold and very cold neutrons

The transmission of ultracold neutrons (UCNs) through flexible polyvinyl chloride (PVC) tubes with lengths of up to 3 m and an internal diameter of 6–8 mm has been studied. High UCN transmission is found even for arbitrarily bent tubes (single bend, double bend, triple bend, figure eight, etc.). The transmission can be improved significantly by coating the inner surface of the tube with a thin layer of liquid fluorine polymer. The prospects of these neutron guides in fundamental and applied research are discussed.

Experimental Verification of the 1/ v Law for the Absorption Cross Section of Ultracold Neutrons in Natural Gadolinium

The results of a new experiment on the transmission of ultracold neutrons through a natural gadolinium film are reported. The results indicate that the transmission of the sample is unchanged when the sample moves parallel to its surface. The neutron velocity in the sample coordinate system varies in a range of 6–35 m/s. It follows from the constancy of the sample transmission that the imaginary part of the scattering length is constant; i.e., the law 1/v is valid for the capture cross section of the free nucleus with an accuracy of about 0.5%.

Space and energy profiling of neutron beams using flexible fluoropolymer neutron guides

Experimental data have been presented for the spatial deflection and energy profiling of reactor neutron beams using flexible polyvinylchloride tubes, the inner surfaces of which are covered by a liquid fluoropolymer thin film.

A convergent neutron lens based on glass capillaries

The properties of a convergent neutron lens in the form of an assembly of bent glass capillaries have been experimentally investigated. Each capillary is a conical tube with a length of 22.5 cm, an entrance diameter of 0.25 mm, and an exit diameter of 0.17 mm. The spectrum of thermal neutrons incident on the lens entry is formed on the beam of the IR-8 reactor by means of a diamond microcrystalline filter and investigated with a time-of-flight spectrometer. The spatial distribution of the neutron beam at the exit from the lens is measured using the position-sensitive image plate detector. The measured focal length of the lens is 75–80 mm. The possibility of focusing neutrons with an increase in the local beam density at the lens axis by a factor of 4.9 is demonstrated.