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A. I. Frank

Publications and source records attributed to A. I. Frank.

14 recordsLinked to original sources

Passage of neutrons through accelerating crystal and the acceleration effect

The problem of changing the energy of a neutron when it passes through an accelerating crystal under conditions close to the Bragg condition is considered. It is shown that, similar to the case of the passage of long-wavelength neutrons through a refractive sample, the accelerated motion of a crystal results in a change in neutron energy. The physical nature of the phenomenon in both cases is determined by the difference in the Doppler frequency shift at the entrance and exit of the wave through the sample. The difference between the case of ordinary refraction of long-wavelength neutrons and the case of wave passage through a crystal under conditions where diffraction has a dominant influence on the nature of wave propagation is only quantitative. The results obtained are qualitatively consistent with the available experimental data.

physics.optics

The concept of a superconducting spin flipper - neutron decelerator for a UCN source at a pulsed reactor

The work is devoted to the development of a conceptual design for a gradient spin flipper - neutron decelerator, which is the main component of a designed UCN source for a pulsed reactor. In close cooperation between the JINR group and SuperOx, a preliminary design of a stationary gradient magnet for the adiabatic spin flipper has been developed. A thorough calculation of the magnetic field configuration has been performed. The movement of neutrons in the magnetic field generated by the designed magnetic system has been simulated, and the deceleration time of neutrons in the spin flipper has been analyzed. The results obtained give grounds for hope that the idea of creating a UCN source based on pulsed accumulation in a trap using non-stationary neutron deceleration is feasible.

physics.ins-det

To the UCN source with pulsed filling of a trap

The paper is devoted to the discussion of the possibility of creating UCN sources based on the principle of pulse accumulation (PA) in traps. The implementation of the PA principle would make it possible to create a source with a flux of UCN in a trap significantly exceeding the time average. The paper provides a comparative analysis of various approaches to the implementation of the idea of PA of UCN in traps remoted from the place of their generation. Based on this analysis, the concept of the UCN source, the creation of which is planned at the IBR-2M pulse reactor, was formulated. A distinctive feature of the designed source is a combination of several approaches to ensuring the pulsed structure of neutron bunches reaching the UCN trap. One of them is the deceleration of the pulsed flux of VCN using a resonant flipper, the second is the use of compensating time lenses.

physics.ins-det

On the new possibility of pulse accumulation of UCN

The paper considers the concept of an ultracold neutron source (UCN) based on the deceleration of very cold neutrons (VCN) by a local decelerating device. As the latter, it is proposed to use a gradient spin flipper. It is shown that in this case, the flux of VCNs, which after deceleration are converted into the UCN, has a pulse structure. In this case, the duration of neutron bunches can be significantly less than their repetition period. Accordingly, the density of the neutron flux in the bunch will significantly exceed the average value. This opens up the possibility of pulse filling of the UCN trap, without preliminary time focusing

physics.ins-det

Acceleration effect and the possibility of its observation in neutron-optical experiment

The development of ideas about the optical phenomenon called the accelerating matter effect led to the hypothesis of the existence of a very general acceleration effect. Its formulation is that the result of the particle interaction with any object moving with acceleration should be a change in its energy and frequency. The validity of the acceleration effect hypothesis in quantum mechanics has recently been confirmed by numerically solving a number of problems related to the interaction of a wave packet with potential structures moving with acceleration. If these ideas are true, they can be fully attributed to the case of neutron scattering on the atomic nuclei of accelerating matter. Since the time of neutron interaction with the nucleus is very short, the observation of the acceleration effect during scattering by nuclei requires them to move with a very high acceleration. This goal can be achieved if centripetal acceleration is used.

quant-ph

On the possibility of creating a UCN source on a periodic pulsed reactor

The possibility of creating a UCN source on a periodic pulsed reactor is considered. It is shown that the implementation of the time focusing principle based on non-stationary neutron diffraction and the idea of the UCN trap pulse filling allow creating a sufficiently intense UCN source in a moderate-power pulsed reactor.

physics.ins-det

Neutron focusing in time and magnification of the time lens

The relation between the duration of the pulse of the neutron flux generated by the neutron source and the time image of this pulse formed by the time lens is considered. It is shown that the ratio of these magnitudes called "time magnification" depends not only on the geometric parameters of the device, as previously assumed, but also on the neutron velocity before and after the lens.

physics.gen-ph

Interaction of a wave packet with potential structures moving with acceleration

The paper is devoted to a numerical study of the problem of interaction of the wave packet with potential structures moving with constant acceleration. In all the cases considered the result of the interaction is a change in the velocity spectrum. In the first approximation the magnitude of the shift in the spectrum is determined by the product of acceleration by group delay time. Also, as the direction of acceleration reverses the effect changes its sign. The results are completely consistent with the idea of universality of the Effect of Acceleration which consists in a change in the frequency of the wave at scattering on an object moving with acceleration.

quant-ph

Interaction of a wave with an accelerating object and the equivalence principle

A new look at the so-called effect of an accelerating matter is presented. It was previously stated that the effect is optical in nature and consists in changing the frequency of the wave passing through a refractive sample moving with acceleration. However, from a simple consideration based on the principle of equivalence, it follows that the idea of the connection of the effect only with the refraction phenomenon is unreasonably narrow, and a change in the wave frequency should inevitably occur during scattering by any object moving with acceleration. Such an object can be either an elementary scatterer or any device transmitting a narrowband signal.

physics.gen-ph

Spectroscopy of ultracold neutrons using diffraction by a moving grating

Spectra of ultracold neutrons that appeared in experiments on neutron diffraction by a moving grating were measured using the time-of-flight Fourier spectrometer. Diffraction lines of five orders were observed simultaneously. The obtained data are in good agreement with the theoretical predictions based on the multiwave dynamical theory of neutron diffraction by a moving grating.

nucl-ex

Time-of-flight Fourier UCN spectrometer

We describe a new time-of-flight Fourier spectrometer for investigation of UCN diffraction by a moving grating. The device operates in the regime of a discrete set of modulation frequencies. The results of the first experiments show that the spectrometer may be used for obtaining UCN energy spectra in the energy range of 60$÷$200 neV with a resolution of about 5 neV. The accuracy of determination of the line position was estimated to be several units of $10^{-10}$ eV

physics.ins-det

A new approach to the experiment intended to test the weak equivalence principle for the neutron

A new approach to the free fall experiment with UCN is proposed. The idea is that the experiment is performed with neutrons from different equidistant lines of a discrete energy spectrum with a precisely known distance between the lines. Such a spectrum may be formed by neutron diffraction from a moving phase grating. Time-of-flight values of neutrons from different lines of the spectrum must be measured. Neither the initial neutron energy, nor the geometry parameters of the installation are required to be known in this method.

nucl-ex

Dynamical theory of diffraction on moving grating

In the framework of the approximation of slowly varying amplitudes a multiwave dynamical theory of neutron diffraction on a moving phase grating was developed. The influence of the velocity of the grating, its period and height of the slits on the discrete energy spectrum and intensity of various diffraction orders was analyzed.

physics.optics

Spectrometer for new gravitational experiment with UCN

We describe an experimental installation for a new test of the weak equivalence principle for neutron. The device is a sensitive gravitational spectrometer for ultra-cold neutrons allowing to precisely compare the gain in kinetic energy of free falling neutrons to quanta of energy ${\hbar}Ω$ 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 $5{\times}10^{-3}$ 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.

physics.ins-det