Papers by Alexander Petukhov
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Abstract We present the new concept and neutron test results of the third generation PASTIS devic... more Abstract We present the new concept and neutron test results of the third generation PASTIS device for XYZ wide-angle polarization analysis for thermal neutrons. PASTIS-3 uses two polarized 3He Neutron Spin filter Cells (NSF) for polarizing and analyzing neutrons spins, flipping the incident neutron beam polarization by reversing the 3He spin state of the polarizing entrance cell. We detail a new coil design for high spatial homogeneity of the magnetic field in any field direction, and the calculation method employed to optimize the geometry and to characterize the field gradients. Various components of the apparatus are described with particular attention to their performance and impact on the relaxation time of the NSF cells. Finally, we present test results of the new device tested on the thermal triple-axis spectrometer IN20 at the ILL.
Physical Review Letters, 2020
In the standard model of particle physics, the weak interaction is described by vector and axialv... more In the standard model of particle physics, the weak interaction is described by vector and axialvector couplings only. Non-zero scalar or tensor interactions would imply an additional contribution to the differential decay rate of the neutron, the Fierz interference term. We derive a limit on this hypothetical term from a measurement using spin polarized neutrons. This method is statistically less sensitive than the determination from the spectral shape but features much cleaner systematics.
Physical Review D, 2003
The lowest stationary quantum state of neutrons in the Earth's gravitational field is identified ... more The lowest stationary quantum state of neutrons in the Earth's gravitational field is identified in the measurement of neutron transmission between a horizontal mirror on the bottom and an absorber/scatterer on top. Such an assembly is not transparent for neutrons if the absorber height is smaller than the ''height'' of the lowest quantum state.
Physical Review A, 2009
Polarized 3 He produced by spin-exchange optical pumping ͑SEOP͒ has potential as a neutron spin f... more Polarized 3 He produced by spin-exchange optical pumping ͑SEOP͒ has potential as a neutron spin filter for polarization and polarization analysis in many neutron-scattering and neutron particle physics applications. The advantage of the SEOP method is its suitability for providing continuous stable polarization over the course of long experiments. However, we have discovered that exposure to high neutron flux leads to additional strong relaxation mechanisms in the optically polarized alkali-metal vapor used to polarize the 3 He. At a neutron flux density of 4.7ϫ 10 9 cm −2 s −1 , the alkali-metal relaxation rate increased from 100 to 1000 s −1 leading to reduced alkali-metal polarization. Other effects such as time dependence and gas composition dependence were explored to help understand the processes. In this paper we discuss our observations and present possible solutions for practical use of SEOP as a neutron spin filter for high-flux density applications.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from... more An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from the SM coating for one spin-component and total absorption for the other, thus providing a perfectly polarized neutron beam at the exit. However, in practice, the substrate's neutron-nuclei optical potential does not match perfectly that for spin-down neutrons in the SM. For a positive step in the optical potential (as in a / SM on substrate), this mismatch results in spin-independent total reflection for neutrons with small momentum transfer , limiting the useful neutron bandwidth in the low-region. To overcome this limitation, we propose to replace single-crystal substrates by media with higher optical potential than that for spin-down neutrons in the SM ferromagnetic layers. We found single-crystal sapphire and single-crystal quartz as good candidates for solid-state / SM polarizers. To verify this idea, we coated a thick plate of single-crystal sapphire with a = 2.4 / SM. At the T3 instrument at the ILL, we measured the spin-up and spin-down reflectivity curves with = 7.5 Å neutrons incident from the substrate to the interface between the substrate and the SM coating. The results of this experimental test were in excellent agreement with our expectations: the bandwidth of high polarizing power extended significantly into the low-region. This finding, together with the possibility to apply a strong magnetizing field, opens a new road to produce high-efficient solid-state SM polarizers with an extended neutron wavelength bandwidth and near-to-perfect polarizing power.
Comptes Rendus Physique, 2011
An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from... more An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from the SM coating for one spin-component and total absorption for the other, thus providing a perfectly polarized neutron beam at the exit. However, in practice, the substrate's neutron-nuclei optical potential does not match perfectly that for spin-down neutrons in the SM. For a positive step in the optical potential (as in a Fe SiN / x SM on Si substrate), this mismatch results in spin-independent total reflection for neutrons with small momentum transfer Q , limiting the useful neutron bandwidth in the low-Q region. To overcome this limitation, we propose to replace Si single-crystal substrates by media with higher optical potential than that for spin-down neutrons in the SM ferromagnetic layers. We found single-crystal sapphire and single-crystal quartz as good candidates for solid-state Fe SiN / x SM polarizers. To verify this idea, we coated a thick plate of single-crystal sapphi...
Nature, 2002
The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle th... more The discrete quantum properties of matter are manifest in a variety of phenomena. Any particle that is trapped in a sufficiently deep and wide potential well is settled in quantum bound states. For example, the existence of quantum states of electrons in an electromagnetic ...
Nuclear Physics A, 2009
We present two measurements of parity-violating secondary particle emission asymmetry in the reac... more We present two measurements of parity-violating secondary particle emission asymmetry in the reactions of polarized cold neutrons and light nuclei. We aim at studies of the neutral weak currents in nucleon-nucleon interaction. First, we describe the triton emission asymmetry in the Li6(n,α)H3 reaction. It is equal to αP−odd6Li=−(8.8±2.1)⋅10−8. Second, we present the γ-rays emission asymmetry in the nuclear reaction B10(n,α)Li∗7→γ→Li7(g.s.).
Polarized H3e produced by spin-exchange optical pumping (SEOP) has potential as a neutron spin fi... more Polarized H3e produced by spin-exchange optical pumping (SEOP) has potential as a neutron spin filter for polarization and polarization analysis in many neutron-scattering and neutron particle physics applications. The advantage of the SEOP method is its suitability for providing continuous stable polarization over the course of long experiments. However, we have discovered that exposure to high neutron flux leads to
An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from... more An ideal solid-state supermirror (SM) neutron polarizer assumes total reflection of neutrons from the SM coating for one spin-component and total absorption for the other, thus providing a perfectly polarized neutron beam at the exit. However, in practice, the substrate's neutron-nuclei optical potential does not match perfectly that for spin-down neutrons in the SM. For a positive step in the optical potential (as in a Fe SiN / x SM on Si substrate), this mismatch results in spin-independent total reflection for neutrons with small momentum transfer Q , limiting the useful neutron bandwidth in the low-Q region. To overcome this limitation, we propose to replace Si single-crystal substrates by media with higher optical potential than that for spin-down neutrons in the SM ferromagnetic layers. We found single-crystal sapphire and single-crystal quartz as good candidates for solid-state Fe SiN / x SM polarizers. To verify this idea, we coated a thick plate of single-crystal sapphire with a = m 2.5 Fe SiN / x SM. At the T3 instrument at the ILL, we measured the spin-up and spin-down reflectivity curves with λ = Å 7.5 neutrons incident from the substrate to the interface between the substrate and the SM coating. Results of this experimental test are in excellent agreement with our expectations: the bandwidth of high polarizing power extends significantly into the low-Q region. This finding, together with the possibility to apply a strong magnetizing field, opens a new road to produce high-efficiency solid-state SM polarizers with an extended neutron wavelength bandwidth and near-to-perfect polarizing power.
Physical Review A, 2015
We discuss the behaviour of the Larmor frequency shift and the longitudinal relaxation rate due t... more We discuss the behaviour of the Larmor frequency shift and the longitudinal relaxation rate due to non-uniform electromagnetic fields on an assembly of spin 1/2 particles, in adiabatic and nonadiabatic regimes. We also show some general relations between the various frequency shifts and between the frequency shifts and relaxation rates. The remarkable feature of all our results is that they were obtained without any specific assumptions on the explicit form of the correlation functions of the fields. Hence, we expect that our results are valid both for diffusive and ballistic regime of motion and arbitrary cell shapes and surface scattering. These results can then be applied to a wide variety of realistic systems. * [email protected] arXiv:1509.04655v1 [physics.atom-ph] 15 Sep 2015 2
JETP Letters
The spatial parity-violating and parity-conserving asymmetry has been investigated in the separat... more The spatial parity-violating and parity-conserving asymmetry has been investigated in the separation of fragments of the fission of ²³âµU and ²³â¹Pu by slow polarized neutrons. The average values of the asymmetry coefficients and the experimental distributions of the coefficients as a function of the mass and total kinetic energy intervals of the fission fragments have been obtained.
The spatial parity-violating and parity-conserving asymmetry has been investigated in the separat... more The spatial parity-violating and parity-conserving asymmetry has been investigated in the separation of fragments of the fission of ²³âµU and ²³â¹Pu by slow polarized neutrons. The average values of the asymmetry coefficients and the experimental distributions of the coefficients as a function of the mass and total kinetic energy intervals of the fission fragments have been obtained.
We propose a new arrangement of super mirror polarisers to polarise a white cold or thermal neutr... more We propose a new arrangement of super mirror polarisers to polarise a white cold or thermal neutron beam. With this method, the dependence of the neutron polarisation on angle and wavelength is suppressed efficiently. For such a neutron beam, the average polarisation can be measured with a precision of better than 10 À3 using opaque spin filters. Average polarisation values of 0.997 for a cold neutron beam can be obtained. Furthermore, the method can be used for efficient polarisation analysis. Here, however, the precision is limited to a few times 10 À3 by depolarisation effects. We present the method and results of experimental tests. r
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Papers by Alexander Petukhov