A. Ioffe

Perfect crystal neutron interferometer set-up at Berlin Neutron Scattering Centre

Abstract A description is given of the perfect crystal neutron interferometer set-up installed at a neutron guide of the BER-II (10 MW) reactor of the Hahn-Meitner-Institut.

Precise determination of the neutron scattering length of lead isotopes 204Pb, 207Pb and 208Pb by neutron interferometry

Abstract: The neutron scattering length of lead isotopes 204Pb, 207Pb and208Pb are determined by a set of neutron interferometry experiments. The obtained values b(208)= 9.494(30) fm, b(207)= 9.286(16) fm, b(204)= 10.893(78) fm have much higher accuracy then current table data. Together with the precise value of b for natural lead, these results represent a complete set of data and allow one to calculate b(206)= 9.221(69) fm, which is in the very good agreement with the present day experimental value.

The study of the electrical charge distribution inside the neutron by neutron scattering methods

The neutron scattering cross section contains significant information about the internal electrical structure of the neutron. Recent achievements in neutron interferometry allow the precision measurements of the neutron scattering length (Δb/b∼10−5) at the crucial point E∼0, where the cross-section measurements are strongly influenced by small-angle scattering at the sample and are not very reliable.

Recent experiments in neutron interferometry and optics at NIST

Abstract The neutron interferometry and optics facility at the National Institute of Standards and Technology (NIST) has been in full operation since September 1996 as both a NIST research facility and as a national user facility. Unprecedented performance characteristics have been achieved in interferometry. A very busy schedule of experiments in fundamental physics, applied physics, and materials science has developed.

Determination of the neutron scattering length of208Pb by the neutron interferometry method

The coherent scattering length of208Pb was measured by means of the neutron interferometry method and the value ofbc=9.494(29) fm was obtained.

Triple-axis spectroscopy with sub-μeV resolution without use of polarized neutrons

Abstract We propose a new method that allows for a drastic increase of the resolution of triple-axis spectrometers, up to μeV/sub-μeV region. In contrast to neutron spin-echo (NSE)-based methods, the proposed method principally does not require the use of polarized neutrons and is free from problems connected with the mutual influence of the magnetic field of precession coils or with the influence of scattered magnetic fields from the sample environment. Featuring the decoupling of the neutron polarization and energy resolution, the proposed method opens new possibilities for the study of magnetic phenomena in solids, especially by combining the polarization analysis with high-resolution spectroscopy. The proposed method also allows for an easy implementation of the principle of the NSE focusing, when the resolution ellipse is aligned along a dispersion curve.

Observation of 4π-symmetry of the neutron wave function under space rotation

Abstract We observed 4π-symmetry of the neutron wave function under rotation in space produced by slowly rotating an adiabatic guide field. In contrast to all previous works, the present experiment is of purely topological nature, i.e. it does not involve the Larmor precession and the result depends only on the topology and not on the value of the magnetic field and the neutron magnetic moment. This is the first experimental observation which cannot be explained by simply applying the common concept of wave optical dynamic phase, consistently with the Stern–Gerlach spin quantization, to each of the “spin-up” and “spin-down” energy eigenstates superposed in the neutron wave function.

Dispersion free measurements in neutron interferometry

Abstract Neutron interferometry is a method of high-accuracy determination of neutron scattering length b c . The phase shift acquired by a neutron wave that propagates through a sample inserted in one of the beams of an interferometer is proportional to the neutron wavelength. A knowledge of it precisely defines the accuracy of the determination of b c . As a solution of this problem, the non-dispersive sample geometry was proposed. In this case the phase shift is λ -independent but the very precise orientation of the sample relative to the crystal planes of the interferometer is required. To overcome this obstacle a new nondispersive phase difference method was developed which achieves an accuracy in the determination of b c of even better than 10 −4 , i.e. at the level of 10 −5 . This method was used for the high-accuracy measurement of the coherent scattering length of Si. Experiments carried out in HMI Berlin and NIST Gaithersburg and NPI Rez on different interferometric facilities at different neutron wavelengths proved that the coherent scattering lengths can be measured with a relative uncertainty of 0.002%.

A new type of high-resolution neutron spectrometer

Abstract The movement of a neutron interferometer transverse to the incoming beam produces an interference pattern in velocity space. A change of the neutron velocity due to the scattering in the sample leads to an observable change in the interference pattern. Such a spectrometer has an extremely high-energy resolution approaching the picoelectronvolt region that is a few orders of magnitude higher than the resolution achievable by neutron spin-echo (NSE) spectrometers. Similar to NSE spectrometers, the resolution is not connected with the monochromatization of the incoming beam. However, in contrast to NSE spectrometers the operation of the proposed spectrometer does not necessarily require a polarized neutron beam. By decoupling the polarization and the resolution new possibilities are opened for the study of magnetic phenomena in solids, where the NSE method is principally not applicable because of neutron precession in the sample. The use of the proposed technique in a low-resolution mode can be useful in combination with triple-axis spectrometers allowing a dramatic improvement in their energy resolution without the use of polarized neutrons, and hence avoiding the problem of parasitic magnetic fields.

Upgrading scientific capabilities of the neutron interferometer in NPI Řež

Abstract Recently, the neutron interferometer set-up installed at NPI Řež has been reconstructed in order to improve the quality of the experimental results and to enlarge its flexibility for solving a wider range of physical problems. A new sample holder permits to position, to rotate in a horizontal plane and tilt the sample in both beams inside the interferometer. The upgraded interferometer facility was tested by measuring the very sensitive coherent scattering length of Si performed by a nondispersive phase difference method. The result of this experiment is in very good agreement with the results obtained from the measurements carried out in HMI Berlin and NIST Gaithersburg . It shows that the coherent scattering length can be measured using our instrument with a relative uncertainty of 0.002%.