Neutron standing waves in layered systems: Formation, detection, and application in neutron physics and for investigatio
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utron Standing Waves in Layered Systems: Formation, Detection, and Application in Neutron Physics and for Investigation of Nanostructures Yu. V. Nikitenko Joint Institute for Nuclear Research, Dubna, Russia e-mail: [email protected] Abstract—Specific features of different regimes of the neutron’s wave field are theoretically considered. The results of experimental studies of the regime of a neutron’s standing waves both in the primary channel of neutron specular reflection and in different channels of registration of secondary emission are considered. Some studies of layered structures performed with the help of a neutron’s standing waves are considered. The prospects of application of a neutron’s standing waves in neutron physics and for investigation of layered nanostructures are considered. PACS numbers: 28.20.-v DOI: 10.1134/S1063779609060069
INTRODUCTION In 1946, E. Fermi discovered the phenomenon of specular reflection of neutrons from matter [1], and in 1951, Hughes and Burgy used the magnetic mirror for obtaining polarized neutrons [2]. Later, specular reflection of neutrons was used episodically mainly for measurement of the amplitude of elastic coherent neutron scattering by matter nuclei. It was not until 1981 when the first publications [3, 4] appeared, in which the application of the method of a neutron’s specular reflection for investigation of the surface and interfaces of a solid, was described. Since then surface studies with neutrons have become systematic. Neutron reflection was first applied in measurements of the transmission of a magnetic mirror’s neutron guides at the IBR-30 reactor [5] at the Laboratory of Neutron Physics (JINR, Dubna). And in 1986, soon after putting into operation the high flux pulsed reactor IBR-2 at the Laboratory of Neutron Physics, the studies using neutron reflectometry with polarized neutrons (neutron polarization reflectometry) began at the new polarized neutron spectrometer. Modern polarization equipment was used at the polarized neutron spectrometer: the polarizer and the polarization analyzer with an FeCo/TiGd bilayer (St. Petersburg Nuclear Physics Institute, Gatchina) and Korneev’s spin flipper with an extended region [6]. At present, standard neutron reflectometry usually means the measurement method using specular reflection of neutrons in the range of a transferred wave vector Q = 0.01–0.3 Å–1; in this case, the neutron’s reflection coefficient is between 10–5 and 10–1. The fundamental specific feature of standard neutron reflectometry is the application of the regime of the traveling neutron wave, for which the reflected wave’s amplitude, is smaller than the incident wave’s amplitude. Taking this into account,
standard neutron reflectometry can be called the traveling wave’s neutron reflectometry. Standard neutron reflectometry has a spatial resolution of 10–1000 Å and is used for investigation of layered structures with a layer thickness larger than 10 Å. Figure 1 shows the reflectometric curves R+(Q) and R–(Q) obtained for the structure 20 × [Fe(3 nm/V(2
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