Elastic Neutron Scattering Measurements Using Larmor Precession of Polarized Neutrons

Abstract

An overview will be given of new instruments using Larmor precession of polarized neutrons in precession regions with inclined front and end faces. These instruments concern small angle scattering, neutron reflectometry and high-resolution diffraction. The advantages of the first application, spin echo small angle scattering (SESANS), with respect to conventional SANS, is the range of applicability and orders of magnitude higher available intensity. The reflectometry application makes it possible to measure the momentum dependent intensity without hindrance of the waviness of the sample also with the high intensity of SESANS. The high resolution application enables one to measure very high resolution diffraction (10 −5 relative in momentum space) without angular of wavelength confinement of the beam, thus with very high intensity.

Characterization and Analysis of Porosity and Pore Structures

“…The fi nal type of small angle scattering instrument to be discussed here is the spin-echo SANS experiment (SESANS, Pynn 1980;Keller et al 1995;Gähler et al 1996;Rekveldt 1996;Bouwman et al , 2004Bouwman et al , 2008Krouglov et al 2003a,b,c;Rekveldt et al 2003Rekveldt et al , 2005Uca et al 2003;Pynn et al 2005;Grigoriev et al 2006;Plomp et al 2007;Andersson et al 2008a,b;Li et al 2010;Washington et al 2014). As with other SAS experiments the spin-echo technique also measures elastic scattering, but begins with a polarized neutron beam, and is based on the Larmor precession of neutron spins in a magnetic fi eld (Mezei 1972(Mezei , 1980.…”

Coherence approach to neutron polarization propagation in instruments

“…Incoherent scattering, large angle coherent scattering, or absorption can be taken into account by a suitable imaginary part of the refraction index. 5 The approximation is valid for thermal neutrons as used in spin echo small angle neutron scattering [18][19][20][21] ͑SESANS͒ or ultrasmall angle neutron scattering [22][23][24] as the refractive index is close to unity. Note that the deviation from unity of the refractive index is proportional to the square of the wavelength so it increases rapidly for increasing wavelength.…”

“…This is called SESANS. 18,20 The basis for this technique was first discussed by Mezei in 1972 ͑Ref. 27͒ and Pynn in 1978.…”

Transformation cycle between the spherically symmetric correlation function, projected correlation function and differential cross section as implemented inSASfit

“…For SEMSANS the normalized V s =V 0 Michelson visibility of the fringes (Strobl et al, 2015;Li et al, 2016) depends in the same way on the projected correlation function as the visibility in DF imaging [equation 1]. For SESANS the normalized depolarization P s ðÞ=P 0 ðÞ as a function of the spin-echo length (Rekveldt et al, 2003;Krouglov et al, 2003) also has the same dependency on the projected correlation function and is given as…”