source:
sasmodels/doc/guide/sesans/sans_to_sesans.rst
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SANS to SESANS conversion
.. currentmodule:: sasmodels
The conversion from SANS into SESANS in absolute units is a simple Hankel transformation when all the small-angle scattered neutrons are detected. First we calculate the Hankel transform including the absolute intensities by
in which J0 is the zeroth order Bessel function, δ the spin-echo length, Q the wave vector transfer and (dΣ)/(dΩ)(Q) the scattering cross section in absolute units. This is a 1-dimensional integral, which can be rather fast. In the numerical calculation we integrate from Qmin = 0.1 × 2π ⁄ Rmax in which Rmax will be model dependent. We determined the factor 0.1 by varying its value until the value of the integral was stable. This happened at a value of 0.3. The have a safety margin of a factor of three we have choosen the value 0.1. For the solid sphere we took 3 times the radius for Rmax . The real integration is performed to Qmax which is an instrumental parameter that is read in from the measurement file. From the equation above we can calculate the polarisation that we measure in a SESANS experiment:
in which t is the thickness of the sample and λ is the wavelength of the neutrons.
