McStas About McStas  Conditions of use  Authors/Contacts  Project funding  Screenshots Download  Components  Install Mailing list Search web/mailinglist Documentation  McStas manual  FAQ  Known problems  Publications  C Compilers  Other  Tutorial Workshops/conferences Developments  Platforms Links Report bugs SVN McStas Ubuntu live-dvd	Basic neutron scattering You may recall the Bragg law from your high school physics $$n\lambda=2d\sin(\theta),$$ giving the scattering condition for a wave of wavelength $\lambda$ against a series of lattice planes with lattice spacing $d$, rotated the angle $\theta$ off the lattice plane normal. $n$ is an integer giving the spectral order of the scattered wave. In neutron science one often refers to the scattering vector, $\vec{Q}$ of a given reflection, where $$Q=\vert\vec{Q}\vert=\frac{2\pi}{d}.$$ This gives us the scattering vector formulation of the Bragg law $$Q=2k\sin(\theta),$$ where $k=\frac{2\pi}{n\lambda}$. The Bragg law / scattering condition is illustrated in Figure 1. Figure 1: Illustration of the Bragg Law. Most of the neutron processes we will study in this paper are elastic, meaning that the wavelength of the neutron is unaltered by the process. Printable version Last Modified: Tuesday, 22-Jun-2004 14:04:14 CEST