[neutron-mc] Bragg's law for single crystals

[Gutmann, MJ (Matthias)]

Hi,

	when using a single crystal sample, it seems that Bragg's law has
been incorporated
as

	lambda = 2 * d * sin(2*theta)

instead of

	lambda = 2 * d * sin(theta)

Maybe worth checking whether this is the case.

Matthias