Divergence_monitor

[Kim Lefmann]

Hi Georg,

I am glad to hear that you are working on McStas. I hope that you have had good 
progress in the past two weeks.

I have included a preliminary manual entry for the component. This will answer 
one of you questions. The question about the coupling between the position and 
divergence I do not understand fully: Of cource if you illuminate a plane with a 
point source, there will be a correlation between the position and divergence 
(to take a simple example), but the detector does not care about that, it simply 
calculates the angle between the neutron path and the detector normal, whereever 
the neutron intersects this plane.

Good luck with your simulations,

Kim

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The divergence sensitive monitor

The component Divergence_monitor is a rectangular single monitor
with an opening in the x-y plane,
which is sensitive to the neutron divergence, i.e. the angle
between the neutron path and the monitor surface normal.
 
The divergence is divided into horisontal and vertical divergencies,
which are calculated as h_div = atan(vx/vz) and v_div = atan(vy/vz),
respectively. Only neutrons within a divergence window
of h_div = (-h_maxdiv ; h_maxdiv), v_div = (-v_maxdiv ; v_maxdiv) are
detected. The counts are binned in an array of nh x nv pixels.

The input parameters for Divergence_monitor are the opening coordinates
(xmin, xmax, ymin, ymax), the number of pixels (nh, nv), the 
parameters h_maxdiv, v_maxdiv defining the divergence interval,
and a name of the file in which to store the detected intensities.

Note that a divergence sensitive monitor with a small opening may be 
thought of as a non-reversing pinhole camera.