Absolute intensities and McStas

[Kristian Nielsen]

> Hi Kristian,
> 
> Thanks for your MAIL. I am a little confused. Am I right in supposing that
> you have assumed a source flux which is constant with energy? If so what
> was the flux?

Yes, the flux is constant with energy, with a value of 10^13
neutrons/(cm^2 * st * AA). I basically re-ran the example we did
together before the workshop.

The main message here is that the results we got then were a factor of
two too low because we used the wrong value for the width of the energy
distribution of the source component. Thus the results agree much better
with experiments than we thought. It is also a good lesson in how
important the correctness aspect of simulation is!

I now have some ideas for how to model absolute intensities in a
useful way. What I will do is to make a source component that takes as
input a tabulation of the flux as a function of energy. The component
will then set the initial neutron weights so that computed intensities
will be absolute.

 - Kristian.