MSCAT etc
John Copley
john.copley at nist.gov
Thu Aug 26 22:17:15 CEST 1999
Kristian
MSCAT does attempt to estimate the statistical error. If you want to run
e.g. 10000 neutrons, you break them up into e.g. 50 groups of 20,
average the results for each group, and then calculate overall means and
variances treating the average results for each group as a single item.
I don't know if I explained this properly but I believe it's pretty
standard. I should point out that since every neutron is scored into
every time channel and every detector at every scattering event, the
results for different times and angles are highly correlated and one
cannot learn anything by looking at the scatter of the points e.g. in a
plot of intensity vs. angle.
Regarding the optical filter calculation, many thanks! I would indeed
appreciate more information, and I'm also wondering if you could do a
few more runs? One of these days I'd like to get familiar with McStas
but I have an instrument to complete before I can do that!
You say the transmission for 0.5 AA neutrons is about 2e-5. What is it
for 5 A neutrons? How much work would it be to calculate the
transmission in steps of 0.1 AA say from 0.1 to 5 AA, using (i) the
reflectivity graphs that I sent you and (ii) idealized reflectivity
graphs with R=1 for Q<=0.265 (sides), R=1 for Q<=0.43 (top/bottom), 0
otherwise?
In terms of running McStas here, Collin Broholm has a student who is
running it. He could probably help me if needed.
Best wishes
John
--
John R.D. Copley
National Institute of Standards and Technology
100 Bureau Drive, Stop 8562
Gaithersburg, MD 20899-8562
Tel: (301)975-5133/6220
FAX: (301)921-9847
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