Sans spheres intensity fix

[Lomholy]

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Please describe what your PR is adding in terms of features or bugfixes:
The Sans_spheres comp was not matching the otherwise validated SANS_spheres2.comp in intensity, when simulated under similar circumstances. Likewise it was not matching an analytical calculation completely.

This PR adds a Sigma to the attenuation factor of the Sans_spheres component that brings it in line with the SANS_spheres2 component and the analytical calculation. This PR also adds a missing attenuation the SANS_spheres2 component, in the case that it only simulates 1 scattering event inside the sample.

Furthermore the Sans_spheres component was missing a conversion from deg to rad in its angular focusing option. This has been added with this PR.

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Declaration of use of AI-tools

• Please add a checkmark here if you used AI-tools during the work for this contribution
• Furter, please describe how / where and for what the tools were used:
  I used an AI to rewrite the header into a readme file.

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:
MacOS Tahoe 26.6.2

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mccode-clangformat tool to apply the standard McCode component indentation scheme
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes a new instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have ensured that basic use of the instrument is OK (e.g. it compiles?)
  • ... and provided reasonable default parameters in that instrument that produce reasonable output
  • ... and maybe even added a %Example: line to describe expected behaviour
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised
  • My new instrument is added within the examples hierarchy in a folder in the style of examples/ESS/New_stuff/New_stuff.instr
  • My new instrument has a new, unique filename, not clashing with existing example instruments

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[Lomholy]

Sans_spheres mcdoc:

SANS_spheres mcdoc:

Test_sans_spheres mcdoc:

[willend]

@Lomholy the work as such looks good, but all instruments including the modified comp require an overhaul of the %Example: line.

(I usually run a series of 1e6 1e7 and 1e8 simulations and use some reasonable mean-value on the target-monitor)

[Lomholy]

Ah this of course makes sense. I will get on it soon! (I am at a conference so no promises before next week :D)

Regarding the templateSANS_Mantid_2 I am quite surprised that the discrepancy is so large. I assume this is caused some old change that has not triggered the instrument. I will investigate when time allows.

[willend]

@Lomholy no worries, take your time and enjoy the conference. :)

[Lomholy]

Hi @willend I've gotten around to having a look at the templateSANS_Mantid and it is strange. It seems that the detector used outputs both detector image, and average detector image, which yields two very different values. Now, for some reason, after this commit the average value is being used for comparison to the value in the %Example, instead of the detector image values.

Here is the output of an mcrun with this pr:

And here is the output of an mcrun with main before the pr:

So while I will change it to the new value around 7.8e+7 I am quite unsure as to how to ensure that the test is not using the "other" value of the detector.

For reference, here is the readout of the CI test:

[Lomholy]

Nevermind the above comment. I think the example is using the correct output, and the issue was merely due to my tests having too low statistics.

[Lomholy]

mcviewtests of the instruments using the two modified components:

[willend]

@Lomholy thanks, nice work!

The README.md’s for instruments are reserved for what mcdoc can directly script from just the instrument file - so I have moved your .md to Test_Sans_spheres.md (which is automatically linked-to from the main README.md)