add mu lookup table

[yucongalicechen]

Problem

let's have a lookup table somewhere here in diffpy.utils. Look in periodic_table which I think is somewhere in diffpy, to figure out how we handle lookup tables (they go in some kind of static directory).

(pasted from Simon's comment in #45)

Proposed solution

[bobleesj]

@yucongalicechen I tried to read the attached comment but couldn't really figure out what this "lookup table" contains. What would be the input/output for this table? Could you pls clarify this for me?

[yucongalicechen]

@yucongalicechen I tried to read the attached comment but couldn't really figure out what this "lookup table" contains. What would be the input/output for this table? Could you pls clarify this for me?

I think the lookup table can be organized by materials sample name, x-ray energy, and possible density (along with other relevant parameters), so the user can easily check and get mu values based on their sample information. I'm not sure how to retrive such a table at this point. I will probably work on UC2 in #45 first and may have a better idea of the best approach for this issue.

There's a similar issue in labpdfproc: diffpy/diffpy.labpdfproc#9.

[bobleesj]

Thanks @yucongalicechen

From the issue above diffpy/diffpy.labpdfproc#9, it seems like we could get a function from pdfgetx3.

• inputs - (1) composition (2) wavelength
• output - muD (optimal)

Yes, let's resolve 3.6.0 issues first asap!

[sbillinge]

I am expecting that we are accessing existing data. We either store it or access through a remote API. Let's discuss before to much work is done. The first task is to make a plan

[yucongalicechen]

^found this website, might be helpful: https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients