Synchrotron emission profile

jespersimonsen

Dear TOPAS user community.

I have a question regarding setting up a synchrotron emission profile. Currently I have the following in my input file:

lam ymin_on_ymax 0.0001 la 1.0 lo =wavlen; lh 0.0001

I am a bit unsure about what the different keywords are.
lam: I assume this takes the following keywords to calculate the peak broadening from the emission profile
ymin_on_ymax: the technical reference isn't helping me a lot, can someone explain further?
la: I can't figure it out,
lo: is the wavelength
lh: seems like it is a peak width? Is it the energy bandwidth?

Are la and lh something I should know from the beamline, need to determine or are they defaults in this case?

Thanks in advance for your help.
Kind regards,
Jesper

rowlesmr

la is the emission line area. You have one emission line, so 1 is fine.
lo is the wavelength in angstroms
lh is the loreztian halfwidth of the emission line in milli-angstroms
lg is the gaussian halfwidth of the emission line in milli-angstroms
ymin_on_ymax is a measure of how far out to calculate a peak. If the height of the peak is 1 at the peak position, then the peak is calculated out until the intensity falls to ymin_on_ymax

jespersimonsen

Hi Matthew,

Thanks for that explanation, that helped a lot. I guess I would have to speak to the beamline scientist about good values for lh and lg? Or are there good default values for a synchrotron?

Cheers,
Jesper

johnsoevans

It's common to assume that the source contribution to the final broadening is small with respect to other contributions and just set a small value for lh as in your first post. If you're using an empirical instrument resolution function (e.g. derived from LaB6 or CeO2) this approach is normally fine.

jespersimonsen

Hi John,

Thank you very much for that!

Cheers,
Jesper