Re: [Ifeffit] Find white line position

Dear Bruce and Carlo, Thank you very much for your reply. Now I understand how Athena find the peak position by the Bruce's answer. I think some kinds of interpolation is made when Athena find the white line position because the peak position that Athena tells seems to be more precise than the energy step in the measurement. Is that right? Actually, I use this function often because it is quite useful for quick check for white line position. But I will be careful when I use it from now on, following the Bruce' advice. I agree with the Carlo's suggestion that it is better to use the curve-fitting method to find the white line position. Best regards, Hiroshi

Date: Thu, 2 Aug 2018 09:48:02 -0500 (CDT) From: Carlo Segre To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Find white line position Message-ID: Content-Type: text/plain; charset=US-ASCII; format=flowed

Hi Hiroshi,

You are probably better off putting a bit more time into the analysis and simply fitting with an arctangent and a gaussian to get the white line position.

Carlo

On Thu, 2 Aug 2018, Bruce Ravel wrote:

...

It's not very sophisticated.

Starting with the "flattened" spectrum (see http://bruceravel.github.io/demeter/documents/Athena/bkg/norm.html#the-flatt...), it simply finds the highest point in the spectrum. Literally just the ceiling function.

The flattened spectrum is used rather than the normalized spectrum because the curvature of the post-edge (or even the curvature of the pre-edge in fluorescence data with a energy dispersive detector) could result in other regions being higher in value than the white line.

This is a pretty horrible algorithm. It is, I think, guaranteed to find an obviously wrong point for a metal. Basically it works for spectra with a white line and it will almost certainly fail for spectra without a white line.

Use with caution!

HTH, B

On 08/02/2018 01:28 AM, Hiroshi OJI wrote:

...

Dear all,

I have a question about one of the useful function, "find white line position" in Athena.

Could anyone tell me how Athena find the white line position by this function? In other words, I would like to know the algorithm to find the white line position in Athena.

Thank you very much for your help, in advance.

Best regards,

Hiroshi Oji

-- Carlo U. Segre -- Duchossois Leadership Professor of Physics Interim Chair, Department of Chemistry Director, Center for Synchrotron Radiation Research and Instrumentation Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://phys.iit.edu/~segre segre@debian.org

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