[Ifeffit] Is good EXAFS data possible with 0.01 transmission coefficient
Damon Turney
dturney at ccny.cuny.edu
Thu Jul 25 17:04:59 CDT 2013
Thank you Matthew Marcus. To answer your questions: Most of the
transmission loss is due to the Mn particulates. The 0.01
transmission coefficient (a.k.a. ~4 absorption lengths) is in regards
to xray energies above the absorption edge. Below the absorption
edge the transmission coefficient should be 0.1 to 0.4. I don't
understand the definition of "edge jump" or how to calculate it (but
trust me I will be reading up on all of this ASAP). Anyway, the
transmission coefficient contains all the required information.
I doubt that I have "pinhole effect" because the MnO2 is small
particulates (10 micron diameter) evenly dispersed throughout the 300
micron thick sample, so I doubt there are any pinholes.
Matthew are these "distortions" that you speak of the same thing as
"harmonics" that I've read about in "XAFS for Everyone" that can
complicate XAFS analysis?
Thanks,
Damon
On Thu, Jul 25, 2013 at 5:09 PM,
<ifeffit-request at millenia.cars.aps.anl.gov> wrote:
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> Today's Topics:
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> 1. Is good EXAFS data possible with 0.01 transmission
> coefficient (Damon Turney)
> 2. Re: Is good EXAFS data possible with 0.01 transmission
> coefficient (Matthew Marcus)
> 3. Re: Is good EXAFS data possible with 0.01 transmission
> coefficient (Scott Calvin)
> 4. Re: Is good EXAFS data possible with 0.01 transmission
> coefficient (Scott Calvin)
> 5. Re: Is good EXAFS data possible with 0.01 transmission
> coefficient (Matthew Marcus)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 25 Jul 2013 16:07:57 -0400
> From: Damon Turney <dturney at ccny.cuny.edu>
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] Is good EXAFS data possible with 0.01 transmission
> coefficient
> Message-ID:
> <CAOHT-BNp4s8fjUdQnwfgkxaFAzDrKrDtyX1BMenM_HWByeyiQw at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi IFEFFIT community,
>
> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
> sample is a powder mixture of carbon powder, MnO2 powder, and
> potassium hydroxide liquid. The transmission coefficient of 6.5keV
> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
> 0.01. I am told that the ionization chamber detectors can easily
> detect the x-ray beam after this ~0.01 transmission loss (by
> increasing the gain on the detector), but I would like to ask the
> IFEFFIT community if there will be other problems with the EXAFS
> technique when the transmission coefficient is so low. Does anybody
> have comments?
>
> Much thanks -- if you have any info I greatly appreciate it!
> Damon Turney
> City College of New York
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 25 Jul 2013 13:33:12 -0700
> From: Matthew Marcus <mamarcus at lbl.gov>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Is good EXAFS data possible with 0.01
> transmission coefficient
> Message-ID: <51F18B88.5020600 at lbl.gov>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Is most of the transmission loss due to the Mn or the matrix (C, KOH, etc)? Is that 0.01 above or below the edge?
> If most of the absorption is due to the matrix with the Mn providing an edge jump of <1, then I'd say that you have a shot.
> However, you become very sensitive to harmonics and glitches. If the Mn provides an edge jump of much less than 1, them fluorescence
> would be the way to go, if possible. With thick samples in transmission, you have an issue with hole effect. For instance, it's
> possible that your 1% transmission comes entirely from 1% area of pinholes, with the actual material being almost completely
> opaque. If that happens, you get a reduced edge jump and reduced EXAFS amplitude, with distortions resembling overabsorption.
>
> If you're in the thick-matrix scenario, a possible workaround would be to make a sample which contains only matrix and is as nearly as
> possible exactly as thick as the real sample, and measure its transmission, and subtract.
> mam
>
> On 7/25/2013 1:07 PM, Damon Turney wrote:
>> Hi IFEFFIT community,
>>
>> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
>> sample is a powder mixture of carbon powder, MnO2 powder, and
>> potassium hydroxide liquid. The transmission coefficient of 6.5keV
>> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
>> 0.01. I am told that the ionization chamber detectors can easily
>> detect the x-ray beam after this ~0.01 transmission loss (by
>> increasing the gain on the detector), but I would like to ask the
>> IFEFFIT community if there will be other problems with the EXAFS
>> technique when the transmission coefficient is so low. Does anybody
>> have comments?
>>
>> Much thanks -- if you have any info I greatly appreciate it!
>> Damon Turney
>> City College of New York
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>
>
> ------------------------------
>
> Message: 3
> Date: Thu, 25 Jul 2013 16:33:40 -0400
> From: Scott Calvin <scalvin at sarahlawrence.edu>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Is good EXAFS data possible with 0.01
> transmission coefficient
> Message-ID: <6A1D5E8E-88FB-4A0B-9CCC-9AF0CDB6623F at slc.edu>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Damon,
>
> So you're saying you expect the total absorption of the sample to be less than 0.01 absorption lengths? In other words, if the detectors and electronics were identical, you would expect It = I0 exp(-0.01)?
>
> While possible to measure in transmission, such a sample would normally be measured in fluorescence. If done that way, the measurement is routine.
>
> Or am I misunderstanding your description? (I am not entirely sure what you mean by "transmission coefficient.")
>
> --Scott Calvin
> Sarah Lawrence College
>
> On Jul 25, 2013, at 4:07 PM, Damon Turney <dturney at ccny.cuny.edu> wrote:
>
>> Hi IFEFFIT community,
>>
>> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
>> sample is a powder mixture of carbon powder, MnO2 powder, and
>> potassium hydroxide liquid. The transmission coefficient of 6.5keV
>> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
>> 0.01. I am told that the ionization chamber detectors can easily
>> detect the x-ray beam after this ~0.01 transmission loss (by
>> increasing the gain on the detector), but I would like to ask the
>> IFEFFIT community if there will be other problems with the EXAFS
>> technique when the transmission coefficient is so low. Does anybody
>> have comments?
>>
>> Much thanks -- if you have any info I greatly appreciate it!
>> Damon Turney
>> City College of New York
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Thu, 25 Jul 2013 17:03:53 -0400
> From: Scott Calvin <scalvin at sarahlawrence.edu>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Is good EXAFS data possible with 0.01
> transmission coefficient
> Message-ID: <0830DFDB-C085-45F5-B434-B79DF12ABD72 at slc.edu>
> Content-Type: text/plain; charset="us-ascii"
>
> Oops--Matthew's interpretation is doubtless what you actually meant--i.e., that It < 0.01 I0. Therefore disregard my previous comment!
>
> And I concur with Matthew's comments, now that I understand the circumstances.
>
> --Scott Calvin
> Sarah Lawrence College
>
> On Jul 25, 2013, at 4:33 PM, Matthew Marcus <mamarcus at lbl.gov> wrote:
>
>> Is most of the transmission loss due to the Mn or the matrix (C, KOH, etc)? Is that 0.01 above or below the edge?
>> If most of the absorption is due to the matrix with the Mn providing an edge jump of <1, then I'd say that you have a shot.
>> However, you become very sensitive to harmonics and glitches. If the Mn provides an edge jump of much less than 1, them fluorescence
>> would be the way to go, if possible. With thick samples in transmission, you have an issue with hole effect. For instance, it's
>> possible that your 1% transmission comes entirely from 1% area of pinholes, with the actual material being almost completely
>> opaque. If that happens, you get a reduced edge jump and reduced EXAFS amplitude, with distortions resembling overabsorption.
>>
>> If you're in the thick-matrix scenario, a possible workaround would be to make a sample which contains only matrix and is as nearly as
>> possible exactly as thick as the real sample, and measure its transmission, and subtract.
>> mam
>>
>> On 7/25/2013 1:07 PM, Damon Turney wrote:
>>> Hi IFEFFIT community,
>>>
>>> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
>>> sample is a powder mixture of carbon powder, MnO2 powder, and
>>> potassium hydroxide liquid. The transmission coefficient of 6.5keV
>>> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
>>> 0.01. I am told that the ionization chamber detectors can easily
>>> detect the x-ray beam after this ~0.01 transmission loss (by
>>> increasing the gain on the detector), but I would like to ask the
>>> IFEFFIT community if there will be other problems with the EXAFS
>>> technique when the transmission coefficient is so low. Does anybody
>>> have comments?
>>>
>>> Much thanks -- if you have any info I greatly appreciate it!
>>> Damon Turney
>>> City College of New York
>>> _______________________________________________
>>> Ifeffit mailing list
>>> Ifeffit at millenia.cars.aps.anl.gov
>>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
>
>
>
> ------------------------------
>
> Message: 5
> Date: Thu, 25 Jul 2013 14:09:49 -0700
> From: Matthew Marcus <mamarcus at lbl.gov>
> To: XAFS Analysis using Ifeffit <ifeffit at millenia.cars.aps.anl.gov>
> Subject: Re: [Ifeffit] Is good EXAFS data possible with 0.01
> transmission coefficient
> Message-ID: <51F1941D.3010507 at lbl.gov>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> I'm pretty sure he has the opposite problem - the transmission is <0.01. That's assuming that "transmission coefficient" == "transmission".
> mam
>
> On 7/25/2013 1:33 PM, Scott Calvin wrote:
>> Hi Damon,
>>
>> So you're saying you expect the total absorption of the sample to be less than 0.01 absorption lengths? In other words, if the detectors and electronics were identical, you would expect It = I0 exp(-0.01)?
>>
>> While possible to measure in transmission, such a sample would normally be measured in fluorescence. If done that way, the measurement is routine.
>>
>> Or am I misunderstanding your description? (I am not entirely sure what you mean by "transmission coefficient.")
>>
>> --Scott Calvin
>> Sarah Lawrence College
>>
>> On Jul 25, 2013, at 4:07 PM, Damon Turney <dturney at ccny.cuny.edu> wrote:
>>
>>> Hi IFEFFIT community,
>>>
>>> I will make measurements soon at Brookhaven's NSLS to do EXAFS, and my
>>> sample is a powder mixture of carbon powder, MnO2 powder, and
>>> potassium hydroxide liquid. The transmission coefficient of 6.5keV
>>> x-rays (the Mn K edge is at ~6.5keV) through the sample is ~0.001 to
>>> 0.01. I am told that the ionization chamber detectors can easily
>>> detect the x-ray beam after this ~0.01 transmission loss (by
>>> increasing the gain on the detector), but I would like to ask the
>>> IFEFFIT community if there will be other problems with the EXAFS
>>> technique when the transmission coefficient is so low. Does anybody
>>> have comments?
>>>
>>> Much thanks -- if you have any info I greatly appreciate it!
>>> Damon Turney
>>> City College of New York
>>> _______________________________________________
>>> Ifeffit mailing list
>>> Ifeffit at millenia.cars.aps.anl.gov
>>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>>
>> _______________________________________________
>> Ifeffit mailing list
>> Ifeffit at millenia.cars.aps.anl.gov
>> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>>
>
>
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