"count rate too low"-help with analyzing small artifacts

[Vanessa Muros]

Hi everyone,

I am doing qualitative analysis of glass beads using various parameters to try to identify colorants and major/minor elements.  Most of the beads are smaller than the detector window. When analyzing some of the beads, especially the very small ones or sometimes just under certain settings, a message appears that the count rate is too low and the data acquisition stops.  I'm wondering if anyone has experienced anything similar in analyzing small artifacts and has any suggestions as to how to work around this.

I'm running the Tracer 5i in Spectrometer Mode and using 3 different acquisition parameters:

-15kV and 25µA, no filter (or sometimes with Ti filter)

-40kV and 10µA, Ti-Al filter

-40kV and 10µA, no filter

I have found that if I increase the current, I can sometimes get around the low count rate issues. So for example I can bump up from 15kV/25µA to 15kV/55µA and can sometimes get it to work.  But I wanted to know if there's anything else I could do to get around this so I can analyze this group of artifacts

thanks!

Vanessa

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Vanessa Muros

Director, Experimental and Archaeological Sciences Lab (EASL)

Cotsen Institute of Archaeology, UCLA

A419 Fowler Building

Los Angeles, CA 90095-1510

t: +1 323 761 9864

vmu...@ucla.edu

https://ucla.academia.edu/VanessaMuros

[Lee Drake]

Hi Vanessa,

This fortunately has a very simple answer. Though keep in mind this circumvents a safety feature. Given that you are not using this in handheld mode, it is ok to consider this. But make sure to take all precautions - make sure the beam is enclosed with the stand, and keep all persons around 2 meters away from the instrument when measuring (using either a wifi connection or long USB cord. Always be mindful of where the beam is. With an object that small it is 100% that x-ray beams are moving around or through the sample. Making sure this analysis is done in a radiation-safe enclosure is very important. Also keep in mind not all states or countries allow this kind of use (Maryland and Canada, to name a couple).

To disable backscatter, go to "Utilities" in the bottom left corner, "System Setup" box in the next menu, and then "Safety". Click the "Disable backscatter button". Read the warning carefully. Then enter the following password: "Not_Safe". You must be logged in as Supervisor to do this - if you need this password consult with your local Bruker representative or lab supervisor.

Again, the backscatter feature in the Tracer 5i's software is designed to prevent x-rays from being emitted in open air. You can prevent this, and disable the instrument's auto features. But remember that you are taking 100% responsibility for the safety of everyone in this case. That said, in designing the Tracer we understood that there would be scenarios where this would be necessary (paper analysis, photography, small archaeological objects, etc.). 

Thanks,

- Lee

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[Vanessa Muros]

Hi Lee,

Thanks so much for this info and for explaining the safety issues. Since the objects are small I’m using the small circular shield so I hope that helps contain the beam and make operation safe with the backscatter feature turned off. But I’ll also make sure no one is around when operated and I’m at a safe distance. I can re-enable the backscatter feature as soon as I’m done with the analysis. 

Thanks,

Vanessa 

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best,

Vanessa

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Vanessa Muros

[Charlotte Parent]

Hi Lee,

Thank you for your explanations.

I am having the same problem when analyzing organic materials (namely, feathers and mummified human remains) with a recently acquired instrument. Thin (feathers) or irregular/curved (mummy fingers) materials are very hard to get a spectra from. Safety protocols of the Canadian Ministry of Labour prevent us from disabling the backscatter safety feature...

Is this a new safety feature in the Tracer 5i? I have used XRF on organic materials (paper, wood, textile) in the past with an older machine and I never had this issue. At the time I was using a Bruker Tracer III SD analyzer and a software that was not Artax for collecting spectra (although analysis was done with Artax) - I can't remember the name of the software but I can find out if relevant.

Are there ways to fix this issue without disabling the safety feature? Or changes I should make to my analytical method?

You will find spectra I got from the feather after increasing current attached to this email in case it's relevant. Data was collected for a second or so before the message popped up and collection stopped. I am also wondering whether I can trust that data or if I should get rid of it since the collection time was so short.

Thank you,

Charlotte

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