Automated EDS standards calibration

• US 9,188,555 B2
• Filed: 07/30/2012
• Issued: 11/17/2015
• Est. Priority Date: 07/30/2012
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Owen, Michael James
• Primary Examiner(s): Le, John H
• Application Number:
  US13/561,821
• Publication Number:
  US 20140032131A1
• Time in Patent Office: 1,205 Days
• Field of Search: 702/28, 702/40, 702/134, 250/305, 250/307, 250/310, 250/339.09, 356/326, 850/10
• US Class Current: 1/1
• CPC Class Codes: G01N 2223/3037 standards (constitution)
• CPC Class Codes: G01N 2223/616 earth materials
• CPC Class Codes: G01N 23/2252 Measuring emitted X-rays, e.g. electron probe microanalysis [EPMA]
• CPC Class Codes: G01N 33/2823 Raw oil, drilling fluid or polyphasic mixtures
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544

Abstract

This invention relates to a method and system for determining the composition of an unknown sample. The present invention is directed to a method of calibrating an x-ray spectrometer that does not require measuring all possible elements under the operating conditions used to measure the unknown sample to be analyzed. According to a preferred embodiment, the local instrument can be calibrated from an x-ray spectrum of a single elemental standard. The instrument will have a stored library containing high quality spectra for all elements being analyzed. The analysis of the single element is compared to the library spectra for that element to define a transformation that is used to create a calibrated spectra library that includes a calibrated spectrum for each spectrum in the original library. The spectra generated by the local instrument can be compared to the calibrated library spectra to determine the elements in an unknown mineral.

Claims

1. A method of performing energy-dispersive x-ray spectroscopy, comprising:

creating, using a source instrument, library spectra by;

directing, using an electron source and focusing options of the source instrument, an electron beam toward one or more elemental standards;

obtaining, using a x-ray detector of the source instrument, energy-dispersive x-ray spectra of the one or more elemental standards;

creating a spectra library from the spectra of the one or more elemental standards;

creating, using a field instrument, calibration spectra, the calibration spectra having a lower resolution than the library spectra by;

directing, using an electron source and focusing options of the field instrument, an electron beam toward an elemental standard sample;

obtaining, using an x-ray detector of the field instrument, an energy-dispersive x-ray spectrum of the elemental standard sample;

comparing the spectrum of the elemental standard sample to an elemental standard of the spectra library;

determining a transformation based on the comparison of the spectrum of the elemental standard sample to the elemental standard of the spectra library;

applying the transformation to the spectra library to generate a calibrated spectra library;

determining, using the field instrument, the elements in an unknown mineral sample, the unknown mineral sample comprising a sample of unknown mineral composition, by;

directing, using an electron source and focusing options of the field instrument, an electron beam toward the unknown mineral sample;

obtaining, using the x-ray detector of the field instrument, an energy-dispersive x-ray spectrum of the unknown mineral sample; and

comparing the obtained spectrum of the unknown mineral sample to the calibrated spectra library.

2. The method of claim 1, in which determining the transformation includes determining coefficients for a smoothing function.

3. The method of claim 1, in which applying the transformation includes applying a smoothing function.

4. The method of claim 3 in which applying the smoothing function includes applying a Gaussian smoothing function.

5. The method of claim 1, further comprising storing the library spectra in a database.

6. The method of claim 1 in which applying the transformation to the spectra library includes applying a Gaussian blur to the spectra library.

7. The method of claim 1 further comprising determining elemental composition of the unknown sample through elemental decomposition based on the comparison of the generated spectrum of the unknown mineral sample to the calibrated sample library.

8. The method of claim 1 in which obtaining spectra of elemental standards includes obtaining spectra of elemental standards in a high resolution instrument in which at least one million x-ray counts are detected.

9. The method of claim 1 in which scanning an elemental standard sample includes scanning an elemental standard sample with an instrument of lower resolution than the high resolution instrument for obtaining the spectra of elemental standards.

10. The method of claim 1 in which obtaining a spectra of elemental standard and scanning an elemental standard sample are performed on different mineral analysis instruments.

11. The method of claim 1 in which obtaining spectra of elemental standards includes obtaining spectra of all 72 elements in mineral analysis.

12. The method of claim 1 in which scanning an elemental standard includes scanning copper.

13. The method of claim 1 in which scanning an elemental standard includes scanning a sample holder.

14. The method of claim 1, further comprising identifying the unknown mineral sample.

15. A method of calibrating an instrument for mineral analysis, comprising:

scanning, using an electron beam of the instrument, an elemental standard sample;

obtaining, using an x-ray detector of the instrument, an energy-dispersive x-ray spectrum of the elemental standard sample;

comparing the obtained spectrum of the elemental standard sample to a library value of a library of elemental standard spectra in which the library value has higher resolution than the obtained spectrum of the elemental standard sample;

generating calibration coefficients from the comparison of the obtained spectrum of the elemental standard sample to the library value; and

applying the calibration coefficients to the library of elemental standard spectra to generate a calibrated library of elemental standard spectra.

16. The method of claim 15 in which applying the calibration coefficients to the library of elemental standard spectra includes applying a Gaussian blur to the elemental standard spectra.

17. The method of claim 15 in which the library of elemental standard spectra is obtained on an instrument different from the instrument being calibrated.

18. The method of claim 15 in which the library of elemental standard spectra includes spectra from 72 minerals for mineral analysis.

19. The method of claim 15 further comprising:

loading an unknown mineral sample into the instrument;

generating an unknown sample spectrum;

comparing the generated unknown sample spectrum to the calibrated library of elemental standard spectra; and

determining elemental composition of the unknown sample.

20. A system for determining composition of an unknown sample, comprising:

a source of electrons for forming an electron beam;

focusing optics for focusing a beam of electrons onto a sample;

an x-ray detector for detecting x-rays emitted from the sample upon impact of the electron beam;

a computer readable memory storing;

library x-ray spectra corresponding to multiple elements;

computer instructions for;

comparing a spectrum acquired from a known element with a library x-ray spectrum of the known element in which the library x-ray spectrum of the known element has a higher resolution than the spectrum acquired from the known element;

determining a transformation between the spectrum acquired from the known element and the library spectrum of the known element;

applying the transformation to all spectra of the library x-ray spectra to determine calibration spectra;

comparing a spectrum of a material of an unknown composition to the calibration spectra to determine the composition of the unknown material.