Mineral identification using sequential decomposition into elements from mineral definitions

• US 9,048,067 B2
• Filed: 10/26/2012
• Issued: 06/02/2015
• Est. Priority Date: 10/26/2012
• 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): Ippolito, Nicole
• Assistant Examiner(s): Chang, Hanway
• Application Number:
  US13/661,830
• Publication Number:
  US 20140117229A1
• Time in Patent Office: 949 Days
• Field of Search: 250/306, 250/307, 250/309, 250/310, 250/311, 250/305
• US Class Current: 1/1
• CPC Class Codes: G01N 23/2252 Measuring emitted X-rays, e.g. electron probe microanalysis [EPMA]
• CPC Class Codes: H01J 2237/221 Image processing
• CPC Class Codes: H01J 2237/24585 Other variables, e.g. energy, mass, velocity, time, temperature
• CPC Class Codes: H01J 2237/2561 electron
• CPC Class Codes: H01J 37/252 Tubes for spot-analysing by electron or ion beams; Microanalysers

Abstract

Mineral definitions each include a list of elements, each of the elements having a corresponding standard spectrum. To determine the composition of an unknown mineral sample, the acquired spectrum of the sample is sequentially decomposed into the standard spectra of the elements from the element list of each of the mineral definitions, and a similarity metric computed for each mineral definition. The unknown mineral is identified as the mineral having the best similarity metric.

Claims

1. A method of determining the mineral present at a point in a sample of unknown composition, comprising:

directing an electron beam toward a point on the sample to acquire an x-ray spectrum;

providing multiple mineral definitions, each mineral definition including a list of elements, each of the elements having a corresponding standard spectrum obtained from a first number of x-ray counts, the x-ray spectrum of the sample being obtained from a second number of x-ray counts, the second number of x-ray counts being fewer than the first number of x-ray counts for the standard spectrum of each element;

comparing the acquired spectrum to a combined standard spectra of the elements from the element list of each of the mineral definitions;

determining which of the combined standard spectra of elements from mineral definitions best matches the acquired spectrum;

classifying the point on the sample as being composed of the mineral whose definition produced the best match.

2. The method of claim 1 in which comparing the spectrum of the unknown mineral sample to the combined spectra of the elements from each mineral definition includes splitting elemental standard spectra into segments and individually fitting segments of the acquired spectrum of the sample to segments of the elemental standard spectra.

3. The method of claim 2 in which the multiple segments correspond to multiple peaks in the standard spectra.

4. The method of claim 1 in which comparing the spectrum of the unknown mineral sample to the combined spectra of the elements from each mineral definition includes calculating an overall probability match between the sample and the combined spectra of the elements from each mineral definition.

5. The method of claim 1 in which calculating an overall probability for the unknown mineral sample to the mineral definition includes determining an average backscattered electron value and standard deviation for the multiple known samples of a mineral and comparing said average backscattered electron value and standard deviation to a backscattered electron value of the unknown mineral sample.

6. The method of claim 1 comparing the spectrum of the unknown mineral sample to the combined spectra of the elements from each mineral definition includes computing a nearest point in the mineral definition to values from the decomposed spectrum.

7. A system for spectrum data analysis, comprising:

an electron beam column for directing an electron beam toward a sample;

an x-ray spectrometer for measuring the energy of x-rays emitted from the sample in response to the electron beam;

a processor for executing computer instructions to analyze a mineral sample; and

a computer memory for storing instructions for carrying out the method of claim 1.

8. A method of spectrum data analysis, the method comprising:

acquiring a spectrum of an unknown mineral sample;

selecting a mineral definition, the mineral definition including an element list, each of the elements in the element list having a corresponding standard spectrum obtained from a first number of x-ray counts, the x-ray spectrum of the unknown mineral sample being obtained from a second number of x-ray counts, the second number of x-ray counts being fewer than the first number of x-ray counts for the standard spectrum of each element;

decomposing the spectrum of the unknown mineral sample using elements from the selected element list; and

calculating an overall match probability between the unknown mineral sample and the mineral definition.

9. The method of claim 8 in which the steps of selecting a mineral definition, decomposing the spectrum of the unknown mineral sample using elements from the element list from the selected mineral definition, and calculating an overall match probability for the unknown mineral sample to the mineral definition are repeated for each of multiple mineral definitions.

10. The method of claim 9 further comprising classifying the sample of unknown composition as the mineral whose definition produced the highest match probability.

11. The method of claim 8, further comprising computing a nearest point in the mineral definition to values from the decomposed spectrum.

12. The method of claim 8, further comprising displaying the overall probability for a user to review.

13. The method of claim 8, further comprising:

creating a mineral definition by measuring multiple known samples of a mineral; and

storing the definition in a database.

14. The method of claim 13 in which the step of creating a mineral definition by measuring multiple known samples of a mineral is repeated multiple times to create multiple mineral definitions.

15. The method of claim 8 in which calculating an overall probability for the unknown mineral sample to the mineral definition includes determining an average backscattered electron value and standard deviation for the multiple known samples of a mineral and comparing said average backscattered electron value and standard deviation to a backscattered electron value of the unknown mineral sample.

16. The method of claim 8, in which decomposing the spectrum of the unknown mineral sample using elements from the selected element list includes obtaining elemental spectra for the mineral definition selected and splitting the elemental spectra into segments based on the number of peaks present in the spectrum of the unknown mineral sample.

17. The method of claim 16, in which splitting the spectrum into segments includes splitting the spectrum into regions around known peak energies.

18. The method of claim 8, in which decomposing the spectrum of the unknown mineral sample includes performing a curve fitting of the elemental spectra to the spectrum of the unknown mineral sample.

19. The method of claim 18 in which performing a curve fitting of elemental spectra includes a linear decomposition.

20. The method of claim 8 in which computing a nearest point in the mineral definition to values from the decomposed spectrum includes a least squares method to determine the minimum distance from the values from the decomposed spectrum to the nearest point in the mineral definition.

21. The method of claim 8 in which calculating an overall probability match for the unknown mineral sample to the mineral definition includes calculating individual element probability matches from the decomposed spectrum to the mineral definition and calculating an overall similarity metric by multiplying the individual element probability matches.

22. A method of spectrum data analysis, the method comprising:

a) acquiring a spectrum of an unknown mineral sample;

b) selecting one mineral definition of multiple mineral definitions obtained from multiple samples of multiple minerals;

c) selecting an element list from the selected mineral definition, each of the elements in the element list having a corresponding standard spectrum obtained from a first number of x-ray counts, the x-ray spectrum of the sample being obtained from a second number of x-ray counts, the second number of x-ray counts being fewer than the first number of x-ray counts for the standard spectrum of each element;

d) decomposing the spectrum of the unknown mineral sample to yield compositional values of the unknown mineral sample;

e) computing a nearest point in the mineral definition from the compositional values of the unknown mineral sample;

f) calculating a mineral probability match for the selected mineral definition

g) repeating steps b-f until all of the multiple mineral definitions have been selected.

23. The method of claim 22 further comprising identifying the unknown mineral sample as the mineral definition with the highest mineral probability match.

24. The method of claim 22 in which decomposing the spectrum of the unknown mineral sample to yield compositional values of the unknown mineral sample includes obtaining elemental spectra for the mineral definition selected, splitting the elemental spectra of the selected element list into segments based on the number of peaks present in the spectrum of the unknown mineral sample and performing a curve-fitting to fit the segments against spectrum of the unknown mineral sample.

25. The method of claim 22 in which calculating a mineral probability match for the selected mineral definition includes calculating a probability match for a backscattered electron value and a count value.

26. A method of spectrum data analysis, the method comprising:

acquiring a spectrum of an unknown mineral sample;

creating a mineral definition by collecting multiple spectrums from multiple samples of a mineral;

selecting an element list from the mineral definition, each of the elements in the element list having a corresponding standard spectrum obtained from a first number of x-ray counts, the x-ray spectrum of the sample being obtained from a second number of x-ray counts, the second number of x-ray counts being fewer than the first number of x-ray counts for the standard spectrum of each element;

splitting the elemental spectra for the element list into segments based on the number of peaks in the spectrum of the unknown mineral sample; and

performing a curve-fitting to fit the segmented elemental spectra against the spectrum of the unknown mineral sample.

27. The method of claim 26 in which performing a curve-fitting to fit the segmented elemental spectra against the spectrum of the unknown mineral sample yields a compositional value.

28. The method of claim 26 further comprising computing a nearest point in the mineral definition to the compositional value.

29. The method of claim 26 further comprising calculating an overall mineral probability match.