Method of processing a particle spectrum

Patent metadata

Field	Value
Publication number	US-10018737-B2
Application number	US-201414893578-A
Country	US
Kind code	B2
Filing date	May 21, 2014
Priority date	May 24, 2013
Publication date	Jul 10, 2018
Grant date	Jul 10, 2018

Abstract

A method is provided for processing a spectrum, obtained using a particle detection system, so as to reduce spectrum artifacts arising from unresolved particle events in the detection system. An input spectrum is obtained which contains artifacts due to “pile up” in the detector. A first effect upon the input spectrum of pairs of unresolved particle events is evaluated and a first corrected input spectrum is generated which comprises the input spectrum with the first effect removed. The effect of a pairs of unresolved particle events is then evaluated for this first corrected input spectrum so as to generate a second corrected input spectrum which comprises the input spectrum with the second effect removed. An output spectrum is then generated based upon a combination of the first and second corrected input spectra. The use of the method in improving sum spectra is also discussed.

First claim

The invention claimed is:

1. A method of processing a spectrum obtained using a particle detection system, so as to reduce spectrum artefacts arising from unresolved particle events in the detection system, the method comprising:
a. Obtaining an input spectrum from the particle detection system, the input spectrum containing spectrum artefacts;
b. Evaluating a first estimate of pairs of particle events, which are unresolvable by the particle detection system, using the input spectrum;
c. Generating a first corrected input spectrum (ac1) comprising the input spectrum with the pairs of particle events according to the first estimate removed;
d. Evaluating a second estimate of pairs of particle events, which are unresolvable by the particle detection system, using the first corrected input spectrum;
e. Generating a second corrected input spectrum (ac2) comprising the input spectrum with the pairs of particle events according to the second estimate removed; and,
f. Generating an output spectrum (ac) based upon a combination of the first and second corrected spectra.

2. A method according to claim 1 , wherein the each of the first and second estimates is a calculated effect of only pairs of particles being received by the detector system during a time period in which the individual particles within a pair may not be resolved.

3. A method according to claim 1 , wherein one or each of the first and second corrected spectra is corrected for lost counts.

4. A method according to claim 1 , wherein one or each of the first and second estimates is evaluated as a sum effect spectrum.

5. A method according to claim 4 , wherein the one or each of the first or second estimates is calculated according to:
sa[p+q]=al[p]*a[q]*T ( p,q )/ L

where p and q denote first and second channel property magnitudes for respective particles; sa[p+q] is the additional contribution to the count value in channel a[p+q]; al[p] is the loss-adjusted value of counts for channel a[p]; a[q] is the number of counts in channel q; T(p,q) is the resolving time for a p channel pulse followed by a q channel pulse; and L is the live time for the spectrum.

6. A method according to claim 1 , wherein in step (f) the combination is a mean average of the first and second corrected spectra.

7. A method according to claim 1 , where in the spectrum is acquired at a count rate in excess of 50000 counts per second.

8. A method according to claim 1 , wherein the input spectrum comprises an x-ray spectral dataset represented as multiple channels, each channel corresponding to an energy range of an x-ray photon and each channel having an associated number of counts representing the number of x-ray photons having an energy within the respective channel energy range.

9. A method according to claim 1 , wherein the first and second estimates calculate the effect of single pile up events upon the spectrum and wherein the output spectrum comprises the input spectrum as corrected for single pile-up and double-pile up events in the detection system.

10. A method according to claim 9 , wherein the data are represented as histograms and wherein the channels represent a contiguous particle property range.

11. A method of processing a spectrum to reduce spectrum artefacts arising from unresolved particle events in a particle detection system, wherein the spectrum is a sum spectrum comprising multiple spectra obtained from multiple locations upon a sample; the method comprising:
a. Assigning the multiple spectra into groups of spectra such that all spectra within a group have a similar distribution of counts as a function of a particle property;
b. Summing the spectra within each group to form a summed spectrum for each group;
c. Processing the summed spectrum of each group using a method according to any of the preceding claims; and
d. Forming an output sum spectrum by combining the output spectrum of each group.

12. A method according to claim 11 , wherein the spectrum is a spectrum of a property selected from the group of: particle energy, particle momentum, particle mass or particle velocity energy.

13. A method according to claim 11 , wherein the method is computer implemented.

Assignees

• Oxford Instruments Nanotechnology Tools Ltd

Inventors

• Statham Peter

Classifications

• G01T1/171

  Compensation of dead-time counting losses · CPC title

• G01T1/17

  Circuit arrangements not adapted to a particular type of detector {(pulse-selection circuits H03K, G01R)} · CPC title

• G01T1/36 Primary

  Measuring spectral distribution of X-rays or of nuclear radiation {spectrometry (pulse selection circuits per se H03K; investigation of materials by radiation diffraction G01N23/20; spectrometer tubes H01J49/00)} · CPC title

• G01T1/172

  with coincidence circuit arrangements (G01T1/178 takes precedence {; combination of detectors, see G01T1/1603, G01T1/30}) · CPC title