Spectral analysis with spectrum deconvolution

Abstract

A method for inferring incident count rates of electromagnetic energy at a detector is provided. In one embodiment, the method includes transmitting electromagnetic radiation through a fluid and receiving a portion of the electromagnetic radiation at a detector. The method also includes measuring the energy spectrum of the portion of the electromagnetic radiation received by the detector and using the measured energy spectrum and a physical model of detector response to electromagnetic radiation to infer incident count rates for discrete energy levels of the portion of the electromagnetic radiation received by the detector. Additional systems, devices, and methods are also disclosed.

1 . A method comprising:
 transmitting electromagnetic radiation through a fluid, the electromagnetic radiation including x-ray or gamma radiation;   receiving a portion of the electromagnetic radiation at a detector;   measuring the energy spectrum of the portion of the electromagnetic radiation received by the detector;   using a processor to deconvolve the measured energy spectrum by fitting a modeled detector response to the measured energy spectrum to infer incident count rates for discrete energy levels of the portion of the electromagnetic radiation received by the detector; and   characterizing a physical attribute of the fluid based on the inferred incident count rates.   
     
     
         2 . The method of  claim 1 , wherein fitting the modeled detector response to the measured energy spectrum includes performing least squares optimization with respect to the measured energy spectrum using a detector response function to infer the incident count rates. 
     
     
         3 . The method of  claim 3 , wherein the detector response function comprises a plurality of response functions, each response function corresponding to a part of a detection chain making up the detector. 
     
     
         4 . The method of  claim 2 , wherein the detector response function includes energy and resolution response components having detector-specific parameters, and the method comprises inferring the detector-specific parameters from the least squares optimization. 
     
     
         5 . The method of  claim 4 , comprising calibrating the detector based on the inferred detector-specific parameters. 
     
     
         6 . The method of  claim 1 , wherein the fluid is a multiphase fluid and characterizing a physical attribute of the fluid includes determining phase fractions for the multiphase fluid. 
     
     
         7 . The method of  claim 4 , further comprising: monitoring the health status of the detector using the measured spectrum. 
     
     
         8 . An apparatus comprising:
 an electromagnetic radiation emitter;   an x-ray or gamma ray detector positioned to receive electromagnetic radiation from the emitter;   a fluid passage between the emitter and the detector;   a multi-channel spectral analyzer configured to measure an energy spectrum of electromagnetic radiation received by the detector; and   a controller including a processor configured to deconvolve the measured energy spectrum using a detector response model to characterize the electromagnetic radiation transmitted through the fluid passage and received by the detector.   
     
     
         9 . The apparatus of  claim 8 , wherein the controller is configured to determine count rates for photons incident on the detector based on the deconvolution of the measured energy spectrum. 
     
     
         10 . The apparatus of  claim 8 , wherein the detector is a solid-state detector. 
     
     
         11 . The apparatus of  claim 8 , comprising a multiphase flow meter having the emitter, the fluid passage, the detector, the multi-channel analyzer, and the controller. 
     
     
         12 . The apparatus of  claim 11 , wherein the controller is a flow computer operable to calculate phase fractions of a fluid passing through the multiphase flow meter based on the deconvolution of the measured energy spectrum using the detector response model. 
     
     
         13 . The apparatus of  claim 8 , wherein the detector includes a shaping amplifier for providing to the multi-channel spectral analyzer output pulses indicative of photons received by the detector. 
     
     
         14 . The apparatus of  claim 13 , wherein the multi-channel spectral analyzer includes a pile-up rejector configured to discard a shaping amplifier output pulse from the detector that is indicative of multiple photons received by the detector within a width of the shaping amplifier output pulse if a time interval between receipt of the multiple photons exceeds a threshold duration. 
     
     
         15 . A method comprising:
 emitting x-ray or gamma radiation into a fluid;   receiving photons of the x-ray or gamma radiation transmitted by the fluid and having different energies at a detector;   measuring an energy spectrum of the received photons;   using a detector response model comprising multiple monoenergetic response models of components of the detector to model spectral components of the energy spectrum for multiple energy levels of the photons;   fitting the detector response model to the energy spectrum to determine count rates for at least two energy levels; and   characterizing a physical attribute of the fluid based on the measured count rates.   
     
     
         16 . The method of  claim 15 , wherein the fluid is a multiphase fluid, and x-ray or gamma ray radiation is emitted into the fluid while the fluid flows through a conduit. 
     
     
         17 . The method of  claim 16 , comprising:
 calculating attenuation rates of the photons by the multiphase fluid for the at least two energy levels; and   calculating phase fractions of the multiphase fluid using the calculated attenuation rates.   
     
     
         18 . A multiphase flow meter comprising:
 an electromagnetic radiation emitter;   an x-ray or gamma ray detector comprising a scintillator and a photomultiplier tube, the detector positioned to receive electromagnetic radiation from the emitter;   a fluid conduit between the emitter and the detector;   a multi-channel spectral analyzer coupled to the detector to receive electrical signals from the detector and output a measured energy spectrum of the photons received by the detector; and   a flow computer encoded with a response model for the detector, the response model based on characteristics of components of the emitter and the detector, wherein the flow computer is operable to compare the measured energy spectrum with the response model to infer count rates for the photons received by the detector.   
     
     
         19 . The multiphase flow meter of  claim 18 , wherein the response model includes detector energy and resolution functions having detector-specific parameters and a set of monoenergetic response functions that model response of the scintillator to photons incident on the scintillator.