Method for measuring the effective atomic number of a material

Patent metadata

Field	Value
Publication number	US-2016363545-A1
Application number	US-201415106569-A
Country	US
Kind code	A1
Filing date	Dec 9, 2014
Priority date	Dec 20, 2013
Publication date	Dec 15, 2016
Grant date	—

Abstract

A method for estimating the effective atomic number of a material from a transmission spectrum of said material in which a likelihood function of the effective atomic number and the thickness of the material is calculated on the basis of the transmission spectrum as well as calibration spectra obtained in a previous calibration phase for a plurality of samples of calibration materials of known effective atomic numbers and known thicknesses. The effective atomic number of the material is then estimated on the basis of values of the likelihood function.

First claim

1 - 17 . (canceled)

18 . A method for measuring the effective atomic number of a material for a predetermined X or gamma spectral band, comprising:
a transmission spectrum (S a =(n 1 a , n 2 a , . . . , n N a ) T ) of a sample of said material in a plurality (N) of energy channels of said spectral band is measured ( 120 , 220 ); a likelihood function of the effective atomic number and of the thickness of the sample of said material is calculated ( 130 , 230 ) from the transmission spectrum measured as such and from a plurality of transmission spectra (S c (Z p c ,e q c ), referred to as calibration spectra, obtained for a plurality of samples of calibration materials having known effective atomic numbers and known thicknesses, the calibration spectra are interpolated in order to obtain an interpolated calibration spectrum for each effective atomic number belonging to a first interval ([Z min , Z max ]), and for each effective atomic number belonging to this interval and each given thickness, a value of said likelihood function is calculated; the effective atomic number ({circumflex over (Z)}) of said material is estimated ( 140 , 240 ) on the basis of values of the likelihood function thus obtained.

19 . The method for measuring the effective atomic number of a material according to claim 18 , wherein the calibration spectra are interpolated in order to obtain an interpolated calibration spectrum for each effective atomic number belonging to a second interval ([e min ,e max ]) and that for each thickness belonging to this interval and each given effective atomic number, a value of said likelihood function is calculated.

20 . The method for measuring the effective atomic number of a material according to claim 19 , wherein for each calibration material (p) of known effective atomic number (Z p c ), an interpolation is carried out between the calibration spectra relative to known thicknesses in order to determine an interpolated calibration spectrum for each thickness of a given thickness interval ([e min ,e max ]), with the likelihood function being evaluated over this thickness interval from the interpolated calibration spectrum, and the maximum value of the likelihood function is determined over said thickness interval, said maximum value being associated with the material.

21 . The method for measuring the effective atomic number of a material according to claim 20 , wherein the effective atomic number ({circumflex over (Z)}) of the material is estimated as the average of the effective atomic numbers belonging to a first interval ([Z min , Z max ]), weighted by the maximum values of the likelihood function that are respectively associated to them.

22 . The method for measuring the effective atomic number of a material according to claim 19 , wherein for each calibration material (p) of known effective atomic number (Z p c ), an interpolation is carried out between the calibration spectra relative to known thicknesses in order to determine an interpolated calibration spectrum for each thickness of a given thickness interval ([e min , e max ]), with the likelihood function being evaluated over this thickness interval from the interpolated calibration spectrum, then integrated over this thickness interval in order to give a marginal likelihood function value associated with this calibration material.

23 . The method for measuring the effective atomic number of a material according to claim 22 , wherein the effective atomic number ({circumflex over (Z)}) of the material is estimated as the average of the known effective atomic numbers of the calibration materials, weighted by the values of the marginal likelihood function respectively associated with these calibration materials.

24 . The method for measuring the effective atomic number of a material according to claim 18 , wherein the values of the likelihood function are determined for each pair (Z p c , e q c ) of effective atomic number and of thickness by:

V


(

Z
p
c

,

e
q
c

)

=

1

∏

i
=
1

N





n
i
c



exp


[

-

∑

i
=
1

N





(

μ
i



n
i
a

-

n
i
c

)

2

2


(

n
i
c

)

2

]

where the n i a , i=1, . . . , N are the values of the transmission spectrum of the material in the various channels, n i c , i=1, . . . , N are the values of the transmission spectrum of the calibration material in these same channels and μ i is the ratio between the number of photons received in the channel i in the absence of material during the calibration (n 0,i c ) and the number of photons received in t

Assignees

• Commissariat Energie Atomique

Inventors

• Gorecki Alexia
• Rinkel Jean

Classifications

• G01N23/087 Primary

  using polyenergetic X-rays · CPC title