Energy dispersion type radiation detecting system and method of measuring content of object element
View Patent ↗To provide an energy dispersion type radiation detecting system and a method of measuring a content of an object element capable of carrying out a measurement by determining an intensity of an incidence radiation to constitute an optimum minimum limit of detection by restraining an influence of a pile up, the energy dispersion type radiation detecting system includes an incidence system of irradiating the incidence radiation to a sample by a predetermined intensity, a detection system of detecting a radiation emitted from the sample by irradiating the incidence radiation for specifying a content of an object element of the sample based on a spectrum of the detected radiation, and the energy dispersion type radiation detecting system includes a control portion capable of irradiating the incidence radiation by an optimum intensity by determining the optimum intensity of the incidence radiation minimizing a minimum limit of detection of the object element based on the spectrum of the detected radiation.
1. A method of measuring an amount of an element contained in a sample based on a fluorescent x-ray excited out from the sample by an irradiation of a primary x-ray, the method comprising:
providing a base function defining a lower detection level of measurement in relation to a sensitivity of the measurement and a background intensity of the fluorescent x-ray, wherein the background intensity is a function of a first background intensity effected by a pileup and a second background intensity effected by other causes;
sequentially irradiating a first and second primary x-rays onto the sample and detecting the respective fluorescent x-rays excited out from the sample by the first and second primary x-rays;
calculating the first background intensity and the second background intensity based on a difference in intensity between the first and second primary x-rays;
calculating the sensitivity, based on a spectrum of the fluorescent x-ray excited out by the first primary x-ray;
calculating an effective sensitivity and an effective background intensity to be exhibited with the primary x-ray irradiated at an optimum intensity, wherein the effective sensitivity is a function of the calculated sensitivity and an intensity ratio between the optimum intensity and the intensity of the first primary x-ray, and the effective background intensity is a function of the calculated first and second background intensities and the intensity ratio;
using the effective sensitivity and the effective background intensity, solving the base function to derive the intensity ratio which minimizes the lower detection level; and
irradiating the primary x-ray onto the sample at the optimum intensity determined from the calculated intensity ratio.
2. The method according to claim 1 , wherein providing the base function comprises providing the base function so as to define the lower detection level in relation further to an dead time of a detector for detecting the fluorescent x-ray from the sample, and the method further comprises determining the dead time when the detector detects the fluorescent x-ray excited out by the first primary x-ray.
3. The method according to claim 2 , wherein providing the base function comprises providing the base function so as to define the lower detection level in relation further to a measurement time spent in measuring the fluorescent x-ray excited out by the first primary x-ray.
4. The method according to claim 3 , wherein providing the base function comprises providing the base function represented by the following equation:
DL
=
3
·
Ib
T
·
(
1
-
τ
)
S
where DL represents the lower detection level, Ib represents the background intensity, T represents the time spent in the measurement, τ represents a ratio between the dead of the detector and the time spent in the measurement, and S is the sensitivity.
5. The method according to claim 1 , wherein
calculating the first background intensity and the second background intensity comprises defining the background intensity of the fluorescent x-ray excited out by the first primary x-ray as a sum of the first background intensity and the second background intensity, and defining the background intensity of the fluorescent x-ray excited out by the second primary x-ray as a sum of the first background intensity multiplied by a squire of a ratio of the intensities of the first and second primary x-rays and the second background intensity multiplied by the same ratio, and
calculating the first background intensity and the second background intensity further comprises solving, on the first background intensity and the second background intensity, the definition of the background intensity caused by the first primary x-ray and the definition of the background intensity caused by the second primary x-ray.
6. The method according to claim 5 , wherein calculating the sensitivity comprises calculating the sensitivity, using a fundamental parameter method.
7. The method according to claim 1 , wherein defining an effective sensitivity comprises defining an effective sensitivity as a multiplicity of the calculated sensitivity and the intensity ratio, and defining the effective background intensity comprises defining the effective background intensity as a sum of the calculated first background intensity multiplied by a square of the intensity ratio and the calculated second background intensity multiplied by the intensity ratio.
8. The method according to claim 1 , wherein solving the base function to derive the intensity ratio which minimizes the lower detection level comprises solving the following equation on the intensity ratio:
DL
=
3
·
α
2
·
Ib
1
+
α
·
Ib
2
T
·
(
1
-
α
·
τ
)
α
·
S
where Ib 1 represents the first background intensity, Ib 2 represents the second background intensity and α represents the intensity ratio.
9. An energy dispersion type radiation detecting system for measuring an amount of an element contained in a sample based on a fluorescent x-ray excited out from the sample by an irradiation of a primary x-ray, the system comprising:
a primary x-ray irradiator configured to irradiate the primary x-ray onto the sample and a detector configured to detect the fluorescent x-ray excited out from the sample by the primary x-ray;
a memory which stores a base function defining a lower detection level of measurement in relation to a sensitivity of the measurement and a background intensity of the fluorescent x-ray, wherein the background intensity is a function of a first background intensity effected by a pileup and a second background intensity effected by other causes;
a primary test operator configured to control the primary x-ray irradiator and the detector in order to sequentially irradiate a first and second primary x-rays onto the sample and detecting the respective fluorescent x-rays excited out from the sample by the first and second primary x-rays;
an intensity calculator configured to calculate the first background intensity and the second background intensity based on a difference in intensity between the first and second primary x-rays;
a sensitivity calculator configured to calculate the sensitivity, based on a spectrum of the fluorescent x-ray excited out by the first primary x-ray;
an effective value determiner configured to determine the calculated sensitivity and calculated background intensity to define an effective sensitivity and an effective background intensity to be exhibited with the primary x-ray irradiated at an optimum intensity, wherein the effective sensitivity is a function of the calculated sensitivity and an intensity ratio between the optimum intensity and the intensity of the first primary x-ray, and the effective background intensity is a function of the calculated first and second background intensities and the intensity ratio;
an optimum intensity calculator configured to solve the base function, using the effective sensitivity and the effective background intensity, to derive the intensity ratio which minimizes the lower detection level; and
a primary test operator configured to irradiate the primary x-ray onto the sample at the optimum intensity determined from the calculated intensity ratio.
10. The system according to claim 9 , wherein the base function defines the lower detection level in relation further to an dead time of a detector for detecting the fluorescent x-ray from the sample, and the system further comprises a dead time detector configured to detect the dead time when the detector detects the fluorescent x-ray excited out by the first primary x-ray.
11. The system according to claim 10 , wherein providing the base function defines the lower detection level in relation further to a measurement time spent in measuring the fluorescent x-ray excited out by the first primary x-ray.
12. The system according to claim 11 , wherein the base function is represented by the following equation:
DL
=
3
·
Ib
T
·
(
1
-
τ
)
S
where DL represents the lower detection level, Ib represents the background intensity, T represents the time spent in the measurement, τ represents a ratio between the dead of the detector and the time spent in the measurement, and S is the sensitivity.
13. The system according to claim 9 , wherein
the intensity calculator defines the background intensity of the fluorescent x-ray excited out by the first primary x-ray as a sum of the first background intensity and the second background intensity, and further defines the background intensity of the fluorescent x-ray excited out by the second primary x-ray as a sum of the first background intensity multiplied by a squire of a ratio of the intensities of the first and second primary x-rays and the second background intensity multiplied by the same ratio, and
the intensity calculator solves, on the first background intensity and the second background intensity, the definition of the background intensity caused by the first primary x-ray and definition of the background intensity caused by the second primary x-ray.
14. The system according to claim 13 , wherein the sensitivity calculator calculates the sensitivity, using a fundamental parameter method.
15. The system according to claim 9 , wherein the effective value determiner determines an effective sensitivity as a multiplicity of the calculated sensitivity and the intensity ratio, and determines the effective background intensity as a sum of the calculated first background intensity multiplied by a square of the intensity ratio and the calculated second background intensity multiplied by the intensity ratio.
16. The system according to claim 9 , wherein the optimum intensity calculator solves the following equation on the intensity ratio:
DL
=
3
·
α
2
·
Ib
1
+
α
·
Ib
2
T
·
(
1
-
α
·
τ
)
α
·
S
where Ib 1 represents the first background intensity, Ib 2 represents the second background intensity and α represents the intensity ratio.