Instrument and method of measuring the concentration of a target element in a multi-layer thin coating
View Patent ↗An instrument and a method of detecting a target element in a multi-layer thin coating. Lα, Lβ and Lγ x-rays are caused to be emitted from the target element (preferably lead paint) with excitation radiation. Upon detecting the emitted x-rays, an areal concentration of the target element is calculated using Lα and Lβ intensities once, and then using the Lβ and Lγ intensities once, by reference to a single layer model; By combining the two concentrations calculated using single layer model, a more accurate concentration can be calculated for the target element in the multi-layered surface coating.
1. A method of measuring an areal concentration of a target element coated by more than one layers near the surface of a substrate, the target element capable of emitting La, LI3 and L7 x-rays when suitably excited, the method comprising the steps of:
a) inducing the L α and L β and L γ x-rays to be emitted from said target element with excitation radiation;
b) detecting said L α , L β and L γ x-rays and determining the intensity of the L α , L β and L γ x-rays separately;
c) calculating the areal concentration of said target element by means of the following equations:
m 1 =I Lβ /A 1/ I LβS Eq. 1
wherein m 1 is the calculated lead concentration based on single layer model using L α and L β intensities; A1 is the absorption factor computed from the L α , L β intensity ratio, wherein during calibration, A1 as a function of L α , L β intensity ratio is fitted as a curve; and this curve is used later to calculate the A1 from measured L α ,L β intensity ratio; I Lβ is the measured L β line intensity of the target element from sample under testing; I LβS is the L β intensity of the target element from a NIST standard without any shielding layers;
m 2 =I Lγ /A 2/ I LγS Eq. 2
wherein m 2 is the calculated lead concentration based on single layer model using L β and L γ intensities; A2 is the absorption factor computed from the L β , L γ intensity ratio, wherein during calibration, A2 as a function of L β , L γ intensity ratio is fitted as a curve; and this curve is used later to calculate the A1 from measured L α , L β intensity ratio; I Lγ is the measured L γ line intensity of the target element from sample under testing; I LγS is the L γ intensity of the target element from a NIST standard without any shielding layers; and
d) calculating the combine areal concentration of said target element according to:
m z =m 2 +C 3 ( m 2 −m 1 ) Eq. 5
wherein C 3 is a constant determined during an instrument calibration, and m z is the target element concentration emitted from the at least one layer of coating containing the target element.
2. The method of measuring an areal concentration of a target element of claim 1 , wherein the target element is comprised of one or more layers of another material that do not contain the target element.
3. The method of measuring an areal concentration of a target element of claim 1 , wherein the target element is lead paint.
4. The method of measuring an areal concentration of a target element of claim 1 , wherein the Lα, Lβ and Lγ for the target element have x-ray fluorescent lines with an energy of 10.5 keV, 12.6 keV and 14.8 keV, respectively.
5. The method of measuring an areal concentration of a target element of claim 1 , further including using a filter to reduce low energy x-rays associated with the excitation radiation.
6. The method of measuring an areal concentration of a target element of claim 5 , including using a filter wheel to select an optimal filter to reduce the low energy x-rays.
7. The method of measuring an areal concentration of a target element of claim 1 , including using an x-ray tube to generate the excitation radiation.
8. The method of measuring an areal concentration of a target element of claim 1 , including comparing m 1 to m 2 and, if m 1 is substantially equal to m 2 , reporting the areal concentration based on m 1 .
9. The method of measuring an areal concentration of a target element of claim 1 , including carrying out measurements of the areal concentration of the target element in a range from 0 to 2 mg/cm 2 and beyond.
10. An instrument configured as an x-ray fluorescence analyzer for measuring an areal concentration of a target element coated by more than one layers near a surface of a substrate, the target element capable of emitting Lα, Lβ and Lγ x-rays when suitably excited, the instrument comprising:
a) a source of excitation radiation capable of inducing the Lα and Lβ and Lγ x-rays to be emitted from said target element;
b) a detector configured to detect said Lα, Lβ and Lγ x-rays and determine the intensity of the Lα, Lβ and Lγ x-rays separately;
c) a calculating unit configured to calculate the areal concentration of said target element by means of the following equations:
m 1 =I Lβ /A 1/ I LβS Eq. 1
wherein m 1 is the calculated lead concentration based on single layer model using Lα and Lβ intensities; A1 is the absorption factor computed from the Lα, Lβ intensity ratio, I Lβ is the measured Lβ line intensity of the target element; and I LβS is the lead Lβ intensity based on a NIST (National Institute of Standards and Technology) standard with 1.0 mg/cm 2 lead concentration, recorded during instrument calibration,
m 2 =I Lγ /A 2/ I LγS Eq. 2
wherein m 2 is the calculated lead concentration based on single layer model using Lβ and Lγ; A2 is the absorption factor computed from the Lβ, Lγ intensity ratio, I Lγ is the measured Lγ line intensity from sample under testing; and I LγS is the lead Lγ intensity from NIST standard with 1.0 mg/cm 2 lead concentration; and
d) further calculating the combined areal concentration of said target element according to:
m z =m 2 +C 3 ( m 2 −m 1 ) Eq. 5
where C 3 is a constant determined during an instrument calibration, m z is the target element concentration emitted from the at least one layer of coating containing the target element.
11. The instrument of claim 10 , wherein the target element is comprised of one or more layers of another material that do not contain the target element.
12. The instrument of claim 10 , wherein the target element is lead paint.
13. The instrument of claim 10 , wherein the Lα, Lβ and Lγ for the target element have x-ray fluorescent lines with an energy of 12.6 keV and 14.8 keV, respectively.
14. The instrument of claim 10 , further including using a filter to reduce low energy x-rays associated with the excitation radiation.
15. The instrument of claim 10 , further including a filter wheel to select an optimal filter to reduce the low energy x-rays.
16. The instrument of claim 10 , including an x-ray tube to generate the excitation radiation.
17. The instrument of claim 10 , wherein the calculating unit is configured to compare m 1 to m 2 and, if m 1 is substantially equal to m 2 , reporting the areal concentration based on m 1 .
18. The instrument of claim 10 , wherein said instrument is configured to carry out measurements of the areal concentration of the target element in a range from 0 to 2 mg/cm 2 and beyond.