Moxtek

Moxi™ X-ray source is calibrated to within ±250 V over all settings between 5 to 50 kV. This impressive accuracy and precision is achieved spectroscopically, by measuring an X-ray spectrum's bremsstrahlung edge and storing correction high voltage offset information on each source.

	One optimization desired by manufactures of X-ray fluorescent (XRF) instruments is X-ray sources that are spectroscopically identical. A spectroscopically identical X-ray source allows one to switch out an X-ray source in an instrument with no other changes to the instrument, for example, with minimal or no recalibration of the instrument. This benefit is desired by handheld XRF manufacturers, which reduces XRF calibration effort and service time for XRF instruments. Each Moxi™ X-ray source is calibrated to within ±250 V over all settings between 5 to 50 kV. This voltage accuracy is tight enough to allow for XRF equivalence for several XRF applications.

	In order to calibrate an X-ray source, two basic requirements are needed:

		A meaningful and accurate way to measure the high voltage.

		A way to store the high-voltage calibration information on each X-ray source, offsetting source-to-source differences due to variance in the source's electrical components.

	The X-ray source's high voltage is measured by collecting an X-ray spectrum from the tube's anode. The source is pointed directly at an energy-dispersive detector, with a pinhole in-between to limit the intensity from the X-ray source. The spectrum's bremsstrahlung edge is fit with a proprietary algorithm, giving the value of the bremsstrahlung edge in keV. This measurement provides the "spectroscopic" voltage in keV, while the electronic monitors on the X-ray source give an electronically measured voltage in kV. The difference between the two gives a correction factor, which can be used to tighten the accuracy and precision between these two values. This test is repeated over several tube voltage settings between 5 and 50 kV.

	The variance in the electronic components in aggregate is the major driving factor for the high-voltage inaccuracy of any particular X-ray source. The electronic components have a partially nonlinear relationship with high voltage. The Moxi™ X-ray source has an onboard memory which can hold a correction factor to correct for the nonlinear relationship.


	Figure 1: This graphic shows the offset between the tube's set voltage and bremsstrahlung edge over seven setting's precalibration, on over 100 separate X-ray sources. Precalibration, the high voltage is typically offset by 800 V, and can vary by up to ±1000 V (@35 kV).

	Comparing Figures 1 and 2 shows the accuracy and precision of the high voltage on the X-ray sources is drastically increased by the high-voltage calibrating procedure. These graphs are intentionally at the same scale to easily show the improvements.


	Figure 2: This graphic shows the offset between the tube's set voltage and bremsstrahlung edge over seven settings post-calibration, on over 100 separate x-ray sources. Post-calibration, the high voltage is typically offset by 100 V, and can vary by up to ±250 V (@35 kV).

	Moxi™ X-ray sources are an "XRF equivalent" X-ray source for XRF instrument manufacturers. The key aspect for achieving this source's spectral equivalence is the high-voltage calibration of the source. Each digital X-ray source is calibrated to within ±250 V over all settings between 4 to 50 kV. The high accuracy and precision is achieved spectroscopically by measuring the bremsstrahlung edge and storing high-voltage offset information on each source. This benefit is very much desired by handheld XRF manufacturers and reduces XRF calibration effort and service time for XRF instruments. This quantification has practical backing; it is working as intended in next-generation XRF handheld instruments sold today.


	452 West 1260 North, Orem, UT 84057
	tel. (801) 225-0930, fax (801) 221-1121
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High Voltage Accuracy and Precision on Small Compact X-ray Sources

 maximum voltage was increased from 60 kV to 70 kV while maintaining the same size profile. This article highlights the advantages of 70 kV excitation of cadmium, an element of interest for the Restriction of Hazardous Substances Directive (RoHS), at parts per million (ppm) levels. 

	The MAGPRO 12 W miniature source is small and low power, which is an advantage for a number of applications. Our 12 W source has several anode materials available: a tungsten anode for either XRF or in X-ray imaging, as well as Rh, Ag, Cr, Cu, and Mo. The entire X-ray source (tube plus high voltage power supply) weights about 700 g (25.0 oz) and can be controlled by your choice of USB, digital, or analog control, and has an interlock connection for X-ray safety (Figure 1). The increase of high voltage from 60 kV to 70 kV for the MAGPRO was primarily motivated for use in handheld imaging applications. This increase in voltage also shows important benefits for spectroscopy applications as well. This article highlights the advantages of the 70 kV excitation for low levels of cadmium.


	Figure 1: Image of the 12 W X-ray source.

	Experimental Conditions and Results for XRF Detection of Cadmium

	Cadmium detection is of interest because it is a toxic metal that needs to be detected for RoHS/WEEE compliance. Detection of cadmium at low concentrations is particularly difficult because cadmium's 23.2 keV K

 emission line is much higher than that of other toxic elements of interest. An X-ray source with a higher voltage helps to increase the X-ray signal from cadmium. For this experiment, we used a typical XRF setup where the sample is placed at 45° to the tube and detector. The X-ray spot on the sample was 4×6 mm, achieved with a collimator and a tube-to-sample distance of 25 mm. A 200 µm molybdenum foil was placed between the tube and sample to suppress the Compton background scattering roughly between 20 to 30 keV; thereby suppressing the background under the cadmium K

 peak. Figure 2 shows four spectra taken from a polyvinyl chloride sample with 10 ppm of Cd, with the tube set at 40, 50, 60, and 70 kV. A 42 mm

 SDD collected the data with a 15 mm sample-to-detector distance over 180 s live time, with the input count rate ranging from 20 to 100 kcps. It is evident that increasing the voltage also increases the cadmium signal. In this set-up, 10 ppm of cadmium is detectable in a reasonable 3–5 min time frame.


	Figure 2: The cadmium line at about 23.2 keV gets larger as the voltage on the tube is increased. This is an advantage for cadmium detection in XRF systems looking for toxic metal at low concentrations.

	The MAGPRO source is meant for use in small benchtop systems where small size is valued. It has increased its high voltage range from 60 kV to 70 kV, which is an advantage in detecting higher atomic number elements such as the hazardous substance cadmium.


	452 West 1260 North, Orem, UT 84057
	tel. (800) 758-3110
	email: 

Miniature 70 kV, 12W X-ray Source

’s maximum voltage was increased from 60 kV to 70 kV while maintaining the same size profile. This article highlights the advantages of 70 kV excitation of cadmium, an element of interest for Restriction of Hazardous Substances Directive (RoHS), at parts per million (ppm) levels.

 12 W miniature source is small and low power, which is an advantage for a number of applications. Our 12 W source has several anode materials available; a tungsten anode for either XRF or in X-ray imaging, as well as Rh, Ag, Cr, Cu, and Mo. The entire X-ray source (tube plus high voltage power supply) weights about 700 g (25.0 oz) and can be controlled by your choice of USB, digital, or analog control and has an interlock connection for X-ray safety (Figure 1). The increase of high voltage from 60 kV to 70 kV for the 

 was primarily motivated for use in handheld imaging applications. This increase in voltage also shows important benefits for spectroscopy applications as well. This article highlights the advantages of the 70 kV excitation for low levels of cadmium.

	Cadmium detection is of interest because it is a toxic metal that needs to be detected under RoHS/WEEE compliance. Detection of cadmium at low levels is particularly difficult to detect at lower concentrations because cadmium’s 23.2 keV K

 emission line is much higher than other toxic elements of interest. An X-ray source with a higher voltage helps to increase the X-ray signal from cadmium. For this experiment, we used a typical XRF setup where the sample is placed at 45° to the tube and detector. The X-ray spot on the sample was 4x6 mm, achieved with a collimator and a tube-to-sample distance of 25 mm. A 200 μm molybdenum foil was placed between the tube and sample to suppress the Compton background scattering roughly between 20 to 30 keV; thereby suppressing the background under the cadmium K

 source is meant for use in small benchtop systems where small size is valued. It has increased its high voltage range from 60 kV to 70 kV, which is an advantage in detecting higher atomic number elements such as the hazardous substance cadmium.

Recently, the compact MAGPRO’s maximum voltage was increased from 60 kV to 70 kV while maintaining the same size profile. This article highlights the advantages of 70 kV excitation of cadmium, an element of interest for Restriction of Hazardous Substances Directive (RoHS), at parts per million (ppm) levels. 

Moxtek's MAGPRO miniature X-ray source is capable of up to 60 kV 200 µA and down to 4 kV and 1000 µA, and limited to an output power of 12 watts. The 12 W source is meant for use in small bench top systems where small size is valued.

	The 12 W miniature source has a higher voltage and a much higher emission current than our present miniature X-ray sources, which is an advantage for a number of applications. The initial release of the 12 W source, our MXDPP-50 electronics comes in two versions: The tungsten anode version, which can be used in either XRF or in X-ray imaging, and the Rh anode version, primarily meant for light element XRF detection (Figure 1). The entire X-ray source (tube plus high voltage power supply) weighs about 700 g (25.0 oz) and can be controlled by your choice of USB, digital, or analog control. It also has an interlock connection for X-ray safety.

	We will show the advantage of the rhodium anode source running at 4 kV 1000 µA for XRF of cement powders.

Experimental Conditions and Results for XRF Detection of Cement Powers

	Concentrations of sulfur (sulfate), silicon (silicon dioxide), and aluminum (aluminum oxide) are important for both identifying and controlling different blends of cement powder. XRF can be used to measure cement powder elemental concentrations. XRF for the desired "light" elements, with emission lines under about 4 keV is challenging because the characteristic X-rays are absorbed by air, thereby attenuating the signal from the sample. For this experiment, we used a typical XRF setup where the sample is placed at 45° to the tube, and 135° to the detector, and no filters on the 12 W X-ray source. For light element XRF, a rhodium anode is often used because it has L emission lines between 2.7 and 3.0 keV, which are used to excite elements with emission lines below 2.5 keV. For this test the 12 W X-ray source was set to the minimum of 4 kV, which is helpful in eliminating the calcium XRF signal from the cement. The calcium signal is unwanted in this application because it will overwhelm the detection of the other elements of interest. A high emission current X-ray source, such as 1000 µA from the 12 W source, is very helpful in increasing the signal.

	Figure 2 shows an XRF spectrum from a Portland cement sample with the 12 W source running at 1000 µA and 200 µA on a rhodium anode tube. The signal level is increased by a bit over fivefold for these light elements, which can be a huge advantage in any application which detection of light elements is needed.

	The new 12 W source is meant for use in small benchtop systems where small size is valued. It has as increased range up to 60 kV at high voltage and increased current to 1000 µA at low voltages; both of which are an advantage in XRF and imaging applications.


	452 West 1260 North, Orem, UT 84057
	tel. (800) 758-3110, email: 

Author | Moxtek

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