Moxtek

Articles

The Mox 140 kV X-ray source weighs less than 1900 grams and runs at 7 Watts X-ray tube power. Applications include X-ray spectroscopy, backscatter, and X-ray imaging.

140 kV Handheld X-ray Sources

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
	Website: 

High Voltage Accuracy and Precision on Small Compact X-ray Source

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.


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

	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.


	Figure 2: Running at 1000 μA, the 12 W source produces much more signal from the desired elements in the cement powder than running at 200 μA.

	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: 

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.

Moxtek

Articles

140 kV Handheld X-ray Sources

High Voltage Accuracy and Precision on Small Compact X-ray Source

Miniature 60 kV, 1000 μA 12 W X-ray Source