Sterling Cornaby

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: 

Articles

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 W. The 12 W source is meant for use in small benchtop systems where small size is valued. 

	The 12 W miniature source has a higher voltage and a much higher emission current then 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, come 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) weights 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.

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

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

Moxtek's ULTRA-LITE X-ray source is a very small self contained X-ray source (X-ray tube and high voltage power supply) for use in portable X-ray applications, such as the handheld X-ray fluorescence (XRF) spectrometers. This note demonstrates that this X-ray source has a stable and repeatable X-ray flux output over time, which is vital for the precision of the calibrated XRF measurements.

	Moxtek's ULTRA-LITE source has a high voltage range of 5–50 kV, an emission current range of 5–200 μA, and comes with an assortment of anode materials including tungsten and silver. The maximum output power on the X-ray tube is 4 Watts. With the X-ray tube running at full power, the source draws approximately 9 Watts. At full power the ULTRA-LITE X-ray source will run for over 3 h on a typical 12 V 2.4 mA-h batteries. It is very small in size, 25 mm × 46 mm × 148 mm, and weighs only 250 g, making it perfect for handheld and portable instruments.

	Two of the key metrics of the X-ray source for XRF applications, and many other applications as well, are X-ray flux and high voltage repeatability. Repeatability means that every time the source is turned on at a particular high voltage and current setting, the high voltage and the X-ray flux stays as constant over time.

	In development of the ULTRA-LITE X-ray source we performed a number of characterization tests on multiple units. One key test is a flux repeatability test, in which the source is turned on and off numerous times. For each on/off cycle we capture an image of the focal spot, record the X-ray energy spectra coming off the tube, the energy spectra coming off a secondary XRF target, as well as input and monitor voltages and currents over several hours to days at room temperature.

	From these tests we have seen that the ULTRA-LITE source has a very stable and repeatable X-ray flux and high voltage. The flux was measured directly from the source with an X-ray PIN diode, which measures the flux by counting X-ray photon events. Figure 1 shows the X-ray photon counts collected from an ULTRA-LITE source over 3.5 days of time. The PIN diode also records the energy spectra of the incoming photons, which contains the bremsstrahlung edge from the source. By tracking the bremsstrahlung edge the high voltage stability of the source was tracked over time.


	Figure 1: This shows the flux repeatability from one ULTRA-LITE source set at the maximum voltage of 50 kV and 80 μA, the full 4 Watts. The flux is stable to under 0.10% RSD (std/mean) over 3.5 days. The source was turned on for 120 s, then off for 10 s, and cycled on and off 2400 times for this test.

	The high voltage of the source does not vary more than ±100 V at 50 (0.2%) kV by measuring the bremsstrahlung edge, and the flux is stable and repeatable within 0.5% RSD or less over the time frame of days. The repeatability of this source will be an asset to any handheld or portable application where excellent flux repeatability is needed, such as XRF.


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

Moxtek's ULTRA-LITE X-ray source is a very small self contained X-ray source (X-ray tube and high voltage power supply) for use in portable X-ray applications, such as the handheld X-ray fluorescence (XRF) spectrometers.

Moxtek’s ULTRA-LITE X-ray Source

Moxtek now has a full energy dispersive X-ray fluorescence detector solution with Moxtek's XPIN®   detectors and our new MXDPP-50 electronics. We will present characterization methods and a few measurement details of the DPP with Moxtek's XPIN® detectors.

One objective for Moxtek has been to develop a DPP to work with our X-ray detector products. This has been achieved with the release of the new MXDPP-50 electronics in 2013, which comes in two versions, a boxed version (Figure 1) and a bare board OEM version. 

Figure 1: Outlines the basic hardware for DPP and X-ray detector functional testing.			

A second objective has been to develop automated testing to fully characterize our DPP and X-ray detectors. The basic testing method is an automated test which multiple different DPP and XPIN detector settings are surveyed. The test generates a report on the performance over all the settings. This allows for rapid, consistent, and meaningful feedback, which has resulted in Moxtek more fully understanding the functionality of our DPP in development. This automated test allows for a "quick" test of our DPP and/or X-ray PIN detector over 4 to 14 standard peaking time settings, which takes about 15 to 30 min. This automated test also allows for extensive tests, takes over 16 h or more, over an array of hundreds of settings changing multiple input parameters, such as peaking time, input count rate, detector temperature, and so on. 

The basic hardware used in this automated testing is outlined in Figure 1. The DPP controls attributes such as the peaking time, the detector's temperature, the detector's high voltage, and more. The linear stage automatically positions a Fe55 isotope source to set a desired detector dead time (or detector input count rate). All the hardware is controlled in a LabVIEW program which automates all the hardware during the survey of desired settings. After each spectra is taken, over 150 independent variables are processed and recorded from both the spectra and detector, such as the Fe55 peak FWHM (for both Fe

  channel position, various peak-to-background ratios, detector internal temperature, detector power draw, input count rate (ICR), output count rate (OCR), and may other variables. 

The automated test generates a report at the end comparing several input parameters against each other. The information generated is far greater than can be shown here (1). Table I shows a sub-set of information collected in automated test collected on a XPIN 6 mm2-BT detector at typical temperature of -35 °C and a detector dead time of 50%. To build statistically relevant results, five spectra were taken at each setting. 

Table I: Outlines a small sub-set of information collected in the automated test			

Many other functional dependencies are readily available as well. For example, critical variables such as the Fe55 K

 FWHM peak width can be expressed as a function of detector temperature, or the detectors count rate (1). 

The MXDPP-50 is a digital pulse processor which now gives Moxtek a complete X-ray energy dispersive detector solution. Moxtek has been able to rigorously test the MXDPP-50, with our new suite of automated testing routines, giving a considerable amount of information quite quickly. This testing has shown the MXDPP-50 works well and works consistently from unit to unit (1). 

http://www.moxtek.com/x-ray-publications.html

tel. (801) 225-0930, fax (801) 221-1121 	

Moxtek now has a full energy dispersive X-ray fluorescence detector solution with Moxtek's XPIN detectors and our new MXDPP-50 electronics.

Moxtek's MXDPP-50: X-ray Detection Performance Characterizations

Moxtek's ULTRA-LITE X-ray source is a very small self contained X-ray source (X-ray tube and high voltage power supply) for use in portable X-ray applications, such as the handheld X-ray florescence (XRF) spectrometers. This note demonstrates that this X-ray source has a stable and repeatable X-ray flux output over time, which is vital for the precision of the calibrated XRF measurements.

Moxtek's ULTRA-LITE source has a high voltage range of 5–50 kV, an emission current range of 5–200 μA and comes with an assortment of anode materials including tungsten and silver. The maximum output power on the X-ray tube is 4 Watts. With the X-ray tube running at full power, the source draws approximately 9 Watts. At full power the ULTRA-LITE X-ray source will run for over 3 h on a typical 12 V 2.4 mA-hour batteries. It is very small in size, 25 mm × 46 mm × 148 mm, and weighs only 250 g, making it perfect for handheld and portable instruments. 

Two of the key metrics of the X-ray source for XRF applications, and many other applications as well, are X-ray flux and high voltage repeatability. Repeatability means that every time the source is turned on at a particular high voltage and current setting, the high voltage and the X-ray flux stays as constant over time.  

In development of the ULTRA-LITE X-ray source we performed a number of characterization tests on multiple units. One key test is a flux repeatability test, in which the source is turned on and off numerous times. For each on/off cycle we capture an image of the focal spot, record the X-ray energy spectra coming off the tube, the energy spectra coming off a secondary XRF target, as well as input and monitor voltages and currents over several hours to days at room temperature. 

From these tests we have seen that the ULTRA-LITE source has a very stable and repeatable X-ray flux and high voltage. The flux was measured directly from the source with an X-ray PIN Diode, which measures the flux by counting X-ray photon events. Figure 1 shows the X-ray photon counts collected from an ULTRA-LITE source over 3.5 days of time. The PIN diode also records the energy spectra of the incoming photons, which contains the bremsstrahlung edge from the source. By tracking the bremsstrahlung edge the high voltage stability of the source was tracked over time.  

Figure 1: This shows the flux repeatability from one ULTRA-LITE source set at the maximum voltage of 50 kV and 80 Î¼A, the full 4 Watts. The flux is stable to under 0.10% RSD (std/mean) over 3.5 days. The source was turned on for 120 s, then off for 10 s, and cycled on & off 2400 times for this test.			

The high voltage of the source does not vary more than ±100 V at 50 (0.2%) kV by measuring the bremsstrahlung edge, and the flux is stable and repeatable within 0.5% RSD or less over the time frame of days. The repeatability of this source will be an asset to any handheld or portable application where excellent flux repeatability is needed, such as XRF. 

Sterling Cornaby

Articles

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

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

Moxtek’s ULTRA-LITE X-ray Source

Moxtek's MXDPP-50: X-ray Detection Performance Characterizations

Moxtek's ULTRA-LITE X-ray Source