CHARACTERIZATION TECHNIQUES FOR MINIATURE LOW POWER X-RAY TUBES
A. Reyes-Mena, Melany Moras, Charles Jensen,
Steven D. Liddiard, and D. Clark Turner
2004
MOXTEK, Inc., Orem, UT USA 84057

ABSTRACT
An X-ray shielded test chamber has been designed and built that includes a CCD-pinhole camera and energy-dispersive silicon PIN-diode detector for spectrum collection. The use of this chamber is an innovative approach that allows rapid imaging of the electron beam spot on the anode, as well as the spectral characterization of the tube. The beamspot dimensions and location can be measured at several high-voltage settings to ensure stability. This setup allows monitoring spectral contamination lines, total output flux, and net target-peak intensity at the anode line. To ensure tube X-ray output stability a spotstability test is performed. Relative standard deviations of less than 1% are typical. Leakage current must be very low since operating conditions are typically less than 10 A of emission current. In the case of arcing tubes the measurement of leakage current is problematic, as arcing will damage the measuring equipment. By using a resistor string and measuring the voltage drop across this string, it is possible to achieve a very sensitive current measurement while protecting the meter from high-voltage transients. Finally, the filament impedance is monitored as an indicator of the tube vacuum integrity and/or the tube high internal pressure.
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IMPROVEMENTS IN LOW POWER, END-WINDOW, TRANSMISSION-TARGET X-RAY TUBES
Charles Jensen, Stephen M. Elliott*, Steven D. Liddiard, A. Reyes-Mena,
Melany Moras, and D. Clark Turner
2004
MOXTEK, Inc., Orem, UT USA 84057
*Thin Film Consulting, Longmont, CO USA 80501

ABSTRACT
End-window transmission-target X-ray tubes are designed for very close anode-to-sample coupling for compact portable XRF instruments. Several recent improvements have been achieved to make these tubes considerably brighter, with better output stability and even smaller size and lower power consumption for handheld instrumentation. Areas of the tube that have been improved include the anode, the cathode, and the high-voltage power supply. 1) The anode can be a sputtered film on the inside of the X-ray window. Densified films of a more uniform thickness provide higher X-ray output and more consistent performance from tube to tube. 2) Changes in the anode geometry have resulted in reduced spectral contamination from metal parts in the anode. 3) The electron beam position on the anode is primarily influenced by the filament placement relative to the cathode optic. Using finite-element analysis (FEA) charged-particle beam modeling software it was possible to design an improved cathode optic with significantly better electron beam performance. This results in higher electron density on the target and a more stable beam position. 4) Finally, innovations in the high-voltage power supply have resulted in significant reductions in size and weight in this component. New power supply designs also require significantly less input power than the earlier designs. The combination of these improvements results in miniature X-ray tubes with higher flux, lower spectral contamination, more stable X-ray beams, smaller and lighter packages, and lower overall power consumption.
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An XRD/XRF instrument for the microanalysis of rocks and minerals
S Cornaby1, A Reyes-Mena1, H K Pew1, P W Moody1, T Hughes2,
A Stradling2, D C Turner1 and L V Knight2
2001
1 MOXTEK, Inc., 452 West 1260 North, Orem, UT 84057, USA
2 Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602, USA
Email: and
Received 20 November 2000, in final form 28 February 2001, accepted for
publication 21 March 2001

Abstract
A breadboard setup constructed at MOXTEK, Inc., is capable of capturing both x-ray diffraction (XRD) and x-ray fluorescence (XRF) information simultaneously using a charge-coupled device (CCD) as the x-ray detector. This preliminary setup will lead to a prototype simultaneous XRD/XRF instrument. NASA is funding the instrument’s construction because of its capabilities and small size; it could be used for future Mars missions for analysis of rocks. The instrument uses a CCD to capture both the energy and the spatial information of an incoming x-ray. This is possible because each pixel acts as a spatially addressable energy-dispersive detector. A powdered sample of material is placed in front of the CCD, which in turn is bombarded by a collimated x-ray beam. The instrument’s critical features—namely the x-ray source, collimation optics and x-ray transparent windows—allow for the first time, to the best of our knowledge, mounting the sample outside the CCD camera. In this paper the instrument’s design parameters as well as the properties of both a front-side-illuminated (FSI) CCD and back-side-illuminated (BSI) CCD as x-ray detectors are investigated.
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MINIATURE X-RAY TUBES UTILIZING CARBON-NANOTUBEBASED COLD CATHODES
A. Reyes-Mena, Charles Jensen, Erik Bard, D. Clark Turner and K. G. Erdmann
2005
MOXTEK, Inc., Orem, UT 84057
Qi Qiu, Bo Gao, Jianping Lu and Otto Zhou
XINTEK, Inc., Chapel Hill, NC 27516

ABSTRACT
The electron field-emission properties of carbon nanotubes enable the fabrication of cold cathodes for a variety of vacuum device applications. The utilization of these cathodes is an attractive alternative for the replacement of thermionic or hot cathodes for generating X-rays. Miniature X-ray tubes have been fabricated using triode-style carbon nanotubebased cathodes. In this paper we report the results of characterization studies, such as beam current dependence on the control gate voltage. Also, results on focal spot measurements and electron-beam modeling allow the possibility of reducing focused spot sizes. Driving gate voltages below 1000 volts for easy pulsing has been achieved, and the extended lifetime data suggests that a regulated power supply would be ideal for a constant AC operation mode. The 1mm focal spot size achieved so far is suitable for most XRF applications.
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SIMULTANEOUS XRD/XRF WITH LOW-POWER X-RAY TUBES
S. Cornaby1, A. Reyes-Mena1, P. W. Moody1, T. Hughes2, A. Stradling2, T. Grow1, and L. V. Knight2
2002
1 MOXTEK, Inc., 452 West 1260 North, Orem, UT 84057
2 Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602

ABSTRACT
A test bench instrument constructed at MOXTEK, Inc. is capable of simultaneously capturing X-ray diffraction (XRD) and X-ray fluorescence (XRF) information using a charge-coupled device (CCD) as the X-ray detector. NASA is funding the instrument’s construction because of its low-power consumption and compact size; it could be used for in-situ planetary exploration missions for mineral analysis. A powdered sample of material is placed in front of the CCD. A collimated X-ray beam bombards the sample, and the CCD captures the scattered X-ray events. Sorting algorithms are used to separate the XRF and the XRD information captured by the CCD. A small low-power X-ray source is needed to make the device portable. We have examined the instrument with a rotating-anode tube, a commercially available Svetlana transmission tube, and two miniature low-power prototype tubes constructed at MOXTEK. The data capturing rates were compared for the different sources. We have verified the feasibility of capturing both XRF and XRD with the MOXTEK source, using under five watts for both the tube and its high-voltage power supply.
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