(L. V. Knight, D. D Allred, R. S. Turley)
| We are working on a portable instrument that
will analyze microsamples simultaneously using both x-ray fluorescence (XRF) and x-ray
diffraction (XRD). A compact, low average power, high peak power, microfocus x-ray source
(tube) produces a bright, microscopic x-ray spot on the sample. An electronic area array
(CCD) detector records the fluorescent x rays and the diffracted x rays that are scattered
from the sample. The results yield both chemical (elemental analysis) and mineralogic
(crystal structure) information. The design is based on a Mars probe which is being
proposed to NASA—BYU is a collaborator. While working with NASA scientists to obtain
funding for this space instrument we propose to test the feasibility of a commercial
version of the instrument. |
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| The key technical innovations are:
1) The use of a low average power, pulsed field emitter cathode (no thermionic emission)
and an advanced electron optic to produce a point x-ray source (tube); 2) The use of an x
ray sensitive CCD detector arranged in a backscatter geometry to detect the energy and
position of x rays scattered from the sample. The goal of the research is to integrate the
key components of the instrument—a compact field emitter x-ray tube (provided by
MOXTEK, Inc.) and an x-ray sensitive CCD camera—and test in several applications.
This work is funded by NASA through MOXTEK, Inc. The viability of
simultaneously doing both x-ray diffraction and fluorescence has been shown in a similar
instrument—a specialized instrument intended for Mars exploration. CHEMIN is the name
of a compact, x-ray diffraction/x-ray fluorescence instrument designed to characterize the
elemental composition and mineralogy of small fine-grained or powdered samples. The name
refers to the instrument’s combined CHEmical and MINeralogic analytical capability.
Both diffraction and fluorescence data are obtained simultaneously by exposing a CCD array
to the scattered x rays and sorting out the photons according to their energies. The
scattered fluorescent x rays have energies that are characteristic of the emitting atom
and an energy that is less than the diffracted x rays. A breadboard version of the CHEMIN
instrument—with a conventional x-ray tube and a low resolution, commercial CCD
array— has been working at Los Alamos National Laboratory since July, 1996.
See figure 1. |
Check out a related
article in the Deseret News.
The Los Alamos Chemin web page is: http://chemin.lanl.gov/
The Los Alamos work is described in more detail in these publications:
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Vaniman, D., D. Bish, D.F. Blake, S.A. Collins, S. Chipera, P. Sarrazin,
and S.T. Elliot, "Use of the prototype CHEMIN XRD/XRF instrument in
analyzing complex mixtures of potential Martian sulfate minerals," Abstr.
No. 1692 (CDROM) IN: Lunar and Planetary Science Conference XXIX, Lunar
and Planetary Institute, Houston, TX (1998).
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Bish,D., D. Vaniman, C. Chipera, S.A. Collins, T. Elliott and D.F. Blake,
"CHEMIN: A miniaturized CCD-based instrument for simultaneous X-ray
diffraction (XRD) and X-ray fluorescence (XRF) analysis," 47th Annual
Denver X-ray conference, abstracts w. prog. p. 55 (Colorado Springs, CO,
Aug. 3-7, (1998).
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Sarrazin, P., D.F. Blake, D. Bish, D. Vaniman and S. Collins, "A miniature
XRD/XRF Instrument for in-situ characterization of Martian soils and
rocks," J. Phys. IV France 8: 465-470 (1998).
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Vaniman, D., D. Bish, D.F. Blake, S.T. Elliott, P. Sarrazin, S.A. Collins
and S. Chipera, "Landed XRD/XRF analysis of prime targets in the search for
past or present Martian life," J. Geophys. Res. 103(E13):31,477-31,489
(1998).
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Vaniman, D., D. Bish, S. Chipera, P. Sarrazin, D. Blake, and S. A. Collins.
"Sample preparation and mounting strategies for robotic XRD/XRF analysis."
IN: Lunar and Planetary Science Conference XXX, Lunar and Planetary
Institute, Houston, TX (1999).
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Vaniman, D., D. Bish, G. Guthrie, S. Chipera, P. Sarrazin, D. Blake, and S.
A. Collins, S.T. Elliott and P. Sarrazin. "Process monitoring and control
with CHEMIN, a miniaturized CCD-based instrument for simultaneous XRD/XRF
analysis" SPIE 44, (In press).
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Blake, David F. ""Remote X-ray Diffraction and X-ray Fluorescence analysis
on planetary surfaces" IN: Advances in X-ray Analysis, Vol. 43, (In
press).
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