- Email: [email protected]
Precise coordinate control in fission track uranium mapping
NUCLEAR INSTRUMENTS
AND METHODS
98 0972) 183-~84; © N O R T H - H O L L A N D
PUBLISHING
CO.
PRECISE C O O R D I N A T E C O N T R O L IN F I S S I O N TRACK U R A N I U M MAPPING* E. L. HAINES
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, U.S.A. and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A. Received 9 August 1971 The problem of locating minute mineral grains by fission track uranium mapping is solved by means of a congruent transformation
of the track detector's coordinate system. transformation of the coordinate system of the detector to the coordinate system of the polished rock section. The system of the rock section may be an (X, Y) system laid out on a photomicrograph, or the "x-y" stage of a microscope or electron microprobe on which the section is mounted for study. Any point on the detector (U,V) is related to its corresponding point (X,Y) on the rock section's coordinate system by the matrix transform
Fission track activation was first used by Price and Walker 1) to map the distribution of uranium in natural materials. Fission track activation employs a dielectric track detector, usually a plastic or mica sheet, to detect fission fragments from U concentrations in polished rock sections. Uranium fission is induced by thermal neutron irradiation. Other investigators have applied this technique to terrestrial, meteoritic, and lunar samples 2 - 11). An important problem in fission track mapping is coordinate control; it is hard to relate locations of track concentrations on the detector to the locations of the U-rich minerals on the polished section. Fleischer 12) approached the coordinate control problem by permanently emplacing a thin plastic film on the polished rock surface. Because the film is thinner than the average fission fragment range, tracks penetrate the sheet and are etched in situ. The use of a permanent film permits accurate location of U-rich phases. However the plastic film prevents the subsequent study of the U-rich phases by microprobe or reflected light microscopy. Also quantitative U determinations are made very difficult. Kleeman and Lovering 13) used very high thermal neutron doses to produce "lexan prints" of the rock fabric on the (lexan) plastic fission track detector. The print of the rock fabric on the plastic permits one to identify corresponding positions on the rock. This method has the disadvantages that hig]h neutron doses are required, and that a moderate concentration of Li or B must be present in some phases to produce the fabric print by (n,~) reactions. In this note, we report a scheme for precisely locating mineral grains related to U concentrations revealed by the track detector. This scheme uses a congruent
--
M
.
\-sin0
* The support of the National Aeronautics and Space Administration under contracts NAS 7-100 (JPL) and NAS 9-8074 (Caltech) is gratefully acknowledged.
cos0/
(1)
V - V0
The transform parameters, magnification (M), rotation (0), and translation (Uo, V0) are uniquely defined if the locations of two or more pre-arranged points, which we call control points, are precisely known. In the following we describe the creation and measurement of control points and the determination of the transform parameters, and finally the precision of the method. Many small control marks ( + ' s ) are scribed on one surface of the lexan plastic detector. An outline of the rock section is first scribed on the plastic sheet so that, with the sheet turned over (detecting surface up), the control marks may be placed near the section's perimeter. The sheet is returned to the sample, control points down, and firmly fixed in place with a fused quartz disk. The disk is fastened securely with small strips of tape. The entire assembly, sample-detectordisk, is examined under a microscope to discover which control marks have points which can be accurately related on both the rock section and the detector sheet. All such control marks are photographed, and these photographs become the control data for determining the transform parameters. After the assembly is irradiated and the track detec-
183
184
E.L. HAINES
tor is r e m o v e d and etched, the (U,V) c o o r d i n a t e s o f the control points a n d t r a c k concentrations on the detector are m e a s u r e d and recorded by means o f a microscope and "x--y" stage. The (U,V) coordinates o f the control points on the detector are m a t c h e d with the (X, Y) c o o r d i n a t e s of the c o n t r o l points on the rock section (coordinates o f a p h o t o g r a p h or stage). If only two control points are used, the t r a n s f o r m p a r a m e t e r s are determined by iterative inversion o f the T a y l o r ' s expansion o f eq. (1). Three or m o r e control p o i n t s are fitted by iterative least-squares analysis o f the T a y l o r ' s expansion. W i t h the t r a n s f o r m p a r a m e t e r s (M,O,Uo,Vo) thus determined, the locations (U,V) o f all the t r a c k concentrations are t r a n s f o r m e d to the new system (X,Y) by eq. (1). The heart o f our present system is an "x-y" stage of m o d e r a t e precision with which coordinates o f control points and t r a c k concentrations are measured. Coordinates are reproducible to + 10/~m. W h e n the (X, Y) system is a p h o t o m i c r o g r a p h o f the r o c k section, the r o o t - m e a n - s q u a r e (rms) fit of the control points is characteristically + 0.2 m m , which is roughly the limit o f o u r precision with a millimeter rule. W h e n the rock section is placed on the m i c r o p r o b e stage and the digital coordinates o f the stage constitute the (X,Y) system, the rms fit of the control points is usually +_ 20 pro. A fit o f _+ 10 # m has been achieved, and we consider this to be the limit o f the present system. A search for 1 to 5/~m U-rich grains in lunar s a m p l e 12013,14 has been carried out by Haines et al. 11) using the present technique and an electron m i c r o p r o b e ( M A C - 5 S A - 3 ) . Least squares analysis o f six c o n t r o l
points yielded rms fits o f 18 /~m and 25 /~m in two separate experiments. Spectrometers of the m i c r o p r o b e were tuned to characteristic X-rays of i m p o r t a n t elements in the mineral, in this case to K X-rays o f Ti and L X-rays o f Zr. W h e r e the grains were not buried b e n e a t h the section's surface, they were always l o c a t e d within a single 1000X p h o t o g r a p h whose center was the t r a n s f o r m e d (X,Y) coordinates, and whose unmagnified area was 75/~m x 100 elm. References
1) p. B. Price and R. M. Walker, Appl. Phys. Letters 2 (1963) 23. 2) E. I. Hamilton, Science 151 (1966) 570. 3) L. M. Kleppe and M. Roger, University of California, Lawrence Radiation Laboratory Report UCRL-17075 (1966). 4) j. D. Kleeman, D, H. Green and J. F. Lovering, Earth Planet. Sci. Letters 5 (1969) 449. 5) R. L. Fleischer, Geochim. Cosmochim. Acta 32 (1968) 989. 6) j. F. Lovering and J. D. Kleeman, Proc. Apollo 11 Lunar Science Conf. 1 (1970) p. 627. 7) D. S. Burnett, M. Monnin, M. Seitz, R. M. Walker, D. Woolum and D. Yuhas, Earth Planet. Sci. Letters 9 (1970) 127. 8) D. S. Burnett, M. Monnin, M. Seitz, R. M. Walker and D. Yuhas, 2nd Lunar Science Conf. (Houston, Texas, Jan. 197l) to be published. ~) C. Frick, T. C. Hughes, J. F. Lovering, A. F. Reid, N. G. Ware and D. A. Wark, 2nd Lunar Science Conf. (Houston, Texas, Jan. 1971) to be published. to) A. L. Albee, D. S. Burnett, A. A. Chodos, E, L. Haines, J. C. Huneke, D. A. Papanastassiou, F. A. Podosek, G. P. Russ [11 and G. J. Wasserburg, Earth Planet. Sci. Letters 9 (1970) 137. 1~) E. L. Haines, A. L. Albee, A. A. Chodos and G. J. Wasserburg, Earth Planet. Sci. Letters, in press. lz) R. L. Fleischer, Rev. Sci. Instr. 37 (1966) 1738. la) j. D. Kleeman and J. F. Lovering, Science 156 (1967) 512.
AND METHODS
98 0972) 183-~84; © N O R T H - H O L L A N D
PUBLISHING
CO.
PRECISE C O O R D I N A T E C O N T R O L IN F I S S I O N TRACK U R A N I U M MAPPING* E. L. HAINES
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, U.S.A. and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, U.S.A. Received 9 August 1971 The problem of locating minute mineral grains by fission track uranium mapping is solved by means of a congruent transformation
of the track detector's coordinate system. transformation of the coordinate system of the detector to the coordinate system of the polished rock section. The system of the rock section may be an (X, Y) system laid out on a photomicrograph, or the "x-y" stage of a microscope or electron microprobe on which the section is mounted for study. Any point on the detector (U,V) is related to its corresponding point (X,Y) on the rock section's coordinate system by the matrix transform
Fission track activation was first used by Price and Walker 1) to map the distribution of uranium in natural materials. Fission track activation employs a dielectric track detector, usually a plastic or mica sheet, to detect fission fragments from U concentrations in polished rock sections. Uranium fission is induced by thermal neutron irradiation. Other investigators have applied this technique to terrestrial, meteoritic, and lunar samples 2 - 11). An important problem in fission track mapping is coordinate control; it is hard to relate locations of track concentrations on the detector to the locations of the U-rich minerals on the polished section. Fleischer 12) approached the coordinate control problem by permanently emplacing a thin plastic film on the polished rock surface. Because the film is thinner than the average fission fragment range, tracks penetrate the sheet and are etched in situ. The use of a permanent film permits accurate location of U-rich phases. However the plastic film prevents the subsequent study of the U-rich phases by microprobe or reflected light microscopy. Also quantitative U determinations are made very difficult. Kleeman and Lovering 13) used very high thermal neutron doses to produce "lexan prints" of the rock fabric on the (lexan) plastic fission track detector. The print of the rock fabric on the plastic permits one to identify corresponding positions on the rock. This method has the disadvantages that hig]h neutron doses are required, and that a moderate concentration of Li or B must be present in some phases to produce the fabric print by (n,~) reactions. In this note, we report a scheme for precisely locating mineral grains related to U concentrations revealed by the track detector. This scheme uses a congruent
--
M
.
\-sin0
* The support of the National Aeronautics and Space Administration under contracts NAS 7-100 (JPL) and NAS 9-8074 (Caltech) is gratefully acknowledged.
cos0/
(1)
V - V0
The transform parameters, magnification (M), rotation (0), and translation (Uo, V0) are uniquely defined if the locations of two or more pre-arranged points, which we call control points, are precisely known. In the following we describe the creation and measurement of control points and the determination of the transform parameters, and finally the precision of the method. Many small control marks ( + ' s ) are scribed on one surface of the lexan plastic detector. An outline of the rock section is first scribed on the plastic sheet so that, with the sheet turned over (detecting surface up), the control marks may be placed near the section's perimeter. The sheet is returned to the sample, control points down, and firmly fixed in place with a fused quartz disk. The disk is fastened securely with small strips of tape. The entire assembly, sample-detectordisk, is examined under a microscope to discover which control marks have points which can be accurately related on both the rock section and the detector sheet. All such control marks are photographed, and these photographs become the control data for determining the transform parameters. After the assembly is irradiated and the track detec-
183
184
E.L. HAINES
tor is r e m o v e d and etched, the (U,V) c o o r d i n a t e s o f the control points a n d t r a c k concentrations on the detector are m e a s u r e d and recorded by means o f a microscope and "x--y" stage. The (U,V) coordinates o f the control points on the detector are m a t c h e d with the (X, Y) c o o r d i n a t e s of the c o n t r o l points on the rock section (coordinates o f a p h o t o g r a p h or stage). If only two control points are used, the t r a n s f o r m p a r a m e t e r s are determined by iterative inversion o f the T a y l o r ' s expansion o f eq. (1). Three or m o r e control p o i n t s are fitted by iterative least-squares analysis o f the T a y l o r ' s expansion. W i t h the t r a n s f o r m p a r a m e t e r s (M,O,Uo,Vo) thus determined, the locations (U,V) o f all the t r a c k concentrations are t r a n s f o r m e d to the new system (X,Y) by eq. (1). The heart o f our present system is an "x-y" stage of m o d e r a t e precision with which coordinates o f control points and t r a c k concentrations are measured. Coordinates are reproducible to + 10/~m. W h e n the (X, Y) system is a p h o t o m i c r o g r a p h o f the r o c k section, the r o o t - m e a n - s q u a r e (rms) fit of the control points is characteristically + 0.2 m m , which is roughly the limit o f o u r precision with a millimeter rule. W h e n the rock section is placed on the m i c r o p r o b e stage and the digital coordinates o f the stage constitute the (X,Y) system, the rms fit of the control points is usually +_ 20 pro. A fit o f _+ 10 # m has been achieved, and we consider this to be the limit o f the present system. A search for 1 to 5/~m U-rich grains in lunar s a m p l e 12013,14 has been carried out by Haines et al. 11) using the present technique and an electron m i c r o p r o b e ( M A C - 5 S A - 3 ) . Least squares analysis o f six c o n t r o l
points yielded rms fits o f 18 /~m and 25 /~m in two separate experiments. Spectrometers of the m i c r o p r o b e were tuned to characteristic X-rays of i m p o r t a n t elements in the mineral, in this case to K X-rays o f Ti and L X-rays o f Zr. W h e r e the grains were not buried b e n e a t h the section's surface, they were always l o c a t e d within a single 1000X p h o t o g r a p h whose center was the t r a n s f o r m e d (X,Y) coordinates, and whose unmagnified area was 75/~m x 100 elm. References
1) p. B. Price and R. M. Walker, Appl. Phys. Letters 2 (1963) 23. 2) E. I. Hamilton, Science 151 (1966) 570. 3) L. M. Kleppe and M. Roger, University of California, Lawrence Radiation Laboratory Report UCRL-17075 (1966). 4) j. D. Kleeman, D, H. Green and J. F. Lovering, Earth Planet. Sci. Letters 5 (1969) 449. 5) R. L. Fleischer, Geochim. Cosmochim. Acta 32 (1968) 989. 6) j. F. Lovering and J. D. Kleeman, Proc. Apollo 11 Lunar Science Conf. 1 (1970) p. 627. 7) D. S. Burnett, M. Monnin, M. Seitz, R. M. Walker, D. Woolum and D. Yuhas, Earth Planet. Sci. Letters 9 (1970) 127. 8) D. S. Burnett, M. Monnin, M. Seitz, R. M. Walker and D. Yuhas, 2nd Lunar Science Conf. (Houston, Texas, Jan. 197l) to be published. ~) C. Frick, T. C. Hughes, J. F. Lovering, A. F. Reid, N. G. Ware and D. A. Wark, 2nd Lunar Science Conf. (Houston, Texas, Jan. 1971) to be published. to) A. L. Albee, D. S. Burnett, A. A. Chodos, E, L. Haines, J. C. Huneke, D. A. Papanastassiou, F. A. Podosek, G. P. Russ [11 and G. J. Wasserburg, Earth Planet. Sci. Letters 9 (1970) 137. 1~) E. L. Haines, A. L. Albee, A. A. Chodos and G. J. Wasserburg, Earth Planet. Sci. Letters, in press. lz) R. L. Fleischer, Rev. Sci. Instr. 37 (1966) 1738. la) j. D. Kleeman and J. F. Lovering, Science 156 (1967) 512.