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Application of PIXE to source identification of Kosa aerosol: analysis of desert soils in China
Nuclear Instruments North-Holland
and Methods
in Physics Research
MM B
B75 (1993) 317-320
Beam Interactions with Materials&Atoms
Application of PIXE to source identification analysis of desert soils in China
of Kosa aerosol:
K. Suzuki a,1, K. Maeda b, Y. Sasa b, A. Okada b, K. Sakamoto a and T. Ozawa a a Faculty of Engineering, Saitama University, Urawa, Saitama, 338, Japan b Institute of Physical and Chemical Research @KEN), Wake, Saitama, 351-01, Japan
Eighteen samples of soil from six areas in three desert regions of China were subjected to X-PIXE and X-ray diffraction analysis. The samples were composed mainly of quartz, feldspar group minerals and calcite. The quartz content differed remarkably depending on the sampling area. Fourteen elements were detected and determined in almost all samples, The concentration ratio Mn/Fe ranged from 0.018 to 0.027 and was almost the same as those values reported previously for airborne mineral dusts and desert soils. Other ratios such as Al/Fe, Si/Fe, K/Fe and Ca/Fe also were in the ranges of the previously reported values for the dusts and soils. Of these ratios, Si/Fe and Ca/Fe showed clear differences among the source regions of soil samples, and it is suggested that these differences can be useful to identify the source region of soil specimens,
1. Introduction
2. Experimental
“Kosa” (arrival of Yellow Sand aerosol or airborne mineral dust) has long been a phenomenon of considerable interest in Japan. Kosa aerosol is presumed to be transported from the deserts of the Asian continent thousands of kilometers from Japan. Information concerning Kosa aerosol (source, mechanism of long range transport and elemental and mineral composition) is important from the viewpoint of environmental and geochemical sciences. Many papers have been presented on elemental and mineral compositions of Kosa aerosol and airborne dusts [2-61. However, there has been scarcely any investigation of the source materials, and detailed information on the chemical composition of likely source materials is required. Particle induced X-ray emission (PIXE) is a very sensitive analytical method and is suitable for multielement determination of very small amounts of environmental samples. We expect to use PIXE as an effective technique to identify the source materials and/or area of origin of Kosa aerosol. In the present research, samples of desert soil, which is are presumed to be the source material of Kosa aerosol, were subjected to PIXE and X-ray diffraction (XRD) analysis. The results were analyzed to elucidate differences in elemental and mineralogical distribution patterns among these samples.
2.1. PIXE analysis Desert soil samples were collected at 18 points in 6 areas (A-F) located in three regions of China (Fig. I). Small amounts of material were fixed on Kapton film (7.5 km thick) affixed to an aluminum frame by using collodion. A 1.16 MeV H+ ion beam was used to irradiate the samples in air by using RIKEN tandem accelerator. The diameter of the H+ beam was 3 mm. The X-rays emitted from the target were detected by a Si(Li) semiconductor detector. The detector was located at an angle of 135” with respect to the incident beam direction, and was set 17 mm away from the sample. Signals from the Si(Li) detector were stored in
50
40 G .s 30 c Z @ 20 10
’ ’ Present address: gawa, 210 Japan. 0168-583X/93/$06.00
Komukai
Toshiba-cho,
Kawasaki,
80
90
KanaFig. 1. Sampling
0 1993 - Elsevier
Science
Publishers
B.V. All rights reserved
120 110 east longitude
100
area of desert
130
140
soils (A-F).
IV. ENVIRONMENTAL
SAMPLES
K. Suzuki et al. / Source identification of Kosa aerosol
318
. . . .
/*.
.
.
.
.
.
2. Calculated absorber.
X-ray yield for NIST 98a. A: without l : with graphite pinhole absorber.
a multichannel analyzer, and then processed by a microcomputer and transferred to floppy disks. Two kinds of X-ray absorbers were used here. One was a 0.8 mm thick carbon sheet (130 mg/cm2) with a 0.3 mm diameter pinhole to reduce the intensity of low energy X-rays, e.g., Si K X-rays from major elements of soil and Ar K X-rays from air. The other was a combination absorber made of a 0.8 mm thick carbon sheet (130 mg/cm2) with a 0.2 mm diameter pinhole and a 25 pm thick vanadium foil (8.92 mg/cm2). The combination absorber was used to selectively reduce the intensity of Fe K X-rays, because the samples contained considerable amounts (up to 10%) of Fe. Yields of characteristic X-rays with and without the pinhole absorber are shown in fig. 2, for a standard clay sample (NIST 98a). As shown in fig. 2, the X-ray yields obtained with the pinhole absorber are two orders smaller in magnitude than that obtained without the absorber for the elements with an atomic number of less than 20. For elements with an atomic number of more than 24, the X-ray yields with and without the absorber are of the same order. As shown in fig. 3, the X-ray yields obtained with the combination absorber made of a graphite pinhole and vanadium film varied extremely at the point of atomic number 25. PIXE spectra obtained from the soil samples were processed by the computer program of Clayton’s PIXAN [l]. In order to correct the matrix effects it was assumed that major elements were present as oxides and the sum of these oxides was 100%. Five reference materials of rocks and clays shown in table 1 were analyzed to examine the reliability of this method. In fig. 4, the elemental concentrations determined by are plotted against those certified by the PIXE (C,,,,) reference material supplier (C,,,). All experimental
.
J
10
atomic number
Fig.
.
.
I I
O.O’l-
.
atomic number
Fig. 3. Calculated X-ray yield for NIST 98a (with a combination absorber made of a graphite pinhole and vanadium film).
Table 1 Reference Sample
material name
Source
JB-la JG-la 98a R-701 feldspar R-601 clay no. 1
Geological Survey of Japan Geological Survey of Japan NIST Ceramic Society of Japan Ceramic Society of Japan
I
I
I
105 E l-,104 :: E 0" 103
102
10' 10'
102
103
104
105
C,,f/wm
Fig. 4. Relation PIXE (Cr.,,,)
of elemental concentration and elemental concentration sources (C,,,).
determined certified
by by
;
E r.n
0.26
0.255 0.270 0.182 0.186 0.172 0.164 0.30 0.039 0.069
AI/Si
0.088
0.0850 0.0900 0.0650 0.0590 0.10 0.11 0.030
0.088 0.104
K/Si
0.16
0.220 0.159 0.216 0.248 0.0400 0.0240 0.08 13 0.11
Ca/Si
ratios relative to Si
0.335 0.652 0.756 0.772 0.944 0.839
Ca/Fe
0.11
0.109 0.112 0.0685 0.0699 0.17 0.16 0.027
0.270 0.160
Fe/Si
0.802 0.993 1.86 2.25 0.586 0.349
0.093 0.080 0.089 0.10 0.11 0.14
Ti/Fe
-
0.025 0.013 0.010 0.011 0.0075 0.0098 -
Ti/Si
a Value of Leith and Mead (shale 82%, sandstone 12%, limestone 6%) f2].
Average composition of sedimentary rocks a
E
; Shale Limestone Sandstone
25.3 31.0 32.6 32.3 37.0 37.0
A B c D
? !z s g 2
Si [wt.%]
Sampling regions
Table 3 Si concentration and element concentration
0.949 1.69 1.58 1.71 2.50 2.34
K/Fe
6.95 4.90 3.76 3.57 2.50 2.60
3.70 6.26 8.93 9.18 14.6 14.3
Si/Fe
Fe [wt.%]
Sampling region
A B c D E F
Al/Fe
ratios relative to Fe
Table 2 Fe concentration and element concentration
-
0.0062 0.0035 0.0030 0.0026 0.0014 0.0013 -
Mn/Si
0.023 0.022 0.027 0.024 0.021 0.018
Mn/Fe
-
0.0032 0.0040 -
0.10 OS3038
S/Si
0.37 0.024 0.035 0.029 -
S/Fe
Cl/Fe
-
0.22 0.0035 0.0076 0.0080 0.0025 0.0012 -
Cl/Si
0.81 0.022 0.066 0.073 0.036 0.017
-
0.00040 0.~87 0.00011 0.00014 -
Cu/Si
0.0015 0.0006 0.0095 0.0013 -
Cu/Fe
Zn/Fe
0.00061 0.~29 0.00025 0.00024 0.00017 0.00011 -
Zn/Si
0.0022 0.0018 0.0022 0.0021 0.0025 0.0016
Rb/Fe
0.00035 0.00035 0.00043 0.00044 0.00024 0.00027
Rb/Si
0.0013 0.0022 0.0038 0~0040 0.0036 0.0038
_
0.0036 0.0014 0.0011 0.00097 0.00041 0.00035 _ -
Sr/Si
0.013 0.088 0.0092 0.0088 0.0060 0.0050
Sr/Fe
-
0.00063 0.0~68 0.00075 0.00077 0.00038 0.0017
Zr/Si
0.0024 0.0043 0.0065 0.0070 0.0056 0.024
Zr/Fe
320
K. Suzuki et al. / Source idenhficalion of Kosa aerosol
data obtained for 18 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Cr, Rb, Sr, Zr) in a concentration range of 10-100000 ppm are shown in the figure. Except for a few points, the concentrations determined by PIXE agree well with the certified concentrations: a ratio C,,,,/C,, of 1.0 k 0.1 was obtained for the NIST 98a and JB-la, and a ratio CPIXE/Cref of 1.0 + 0.2 was obtained for the other three reference materials.
high in Fe and low in Si, is similar to that of the average sedimentary rock [7] shown on the bottom line of table 3. There are some elements whose concentrations in one region are different clearly from those in the other two regions. For exampie Ca concentrations in the north region of the L.oess plateau (E and F) are much lower than those in the other two regions. Aluminum and Mn are other examples which exhibit this trend. Only the ratio Fe/Si differs among three regions.
2.2. Powder-XRI) study Powder X-ray diffraction analysis was performed in order to identify mineral species in the samples of desert soil. The Rigaku High Brilliance X-ray diffractometer equipped with a Cu radiation source and a NaI scintillation counter was used. Operation conditions were as follows: voltage: 40 kV; current: 30 mA, goniometer scanning speed: 26 (deg/min) = 2; and time constant, 1 s. Mineral species were determined in reference to the JCPDS data file.
3. Results and discussion Results obtained by the XRD method showed that the soil samples were mainly composed of quartz, several feldspar group minerals (bytownite, oligoclase plagioclase, etc.) and calcite. There seemed to be some differences in quartz content of the samples among the sampling regions. The order of the quartz content was as follows: A < B, C, D, < E, F. Results from the PIXE analysis are compiled in tables 2 and 3. Concentrations of 14 elements are shown in table 2 relative to iron. Our data were in the range of the values rep&ted on airborne mineral dusts collected in Japan (Kosa, [2]) and China [3] and desert soils [4] and loess [5,6] in China. Especially the ratios Mn/Fe were in a narrow range of 0.018-0.027 and almost the same as the reported values. The PIXE data suggest that there is similarity in element concentrations between closely located areas in each region (A and B, C and D, or E and F) though some differences are observed between A and B. The concentrations of Si and Ca are clearly different among the three regions. We may use the ratios Si/Fe and Ca/Fe to identify a specific source region of soil samples. Table 3 shows the element concentrations relative to Si. The concentration of Si differs among the six areas and the highest con~ntration is found in the samples from E and F. The Si concentration seems to correlate with the quartz content of the samples. The chemical composition of the sample from A, which is
4. Conclusion The chemical composition of soil samples from Chinese deserts, which are presumed to be likely source material of airborne mineral dusts transported to the Pacific area, are given. With the exception of the ratios Ti/Fe and Mn/Fe there are some differences in the concentration ratios of elements among the sampling areas and/or the regions. Of these ratios, it is suggested that the ratios Si/Fe (or Fe/%) and Ca/Fe can be useful to identify the source region of soil specimens in Chinese deserts. These ratios give also useful basic information to estimate sources of airborne mineral dusts transported to Japan and the Pacific area, though further studies on size distribution are required to investigate processes of elemental and mineral fractionations.
Acknowledgements
The authors are most grateful for helpful suggestions from J. Kawai, M. Maeda, R. Saito and the staff of Environmental Engineering Lab., R and D Center, Toshiba Corp. We also wish to thank to M. Uda for making ~experimental equipment available for our use.
References E. Clayton, P. Dureden and D.D. Cohen, Nucl. Instr. and Meth. B22 (1987) 64. @I A. Mizohata and T. Mamuro, J. Jpn. Sot. Pollut. 17 (1982) 377. w Wang Mingxing, J.W. Winchester and Li Shaomeng, Nucl. Instr. and Meth. B22 (1987) 275. [41 J.W. Winchester, W. Lu, I. Ren, M. Wang and W. Maenhaut, Atmos. Environ. 15 (1981) 933. (Science Press, Beijing, ISI T. Liu, Loess and Environment 1985). I61 S. Tanaka, M. Tajima, S. Sato and Y. Hashimoto, Adv. X-ray Chem. Anal. Jpn. 17 (1986) 2.53. [71 F.J. Pettijohon, Sedimentary Rocks (Harper, 1957).
[ll
and Methods
in Physics Research
MM B
B75 (1993) 317-320
Beam Interactions with Materials&Atoms
Application of PIXE to source identification analysis of desert soils in China
of Kosa aerosol:
K. Suzuki a,1, K. Maeda b, Y. Sasa b, A. Okada b, K. Sakamoto a and T. Ozawa a a Faculty of Engineering, Saitama University, Urawa, Saitama, 338, Japan b Institute of Physical and Chemical Research @KEN), Wake, Saitama, 351-01, Japan
Eighteen samples of soil from six areas in three desert regions of China were subjected to X-PIXE and X-ray diffraction analysis. The samples were composed mainly of quartz, feldspar group minerals and calcite. The quartz content differed remarkably depending on the sampling area. Fourteen elements were detected and determined in almost all samples, The concentration ratio Mn/Fe ranged from 0.018 to 0.027 and was almost the same as those values reported previously for airborne mineral dusts and desert soils. Other ratios such as Al/Fe, Si/Fe, K/Fe and Ca/Fe also were in the ranges of the previously reported values for the dusts and soils. Of these ratios, Si/Fe and Ca/Fe showed clear differences among the source regions of soil samples, and it is suggested that these differences can be useful to identify the source region of soil specimens,
1. Introduction
2. Experimental
“Kosa” (arrival of Yellow Sand aerosol or airborne mineral dust) has long been a phenomenon of considerable interest in Japan. Kosa aerosol is presumed to be transported from the deserts of the Asian continent thousands of kilometers from Japan. Information concerning Kosa aerosol (source, mechanism of long range transport and elemental and mineral composition) is important from the viewpoint of environmental and geochemical sciences. Many papers have been presented on elemental and mineral compositions of Kosa aerosol and airborne dusts [2-61. However, there has been scarcely any investigation of the source materials, and detailed information on the chemical composition of likely source materials is required. Particle induced X-ray emission (PIXE) is a very sensitive analytical method and is suitable for multielement determination of very small amounts of environmental samples. We expect to use PIXE as an effective technique to identify the source materials and/or area of origin of Kosa aerosol. In the present research, samples of desert soil, which is are presumed to be the source material of Kosa aerosol, were subjected to PIXE and X-ray diffraction (XRD) analysis. The results were analyzed to elucidate differences in elemental and mineralogical distribution patterns among these samples.
2.1. PIXE analysis Desert soil samples were collected at 18 points in 6 areas (A-F) located in three regions of China (Fig. I). Small amounts of material were fixed on Kapton film (7.5 km thick) affixed to an aluminum frame by using collodion. A 1.16 MeV H+ ion beam was used to irradiate the samples in air by using RIKEN tandem accelerator. The diameter of the H+ beam was 3 mm. The X-rays emitted from the target were detected by a Si(Li) semiconductor detector. The detector was located at an angle of 135” with respect to the incident beam direction, and was set 17 mm away from the sample. Signals from the Si(Li) detector were stored in
50
40 G .s 30 c Z @ 20 10
’ ’ Present address: gawa, 210 Japan. 0168-583X/93/$06.00
Komukai
Toshiba-cho,
Kawasaki,
80
90
KanaFig. 1. Sampling
0 1993 - Elsevier
Science
Publishers
B.V. All rights reserved
120 110 east longitude
100
area of desert
130
140
soils (A-F).
IV. ENVIRONMENTAL
SAMPLES
K. Suzuki et al. / Source identification of Kosa aerosol
318
. . . .
/*.
.
.
.
.
.
2. Calculated absorber.
X-ray yield for NIST 98a. A: without l : with graphite pinhole absorber.
a multichannel analyzer, and then processed by a microcomputer and transferred to floppy disks. Two kinds of X-ray absorbers were used here. One was a 0.8 mm thick carbon sheet (130 mg/cm2) with a 0.3 mm diameter pinhole to reduce the intensity of low energy X-rays, e.g., Si K X-rays from major elements of soil and Ar K X-rays from air. The other was a combination absorber made of a 0.8 mm thick carbon sheet (130 mg/cm2) with a 0.2 mm diameter pinhole and a 25 pm thick vanadium foil (8.92 mg/cm2). The combination absorber was used to selectively reduce the intensity of Fe K X-rays, because the samples contained considerable amounts (up to 10%) of Fe. Yields of characteristic X-rays with and without the pinhole absorber are shown in fig. 2, for a standard clay sample (NIST 98a). As shown in fig. 2, the X-ray yields obtained with the pinhole absorber are two orders smaller in magnitude than that obtained without the absorber for the elements with an atomic number of less than 20. For elements with an atomic number of more than 24, the X-ray yields with and without the absorber are of the same order. As shown in fig. 3, the X-ray yields obtained with the combination absorber made of a graphite pinhole and vanadium film varied extremely at the point of atomic number 25. PIXE spectra obtained from the soil samples were processed by the computer program of Clayton’s PIXAN [l]. In order to correct the matrix effects it was assumed that major elements were present as oxides and the sum of these oxides was 100%. Five reference materials of rocks and clays shown in table 1 were analyzed to examine the reliability of this method. In fig. 4, the elemental concentrations determined by are plotted against those certified by the PIXE (C,,,,) reference material supplier (C,,,). All experimental
.
J
10
atomic number
Fig.
.
.
I I
O.O’l-
.
atomic number
Fig. 3. Calculated X-ray yield for NIST 98a (with a combination absorber made of a graphite pinhole and vanadium film).
Table 1 Reference Sample
material name
Source
JB-la JG-la 98a R-701 feldspar R-601 clay no. 1
Geological Survey of Japan Geological Survey of Japan NIST Ceramic Society of Japan Ceramic Society of Japan
I
I
I
105 E l-,104 :: E 0" 103
102
10' 10'
102
103
104
105
C,,f/wm
Fig. 4. Relation PIXE (Cr.,,,)
of elemental concentration and elemental concentration sources (C,,,).
determined certified
by by
;
E r.n
0.26
0.255 0.270 0.182 0.186 0.172 0.164 0.30 0.039 0.069
AI/Si
0.088
0.0850 0.0900 0.0650 0.0590 0.10 0.11 0.030
0.088 0.104
K/Si
0.16
0.220 0.159 0.216 0.248 0.0400 0.0240 0.08 13 0.11
Ca/Si
ratios relative to Si
0.335 0.652 0.756 0.772 0.944 0.839
Ca/Fe
0.11
0.109 0.112 0.0685 0.0699 0.17 0.16 0.027
0.270 0.160
Fe/Si
0.802 0.993 1.86 2.25 0.586 0.349
0.093 0.080 0.089 0.10 0.11 0.14
Ti/Fe
-
0.025 0.013 0.010 0.011 0.0075 0.0098 -
Ti/Si
a Value of Leith and Mead (shale 82%, sandstone 12%, limestone 6%) f2].
Average composition of sedimentary rocks a
E
; Shale Limestone Sandstone
25.3 31.0 32.6 32.3 37.0 37.0
A B c D
? !z s g 2
Si [wt.%]
Sampling regions
Table 3 Si concentration and element concentration
0.949 1.69 1.58 1.71 2.50 2.34
K/Fe
6.95 4.90 3.76 3.57 2.50 2.60
3.70 6.26 8.93 9.18 14.6 14.3
Si/Fe
Fe [wt.%]
Sampling region
A B c D E F
Al/Fe
ratios relative to Fe
Table 2 Fe concentration and element concentration
-
0.0062 0.0035 0.0030 0.0026 0.0014 0.0013 -
Mn/Si
0.023 0.022 0.027 0.024 0.021 0.018
Mn/Fe
-
0.0032 0.0040 -
0.10 OS3038
S/Si
0.37 0.024 0.035 0.029 -
S/Fe
Cl/Fe
-
0.22 0.0035 0.0076 0.0080 0.0025 0.0012 -
Cl/Si
0.81 0.022 0.066 0.073 0.036 0.017
-
0.00040 0.~87 0.00011 0.00014 -
Cu/Si
0.0015 0.0006 0.0095 0.0013 -
Cu/Fe
Zn/Fe
0.00061 0.~29 0.00025 0.00024 0.00017 0.00011 -
Zn/Si
0.0022 0.0018 0.0022 0.0021 0.0025 0.0016
Rb/Fe
0.00035 0.00035 0.00043 0.00044 0.00024 0.00027
Rb/Si
0.0013 0.0022 0.0038 0~0040 0.0036 0.0038
_
0.0036 0.0014 0.0011 0.00097 0.00041 0.00035 _ -
Sr/Si
0.013 0.088 0.0092 0.0088 0.0060 0.0050
Sr/Fe
-
0.00063 0.0~68 0.00075 0.00077 0.00038 0.0017
Zr/Si
0.0024 0.0043 0.0065 0.0070 0.0056 0.024
Zr/Fe
320
K. Suzuki et al. / Source idenhficalion of Kosa aerosol
data obtained for 18 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Cr, Rb, Sr, Zr) in a concentration range of 10-100000 ppm are shown in the figure. Except for a few points, the concentrations determined by PIXE agree well with the certified concentrations: a ratio C,,,,/C,, of 1.0 k 0.1 was obtained for the NIST 98a and JB-la, and a ratio CPIXE/Cref of 1.0 + 0.2 was obtained for the other three reference materials.
high in Fe and low in Si, is similar to that of the average sedimentary rock [7] shown on the bottom line of table 3. There are some elements whose concentrations in one region are different clearly from those in the other two regions. For exampie Ca concentrations in the north region of the L.oess plateau (E and F) are much lower than those in the other two regions. Aluminum and Mn are other examples which exhibit this trend. Only the ratio Fe/Si differs among three regions.
2.2. Powder-XRI) study Powder X-ray diffraction analysis was performed in order to identify mineral species in the samples of desert soil. The Rigaku High Brilliance X-ray diffractometer equipped with a Cu radiation source and a NaI scintillation counter was used. Operation conditions were as follows: voltage: 40 kV; current: 30 mA, goniometer scanning speed: 26 (deg/min) = 2; and time constant, 1 s. Mineral species were determined in reference to the JCPDS data file.
3. Results and discussion Results obtained by the XRD method showed that the soil samples were mainly composed of quartz, several feldspar group minerals (bytownite, oligoclase plagioclase, etc.) and calcite. There seemed to be some differences in quartz content of the samples among the sampling regions. The order of the quartz content was as follows: A < B, C, D, < E, F. Results from the PIXE analysis are compiled in tables 2 and 3. Concentrations of 14 elements are shown in table 2 relative to iron. Our data were in the range of the values rep&ted on airborne mineral dusts collected in Japan (Kosa, [2]) and China [3] and desert soils [4] and loess [5,6] in China. Especially the ratios Mn/Fe were in a narrow range of 0.018-0.027 and almost the same as the reported values. The PIXE data suggest that there is similarity in element concentrations between closely located areas in each region (A and B, C and D, or E and F) though some differences are observed between A and B. The concentrations of Si and Ca are clearly different among the three regions. We may use the ratios Si/Fe and Ca/Fe to identify a specific source region of soil samples. Table 3 shows the element concentrations relative to Si. The concentration of Si differs among the six areas and the highest con~ntration is found in the samples from E and F. The Si concentration seems to correlate with the quartz content of the samples. The chemical composition of the sample from A, which is
4. Conclusion The chemical composition of soil samples from Chinese deserts, which are presumed to be likely source material of airborne mineral dusts transported to the Pacific area, are given. With the exception of the ratios Ti/Fe and Mn/Fe there are some differences in the concentration ratios of elements among the sampling areas and/or the regions. Of these ratios, it is suggested that the ratios Si/Fe (or Fe/%) and Ca/Fe can be useful to identify the source region of soil specimens in Chinese deserts. These ratios give also useful basic information to estimate sources of airborne mineral dusts transported to Japan and the Pacific area, though further studies on size distribution are required to investigate processes of elemental and mineral fractionations.
Acknowledgements
The authors are most grateful for helpful suggestions from J. Kawai, M. Maeda, R. Saito and the staff of Environmental Engineering Lab., R and D Center, Toshiba Corp. We also wish to thank to M. Uda for making ~experimental equipment available for our use.
References E. Clayton, P. Dureden and D.D. Cohen, Nucl. Instr. and Meth. B22 (1987) 64. @I A. Mizohata and T. Mamuro, J. Jpn. Sot. Pollut. 17 (1982) 377. w Wang Mingxing, J.W. Winchester and Li Shaomeng, Nucl. Instr. and Meth. B22 (1987) 275. [41 J.W. Winchester, W. Lu, I. Ren, M. Wang and W. Maenhaut, Atmos. Environ. 15 (1981) 933. (Science Press, Beijing, ISI T. Liu, Loess and Environment 1985). I61 S. Tanaka, M. Tajima, S. Sato and Y. Hashimoto, Adv. X-ray Chem. Anal. Jpn. 17 (1986) 2.53. [71 F.J. Pettijohon, Sedimentary Rocks (Harper, 1957).
[ll