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An automatic target chamber for PIXE and its application to aerosol analysis
Nuclear
Instruments
and Methods
in Physics
Research
B22 (1987)
North-Holland,
AN AUTOMATIC TARGET TO AEROSOL ANALYSIS TANG Fudan
Guohun, University,
SUN Shanghai,
Changnian,
CHAMBER
ZHU
FOR
Liang
and
PIXE
CHEN
AND
364-367
Amsterdam
ITS APPLICATION
Jianxin
China
A new automatic chamber has been installed and used for PIXE analysis. Four slip samples of 200 mm long or other kinds of samples can be mounted on the holders. They can be turned round or moved perpendicularly by two motors. The maximum movable distance is 250 mm, and about 100 sampling spots can be analyzed. The shell of the chamber is made of Lucite. Easy fabrication and low bremsstrahlung background are the main advantages. It is also convenient for observing and exchanging the samples. Some analysis results of aerosol samples are reported
1. Introduction Since 1970, PIXE has developed into a mature multielemental trace analysis technique [l]. During its development, some new requirements for analyses have been suggested and efforts to fulfil them have been made by many laboratories in the world. For example, in order to analyze rapidly and efficiently a great number of samples of ambient aerosol at relatively low cost, automatic analysis systems have been installed [2-31. Since we started PIXE research in 1977, an external beam analysis system, a vacuum chamber and microbeam equipment etc. have been installed [4-71. Recently, an automatic target chamber has also been installed to improve the analysis speed and to resolve the knotty problem of analyzing long slip aerosol samples of the streakers (81. Aerosols are particulates with diameters smaller than 10 pm, which are floating in the air. Aerosol composition analysis might help to monitor the environmental pollution and offers data for the study of atmospheric chemistry and atmospheric circulation. The automatic chamber has been designed and is suitable to analyze the long slip samples which can yield the temporal distribution of elemental concentrations in aerosols.
2. Experiment
The automatic target chamber for PIXE is shown schematically in fig. 1. The proton beam obtained from a 3 MV Van de Graaff accelerator at Fudan University is deflected by an analyzing magnet into a 90” exit port. The focused proton beam passes through three graphite collimators and is then impinging on the 0168-583X/87/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V
target. In order to obtain a homogeneous beam, a thin Al foil (1.8 mglcm’) is placed before the first collimator to diffuse the beam. The beam spot size on the target can be changed in the range of 12 to 60mm’? The chamber shell is made of Lucite. Easy fabrication and lower bremsstrahlung background are the main advantages of using Lucite, in addition to transparency, which is convenient for checking the sample position and the beam location on it. The chamber window for the outgoing X-rays is covered with a 12.7 pm Kapton foil. The X-rays are detected by a 28 mm’ x 5 mm Si(Li) detector with a resolution of 165 eV at 5.9 keV. The pulse signals are recorded by a data acquisition system (via an amplifier, a MCA and a PDP 11134 computer to a disk). In order to reduce the measured background, a 637 km Mylar absorber is placed before the Si(Li) detector. The absorber has a small hole constituting 0.66% of the detector’s sensitive area. It might also help to improve the sensitivity for lighter elements (Z > 12). In the chamber, four sample holders of 300 mm long can be mounted between two disks which can be turned by a stepping motor (model 45BF) and moved perpendicularly by another stepping motor (Model 75BF003). Turning and moving of the disk can be done simultaneously. The stepping motors are controlled by an electronic circuit. The maximum movable distance of these holders is 250 mm. On each holder, a long slip sample of the streaker can be mounted and about 100 sampling spots can be analyzed. It can also be used for the analysis of other samples, such as hair, serum etc. In that case, 11 disk samples of cascade impactor or 25 thin targets are fixed on each slip. After a sampling spot was analyzed, the X-ray spectrum was transferred from MCA to the disk of the PDP 11134. Then a signal was sent to the stepping motor. The holder was moved vertically to the preset
365
Tang Guohun et al. I An automatic target chamber for PIXE
Di
SC
Shei
I
SamPle Diffuser
Faraday (A
Co1
cup 1)
Counting
limator
(Craphi
Plate
te)
SCreW
Worm
and
Worm
Gear
Nut
Slide
Step
Motor
Gear
75BF
Fig. 1. Schematic diagram of an automatic target chamber for PIXE Table 1 NBS values and PIXE results (ppm) Element
S
Ca
Fe
CU
Zn
Se
Rb
PIXE NBS
303 +- 18
111 +s 124k6
287 2 7 270 2 20
219 2 5 193 + 10
148 i 5 130 t 13
0.7 k 0.4 1.1 -c 0.1
17.4 2 0.8 18.3 f 1.0
distance and then the next sampling spot was analyzed. After all sampling spots on one long slip sample were analyzed, the disks were turned 90” and the next slip sample was analyzed. Vacuum inside is IO-’ -lo-’ Torr for eliminating the charge buildup on the insulating thick target. The accuracy of moving the holder in the vertical direction is less than 0.2mm. The disk turning accuracy is less than 1”. Some elemental sensitive factors for analyzing aerosol samples have been measured. These elemental specimens were obtained from Micromatter Co. (USA). Table 1 shows the results obtained with the NBS biological reference material SRM 1577 (bovine liver). We can see that our PIXE results are in agreement with the NBS certified values.
3. Results and discussion Thousands of samples, such as aerosol, hair and tea leaves etc. have been analyzed since the chamber was
installed. A part of the aerosol analysis results is given below. The temporal distributions of Pb, Br, Si, Ca, Ti and Fe concentrations are shown in fig. 2. These samples of the streaker were sampled in Taiyuan during February L-18, 1982. (They were supplied by the Institute of Atmospheric Physics, Academia Sinica, Beijing.) We note that the temporal distributions of Pb and Br concentrations are similar, which shows that they might come from the same source. The temporal distributions of Si, Ca, Ti and Fe concentrations are also similar, because of the same reason. The lead concentration was mainly distributed in ultrafine particulates (CO.25 pm), as can be seen in fig. 3, which meant that it came mainly from the exhaust gases of automobiles since lead is a component of the antiexploder in gasoline. The variation of Pb concentrations with time in Beijing is shown in fig. 4. These streaker samples were sampled in the period of August 16-28, 1982. We can see that the Pb concentration is higher during the day and is lower at night. Its periodic III. ATMOSPHERIC
APPLICATIONS
Tang Guohun et al.
/ An automatic target chamber
for PIXE
10
1 0
I
I
I
I
I
1
2
3
4
5
with
aerosol
-
6
STAGE Fig. 3. Variation
of Pb concentration size.
Fig. 2. Temporal
distribution of Pb, Br, Si, Ca, Ti and Fe concentrations.
SAMPLE
Fig. 4. Variation
of Pb concentration
NUMBER
with time in Beijing.
particle
Tang Guohun
et al. I An automatic
target chamber
367
for PIXE
the most serious in our country. In the cities mentioned above, the concentrations of some elements, such as Si, S, Ca, Ti and Fe were found to be higher than those in the cities of the West, such as Washington, Copenhagen, Milan and Sao Paulo as shown in fig. 5. These elements might come from the coal combustion and the soil. The concentrations of Pb and Br were found to be less than those in the West, which is consistent with the fact that there are less automobiles used in China at present.
was
Acknowledgements Wish to thank Prof. F.J. Yang for his help and interests. Appreciation is expressed to Prof. Y.Z. Gu and C.G. Ren, P.C. Wu and X.R. Pan for their helpful suggestions in the design and fabrication of the chamber, as well as to J.M. Che, X.D. Wang, X.Z. Zeng, C.G. Ren and H.Y. Yao for their participation in parts of the experiment. Also the assistance of C.D. Yi in drawing is acknowledged.
References
change is remarkable. It is well known that there is much transport during the day, so this also shows that Pb might come from the exhaust gases of automobiles. The elements Si, Ca, Ti and Fe were mainly distributed in coarse particulates (>2 pm), which meant that they might come directly from the coal combustion and the soil. They were not only affected by human activities but also by the weather. The periodic change of these elemental concentrations is not so remarkable as of Pb. The 12 main elemental concentrations, e.g. Al, Si, S, Cl, K, Ca, Ti, Fe, Cu, Zn, Pb and Br in aerosol are shown in fig. 5 [9]. These samples were taken in Shanghai, Beijing, Tianjin, Taiyuan, Lhasa, at the Great Wall Station of China in the Antarctic Continent, on Mt. Jolmo Lungma and at some other places. These results showed that the South Pole is the cleanest area in the whole world and Mt. Jolmo Lungma is the second. The environmental pollution in Shanghai
[l] Sven A.E. Johansson, Nucl. Instr. and Meth. B3 (1984) 1. [2] R. Lecomte, P. Paradis and S. Monaro, Nucl. Instr. and Meth. 150 (1978) 28Y. [3] M.C. Li, K.L. Sheng, P.K. Chin, Z.X. Chen, X.P. Wang, J.F. Chin, T.W. Rong, M.G. Tan and Y.L. Xu, Nucl. Instr. and Meth. 181 (1981) 37. [4] J.X. Chen, H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.J. Yang and H.Y. Yao. Nucl. Instr. and Meth. 168 (1980) 437. [5] J.X. Chen, Y.Z. Guo. H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.J. Yang and H.Y. Yao, Nucl. Instr. and Meth. 181 (1981) 269. [6] J.X. Chen, C.G. Ren, X.Z. Zeng. L.X. Ren, M.X. Wang, W.X. Lu. J.M. Che. Z.Q. Feng, G.H. Tang, H.Y. Yao, J.Y. Tang and X.D. Wang, Proc. of the 2nd ChinaJapan Joint Symp. on Accelerators for Nuclear Science and Their Applications, Lanzhou, China (Oct. 1983) p. 349. [7] X.Z. Zeng, J.X. Chen, C.G. Ren, G.H. Tang and X.D. Wang, Acta. Sci. Nat. Univ. Fudan 4 (1984) 385, in Chinese. [8] H.J. Annegarn, C.C.P. Madiba, J.W. Winchester, S. Bauman and J.P.F. Sellschop, Nucl. Instr. and Meth. 181 (1981) 435. [9] Chen Jianxin, Ion Beam Analysis, eds.. Yang Fujia and Zhao Guoqing (Fudan University Press, Shanghai, 1985) chap. 3. p, 106, in Chinese.
III.
ATMOSPHERIC
APPLICATIONS
Instruments
and Methods
in Physics
Research
B22 (1987)
North-Holland,
AN AUTOMATIC TARGET TO AEROSOL ANALYSIS TANG Fudan
Guohun, University,
SUN Shanghai,
Changnian,
CHAMBER
ZHU
FOR
Liang
and
PIXE
CHEN
AND
364-367
Amsterdam
ITS APPLICATION
Jianxin
China
A new automatic chamber has been installed and used for PIXE analysis. Four slip samples of 200 mm long or other kinds of samples can be mounted on the holders. They can be turned round or moved perpendicularly by two motors. The maximum movable distance is 250 mm, and about 100 sampling spots can be analyzed. The shell of the chamber is made of Lucite. Easy fabrication and low bremsstrahlung background are the main advantages. It is also convenient for observing and exchanging the samples. Some analysis results of aerosol samples are reported
1. Introduction Since 1970, PIXE has developed into a mature multielemental trace analysis technique [l]. During its development, some new requirements for analyses have been suggested and efforts to fulfil them have been made by many laboratories in the world. For example, in order to analyze rapidly and efficiently a great number of samples of ambient aerosol at relatively low cost, automatic analysis systems have been installed [2-31. Since we started PIXE research in 1977, an external beam analysis system, a vacuum chamber and microbeam equipment etc. have been installed [4-71. Recently, an automatic target chamber has also been installed to improve the analysis speed and to resolve the knotty problem of analyzing long slip aerosol samples of the streakers (81. Aerosols are particulates with diameters smaller than 10 pm, which are floating in the air. Aerosol composition analysis might help to monitor the environmental pollution and offers data for the study of atmospheric chemistry and atmospheric circulation. The automatic chamber has been designed and is suitable to analyze the long slip samples which can yield the temporal distribution of elemental concentrations in aerosols.
2. Experiment
The automatic target chamber for PIXE is shown schematically in fig. 1. The proton beam obtained from a 3 MV Van de Graaff accelerator at Fudan University is deflected by an analyzing magnet into a 90” exit port. The focused proton beam passes through three graphite collimators and is then impinging on the 0168-583X/87/$03.50 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V
target. In order to obtain a homogeneous beam, a thin Al foil (1.8 mglcm’) is placed before the first collimator to diffuse the beam. The beam spot size on the target can be changed in the range of 12 to 60mm’? The chamber shell is made of Lucite. Easy fabrication and lower bremsstrahlung background are the main advantages of using Lucite, in addition to transparency, which is convenient for checking the sample position and the beam location on it. The chamber window for the outgoing X-rays is covered with a 12.7 pm Kapton foil. The X-rays are detected by a 28 mm’ x 5 mm Si(Li) detector with a resolution of 165 eV at 5.9 keV. The pulse signals are recorded by a data acquisition system (via an amplifier, a MCA and a PDP 11134 computer to a disk). In order to reduce the measured background, a 637 km Mylar absorber is placed before the Si(Li) detector. The absorber has a small hole constituting 0.66% of the detector’s sensitive area. It might also help to improve the sensitivity for lighter elements (Z > 12). In the chamber, four sample holders of 300 mm long can be mounted between two disks which can be turned by a stepping motor (model 45BF) and moved perpendicularly by another stepping motor (Model 75BF003). Turning and moving of the disk can be done simultaneously. The stepping motors are controlled by an electronic circuit. The maximum movable distance of these holders is 250 mm. On each holder, a long slip sample of the streaker can be mounted and about 100 sampling spots can be analyzed. It can also be used for the analysis of other samples, such as hair, serum etc. In that case, 11 disk samples of cascade impactor or 25 thin targets are fixed on each slip. After a sampling spot was analyzed, the X-ray spectrum was transferred from MCA to the disk of the PDP 11134. Then a signal was sent to the stepping motor. The holder was moved vertically to the preset
365
Tang Guohun et al. I An automatic target chamber for PIXE
Di
SC
Shei
I
SamPle Diffuser
Faraday (A
Co1
cup 1)
Counting
limator
(Craphi
Plate
te)
SCreW
Worm
and
Worm
Gear
Nut
Slide
Step
Motor
Gear
75BF
Fig. 1. Schematic diagram of an automatic target chamber for PIXE Table 1 NBS values and PIXE results (ppm) Element
S
Ca
Fe
CU
Zn
Se
Rb
PIXE NBS
303 +- 18
111 +s 124k6
287 2 7 270 2 20
219 2 5 193 + 10
148 i 5 130 t 13
0.7 k 0.4 1.1 -c 0.1
17.4 2 0.8 18.3 f 1.0
distance and then the next sampling spot was analyzed. After all sampling spots on one long slip sample were analyzed, the disks were turned 90” and the next slip sample was analyzed. Vacuum inside is IO-’ -lo-’ Torr for eliminating the charge buildup on the insulating thick target. The accuracy of moving the holder in the vertical direction is less than 0.2mm. The disk turning accuracy is less than 1”. Some elemental sensitive factors for analyzing aerosol samples have been measured. These elemental specimens were obtained from Micromatter Co. (USA). Table 1 shows the results obtained with the NBS biological reference material SRM 1577 (bovine liver). We can see that our PIXE results are in agreement with the NBS certified values.
3. Results and discussion Thousands of samples, such as aerosol, hair and tea leaves etc. have been analyzed since the chamber was
installed. A part of the aerosol analysis results is given below. The temporal distributions of Pb, Br, Si, Ca, Ti and Fe concentrations are shown in fig. 2. These samples of the streaker were sampled in Taiyuan during February L-18, 1982. (They were supplied by the Institute of Atmospheric Physics, Academia Sinica, Beijing.) We note that the temporal distributions of Pb and Br concentrations are similar, which shows that they might come from the same source. The temporal distributions of Si, Ca, Ti and Fe concentrations are also similar, because of the same reason. The lead concentration was mainly distributed in ultrafine particulates (CO.25 pm), as can be seen in fig. 3, which meant that it came mainly from the exhaust gases of automobiles since lead is a component of the antiexploder in gasoline. The variation of Pb concentrations with time in Beijing is shown in fig. 4. These streaker samples were sampled in the period of August 16-28, 1982. We can see that the Pb concentration is higher during the day and is lower at night. Its periodic III. ATMOSPHERIC
APPLICATIONS
Tang Guohun et al.
/ An automatic target chamber
for PIXE
10
1 0
I
I
I
I
I
1
2
3
4
5
with
aerosol
-
6
STAGE Fig. 3. Variation
of Pb concentration size.
Fig. 2. Temporal
distribution of Pb, Br, Si, Ca, Ti and Fe concentrations.
SAMPLE
Fig. 4. Variation
of Pb concentration
NUMBER
with time in Beijing.
particle
Tang Guohun
et al. I An automatic
target chamber
367
for PIXE
the most serious in our country. In the cities mentioned above, the concentrations of some elements, such as Si, S, Ca, Ti and Fe were found to be higher than those in the cities of the West, such as Washington, Copenhagen, Milan and Sao Paulo as shown in fig. 5. These elements might come from the coal combustion and the soil. The concentrations of Pb and Br were found to be less than those in the West, which is consistent with the fact that there are less automobiles used in China at present.
was
Acknowledgements Wish to thank Prof. F.J. Yang for his help and interests. Appreciation is expressed to Prof. Y.Z. Gu and C.G. Ren, P.C. Wu and X.R. Pan for their helpful suggestions in the design and fabrication of the chamber, as well as to J.M. Che, X.D. Wang, X.Z. Zeng, C.G. Ren and H.Y. Yao for their participation in parts of the experiment. Also the assistance of C.D. Yi in drawing is acknowledged.
References
change is remarkable. It is well known that there is much transport during the day, so this also shows that Pb might come from the exhaust gases of automobiles. The elements Si, Ca, Ti and Fe were mainly distributed in coarse particulates (>2 pm), which meant that they might come directly from the coal combustion and the soil. They were not only affected by human activities but also by the weather. The periodic change of these elemental concentrations is not so remarkable as of Pb. The 12 main elemental concentrations, e.g. Al, Si, S, Cl, K, Ca, Ti, Fe, Cu, Zn, Pb and Br in aerosol are shown in fig. 5 [9]. These samples were taken in Shanghai, Beijing, Tianjin, Taiyuan, Lhasa, at the Great Wall Station of China in the Antarctic Continent, on Mt. Jolmo Lungma and at some other places. These results showed that the South Pole is the cleanest area in the whole world and Mt. Jolmo Lungma is the second. The environmental pollution in Shanghai
[l] Sven A.E. Johansson, Nucl. Instr. and Meth. B3 (1984) 1. [2] R. Lecomte, P. Paradis and S. Monaro, Nucl. Instr. and Meth. 150 (1978) 28Y. [3] M.C. Li, K.L. Sheng, P.K. Chin, Z.X. Chen, X.P. Wang, J.F. Chin, T.W. Rong, M.G. Tan and Y.L. Xu, Nucl. Instr. and Meth. 181 (1981) 37. [4] J.X. Chen, H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.J. Yang and H.Y. Yao. Nucl. Instr. and Meth. 168 (1980) 437. [5] J.X. Chen, Y.Z. Guo. H.K. Li, C.G. Ren, G.H. Tang, X.D. Wang, F.J. Yang and H.Y. Yao, Nucl. Instr. and Meth. 181 (1981) 269. [6] J.X. Chen, C.G. Ren, X.Z. Zeng. L.X. Ren, M.X. Wang, W.X. Lu. J.M. Che. Z.Q. Feng, G.H. Tang, H.Y. Yao, J.Y. Tang and X.D. Wang, Proc. of the 2nd ChinaJapan Joint Symp. on Accelerators for Nuclear Science and Their Applications, Lanzhou, China (Oct. 1983) p. 349. [7] X.Z. Zeng, J.X. Chen, C.G. Ren, G.H. Tang and X.D. Wang, Acta. Sci. Nat. Univ. Fudan 4 (1984) 385, in Chinese. [8] H.J. Annegarn, C.C.P. Madiba, J.W. Winchester, S. Bauman and J.P.F. Sellschop, Nucl. Instr. and Meth. 181 (1981) 435. [9] Chen Jianxin, Ion Beam Analysis, eds.. Yang Fujia and Zhao Guoqing (Fudan University Press, Shanghai, 1985) chap. 3. p, 106, in Chinese.
III.
ATMOSPHERIC
APPLICATIONS