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Imaging plates used as positron microscopy – Effect of positrons and γ-rays
Nuclear Instruments and Methods in Physics Research B 171 (2000) 194±198
www.elsevier.nl/locate/nimb
Imaging plates used as positron microscopy ± Eect of positrons and c-rays Masao Doyama a
a,*
, M. Inoue a, T. Yoshiie b, Y. Hayashi b, I. Kanazawa c, T. Kurihara d, T. Oikawa e
Teikyo University of Science and Technology, Uenohara, Yamanashi 409-0193, Japan b Reactor Research Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan c Tokyo Gakugei University, Koganei, Tokyo 184-0015, Japan d Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan e JEOL Ltd., Musashino, Akishima, Tokyo 196-0021, Japan Received 14 December 1999; received in revised form 24 February 2000
Abstract Imaging plates have been used as position sensitive detectors for positrons. A linear relation is obtained between the positron ¯uence and the output signal intensity readout by a ``PIXsysTEM II'' (pixelized to 25 lm 25 lm), using 58 Co and 22 Na positron emitters. The linearity extends to six decades from 105 to 1011 positrons/cm2 . The plates are good to use for positron microscopy. Sensitivities of one c-ray photon relative to a positron are 0.0125, 8:28 10ÿ3 and 3:4 10ÿ3 for 65 Zn, 58 Co and 22 Na, respectively. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: Imaging plates; Positrons; c-rays
1. Introduction Films have been commonly used to record position sensitive optical memories. In recent years imaging plates based on photo-simulated material have been widely used for X-ray and electron records [1±12]. Imaging plates are quite useful because of their wide dynamic ranges and high sensitivity for X-rays and electron images, proportionality between the output signal intensity and the dose, and high position resolution of the
images. We have demonstrated that imaging plates are also sensitive to positrons and can be used as an integrated type position sensitive detector and the potential applications may be vast in the future. It is important to obtain the relation between the positron ¯uence per pixel and the output intensity of the analyzer. Furthermore, the eect of c-rays present simultaneously with positron emission is also studied. 2. Imaging plates, data collection and readout
*
Corresponding author. Tel.: +81-554-63-4411; fax: +81554-63-4431. E-mail address: [email protected] (M. Doyama).
The imaging plates used were of type FDL URV (81 mm 100 mm) manufactured by Fuji Film.
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 1 0 9 - 9
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
The plates are covered with crystallites (4 lm) of photo-stimulated luminescent material based on BaFX: Eu2 (X Cl, Br, I) coated on a plastic plate of 130-lm thickness. Electrons, X-rays, positrons and c-rays excite electrons leaving holes in the photo-stimulated luminescent material. The minimum energy to excite an electron and a hole is the band gap, i.e. 8.2 eV. The electrons are trapped by F centers forming F centers in a metastable site and holes are caught by Eu2 centers forming Eu3 . This is the well-established memory mechanism of imaging plates. When the exposed imaging plate is irradiated by He±Ne laser light (633 nm), electrons caught by F centers are excited into the conduction band and combine with holes caught by Eu3 emitting 3.2 eV photons, i.e. a violet blue light of 390 nm wavelength, which is the transition 5d±4f of Eu2 with an emitting life of 0.8 ls. The 3.2 eV photons are detected by a photo multiplier [8]. 3. The analyzer The analyzer used in this work is a ``PIXsysTEM II'', which is manufactured by Fuji Film [1] to analyze the imaging plates for electron microscopy. The ``PIXsysTEM II'' consists of an ``IP Reader II'' and an ``IP Processor''. An exposed imaging plate is loaded to an ``IP Reader II''. The number of 3.2 eV photons emitted from a pixel is detected by a photo multiplier. The pixel number and the number of photons (output digital signal intensity readout) detected by the photo multiplier are recorded on a recording tape. The data are transmitted to an ``IP Processor II'' and are analyzed by a Macintosh computer with software called ``Image Gauge'', supplied by the same company. 4. Experiments Four experiments have been performed. In the ®rst experiment, nickel foils of 0.1-mm thick, 3.0-mm diameter were irradiated by neutrons at the Kyoto University Reactor in the pneumatic tube for 1 h at 50°C, with a neutron ¯ux of
195
2:75 1013 n= cm2 s. The activity of the foil was about 20 lCi (740 kBq) 3 h after irradiation. Ni was converted to 58 Co by the 58 Ni(n,p) 58 Co reaction. 58 Co emits continuous energy positrons with a maximum energy of 0.474 MeV and an average energy of 0.201 MeV. The Ni foil was placed on an imaging plate for various periods of time. After irradiation, the c-ray intensities of the positron source Ni foil (58 Co) were measured by a high purity Ge detector. The eciency of the Ge detector has been calibrated using a standard source to calculate the absolute intensities of crays. The positron ¯uence to the imaging plate was obtained assuming that half of the positrons fall into the imaging plate. The second experiment was the same as above but run with a commercially available positron source of 22 NaCl. A NaCl aqueous solution was dropped on a Kapton ®lm, dried and sealed. 22 Na emits a continuous energy spectrum of positrons, with a maximum energy of 0.545 MeV and an average energy of 0.216 MeV. The source was placed on an imaging plate for various periods of time for exposure. The radioactive source in the third experiment was a 60 Co source placed directly on an imaging plate of about 20 lCi. 60 Co emits 1.17 and 1.33 MeV c-rays. In the fourth experiment, 22 Na, 58 Co and 65 Zn sources are used. A polyvinyl chloride plate, 8 mm thick, was used to absorb positrons. The polyvinyl chloride plate has a window. Zinc and nickel were irradiated in the Kyoto University Reactor for 24 h, then cooled for more than ®ve days after irradiation, to eliminate the eect of radioactive nuclei other than 65 Zn or 58 Co. 22 Na is already used above (see Fig. 1). 5. Results and discussions The relation between the positron ¯uence (fe ) and the output signal intensity (fp ) detected by the PIXsysTEM II was obtained both for 58 Co and 22 Na. The results are given in Fig. 1. Closed circles in Fig. 1 (line 1) are for 58 Co. The size of the pixel was 25 lm 25 lm. The output digital signal intensity was recorded with 16,384 gray levels. The plot of the logarithm of the positron ¯uence per
196
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
Fig. 1. The characteristic curve between positron and electron ¯uence and output signal intensity of the analyzer. Line 1 is for positrons. Closed circles are for 58 Co, triangles are for 22 Na. Line 2 is for 200 keV electrons and the characteristic curves for a ®lm (Fuji FG) by 200 keV electrons, respectively.
pixel, log fe and the logarithm of the output signal intensity per pixel, log fp is linear and the gradient is almost 45°. b
fp a fe ; i.e. log fp b log fe log a;
1
where log a and b were found to be ÿ4:20 0:05 and 0:973 0:008, respectively. For exact pro-
Table 1 Nuclear data for
22
Na,
58
Co, and
65
portionality b should be 1.0. The output digital signal intensity is not an absolute value and a contains many factors such as the eciency of the detection of 3.2 eV violet-blue light and the geometry of the detectors, but the same type of PIXsysTEM II gives almost the same factors, particularly when the same analyzer is used throughout the experiment. In the fourth experiment, 22 Na, 58 Co and 65 Zn sources are set on a window covered with a thin polyvinyl chloride ®lm and exposed for various periods (Table 1). The imaging plate was exposed simultaneously to c-rays and positrons (c b ). Then the source was moved on the plate (8 mm thick) and exposed for various periods (c-rays only), because almost all positrons were absorbed in the plate emitting 0.511 MeV and other c-rays. 65 Zn emits 0.511 MeV c-rays of 2.92% and 1.116 MeV c-rays of 50.75%. Average positron energy emitted is 0.143 MeV with the maximum energy of 0.330 MeV. The radiation rate is 1.46%. The relation between relative c-ray ¯uence and output signal intensity for 65 Zn is plotted in Fig. 2(a). This gives us the result that one photon of c-rays and 0.0113 positrons from 65 Zn have the same eect on the imaging plate. Similar treatments can be made for 58 Co. 58 Co emitts 0.511 MeV c-rays of 30.0%, 0.811 MeV crays, 99.4%, 0.864 MeV c-rays, 0.68% and 1.675 MeV c-rays of 0.52%. Average positron energy emitted is 0.201 MeV with the maximum energy of
Zn b
Gamma rays (c)
b /c
Energy (MeV)
%
Energy (MeV)
%
Na
0.511 1.275
181.1 99.93
0.545 1.280 b 0.216
90.4 0.06
0.322
65
Zn
0.511 1.116
2.92 50.75
0.330 b 0.143
1.46
0.0272
58
Co
0.511 0.811 0.864 1.675
30.0 99.4 0.68 0.52
0.474
22
b 0.201
15.0
0.115
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
Fig. 2. Relation between relative c-rays and output signal intensity for 65 Zn (a) and for 22 Na (b).
0.474 MeV. The radiation rate is 15.0%. The relation between relative c-ray ¯uence and output signal intensity has been plotted in Fig. 2(b). This gives us the result that one photon of c-rays and 1:25 10ÿ2 positrons from 58 Co have the same eect on the imaging plate. The imaging plates are not very sensitive to the 0.511 MeV c-rays. A similar treatment can be made for 22 Na. 22 Na emitts 0.511 MeV c-rays of 181.1% and 1.275 MeV c-rays of 99.93%. Average positron energy emitted is 0.216 MeV with the maximum energy of 0.545 MeV. The radiation rate is 90.4%. The relation between relative c-ray ¯uence and output signal
197
intensity has been plotted in Fig. 2(b). From Fig. 2(a) the c-ray counts are 4:47 104 after passing through the polyvinyl chloride plate (Table 2). The total counts of c-rays and positrons through the window of the plate were 2:71 106 . The dierence is 2:67 106 , which is only due to positrons. 2:67 106 =3:22 10ÿ1 8:29 106 is the intensity of positrons. Therefore, the c=b is 4:47 104 =8:29 106 5:39 10ÿ3 . This gives us the result that one photon of c-rays and 5:39 10ÿ3 positrons from 22 Na have the same eect to the imaging plate. Similarly for 65 Zn and 58 Co are 8:28 10ÿ3 and 1:25 10ÿ2 , respectively. The imaging plates are not very sensitive to the 0.511 MeV c-rays (see Figs. 3 and 4). Nuclear counters usually count positrons one by one so that when several positrons come in within the time resolution they cannot be counted separately. Imaging plates are integrated type recorders so the time resolution is not a problem. Imaging plates can be used as position sensitive detectors for positrons like photographic ®lms but with much wider dynamic ranges. Future applications of imaging plates for positrons will be
Fig. 3. Relation between relative c-rays and output signal intensity for 58 Co and 65 Zn.
Table 2 Calculations of eectiveness to imaging plate of c-rays compared with positrons
22
Na Zn 58 Co 65
c (count)
a b (count)
b intensity1 (count)
b intensity2 (count)
c/b
4:47 104 2:8 105 4:2 105
2:71 106 1:2 106 4:3 106
2:67 106 9:20 105 3:88 106
8:29 106 3:38 107 3:37 107
5:39 10ÿ3 8:28 10ÿ3 1:25 10ÿ2
198
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
scanning positron microscopy, positron diraction, etc. Acknowledgements This work is supported by a Grant-in-Aid for scienti®c research from the Ministry of Education, Science, Sports and Culture. References Fig. 4. Relation between intensity of positrons and output signal intensity for 65 Zn and for 58 Co.
more powerful and more quantitative than photographic ®lms. Some applications for positrons are transmission positron microscopy [13,14], positron re-emission microscopy [15±18], positron diraction [18], and positron holography, etc. in which the coincidence measurements are not required. Imaging plates can be used repeatedly and the applications for position detectors of positrons are quite wide and promising.
6. Conclusions It has been shown that Ba halogenide imaging plates are sensitive to positrons. The output digital intensity readout is proportional to the positron ¯uence (dose) over a wide range of six decades. Imaging plates are about 10,000 times sensitive than photographic ®lms. Imaging plates may become interesting for quantitative analysis of positron induced images, such as transmission positron microscopy, re-emission positron microscopy,
[1] M. Sonda, M. Takano, J. Miyahara, H. Kato, Radiology 148 (1983) 833. [2] J. Miyahara, Kotaibutsuri 21 (1986) 192 (in Japanese). [3] N. Mori, et al., Ultramicroscopy 25 (1988) 195. [4] H. Amado, Kotaibutsuri 28 (1993) I19 (in Japanese). [5] Y. Amemiya, K. Ohsumi, K. Takemura, Y. Murakami, Kotaibutsuri 29 (1994) 789 (in Japanese). [6] S. Ichikawa, et al., J. Electron Microsc. 33 (1984) 255. [7] N. Mori, T. Katoh, T. Oikawa, J. Miyahara, T. Harada, in: Proceedings of Eleventh International Congress on Electron Microscopy, Vol. 1, Kyoto, 1986, p. 29. [8] J. Miyahara, Kotaibutsuri 30 (1995) 674 (in Japanese). [9] J. Miyahara, K. Takahashi, Y. Amemiya, N. Kamiya, Y. Satow, Nucl. Instr. and Meth. A 246 (1986) 572. [10] Y. Amemiya, T. Matsushita, A. Nadagawa, Y. Satow, J. Miyahara, J. Chikawa, Nucl. Instr. and Meth. A 266 (1988) 645. [11] R.H. Templer, Nucl. Instr. and Meth. A 300 (1991) 357. [12] M.S. Lehmann, T. Zemb, F. Ne, SPIE, 1737, Neutrons, X-rays and Gamma Rays, 1992, p. 324. [13] J. van House, A. Rich, Phys. Rev. Lett. 61 (1988) 488. [14] A. Zecca, Mater. Sci. Forum 175±178 (1995) 125. [15] L.D. Hulett, J.M. Dale, S. Pendyala, Mater. Sci. Forum 2 (1984) 133. [16] L.D. Hulett Jr., Mater. Sci. Forum 175±178 (1995) 99. [17] G.R. Brandes, K.F. Canter, A.P. Mills Jr., Phys. Rev. B 43 (1991) 10103. [18] K.F. Canter, G. Amarenda, D. Vasumathi, S.A. Wesley, R. Xie, A.P. Milles Jr., R.L. Sabatini, Y. Zhu, Appl. Surf. Sci. 85 (1995) 339.
www.elsevier.nl/locate/nimb
Imaging plates used as positron microscopy ± Eect of positrons and c-rays Masao Doyama a
a,*
, M. Inoue a, T. Yoshiie b, Y. Hayashi b, I. Kanazawa c, T. Kurihara d, T. Oikawa e
Teikyo University of Science and Technology, Uenohara, Yamanashi 409-0193, Japan b Reactor Research Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan c Tokyo Gakugei University, Koganei, Tokyo 184-0015, Japan d Institute of Materials Structure Science, KEK, Tsukuba 305-0801, Japan e JEOL Ltd., Musashino, Akishima, Tokyo 196-0021, Japan Received 14 December 1999; received in revised form 24 February 2000
Abstract Imaging plates have been used as position sensitive detectors for positrons. A linear relation is obtained between the positron ¯uence and the output signal intensity readout by a ``PIXsysTEM II'' (pixelized to 25 lm 25 lm), using 58 Co and 22 Na positron emitters. The linearity extends to six decades from 105 to 1011 positrons/cm2 . The plates are good to use for positron microscopy. Sensitivities of one c-ray photon relative to a positron are 0.0125, 8:28 10ÿ3 and 3:4 10ÿ3 for 65 Zn, 58 Co and 22 Na, respectively. Ó 2000 Elsevier Science B.V. All rights reserved. Keywords: Imaging plates; Positrons; c-rays
1. Introduction Films have been commonly used to record position sensitive optical memories. In recent years imaging plates based on photo-simulated material have been widely used for X-ray and electron records [1±12]. Imaging plates are quite useful because of their wide dynamic ranges and high sensitivity for X-rays and electron images, proportionality between the output signal intensity and the dose, and high position resolution of the
images. We have demonstrated that imaging plates are also sensitive to positrons and can be used as an integrated type position sensitive detector and the potential applications may be vast in the future. It is important to obtain the relation between the positron ¯uence per pixel and the output intensity of the analyzer. Furthermore, the eect of c-rays present simultaneously with positron emission is also studied. 2. Imaging plates, data collection and readout
*
Corresponding author. Tel.: +81-554-63-4411; fax: +81554-63-4431. E-mail address: [email protected] (M. Doyama).
The imaging plates used were of type FDL URV (81 mm 100 mm) manufactured by Fuji Film.
0168-583X/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 0 0 ) 0 0 1 0 9 - 9
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
The plates are covered with crystallites (4 lm) of photo-stimulated luminescent material based on BaFX: Eu2 (X Cl, Br, I) coated on a plastic plate of 130-lm thickness. Electrons, X-rays, positrons and c-rays excite electrons leaving holes in the photo-stimulated luminescent material. The minimum energy to excite an electron and a hole is the band gap, i.e. 8.2 eV. The electrons are trapped by F centers forming F centers in a metastable site and holes are caught by Eu2 centers forming Eu3 . This is the well-established memory mechanism of imaging plates. When the exposed imaging plate is irradiated by He±Ne laser light (633 nm), electrons caught by F centers are excited into the conduction band and combine with holes caught by Eu3 emitting 3.2 eV photons, i.e. a violet blue light of 390 nm wavelength, which is the transition 5d±4f of Eu2 with an emitting life of 0.8 ls. The 3.2 eV photons are detected by a photo multiplier [8]. 3. The analyzer The analyzer used in this work is a ``PIXsysTEM II'', which is manufactured by Fuji Film [1] to analyze the imaging plates for electron microscopy. The ``PIXsysTEM II'' consists of an ``IP Reader II'' and an ``IP Processor''. An exposed imaging plate is loaded to an ``IP Reader II''. The number of 3.2 eV photons emitted from a pixel is detected by a photo multiplier. The pixel number and the number of photons (output digital signal intensity readout) detected by the photo multiplier are recorded on a recording tape. The data are transmitted to an ``IP Processor II'' and are analyzed by a Macintosh computer with software called ``Image Gauge'', supplied by the same company. 4. Experiments Four experiments have been performed. In the ®rst experiment, nickel foils of 0.1-mm thick, 3.0-mm diameter were irradiated by neutrons at the Kyoto University Reactor in the pneumatic tube for 1 h at 50°C, with a neutron ¯ux of
195
2:75 1013 n= cm2 s. The activity of the foil was about 20 lCi (740 kBq) 3 h after irradiation. Ni was converted to 58 Co by the 58 Ni(n,p) 58 Co reaction. 58 Co emits continuous energy positrons with a maximum energy of 0.474 MeV and an average energy of 0.201 MeV. The Ni foil was placed on an imaging plate for various periods of time. After irradiation, the c-ray intensities of the positron source Ni foil (58 Co) were measured by a high purity Ge detector. The eciency of the Ge detector has been calibrated using a standard source to calculate the absolute intensities of crays. The positron ¯uence to the imaging plate was obtained assuming that half of the positrons fall into the imaging plate. The second experiment was the same as above but run with a commercially available positron source of 22 NaCl. A NaCl aqueous solution was dropped on a Kapton ®lm, dried and sealed. 22 Na emits a continuous energy spectrum of positrons, with a maximum energy of 0.545 MeV and an average energy of 0.216 MeV. The source was placed on an imaging plate for various periods of time for exposure. The radioactive source in the third experiment was a 60 Co source placed directly on an imaging plate of about 20 lCi. 60 Co emits 1.17 and 1.33 MeV c-rays. In the fourth experiment, 22 Na, 58 Co and 65 Zn sources are used. A polyvinyl chloride plate, 8 mm thick, was used to absorb positrons. The polyvinyl chloride plate has a window. Zinc and nickel were irradiated in the Kyoto University Reactor for 24 h, then cooled for more than ®ve days after irradiation, to eliminate the eect of radioactive nuclei other than 65 Zn or 58 Co. 22 Na is already used above (see Fig. 1). 5. Results and discussions The relation between the positron ¯uence (fe ) and the output signal intensity (fp ) detected by the PIXsysTEM II was obtained both for 58 Co and 22 Na. The results are given in Fig. 1. Closed circles in Fig. 1 (line 1) are for 58 Co. The size of the pixel was 25 lm 25 lm. The output digital signal intensity was recorded with 16,384 gray levels. The plot of the logarithm of the positron ¯uence per
196
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
Fig. 1. The characteristic curve between positron and electron ¯uence and output signal intensity of the analyzer. Line 1 is for positrons. Closed circles are for 58 Co, triangles are for 22 Na. Line 2 is for 200 keV electrons and the characteristic curves for a ®lm (Fuji FG) by 200 keV electrons, respectively.
pixel, log fe and the logarithm of the output signal intensity per pixel, log fp is linear and the gradient is almost 45°. b
fp a fe ; i.e. log fp b log fe log a;
1
where log a and b were found to be ÿ4:20 0:05 and 0:973 0:008, respectively. For exact pro-
Table 1 Nuclear data for
22
Na,
58
Co, and
65
portionality b should be 1.0. The output digital signal intensity is not an absolute value and a contains many factors such as the eciency of the detection of 3.2 eV violet-blue light and the geometry of the detectors, but the same type of PIXsysTEM II gives almost the same factors, particularly when the same analyzer is used throughout the experiment. In the fourth experiment, 22 Na, 58 Co and 65 Zn sources are set on a window covered with a thin polyvinyl chloride ®lm and exposed for various periods (Table 1). The imaging plate was exposed simultaneously to c-rays and positrons (c b ). Then the source was moved on the plate (8 mm thick) and exposed for various periods (c-rays only), because almost all positrons were absorbed in the plate emitting 0.511 MeV and other c-rays. 65 Zn emits 0.511 MeV c-rays of 2.92% and 1.116 MeV c-rays of 50.75%. Average positron energy emitted is 0.143 MeV with the maximum energy of 0.330 MeV. The radiation rate is 1.46%. The relation between relative c-ray ¯uence and output signal intensity for 65 Zn is plotted in Fig. 2(a). This gives us the result that one photon of c-rays and 0.0113 positrons from 65 Zn have the same eect on the imaging plate. Similar treatments can be made for 58 Co. 58 Co emitts 0.511 MeV c-rays of 30.0%, 0.811 MeV crays, 99.4%, 0.864 MeV c-rays, 0.68% and 1.675 MeV c-rays of 0.52%. Average positron energy emitted is 0.201 MeV with the maximum energy of
Zn b
Gamma rays (c)
b /c
Energy (MeV)
%
Energy (MeV)
%
Na
0.511 1.275
181.1 99.93
0.545 1.280 b 0.216
90.4 0.06
0.322
65
Zn
0.511 1.116
2.92 50.75
0.330 b 0.143
1.46
0.0272
58
Co
0.511 0.811 0.864 1.675
30.0 99.4 0.68 0.52
0.474
22
b 0.201
15.0
0.115
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
Fig. 2. Relation between relative c-rays and output signal intensity for 65 Zn (a) and for 22 Na (b).
0.474 MeV. The radiation rate is 15.0%. The relation between relative c-ray ¯uence and output signal intensity has been plotted in Fig. 2(b). This gives us the result that one photon of c-rays and 1:25 10ÿ2 positrons from 58 Co have the same eect on the imaging plate. The imaging plates are not very sensitive to the 0.511 MeV c-rays. A similar treatment can be made for 22 Na. 22 Na emitts 0.511 MeV c-rays of 181.1% and 1.275 MeV c-rays of 99.93%. Average positron energy emitted is 0.216 MeV with the maximum energy of 0.545 MeV. The radiation rate is 90.4%. The relation between relative c-ray ¯uence and output signal
197
intensity has been plotted in Fig. 2(b). From Fig. 2(a) the c-ray counts are 4:47 104 after passing through the polyvinyl chloride plate (Table 2). The total counts of c-rays and positrons through the window of the plate were 2:71 106 . The dierence is 2:67 106 , which is only due to positrons. 2:67 106 =3:22 10ÿ1 8:29 106 is the intensity of positrons. Therefore, the c=b is 4:47 104 =8:29 106 5:39 10ÿ3 . This gives us the result that one photon of c-rays and 5:39 10ÿ3 positrons from 22 Na have the same eect to the imaging plate. Similarly for 65 Zn and 58 Co are 8:28 10ÿ3 and 1:25 10ÿ2 , respectively. The imaging plates are not very sensitive to the 0.511 MeV c-rays (see Figs. 3 and 4). Nuclear counters usually count positrons one by one so that when several positrons come in within the time resolution they cannot be counted separately. Imaging plates are integrated type recorders so the time resolution is not a problem. Imaging plates can be used as position sensitive detectors for positrons like photographic ®lms but with much wider dynamic ranges. Future applications of imaging plates for positrons will be
Fig. 3. Relation between relative c-rays and output signal intensity for 58 Co and 65 Zn.
Table 2 Calculations of eectiveness to imaging plate of c-rays compared with positrons
22
Na Zn 58 Co 65
c (count)
a b (count)
b intensity1 (count)
b intensity2 (count)
c/b
4:47 104 2:8 105 4:2 105
2:71 106 1:2 106 4:3 106
2:67 106 9:20 105 3:88 106
8:29 106 3:38 107 3:37 107
5:39 10ÿ3 8:28 10ÿ3 1:25 10ÿ2
198
M. Doyama et al. / Nucl. Instr. and Meth. in Phys. Res. B 171 (2000) 194±198
scanning positron microscopy, positron diraction, etc. Acknowledgements This work is supported by a Grant-in-Aid for scienti®c research from the Ministry of Education, Science, Sports and Culture. References Fig. 4. Relation between intensity of positrons and output signal intensity for 65 Zn and for 58 Co.
more powerful and more quantitative than photographic ®lms. Some applications for positrons are transmission positron microscopy [13,14], positron re-emission microscopy [15±18], positron diraction [18], and positron holography, etc. in which the coincidence measurements are not required. Imaging plates can be used repeatedly and the applications for position detectors of positrons are quite wide and promising.
6. Conclusions It has been shown that Ba halogenide imaging plates are sensitive to positrons. The output digital intensity readout is proportional to the positron ¯uence (dose) over a wide range of six decades. Imaging plates are about 10,000 times sensitive than photographic ®lms. Imaging plates may become interesting for quantitative analysis of positron induced images, such as transmission positron microscopy, re-emission positron microscopy,
[1] M. Sonda, M. Takano, J. Miyahara, H. Kato, Radiology 148 (1983) 833. [2] J. Miyahara, Kotaibutsuri 21 (1986) 192 (in Japanese). [3] N. Mori, et al., Ultramicroscopy 25 (1988) 195. [4] H. Amado, Kotaibutsuri 28 (1993) I19 (in Japanese). [5] Y. Amemiya, K. Ohsumi, K. Takemura, Y. Murakami, Kotaibutsuri 29 (1994) 789 (in Japanese). [6] S. Ichikawa, et al., J. Electron Microsc. 33 (1984) 255. [7] N. Mori, T. Katoh, T. Oikawa, J. Miyahara, T. Harada, in: Proceedings of Eleventh International Congress on Electron Microscopy, Vol. 1, Kyoto, 1986, p. 29. [8] J. Miyahara, Kotaibutsuri 30 (1995) 674 (in Japanese). [9] J. Miyahara, K. Takahashi, Y. Amemiya, N. Kamiya, Y. Satow, Nucl. Instr. and Meth. A 246 (1986) 572. [10] Y. Amemiya, T. Matsushita, A. Nadagawa, Y. Satow, J. Miyahara, J. Chikawa, Nucl. Instr. and Meth. A 266 (1988) 645. [11] R.H. Templer, Nucl. Instr. and Meth. A 300 (1991) 357. [12] M.S. Lehmann, T. Zemb, F. Ne, SPIE, 1737, Neutrons, X-rays and Gamma Rays, 1992, p. 324. [13] J. van House, A. Rich, Phys. Rev. Lett. 61 (1988) 488. [14] A. Zecca, Mater. Sci. Forum 175±178 (1995) 125. [15] L.D. Hulett, J.M. Dale, S. Pendyala, Mater. Sci. Forum 2 (1984) 133. [16] L.D. Hulett Jr., Mater. Sci. Forum 175±178 (1995) 99. [17] G.R. Brandes, K.F. Canter, A.P. Mills Jr., Phys. Rev. B 43 (1991) 10103. [18] K.F. Canter, G. Amarenda, D. Vasumathi, S.A. Wesley, R. Xie, A.P. Milles Jr., R.L. Sabatini, Y. Zhu, Appl. Surf. Sci. 85 (1995) 339.