Author's Accepted Manuscript
Optimised mounting conditions for poly (ether sulfone) in radiation detection Hidehito Nakamura, Yoshiyuki Shirakawa, Nobuhiro Sato, Tatsuya Yamada, Hisashi Kitamura, Sentaro Takahashi
www.elsevier.com/locate/apradiso
PII: DOI: Reference:
S0969-8043(14)00207-3 http://dx.doi.org/10.1016/j.apradiso.2014.05.013 ARI6690
To appear in:
Applied Radiation and Isotopes
Received date: 13 March 2014 Revised date: 2 May 2014 Accepted date: 15 May 2014 Cite this article as: Hidehito Nakamura, Yoshiyuki Shirakawa, Nobuhiro Sato, Tatsuya Yamada, Hisashi Kitamura, Sentaro Takahashi, Optimised mounting conditions for poly (ether sulfone) in radiation detection, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2014.05.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title Optimised mounting conditions for poly (ether sulfone) in radiation detection
Author name and affiliations Hidehito Nakamuraa,b,*, Yoshiyuki Shirakawab, Nobuhiro Satoa, Tatsuya Yamadaa, Hisashi Kitamurab, and Sentaro Takahashia aKyoto
University, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan
bNational
Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba, 263-8555, Japan
*Corresponding author Tel.: +81 72 451 2463; Fax: +81 72 451 2463 E-mail address: [email protected] (H. Nakamura)
Abstract Poly (ether sulfone) (PES) is a candidate for use as a scintillation material in radiation detection. Its characteristics, such as its emission spectrum and its effective refractive index (based on the emission spectrum), directly affect the propagation of light generated to external photodetectors. It is also important to examine the presence of background radiation sources in manufactured PES. Here, we optimise the optical coupling and surface treatment of the PES, and characterise its background. Optical grease was used to enhance the optical coupling between the PES and the photodetector; absorption by the grease of short-wavelength light emitted from PES was negligible. Diffuse reflection induced by surface roughening increased the light yield for PES, despite the high effective refractive index. Background radiation derived from the PES sample and its impurities was negligible above the ambient, natural level. Overall, these results serve to optimise the mounting conditions for PES in radiation detection.
Keywords Poly (ether sulfone); Aromatic ring polymer; Optical coupling; Surface treatment; Background source;
1
1. Introduction Advances in materials refining techniques and in ultraviolet photodetectors have resulted in the discovery of previously unknown characteristics of aromatic ring polymers (Nakamura et al., 2013a, 2013b). Examples include poly (ethylene terephthalate) (PET) and poly (ethylene naphthalate) (PEN), which are used in radiation detection (Nakamura et al., 2010, 2011). One of their advantages is that they do not need doped fluorescent guest molecules to function as scintillation materials. Now, worldwide efforts are being made to identify other potential polymers, and to characterise light propagation generated in them (Kumar et al., 2012, Nakamura et al., 2012, 2013c, 2014a, Nagata et al., 2013a, 2013b and Sen et al., 2012). In addition, there is also an effort to develop prototypes for radiation detectors that use aromatic ring polymers (Shirakawa et al., 2013a, 2013b). There recently have been reports on the use of undoped poly (ether sulfone) (PES) as a scintillation material (Nakamura et al., 2014b). However, relative to PET and PEN, PES has short emission wavelengths , while its effective refractive index, based on its emission spectrum, is high (Nakamura et al., 2014c). These characteristics directly affect the propagation of light generated in PES to external photodetectors (Beringer et al., 2012, Leo, 1992, Knoll, 2010 and Sellmeier, 1871). It is also important to examine the presence of background radiation sources in manufactured PES (Nakamura et al., 2013d). Here, we characterise the optical coupling, surface treatment, and background levels for PES. Overall, these results help to optimise the mounting conditions for PES in radiation detection.
2. Materials and methods PES resin (4100G; Sumitomo Chemical Co., Ltd.) was formed into two 31×31×5 mm plates. Amber-coloured, transparent PES possesses sulfone in the repeat unit and its density is 1.37 g/cm3. The emission maximum is 350 nm, and the effective refractive index of 1.74 was determined by taking into account its emission spectrum (Nakamura et al., 2014b). To boost the detectable light yield, all six faces of one plate were roughened by a milling machine (VHR-G, Shizuoka Machine Tool Co., Ltd.). The other plate was unmodified and was also examined for background sources. To determine the light yield from the roughened PES plate, a radioactive source was positioned at the centre of a 31×31 mm face to excite the plate. The sources were 137Cs (CS21; Japan Radioisotope Association) and 207Bi (BIRB4391; High Technology Source Ltd.). The light yield was detected with a photomultiplier tube (PMT, R878-SBA; Hamamatsu Photonics Co., Ltd.) mounted on the opposite 31×31 mm face. A charge-sensitive analogue-to-digital converter (RPC022; REPIC Co.) was used to digitise the output signals from the PMT. Between the PES plate and the PMT window was a thin layer of optical grease (BC-630 Saint-Gobain Ceramics & Plastic Inc.). Light absorbance by the grease was determined with a UV-Vis photometer (V-670; JASCO Co.) by placing it in a 2-mm thick optical cell formed by two quartz windows. 2
To assess background radiation emitted from the PES plate itself, alpha and beta particles were measured with a background counter (LBC4351; Hitachi Aloka Medical, Ltd.) equipped with ZnS(Ag) and plastic scintillators. Gamma rays were measured with a shielded germanium detector (IGC3019SD; Toshiba Co.). The energy and detection efficiency of the germanium detector were calibrated with standard gamma-ray sources.
3. Results and discussion The absorption spectrum for the 2-mm thick silicon optical grease is shown in Fig. 1. It overlaps a section of the PES emission spectrum. However, the thickness of the grease used to couple the PES plate to the PMT window is less than 0.1 mm; thus absorption of light emitted from the PES should be negligible. The light yield distribution excited by radiation from the 137Cs radioactive source is plotted in Fig. 2. The small peak is from 624 keV internal conversion electrons. The counts in the low light yield region are predominately from beta particles with an endpoint-energy of 514 keV, with smaller contributions from Compton recoil electrons generated by gamma rays. The light yield distribution excited by radiation from the 207Bi radioactive source is plotted in Fig. 3. The large peak is from 976 keV internal conversion electrons. The counts in the low light yield region are primarily from Compton recoil electrons generated by gamma rays; the light yield from 482 keV internal conversion electrons is included in the counts. It was determined that the light yields from the PES plate having all six faces roughened was 1.02 times that from the unmodified plate. Thus, diffuse reflections provided by the surface treatment helped to efficiently propagate the light generated in PES to the external photodetector, despite the high effective refractive index. Alpha and beta particle emission from the PES plate were below the detection limit of the background counter. The energy spectrum of the gamma-rays emission is plotted in Fig. 4. There was no significant emission from the PES sample above the natural background (absence of plate). Activities for the detected radioactive nuclides are listed in Table 1. In summary, the results indicate that radiation background derived from the PES and its impurities was not above the ambient level.
4. Conclusions We have characterised the optical coupling, the surface treatment, and the background sources for PES. There was negligible absorption of short-wavelength light emitted from PES by the thin layer of optical grease used to couple the plate to the PMT. Despite the high effective refractive index for PES, the light yield increased because of diffuse reflections provided by surface roughness. Radiation background from the PES plate was not above the ambient level. These results serve to optimise the 3
mounting conditions for PES as a scintillation material in radiation detection. Furthermore, it is anticipated that PES will be evaluated and widely applied in radiation detectors (Shirakawa 2005).
Acknowledgements This research was supported by the Kyoto University and the National Institute of Radiological Sciences. The authors thank the KUR Research Program for the Scientific Basis of Nuclear Safety for partial support at this work. The authors are grateful to Dr. T. Murata, Dr. T. Fukunaga, Dr. H. Yamana and Ms. M. Yasaku for their cooperation.
4
Figure Fig. 1. Absorption spectrum of the optical grease used between the PES sample and the PMT window. The highlighted region (light blue) shows the emission spectrum of PES, where the maximum is 350 nm. The thickness of the grease used to couple the PES to the PMT is less than 0.1 mm; here it is 2 mm thick. Fig. 2. Light-yield distribution from a PES plate that had all six faces roughened, when excited by radiation from a 137Cs radioactive source. The small peak is from 624-keV internal conversion electrons. The counts for the low light-yield region are predominately from beta particles with an endpoint-energy of 514 keV, with smaller contributions from Compton recoil electrons generated by gamma rays. Fig. 3. Light-yield distribution of a PES plate that had all six faces roughened, when excited by radiation from a 207Bi radioactive source. The large peak is from 976-keV internal conversion electrons. The counts for the low light yield region are primarily from Compton recoil electrons generated by gamma rays, with smaller contributions from 482 keV internal conversion electrons. Fig. 4. Energy spectrum of gamma rays obtained from the PES plate. The presence (absence) of the PES plate on the shielded germanium detector is indicated by the blue (light blue) lines, respectively. The measurement times were 600,000 sec.
5
Table Table 1. Activities of radioactive nuclides in the presence or absence of the PES plate on the germanium detector.
Nuclide
Energy (keV)
40K
Activity (Bq/cm3) Absence
Presence
1461
1.9 × 10－2
2.0 × 10－2
60Co
1332
< 4.4 × 10－4
< 4.9 × 10－4
137Cs
662
< 6.5 × 10－4
< 6.4 × 10－4
214Pb
352
7.0 × 10－3
6.9 × 10－3
214Bi
609
7.0 × 10－3
7.3 × 10－3
226Ra
186
1.1 × 10－1
1.0 × 10－1
234Th
93
1.1 × 10－1
1.1 × 10－1
234mPa
1001
1.9 × 10－1
1.3 × 10－1
208Tl
2615
2.2 × 10－3
1.7 × 10－3
212Pb
239
7.9 × 10－3
6.9 × 10－3
212Bi
727
< 6.7× 10－3
< 6.7 × 10－3
228Ac
911
5.3 × 10－3
5.8 × 10－3
6
Reference Beringer, J. et al.(Particle data group), 2012. Phys. Rev. D, 86, 010001. Knoll, G. F., 2010. Radiation Detection and Measurement, 4th ed. Wiley, New York. Kumar, V., Ali, Y., Sonkawade, R. G., Dhaliwal, A. S., 2012. Effect of gamma irradiation on the properties of plastic bottle sheet, Nucl. Instrum. Method Phys. Res. B, 287, 10. http://dx.doi.org/10.1016/j.nimb.2012.07.007 Leo, W. R., 1992. Techniques for Nuclear and Particle Physics Experiments: A How-to Approach. 2nd ed. Springer-Verlag, Berlin and Heidelberg. Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S., 2013a. Light propagation characteristics of high-purity polystyrene. Applied Physics Letters,103, 161111. http://dx.doi.org/10.1063/1.4824467 Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S., 2013b. Mechanism of wavelength conversion in polystyrene doped with benzoxanthene: emergence of a complex. Scientific Reports, 3, 2502. http://dx.doi.org/10.1038/srep02502 Nakamura, H., Kitamura, H., Hazama, R., 2010. Radiation measurements with heat-proof polyethylene terephthalate bottles. Proc. R. Soc. A., 466, 2847. http://dx.doi.org/10.1098/rspa.2010.0118 Nakamura, H., Shirakawa, Y., Takahashi, S., Shimizu, H., 2011. Evidence of deep-blue photon emission at high efficiency by common plastic. EPL (Europhysics Letters), 95 (2), 22001. http://dx.doi.org/10.1209/0295-5075/95/22001 Nakamura, H., Kitamura, H., Shinji, O., Saito, K., Shirakawa, Y., Takahashi, S., 2012. Development of polystyrene-based scintillation materials and its mechanisms. Applied Physics Letters, 101, 261110. http://dx.doi.org/10.1063/1.4773298 Nakamura, H., Shirakawa, Y., Kitamura, H., Yamada, T., Shidara, Z., Yokozuka, T., Nguyen, P., Takahashi, T., Takahashi, S., 2013c, Blended polyethylene terephthalate and polyethylene naphthalate polymers for scintillation base substrates. Radiation Measurements, 59, 172. http://dx.doi.org/10.1016/j.radmeas.2013.06.006 7
Nakamura, H., Shirakawa, Y., Sato, N., Takahashi, S., 2014a, Characterising radiation spectra with stacked plastic sheets. Physics Education, 49, 135. http://dx.doi.org/10.1088/0031-9120/49/2/135 Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Takahashi, S., 2014b. Poly (ether sulfone) as a scintillation material for radiation detection, Applied Radiation and Isotopes, 86, 36. http://dx.doi.org/10.1016/j.apradiso.2013.12.028 Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Takahashi, S., 2014c. Detection of alpha particles with undoped poly (ethylene naphthalate). Nuclear Instruments and Methods in Physics Research A, 739, 6. http://dx.doi.org/10.1016/j.nima.2013.12.021 Nakamura, H., Yamada, T., Shirakawa, Y., Kitamura, H., Shidara, Z., Yokozuka, T., Nguyen, P., Kanayama, M., Takahashi, S., 2013d. Optimized mounting of a polyethylene naphthalate scintillation material in a radiation detector. Applied Radiation and Isotopes, 80, 84. http://dx.doi.org/10.1016/j.apradiso.2013.06.011 Nagata, S., Katsui, H., Hoshi, K., Tsuchiya, B., Toh, K., Zhao, M., Shikama, T., Hodgson, E. R., 2013a. Recent research activities on functional ceramics for insulator, breeder and optical sensing systems in fusion reactors, Journal of Nuclear Materials, 442, supplement 1, S501. http://dx.doi.org/10.1016/j.jnucmat.2013.05.039 Nagata, S., Mitsuzuka, M., Onodera, S., Yaegashi, T., Hoshi, K., Zhao, M., Shikama, T., 2013b. Damage and recovery processes for the luminescence of irradiated PEN films, Nucl. Instrum. Method Phys. Res. B, 315, 157. http://dx.doi.org/10.1016/j.nimb.2013.03.027 Sellmeier, W., 1871. Zur Erklärung der abnormen Farbenfolge im Spectrum einiger Substanzen. Annalen der Physik, 219, 272. http://dx.doi.org/10.1002/andp.18712190612 Sen, I., Urffer, M., Penumadu, D., Young, S. A., Miller, L. F., Mabe, A. N., 2012. Polyester composite thermal neutron scintillation films. IEEE Trans. Nucl. Sci., 59 (4), 1781. http://dx.doi.org/10.1109/TNS.2012.2201503 Shirakawa, Y., Nakamura, H., Kamata, T., Watai, K., Mitsunaga, M., Shidara, Z., Murakawa, F., 8
2013a. Radiation counting characteristics on surface-modified polyethylene naphthalate scintillators. Radioisotopes, 62, 879. http://dx.doi.org/10.3769/radioisotopes.62.879 Shirakawa, Y., Nakamura, H., Kamata, T., Watai, K., 2013b. A fast response radiation detector based on a response prediction method for decontamination. Radiation Measurements, 49, 115. http://dx.doi.org/10.1016/j.radmeas.2012.12.001 Shirakawa, Y., 2005, Quick Response of a Survey Meter in Static Condition, Radioisotopes, 54, 199. http://dx.doi.org/10.3769/radioisotopes.54.199
Highlights (3-5 bullet points) ¾
Mounting conditions for PES in radiation detection are optimised.
¾
Optical coupling, surface treatment, and background sources are discussed.
¾
Absorption by optical grease of short-wavelength light emitted from PES was negligible.
¾
Despite the high effective refractive index for PES, light yield was increased by surface roughness.
¾
Radiation background from the PES plate itself was not above the ambient level.
9
Figure1
Figure2
Figure3
Figure4
Presence Absence
Optimised mounting conditions for poly (ether sulfone) in radiation detection Hidehito Nakamura, Yoshiyuki Shirakawa, Nobuhiro Sato, Tatsuya Yamada, Hisashi Kitamura, Sentaro Takahashi
www.elsevier.com/locate/apradiso
PII: DOI: Reference:
S0969-8043(14)00207-3 http://dx.doi.org/10.1016/j.apradiso.2014.05.013 ARI6690
To appear in:
Applied Radiation and Isotopes
Received date: 13 March 2014 Revised date: 2 May 2014 Accepted date: 15 May 2014 Cite this article as: Hidehito Nakamura, Yoshiyuki Shirakawa, Nobuhiro Sato, Tatsuya Yamada, Hisashi Kitamura, Sentaro Takahashi, Optimised mounting conditions for poly (ether sulfone) in radiation detection, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2014.05.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Title Optimised mounting conditions for poly (ether sulfone) in radiation detection
Author name and affiliations Hidehito Nakamuraa,b,*, Yoshiyuki Shirakawab, Nobuhiro Satoa, Tatsuya Yamadaa, Hisashi Kitamurab, and Sentaro Takahashia aKyoto
University, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan
bNational
Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba, 263-8555, Japan
*Corresponding author Tel.: +81 72 451 2463; Fax: +81 72 451 2463 E-mail address: [email protected] (H. Nakamura)
Abstract Poly (ether sulfone) (PES) is a candidate for use as a scintillation material in radiation detection. Its characteristics, such as its emission spectrum and its effective refractive index (based on the emission spectrum), directly affect the propagation of light generated to external photodetectors. It is also important to examine the presence of background radiation sources in manufactured PES. Here, we optimise the optical coupling and surface treatment of the PES, and characterise its background. Optical grease was used to enhance the optical coupling between the PES and the photodetector; absorption by the grease of short-wavelength light emitted from PES was negligible. Diffuse reflection induced by surface roughening increased the light yield for PES, despite the high effective refractive index. Background radiation derived from the PES sample and its impurities was negligible above the ambient, natural level. Overall, these results serve to optimise the mounting conditions for PES in radiation detection.
Keywords Poly (ether sulfone); Aromatic ring polymer; Optical coupling; Surface treatment; Background source;
1
1. Introduction Advances in materials refining techniques and in ultraviolet photodetectors have resulted in the discovery of previously unknown characteristics of aromatic ring polymers (Nakamura et al., 2013a, 2013b). Examples include poly (ethylene terephthalate) (PET) and poly (ethylene naphthalate) (PEN), which are used in radiation detection (Nakamura et al., 2010, 2011). One of their advantages is that they do not need doped fluorescent guest molecules to function as scintillation materials. Now, worldwide efforts are being made to identify other potential polymers, and to characterise light propagation generated in them (Kumar et al., 2012, Nakamura et al., 2012, 2013c, 2014a, Nagata et al., 2013a, 2013b and Sen et al., 2012). In addition, there is also an effort to develop prototypes for radiation detectors that use aromatic ring polymers (Shirakawa et al., 2013a, 2013b). There recently have been reports on the use of undoped poly (ether sulfone) (PES) as a scintillation material (Nakamura et al., 2014b). However, relative to PET and PEN, PES has short emission wavelengths , while its effective refractive index, based on its emission spectrum, is high (Nakamura et al., 2014c). These characteristics directly affect the propagation of light generated in PES to external photodetectors (Beringer et al., 2012, Leo, 1992, Knoll, 2010 and Sellmeier, 1871). It is also important to examine the presence of background radiation sources in manufactured PES (Nakamura et al., 2013d). Here, we characterise the optical coupling, surface treatment, and background levels for PES. Overall, these results help to optimise the mounting conditions for PES in radiation detection.
2. Materials and methods PES resin (4100G; Sumitomo Chemical Co., Ltd.) was formed into two 31×31×5 mm plates. Amber-coloured, transparent PES possesses sulfone in the repeat unit and its density is 1.37 g/cm3. The emission maximum is 350 nm, and the effective refractive index of 1.74 was determined by taking into account its emission spectrum (Nakamura et al., 2014b). To boost the detectable light yield, all six faces of one plate were roughened by a milling machine (VHR-G, Shizuoka Machine Tool Co., Ltd.). The other plate was unmodified and was also examined for background sources. To determine the light yield from the roughened PES plate, a radioactive source was positioned at the centre of a 31×31 mm face to excite the plate. The sources were 137Cs (CS21; Japan Radioisotope Association) and 207Bi (BIRB4391; High Technology Source Ltd.). The light yield was detected with a photomultiplier tube (PMT, R878-SBA; Hamamatsu Photonics Co., Ltd.) mounted on the opposite 31×31 mm face. A charge-sensitive analogue-to-digital converter (RPC022; REPIC Co.) was used to digitise the output signals from the PMT. Between the PES plate and the PMT window was a thin layer of optical grease (BC-630 Saint-Gobain Ceramics & Plastic Inc.). Light absorbance by the grease was determined with a UV-Vis photometer (V-670; JASCO Co.) by placing it in a 2-mm thick optical cell formed by two quartz windows. 2
To assess background radiation emitted from the PES plate itself, alpha and beta particles were measured with a background counter (LBC4351; Hitachi Aloka Medical, Ltd.) equipped with ZnS(Ag) and plastic scintillators. Gamma rays were measured with a shielded germanium detector (IGC3019SD; Toshiba Co.). The energy and detection efficiency of the germanium detector were calibrated with standard gamma-ray sources.
3. Results and discussion The absorption spectrum for the 2-mm thick silicon optical grease is shown in Fig. 1. It overlaps a section of the PES emission spectrum. However, the thickness of the grease used to couple the PES plate to the PMT window is less than 0.1 mm; thus absorption of light emitted from the PES should be negligible. The light yield distribution excited by radiation from the 137Cs radioactive source is plotted in Fig. 2. The small peak is from 624 keV internal conversion electrons. The counts in the low light yield region are predominately from beta particles with an endpoint-energy of 514 keV, with smaller contributions from Compton recoil electrons generated by gamma rays. The light yield distribution excited by radiation from the 207Bi radioactive source is plotted in Fig. 3. The large peak is from 976 keV internal conversion electrons. The counts in the low light yield region are primarily from Compton recoil electrons generated by gamma rays; the light yield from 482 keV internal conversion electrons is included in the counts. It was determined that the light yields from the PES plate having all six faces roughened was 1.02 times that from the unmodified plate. Thus, diffuse reflections provided by the surface treatment helped to efficiently propagate the light generated in PES to the external photodetector, despite the high effective refractive index. Alpha and beta particle emission from the PES plate were below the detection limit of the background counter. The energy spectrum of the gamma-rays emission is plotted in Fig. 4. There was no significant emission from the PES sample above the natural background (absence of plate). Activities for the detected radioactive nuclides are listed in Table 1. In summary, the results indicate that radiation background derived from the PES and its impurities was not above the ambient level.
4. Conclusions We have characterised the optical coupling, the surface treatment, and the background sources for PES. There was negligible absorption of short-wavelength light emitted from PES by the thin layer of optical grease used to couple the plate to the PMT. Despite the high effective refractive index for PES, the light yield increased because of diffuse reflections provided by surface roughness. Radiation background from the PES plate was not above the ambient level. These results serve to optimise the 3
mounting conditions for PES as a scintillation material in radiation detection. Furthermore, it is anticipated that PES will be evaluated and widely applied in radiation detectors (Shirakawa 2005).
Acknowledgements This research was supported by the Kyoto University and the National Institute of Radiological Sciences. The authors thank the KUR Research Program for the Scientific Basis of Nuclear Safety for partial support at this work. The authors are grateful to Dr. T. Murata, Dr. T. Fukunaga, Dr. H. Yamana and Ms. M. Yasaku for their cooperation.
4
Figure Fig. 1. Absorption spectrum of the optical grease used between the PES sample and the PMT window. The highlighted region (light blue) shows the emission spectrum of PES, where the maximum is 350 nm. The thickness of the grease used to couple the PES to the PMT is less than 0.1 mm; here it is 2 mm thick. Fig. 2. Light-yield distribution from a PES plate that had all six faces roughened, when excited by radiation from a 137Cs radioactive source. The small peak is from 624-keV internal conversion electrons. The counts for the low light-yield region are predominately from beta particles with an endpoint-energy of 514 keV, with smaller contributions from Compton recoil electrons generated by gamma rays. Fig. 3. Light-yield distribution of a PES plate that had all six faces roughened, when excited by radiation from a 207Bi radioactive source. The large peak is from 976-keV internal conversion electrons. The counts for the low light yield region are primarily from Compton recoil electrons generated by gamma rays, with smaller contributions from 482 keV internal conversion electrons. Fig. 4. Energy spectrum of gamma rays obtained from the PES plate. The presence (absence) of the PES plate on the shielded germanium detector is indicated by the blue (light blue) lines, respectively. The measurement times were 600,000 sec.
5
Table Table 1. Activities of radioactive nuclides in the presence or absence of the PES plate on the germanium detector.
Nuclide
Energy (keV)
40K
Activity (Bq/cm3) Absence
Presence
1461
1.9 × 10－2
2.0 × 10－2
60Co
1332
< 4.4 × 10－4
< 4.9 × 10－4
137Cs
662
< 6.5 × 10－4
< 6.4 × 10－4
214Pb
352
7.0 × 10－3
6.9 × 10－3
214Bi
609
7.0 × 10－3
7.3 × 10－3
226Ra
186
1.1 × 10－1
1.0 × 10－1
234Th
93
1.1 × 10－1
1.1 × 10－1
234mPa
1001
1.9 × 10－1
1.3 × 10－1
208Tl
2615
2.2 × 10－3
1.7 × 10－3
212Pb
239
7.9 × 10－3
6.9 × 10－3
212Bi
727
< 6.7× 10－3
< 6.7 × 10－3
228Ac
911
5.3 × 10－3
5.8 × 10－3
6
Reference Beringer, J. et al.(Particle data group), 2012. Phys. Rev. D, 86, 010001. Knoll, G. F., 2010. Radiation Detection and Measurement, 4th ed. Wiley, New York. Kumar, V., Ali, Y., Sonkawade, R. G., Dhaliwal, A. S., 2012. Effect of gamma irradiation on the properties of plastic bottle sheet, Nucl. Instrum. Method Phys. Res. B, 287, 10. http://dx.doi.org/10.1016/j.nimb.2012.07.007 Leo, W. R., 1992. Techniques for Nuclear and Particle Physics Experiments: A How-to Approach. 2nd ed. Springer-Verlag, Berlin and Heidelberg. Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S., 2013a. Light propagation characteristics of high-purity polystyrene. Applied Physics Letters,103, 161111. http://dx.doi.org/10.1063/1.4824467 Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S., 2013b. Mechanism of wavelength conversion in polystyrene doped with benzoxanthene: emergence of a complex. Scientific Reports, 3, 2502. http://dx.doi.org/10.1038/srep02502 Nakamura, H., Kitamura, H., Hazama, R., 2010. Radiation measurements with heat-proof polyethylene terephthalate bottles. Proc. R. Soc. A., 466, 2847. http://dx.doi.org/10.1098/rspa.2010.0118 Nakamura, H., Shirakawa, Y., Takahashi, S., Shimizu, H., 2011. Evidence of deep-blue photon emission at high efficiency by common plastic. EPL (Europhysics Letters), 95 (2), 22001. http://dx.doi.org/10.1209/0295-5075/95/22001 Nakamura, H., Kitamura, H., Shinji, O., Saito, K., Shirakawa, Y., Takahashi, S., 2012. Development of polystyrene-based scintillation materials and its mechanisms. Applied Physics Letters, 101, 261110. http://dx.doi.org/10.1063/1.4773298 Nakamura, H., Shirakawa, Y., Kitamura, H., Yamada, T., Shidara, Z., Yokozuka, T., Nguyen, P., Takahashi, T., Takahashi, S., 2013c, Blended polyethylene terephthalate and polyethylene naphthalate polymers for scintillation base substrates. Radiation Measurements, 59, 172. http://dx.doi.org/10.1016/j.radmeas.2013.06.006 7
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Highlights (3-5 bullet points) ¾
Mounting conditions for PES in radiation detection are optimised.
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Optical coupling, surface treatment, and background sources are discussed.
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Absorption by optical grease of short-wavelength light emitted from PES was negligible.
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Despite the high effective refractive index for PES, light yield was increased by surface roughness.
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Radiation background from the PES plate itself was not above the ambient level.
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Figure1
Figure2
Figure3
Figure4
Presence Absence
