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Radiation Measurements 73 (2015) 14e17

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Radiation Measurements

journal homepage: www.elsevier .com/locate/radmeas

Undoped poly (phenyl sulfone) for radiation detection

Hidehito Nakamura a, b, *, Yoshiyuki Shirakawa b, Nobuhiro Sato a, Hisashi Kitamura b,Sentaro Takahashi a

a Kyoto University, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japanb National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba 263-8555, Japan

h i g h l i g h t s

� Poly (phenyl sulfone) (PPSU) has suitable characteristics as a scintillation material.� PPSU is an amber-coloured transparent resin that emits bluish white fluorescence with 390-nm maximum.� The 1.75 effective refractive index over the emission spectrum is relatively high.� The light yield is 0.95 times that of poly (ethylene terephthalate), which is a transparent resin.� PPSU can potentially alter optical characteristics in polymer blends.

a r t i c l e i n f o

Article history:Received 3 July 2014Received in revised form19 September 2014Accepted 1 December 2014Available online 2 December 2014

Keywords:Poly (phenyl sulfone)Aromatic ring polymerExcitation and emissionRefractive indexLight yield

* Corresponding author. Kyoto University, 2, ASennan-gun, Osaka 590-0494, Japan.

E-mail address: hidehito@rri.kyoto-u.ac.jp (H. Nak

http://dx.doi.org/10.1016/j.radmeas.2014.12.0021350-4487/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

Undoped aromatic ring polymers are potential scintillation materials. Here, we characterise poly (phenylsulfone) (PPSU) for radiation detection. The amber-coloured transparent resin emits bluish-white fluo-rescence with 390-nm maximum. It has an excitation maximum of 340 nm, and has a density of 1.29 g/cm3. The effective refractive index based on its emission spectrum is 1.75. The light yield is almost equalto that of poly (ethylene terephthalate), which is a transparent resin. These results demonstrate thatPPSU can be used as a component substrate in polymer blends for altering optical characteristics.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Organic scintillation materials are usually composed of aromaticring polymers that have been doped with fluorescent guest mole-cules (Beringer et al., 2012; Knoll, 2010; Leo, 1992). Advancedrefining techniques, however, have revealed that high-purity aro-matic ring polymers can be used as scintillation materials withoutthe need for the guest molecules (Nakamura et al., 2013a, 2013b).For example, radiation detection by familiar plastics, such as poly(ethylene terephthalate) (PET) or polycarbonates, has had aworldwide impact (Kumar et al., 2012; Nakamura et al., 2010,2014a). We have previously demonstrated that poly (ethylene

sashiro-Nishi, Kumatori-cho,

amura).

naphthalate) (PEN) and poly (ether sulfone) (PES) are also suitablefor radiation detection (Nakamura et al., 2011, 2013c, 2014b, 2014c,2014d). Additionally, an optimised mounting for an undoped aro-matic ring polymer in a radiation detector was described(Nakamura et al., 2013d, 2014e; Shirakawa et al., 2013a, 2013b).

Blending aromatic ring polymers is an effective way to alter thecharacteristics of scintillation materials. Polymer blends generallyhave characteristics that are an average of the component sub-strates. Thus, by identifying aromatic ring polymers that are po-tential blend components, the variety of available scintillationmaterials can be increased. For example, a PETePEN blend (similarrepeat units) and a PESePEN blend (dissimilar repeat units) havebeen reported (Nakamura et al., 2013e, 2014f).

Poly (phenyl sulfone) (PPSU) has several advantages: trans-parency, heat tolerance, hydrolysis resistance, chemical inertness,and mechanical strength. Thus, it has been used in ductworks forvisually monitoring high-temperature fluids in the manufacture of

H. Nakamura et al. / Radiation Measurements 73 (2015) 14e17 15

foods, drinks, drugs, and beauty products. The repeat unit of PPSUis:

The repeat unit contains sulfur as a heavy element. Its relativelyhigh density contributes to enhancing radiation interactions. PPSUis amorphous because of the geometric constraints induced by thepresence of a sulfonyl group. We demonstrate here that undopedPPSU has the potential for radiation detection as a componentsubstrate in polymer blends. In that regard, these indicate thatPPSU ductworks are not only rust resistant and lightweight, butalso can function as sensors to monitor the flow of radioactivecontaminants.

2. Materials and methods

A 31 � 31 � 5 mm PPSU plate (R-5000 NT; Solvay SpecialtyPolymers Co., Ltd.) was characterised. It is an amber-colouredtransparent resin with a density of 1.29 g/cm3, and emits bluishwhite fluorescence when excited by ultra-violet light (Fig. 1). The

Fig. 1. Photographs of a 31 � 31 � 5 mm PPSU plate. PPSU is an amber-colouredtransparent resin (top), and emits bluish white light when excited by ultra-violetlight (bottom). (For interpretation of the references to colour in this figure legend,the reader is referred to the web version of this article.)

PPSU fluorescence was examined with a fluorescence spectrometer(F-2700; Hitachi High-Technologies Co.).

A refractometer (PR-2; Carl Zeiss Jena) was used to acquire thewavelength dependence of the PPSU refractive index. Four atomiclines were used: the g and e lines of a mercury lamp (436 and546 nm), the D line of a sodium lamp (589 nm), and the C line of ahydrogen lamp (656 nm). Based on these results, an effectiverefractive index based on the emission spectrum was determined.

To evaluate the fluorescence light yield, the 31 � 31 mm PPSUplate was excited by radiation emitted from a 207Bi radioactivesource (BIRB4391; High Technology Source Ltd.) placed at thecentre of one face. The light was detected with a photomultipliertube (PMT; R878-SBA, Hamamatsu Photonics Co., Ltd.) in contact,via optical grease, with the opposite face (BC-630; Saint-GobainCeramics & Plastic Inc.). The PMT is sensitive to short-wavelengthlight (Nakamura et al., 2012), and its output was digitised with acharge-sensitive analogue-to-digital converter (RPC022; REPIC Co.)without amplification.

3. Results and discussion

PPSU fluorescence is plotted in Fig. 2, where the 340-nm exci-tation and 390-nm emission maxima are at the intersection of thetwo white lines. The excitation and emission maxima are similar tothose for PET (Nakamura et al., 2013e). In Fig. 3 the excitationspectrummonitored at 390 nm, and the emission spectrum excitedat 340 nm are plotted. The light emitted from PPSU can efficientlybe detected with the PMT.

The refractive index (ND) for the sodium D line is 1.67, which islarger than that for PET (1.57). However, since PPSU emission is atmuch shorter wavelengths than 589 nm, a more appropriate indexmust be determined. The refractive indices are plotted as a functionof wavelength in Fig. 4. The wavelength dependence was acquiredwith the Sellmeier dispersion function (Sellmeier, 1871). Fromthese results, an effective refractive index (Neff ¼ 1.75), based on theemission spectrum, was determined (Nakamura et al., 2013b).

Fig. 2. PPSU fluorescence. The 340-nm excitation and 390-nm emission maxima are atthe intersection of the two white lines.

Emission

Excitation

Fig. 3. Excitation spectrum for 390-nm PPSU emission (green), and the emissionspectrum for 340-nm excitation (blue). (For interpretation of the references to colourin this figure legend, the reader is referred to the web version of this article.)

Fig. 5. The light yield distribution from PPSU when excited by a 207Bi radioactivesource. Monoenergetic 976 keV internal conversion electrons account for the smallpeak in the distribution.

H. Nakamura et al. / Radiation Measurements 73 (2015) 14e1716

The light yield distribution generated in PPSU by radiationemitted from the 207Bi radioactive source is shown in Fig. 5. It canbe seen that undoped PPSU can be used as a scintillation materialfor radiation detection. The small peak in the distribution is pri-marily caused by monoenergetic 976 keV internal conversionelectrons. The light yield of PPSU is 0.95 times that of PET, which isapproximately one-seventh that of a typical organic scintillationmaterial (Nakamura et al., 2014b). The relatively low light yield forPPSU makes it difficult to use as an effective scintillation material.

Fig. 4. Wavelength dependence of PPSU refractive indices. Fluorescence is shown inthe highlighted region (light blue). The maximum emission of PPSU is 390-nm. (Forinterpretation of the references to colour in this figure legend, the reader is referred tothe web version of this article.)

However, it could be used as a component substrate in polymerblends for altering optical characteristics.

4. Conclusions

PPSU is an amber-coloured transparent resin that emits bluishwhite fluorescence with a 340-nm excitation maximum and 390-nm emission maximum. Its effective refractive index of 1.75 for theemission wavelengths is relatively high. However, the PPSU lightyield is 0.95 times that of undoped PET. These results demonstratethat undoped PPSU increases the variety of available scintillationmaterials (Shirakawa, 2005; Nagata et al., 2013a, 2013b; Sen et al.,2012; Uppal et al., 2013). The PPSU ductworks have the potential fordirectly monitoring the radiological contaminations in thedrainage.

Acknowledgements

This research was supported by the Kyoto University and theNational Institute of Radiological Sciences. The authors thank theKUR Research Program for the Scientific Basis of Nuclear Safety forpartial support at this work. The authors are grateful to Dr. T.Murata, Dr. T. Fukunaga, Dr. H. Yamana, Ms. Y. Akahoshi and Ms. M.Yasaku for their cooperation.

References

Beringer, J., et al., Particle data group, 2012. Phys. Rev. D. 86, 010001. http://dx.doi.org/10.1103/PhysRevD.86.010001.

Knoll, G.F., 2010. Radiation Detection and Measurement, fourth ed. Wiley, NewYork.

Kumar, V., Ali, Y., Sonkawade, R.G., Dhaliwal, A.S., 2012. Effect of gamma irradiationon the properties of plastic bottle sheet. Nucl. Instrum. Methods Phys. Res. B287, 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-toApproach, second ed. Springer-Verlag, Berlin and Heidelberg.

Nagata, S., Katsui, H., Hoshi, K., Tsuchiya, B., Toh, K., Zhao, M., Shikama, T.,Hodgson, E.R., 2013a. Recent research activities on functional ceramics forinsulator, breeder and optical sensing systems in fusion reactors. J. Nucl. Mater.442 (Suppl. 1), S501. http://dx.doi.org/10.1016/j.jnucmat.2013.05.039.

H. Nakamura et al. / Radiation Measurements 73 (2015) 14e17 17

Nagata, S., Mitsuzuka, M., Onodera, S., Yaegashi, T., Hoshi, K., Zhao, M., Shikama, T.,2013b. Damage and recovery processes for the luminescence of irradiated PENfilms. Nucl. Instrum. Method Phys. Res. B 315, 157. http://dx.doi.org/10.1016/j.nimb.2013.03.027.

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-bluephoton emission at high efficiency by common plastic. EPL Europhys. Lett. 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.Appl. Phys. Lett. 101, 261110. http://dx.doi.org/10.1063/1.4773298.

Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S.,2013a. Mechanism of wavelength conversion in polystyrene doped with ben-zoxanthene: emergence of a complex. Sci. Rep. 3, 2502. http://dx.doi.org/10.1038/srep02502.

Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Shinji, O., Saito, K., Takahashi, S.,2013b. Light propagation characteristics of high-purity polystyrene. Appl. Phys.Lett. 103, 161111. http://dx.doi.org/10.1063/1.4824467.

Nakamura, H., Shirakawa, Y., Yamada, T., Nguyen, P., Takahashi, S., 2013c. Sensesalone cannot detect different properties. Phys. Educ. 48, 556. http://dx.doi.org/10.1088/0031-9120/48/5/F02.

Nakamura, H., Yamada, T., Shirakawa, Y., Kitamura, H., Shidara, Z., Yokozuka, T.,Nguyen, P., Kanayama, M., Takahashi, S., 2013d. Optimized mounting of apolyethylene naphthalate scintillation material in a radiation detector. Appl.Radiat. Isot. 80, 84. http://dx.doi.org/10.1016/j.apradiso.2013.06.011.

Nakamura, H., Shirakawa, Y., Kitamura, H., Yamada, T., Shidara, Z., Yokozuka, T.,Nguyen, P., Takahashi, T., Takahashi, S., 2013e. Blended polyethylene tere-phthalate and polyethylene naphthalate polymers for scintillation base sub-strates. Radiat. Meas. 59, 172. http://dx.doi.org/10.1016/j.radmeas.2013.06.006.

Nakamura, H., Shirakawa, Y., Sato, N., Kitamura, H., Takahashi, S., 2014a. Undopedpolycarbonate for detection of environmental radiation. Jpn. J. Health Phys. 49(2), 98. http://dx.doi.org/10.5453/jhps.49.98.

Nakamura, H., Shirakawa, Y., Kitamura, H., Sato, N., Takahashi, S., 2014b. Poly (ethersulfone) as a scintillation material for radiation detection. Appl. Radiat. Isot. 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 ofalpha particles with undoped poly (ethylene naphthalate). Nucl. Instrum.Methods Phys. Res. A 739, 6. http://dx.doi.org/10.1016/j.nima.2013.12.021.

Nakamura, H., Shirakawa, Y., Sato, N., Takahashi, S., 2014d. Characterising radiationspectra with stacked plastic sheets. Phys. Educ. 49, 135. http://dx.doi.org/10.1088/0031-9120/49/2/135.

Nakamura, H., Shirakawa, Y., Sato, N., Yamada, T., Kitamura, H., Takahashi, S., 2014e.Optimised mounting conditions for poly (ether sulfone) in radiation detection.Appl. Radiat. Isot. 91, 131. http://dx.doi.org/10.1016/j.apradiso.2014.05.013.

Nakamura, H., Shirakawa, Y., Sato, N., Kitamura, H., Takahashi, S., 2014f. Blendedpoly (ether sulfone) and poly (ethylene naphthalate) as a scintillation material.Nucl. Instrum. Methods Phys. Res. A 759, 1. http://dx.doi.org/10.1016/j.nima.2014.05.053.

Sellmeier, W., 1871. Zur Erkl€arung der abnormen Farbenfolge im Spectrum einigerSubstanzen. Ann. Phys. 219, 272. http://dx.doi.org/10.1002/andp.18712190612.

Sen, I., Urffer, M.J., Penumadu, D., Young, S.A., Miller, L.F., Mabe, A.N., 2012. Polyestercomposite 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., 2013a. Radiation counting characteristics on surface-modifiedpolyethylene 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 radiationdetector based on a response prediction method for decontamination. Radiat.Meas. 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. Radio-isotopes 54, 199. http://dx.doi.org/10.3769/radioisotopes.54.199.

Uppal, R., Sen, I., Penumadu, D., Young, S., Urffer, M.J., Miller, L.F., 2013. 6Liembedded biaxially stretched scintillation films for thermal neutron detectionand neutron/gamma discrimination. Adv. Eng. Mater. 16, 196. http://dx.doi.org/10.1002/adem.201300237.