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Characterizing radiation spectra with stacked plastic sheets
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2014 Phys. Educ. 49 135
(http://iopscience.iop.org/0031-9120/49/2/135)
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Characterizing radiation spectrawith stacked plastic sheetsHidehito Nakamura1,2, Yoshiyuki Shirakawa2, Nobuhiro Sato1 andSentaro Takahashi1
1 Kyoto University, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan2 National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba 263-8555,Japan
E-mail: [email protected], [email protected], [email protected] [email protected]
AbstractRadiation spectra are demonstrated for educational purposes usinginexpensive and readily available materials.
We recently demonstrated that ordinary plasticsused for commercial products possess character-istics suitable for radiation detection [1–3]. Therequired thickness of the plastic depends on theenergy of the radiation. Thick pieces must becarefully formed by injection moulding, whereasthin sheets are readily available. Here, we showthat a stack of thin plastic sheets is an alternativeto a thick piece, and can be used as educationalmaterial to demonstrate radiation spectra.
Undoped aromatic ring polymers, such aspoly (ethylene terephthalate) (PET) or poly (ethy-lene naphthalate) (PEN), emit short-wavelengthlight when excited by radiation [4–6]. The char-acteristics of the light emitted from these deter-mine its performance as a detector [7–12]. Wehave characterized light emitted from stacked PENsheets.
As shown in figure 1, five 31 mm× 31 mm×1 mm sections were cut from a PEN sheet (TeijinLtd) and stacked without optical grease or cement.The light yield of the stack was measured by irra-diating it with a 137Cs radioactive source (CS21;Japan Radioisotope Association) that emits mo-noenergetic internal conversion electrons in ad-dition to beta particles and gamma-rays. A pho-tomultiplier tube (PMT, R878-SBA; HamamatsuPhotonics Co., Ltd) was used as the photodetector(figure 2). One 31 mm×31 mm sheet was directly
Figure 1. Five stacked PEN sheets (31 mm×31 mm×1 mm) excited by ultraviolet light.
interfaced to the PMT window and the radioactivesource was positioned in the centre of the lastsheet.
Figure 3 plots a light yield distribution fromthe stacked thin sheets generated by the 137Csradioactive source. The peak is from 624 keVinternal conversion electrons, while counts for thelow light-yield region are from the beta particlesand Compton recoil electrons generated by thegamma-rays. Thus, the stacked sheets have theability to characterize radiation spectra. In addi-tion, the light yield is 0.92 times that of a singlepiece of the same thickness.
In summary, we characterized light from asimple stack of plastic sheets excited by radiation.
0031-9120/14/020135+02$33.00 c© 2014 IOP Publishing Ltd P H Y S I C S E D U C A T I O N 49 (2) 135
H Nakamura et al Frontlines
Figure 2. Arrangement for measuring light yields inPEN sheets. No optical coupling is required betweenthe first 31 mm × 31 mm sheet and the PMT window.The 137Cs radioactive source is positioned in the centreof the last sheet.
Figure 3. Light-yield distribution from stacked PENsheets when excited by a 137Cs radioactive source.The peak in the distribution is due to 624 keV internalconversion electrons.
The readily available plastic sheets are suitable fordemonstrating radiation spectra educationally.
AcknowledgmentsThis research was supported by Kyoto Univer-sity and the National Institute of RadiologicalSciences. The authors thank the KUR ResearchProgram for the Scientific Basis of Nuclear Safetyfor partial support. The authors are grateful toDrs T Murata, T Fukunaga and H Yamana,Messrs H Kitamura, Z Shidara, F Murakawa,Y Okamoto and Ms M Yasaku for their coop-eration.
Received 4 October 2013, in final form 24 October 2013,accepted for publication 30 October 2013doi:10.1088/0031-9120/49/2/135
References[1] Nakamura H et al 2013 Appl. Phys. Lett.
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Measurement 4th edn (New York: Wiley)[8] Leo W R 1992 Techniques for Nuclear and
Particle Physics Experiments: A How-toApproach 2nd edn (Berlin: Springer)
[9] Nakamura H et al 2012 Appl. Phys. Lett.101 261110
[10] Nakamura H et al 2013 Phys. Educ.48 556
[11] Nakamura H et al 2013 Appl. Radiat. Isotopes80 84
[12] Shirakawa Y et al 2013 Radiat. Meas. 49 115
Hidehito Nakamura is an assistantprofessor at Kyoto University, Japan,and a visiting researcher at the NationalInstitute of Radiological Sciences,Japan.
Yoshiyuki Shirakawa is a director at theNational Institute of RadiologicalSciences.
Nobuhiro Sato is an assistant professorat Kyoto University.
Sentaro Takahashi is a professor atKyoto University.
136 P H Y S I C S E D U C A T I O N March 2014
