The convertible source system for the neutron and the X-ray

imagings was installed in the 45MeV electron linear accelerator facility at Hokkaido University. The source system is very useful for a complementary imaging. The

imaging measurements for a sample were performed with both beams by using a vacuum tube type image intensifier. The enhanced contrast was obtained from the dataset of the radiograms measured with the neutron and X-ray beams

Hara, K. Y.

Kamiyama, T.

Sato, H.

Taira, H.

English

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DOI 10.1393/ncc/i2015-15187-9Colloquia: UCANS-VIL NUOVO CIMENTO 38 C (2015) 187Convertible source system of thermal neutron and X-rayat Hokkaido University electron linac facilityT. Kamiyama(∗), K. Y. Hara, H. Taira(∗∗) and H. SatoFaculty of Engineering, Hokkaido University - Sapporo 060-8628, Japanreceived 22 February 2016Summary. — The convertible source system for the neutron and the X-rayimagings was installed in the 45MeV electron linear accelerator facility at HokkaidoUniversity. The source system is very useful for a complementary imaging. Theimaging measurements for a sample were performed with both beams by using avacuum tube type image intensifier. The enhanced contrast was obtained from thedataset of the radiograms measured with the neutron and X-ray beams.PACS 07.85.Fv – X- and γ-ray sources, mirrors, gratings, and detectors.PACS 28.20.Pr – Neutron imaging; neutron tomography.PACS 29.25.Dz – Neutron source.PACS 87.59.B- – Radiography.1. – IntroductionComplementary usage of neutron and X-ray imaging is expected to extend theapplicable fields in nondestructive radiography [1-3]. Different cross sections of objectfor each beam give images with different information. The conventional neutron radiog-raphy has been generally carried out at the reactor facility [4]. On the other hand, theX-ray radiography is often carried out in relatively accessible devices. Therefore, manycases of the complementary radiography take place separately in different beam lines.However, the imagings under different experimental conditions, such as the object anddetector positions or the detector type, are not expedient for the reasonable compari-son of their radiograms. Fortunately, at electron accelerator-based radiation sources itis possible to obtain neutrons and X-rays relatively easily. Furthermore, higher energyX-rays can be obtainable with the accelerator-based X-ray source, reaching a penetra-tion length comparable to neutrons. Because of these advantages, an electron beam(∗) E-mail: takashik@qe.eng.hokudai.ac.jp (corresponding author)(∗∗) Present address: Hokkaido University of Education, Sapporo 002-8502, Japan.Creative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 T. KAMIYAMA et al.lectron linear acceleratorConcrete shieldSample & DetectorControl roomModulator roomExperiment roomCold neutron sourceThermal neutron & x-ray sourceElectron beamNeutron production targetX-ray production target Beam line44 cmGraphite reflectorLead shieldLead shieldLead shieldBoron resin shieldBoron resin shieldPolyethylene moderatorUp-and-down stageFig. 1. – Schematic view of the electron linear accelerator facility at Hokkaido University. Theinset presents the convertible source system of thermal neutron and X-ray.accelerator-based convertible source system for neutrons and X-rays has been installedat Hokkaido University facility. In this paper, we explain about the configuration of thesource system, and show the first result of the complementary radiography with thissystem.2. – Convertible source systemA schematic view of the 45MeV electron linear accelerator facility at HokkaidoUniversity is shown in fig. 1. A convertible source system of thermal neutron and X-ray was newly installed on a center beam line in 2014. As shown in the inset of fig. 1,the source system mainly consists of two production targets, a polyethylene moderator,graphite reflectors, lead shield, boron-resin shields. We can choice the alternative ofneutron and X-ray sources by remote control when the positions of the targets with re-spect to the electron beam axis are changed by moving up (or down) a stage, where theswitching time is several minutes. The source system, therefore, allows us to do imagingmeasurements using both beams without a change of sample and detector positions.2.1. X-ray source. – The cross-sectional view of the X-ray source is shown in fig. 2(a).The X-ray production target is a copper plate with a thickness of 4mm that is tilted at 60◦Electron beamX-ray beamX-ray production target Water-cooling beam dumpLead shield Lead shield Lead shield Lead shield Graphite reflectorShieldElectron beamThermal neutron beamNeutron production targetPolyethylene moderatorShieldShieldLead(a) (b) Fig. 2. – Cross-sectional views of the X-ray (a) and neutron production targets (b).CONVERTIBLE SOURCE SYSTEM OF THERMAL NEUTRON AND X-RAY ETC. 310-810-710-610-510-410-2 10-1 100 101Intensity [a.u.]Eγ [MeV](a) 10-710-610-510-410-310-210-110010110210-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101Intensity [a.u.]En [MeV](b) Fig. 3. – Calculated energy distributions of the X-ray (a) and neutron beams (b).with respect to the electron beam axis. Bremsstrahlung photons are generated by hittingthe copper plate with the 9MeV electron beam and then extracted to the experimentalroom as the X-ray beam in the direction perpendicular to the electron beam axis. Forsuppressing neutron backgrounds in the X-ray beam, the energy of electron beam is setbelow the threshold of the 63,65Cu(γ,n) reactions. The energy distribution of the X-raybeam which was calculated with the PHITS code [5] is shown in fig. 3(a). The peakenergy of the X-ray beam is estimated to be around 0.1MeV. For the simulation, thepencil-like electron beam with a diameter of 1 cm and the energy of 9MeV was definedas an initial source. The incident electrons induced the bremsstrahlung photons in thecopper plate. The emitted photons were counted at the distance of 1 m between theelectron beam axis and the tally surface.2.2. Thermal neutron source. – The cross-sectional view of the thermal neutron sourceis shown in fig. 2(b). In the neutron production, the bremsstrahlung photon is alsogenerated in a similar manner as the X-ray source. The higher energy electron beam,however, is used to induce the photonuclear reactions of lead isotopes by the generatedphotons. After the photons are generated by hitting a 4-mm-thick tungsten disc with the34MeV electron beam, the neutrons are produced in the thick lead blocks by the photonu-clear reactions. The produced neutrons are thermalized with a polyethylene moderator(12 cm × 12 cm × 5 cm) which is surrounded graphite reflectors at room temperature.The thermalized neutrons are extracted as neutron beam through the exit aperture withan area of 10 cm × 10 cm in the perpendicular direction to the electron beam axis asshown in fig. 2(b). Three lead blocks which are mounted in the graphite reflectors area shield to prevent the bremsstrahlung photons from entering into the neutron beamcourse. The energy distribution of the neutron beam, which was also calculated with thePHITS code, is shown in fig. 3(b). The distribution ranges from 0.01 eV to 10MeV andthe peak energy is 0.03 eV. A point neutron source with the Maxwell-Boltzmann distri-bution of kT = 1.3MeV was defined at the neutron production target as an initial sourcebecause of the computed time limitations. The thermal neutrons emitted from the mod-erator were counted at the distance of 1m between the electron beam axis and the tallysurface.3. – Test measurements for a complementary imagingTest measurements were performed to demonstate a complementary imaging by usingthe convertible source system. A detector based on a Gd-type neutron image intensifier(TOSHIBA UltimageTM-nγ-04) [6, 7] was applied to the sources for the purpose of dualuse, where a digital camera (CANON EOS 5D markII) was used as an image recorder.4 T. KAMIYAMA et al.Steel canResin exterior label+ -SeparatorAnode current collectorAnode CathodeMetal washerPlastic sealing gasket(d) (c)  )b( )a(Fig. 4. – Radiography images of the C-size alkaline battery measured with the X-ray (a) andneutron beams (b). (c) shows the result which is divided the brightness value of (a) by the oneof (b) at each pixel. An illustration of typical alkaline battery (d) is presented for comparison.The distance between the source (i.e., the electron beam axis) and the detector wasapproximately 6m. A sample, alkaline battery, was located on the front of the inputwindow of the detector. Each measurement time was 20minutes.Figures 4(a) and (b) present the images that were measured with the X-ray and neu-tron beams, respectively. The brightness values of the images can be directly comparedowing to the complementary imaging. The result which is divided the brightness valueof fig. 4(a) by the one of (b) at each pixel is shown in fig. 4(c). A difference betweenthe images measured with the X-ray and neutron beams is clearly observed on the rightside. It implicates that the substance of the portion is including hydrogen since theportion is radiopaque for neutrons and radiolucent for X-rays. For comparison, a typicalalkaline battery is also illustrated in fig. 4(d). A plastic sealing gasket is generally embed-ded in the battery on the negative terminal side to vent interior gas pressure for safetyreasons.In the test measurements, the neutron time-of-flight (TOF) method was not applied,although the electron accelerator was operated at a repetition rate of 50Hz and pulsewidth of 3μs. Therefore, more detailed information about substances of a sample wouldbe obtained from the neutron TOF images by utilizing the detector combined with otherrecorders such as a high-speed camera. In addition, the γ-flash event contaminated inthe neutron beam would be distinguished.4. – ConclusionThe convertible source system for the neutron and the X-ray imagings has been in-stalled in the 45MeV electron linear accelerator facility at Hokkaido University. Thesystem allows us to selectively use both beams without change of sample and detectorpositions. We demonstrated the test measurements to present that the convertible sourcesystem is very useful for the complementary imaging. As the results, the different imagesfor the same sample were obtained with the neutron and X-ray beams. Moreover, theenhanced contrast could be simply obtained by comparing the brightness value of bothimages at the same pixel. Further work is carrying on adding the neutron TOF mea-surements in combination with the X-ray radiography in order to provide more detailedinformation about substances and structures of a sample.CONVERTIBLE SOURCE SYSTEM OF THERMAL NEUTRON AND X-RAY ETC. 5∗ ∗ ∗The research is supported under the Photon and Quantum Basic Research Coordi-nated Development Program by the Ministry of Education, Culture, Sports, Science andTechnology (MEXT), Japan.REFERENCES[1] Harvel G. D. et al., Nucl. Instrum. Methods A, 371 (1996) 544.[2] Banhart J. et al., Int. J. Mater. Res., 101 (2010) 1069.[3] Kamiyama T. et al., Nucl. Instrum. Methods A, 651 (2011) 28.[4] de Beer F. C. et al., Nucl. Instrum. Methods A, 542 (2005) 1.[5] Sato T. et al., J. Nucl. Sci. Technol., 50 (2013) 913.[6] Nitto K. et al., Nucl. Instrum. Methods A, 535 (2004) 686.[7] Kamiyama T. et al., Phys. Procedia, 26 (2012) 231.

Convertible source system of thermal neutron and X-ray at Hokkaido University electron linac facility

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Convertible source system of thermal neutron and X-ray at Hokkaido University electron linac facility

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