The properties of parametric X-ray radiation (PXR) emitted from a wedge-shaped Si(111) crystal plate were experimentally investigated using the PXR generator at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. The wedge surface was imposed on a symmetric-cut Si(111) plate and has an asymmetric cut-surface with respect to the (111) crystal planes. As a result of the experiment, it was found that the PXR intensity improved can be obtained suppressing the degradation of the X-ray performance using a wedgeshaped

target. With this improvement, phase-contrast images without absorption contrast could be obtained from DEI images taken with the exposure of severalten seconds. The reduction of the exposure time made it possible to carry out a computed tomography (CT) experiment by DEI within a practical machine time, and phase-contrast tomograms of a biological sample were obtained at the PXR energy of 17.5 keV

Hayakawa, K.

Hayakawa, Y.

Inagaki, M.

Kuwada, T.

Nakao, K.

Nogami, K.

Sato, I.

Takahashi, Y.

Tanaka, T.

English

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2011-10910-2Colloquia: Channeling 2010IL NUOVO CIMENTO Vol. 34 C, N. 4 Luglio-Agosto 2011Improvement in the performance of the X-ray source based onparametric X-ray radiation using a wedge-shaped target crystalY. Hayakawa(1)(2)(∗), K. Hayakawa(1)(2), M. Inagaki(1)(2), T. Kuwada(1)(3),K. Nakao(1)(2), K. Nogami(1)(2), I. Sato(1)(4), Y. Takahashi(1)(3)and T. Tanaka(1)(2)(1) Laboratory for Electron Beam Research and Application, Nihon University7-24-1 Narashinodai, Funabashi, 274-8501 Japan(2) Institute of Quantum Science, Nihon University - 7-24-1 Narashinodai, Funabashi274-8501 Japan(3) Research Institute of Sciences and Technology, Nihon University - 7-24-1 NarashinodaiFunabashi, 274-8501 Japan(4) Advanced Research Institute for the Sciences and Humanities, Nihon University12-5 Gobancho, Chiyoda-ku, Tokyo, 102-8251 Japan(ricevuto il 22 Dicembre 2010; pubblicato online il 7 Luglio 2011)Summary. — The properties of parametric X-ray radiation (PXR) emitted from awedge-shaped Si(111) crystal plate were experimentally investigated using the PXRgenerator at the Laboratory for Electron Beam Research and Application (LEBRA)of Nihon University. The wedge surface was imposed on a symmetric-cut Si(111)plate and has an asymmetric cut-surface with respect to the (111) crystal planes.As a result of the experiment, it was found that the PXR intensity improved canbe obtained suppressing the degradation of the X-ray performance using a wedge-shaped target. With this improvement, phase-contrast images without absorptioncontrast could be obtained from DEI images taken with the exposure of several-ten seconds. The reduction of the exposure time made it possible to carry out acomputed tomography (CT) experiment by DEI within a practical machine time,and phase-contrast tomograms of a biological sample were obtained at the PXRenergy of 17.5 keV.PACS 41.60.-m – Radiation by moving charges.PACS 41.50.+h – X-ray beams and x-ray optics.PACS 87.59.-e – X-ray imaging.(∗) E-mail: yahayak@lebra.nihon-u.ac.jpc© Societa` Italiana di Fisica 253254 Y. HAYAKAWA, K. HAYAKAWA, M. INAGAKI, ETC.Fig. 1. – Schematic top view of the LEBRA-PXR generator equipped with a double-crystalsystem for tunability and its dedicated beamline.1. – IntroductionA novel X-ray source based on parametric X-ray radiation (PXR) has been conductedat the Laboratory for Electron Beam Research and Application (LEBRA), Nihon Uni-versity. The PXR source, which is equipped with a double-crystal system for tunabilityas shown in fig. 1, has been installed in a dedicated beamline connecting to a 125MeVelectron linac, and its tunable monochromatic X-ray beam has actually provided to userapplications [1-3]. So far, the PXR beam in an energy range from 5 to 34 keV has beenproduced, using Si(111) or Si(220) planes as the radiation source [4, 5]. Since the PXRbeam obtained from the LEBRA-PXR source has a large irradiation field, 100mm in di-ameter, X-ray imaging at various X-ray energies have been the most popular applicationperformed [6]. In particular, results of diffraction-enhanced imaging (DEI), which is asort of X-ray phase-contrast imaging, have demonstrated the high performance of PXRwith respect to spatial coherence [7, 8].Due to the low repetition rate of the LEBRA linac, however, the average currentof the electron beam is less than 5μA. Thus, the properties of PXR emitted fromasymmetrically cut target crystals have recently been studied to improve the intensity ofthe X-rays [9-11]. As the result of the increase of the available PXR intensity from thedouble-crystal system, the exposure required for adequate-quality imaging using ordinaryimage sensors such as an imaging plate has been reduced to several ten seconds [12]. Thecurrent specifications of the LEBRA-PXR source are listed in table I [13].2. – Multi-beam effect at the edge of the targetOrdinary silicon perfect-crystal wafers with symmetric cut-surfaces have been usedas the target crystal for PXR production since the advent of the LEBRA PXR source.Recently, target crystals with asymmetric cut-surfaces have been tested to increase theavailable X-ray yield. Figure 2(a) shows drawings of the symmetric and asymmetrictarget crystals. However, serious problems due to the geometrical effect of the targetcrystal have been found in both cases. When the edge of the target was irradiated with anelectron beam, a strong image blur was observed in the imaging with a long propagationas shown in fig. 2(b) [14]. This phenomenon seems to result from the contributions oftwo X-ray beams at slightly different directions. Naturally, this effect seriously affectsexperiments requiring high accuracy such as DEI.IMPROVEMENT OF PXR PERFORMANCE USING A WEDGE-SHAPED TARGET CRYSTAL 255Table I. – Typical parameters of the linac and the PXR generator of LEBRA.Typical electron energy 100MeVAccelerating frequency 2856MHz (S-band)Macropulse beam current 120–135mAMacropulse duration 4–10μsMacropulse repetition rate 2–5 ppsBunch length ∼ 3 psAverage beam current at the linac exit 1–5μARange of the Bragg angle 5.0–30◦PXR energy range Si(111) target: 4.0–21 keVSi(220) target: 6.5–34 keVIrradiation field size at the X-ray exit 100mm in diameterTotal X-ray photon rate 106–108 /s3. – Wedge-shaped crystal targets for PXR generationAlthough the experimental results have suggested that the use of an asymmetric cut-surface has an advantage in terms of increasing the PXR intensity, the deterioration dueto the multi-beam effect, which seems to depend on the side and reverse surfaces atthe target edge, reduces the performance of the X-ray beam. Thus, new wedge-shapedcrystal plates as shown in fig. 3(a) have been prepared to solve the problem and havebeen experimentally tested as PXR targets. An asymmetric cut-surface was made as awedge-shaped surface on a symmetrically cut Si(111) plate. One of the wedge-shapedtargets has a 1.15◦ wedge angle and the other has a 6.5◦ angle. Therefore, these targetshave asymmetric cut-surfaces on the front side with asymmetric angles of 1.15◦ and 6.5◦,respectively. In particular, the incident electrons graze the target at the PXR energy of17.5 keV using the 6.5◦ wedge-shaped crystal.In the imaging experiments using the same setup as in fig. 2(b), the image blur wassuppressed using the new wedge-shaped targets. Figure 3(b) shows a typical result ofthe imaging experiments. Shaping the target edge as a wedge is a practical method forimproving the PXR imaging quality.Fig. 2. – (a) Si target crystals with symmetric and asymmetric cut-surfaces with respect to the(111) plane. (b) Image blur observed in the imaging experiment with 2.2m propagation betweenthe sample (IC gauge) and the detector (imaging plate).256 Y. HAYAKAWA, K. HAYAKAWA, M. INAGAKI, ETC.Fig. 3. – (a) Sketch of new wedge-shaped crystal plates for PXR targets with wedge angles of1.15◦ and 6.5◦. (b) A typical image observed in the same setup as in fig. 2(b) but using awedge-shaped crystal target.In addition to the imaging performance, the available X-ray yield was investigatedusing the wedge-shaped targets. The reverse case of the 6.5◦ wedge-shaped target, inwhich the symmetric cut-surface faces the incident electrons, was also tested as thereference. The relative PXR intensity from the double-crystal system using each targetwas measured using an ionizing-mode solid-state detector depending on the angle of the2nd reflector crystal. These rocking curves at the PXR energy of 17.5 keV are shown infig. 4(a). When the asymmetric cut-surface of the wedge-shaped edge faced the incidentelectrons, the widths of the rocking curves became narrower than that of the reverse case.In the front cases, therefore, the curves have higher peaks especially when the wedgeangle is 6.5◦. Since the LEBRA-PXR source is based on the double-crystal system, thepeak height of the 2nd crystal’s rocking curve represents the maximum X-ray yield thatFig. 4. – (a) The intensities of PXR from the double-crystal PXR generator using the newwedge-shaped targets measured as functions of the 2nd crystal’s angle. (b) A typical PXRimage obtained at the peak intensity of 17.5 keV using a flat-panel detector with 10 s exposure,where the average current of the electron beam at the target was 2.6μA.IMPROVEMENT OF PXR PERFORMANCE USING A WEDGE-SHAPED TARGET CRYSTAL 257Fig. 5. – (a) The setup of the DEI experiment using the LEBRA-PXR source, where the phase-shift of X-rays due to the sample can be detected as the refraction angle of the X-rays usingan analyzer of perfect crystal. (b) The typical DEI images of a mouse kidney obtained at theanalyzer angles marked A and B on the rocking curve. (c) The absorption-contrast (left) andthe phase-contrast (right) images obtained as the sum and difference of the two DEI images.can be used for applications. Using the maximum yield at the energy of 17.5 keV withthe 6.5◦ wedge-shaped target, ordinary X-ray images could be obtained with relativelyshort exposure times. The typical absorption image obtained using a flat-panel detector,which has a pixel size of 50μm × 50μm, with 10 s exposure is shown in fig. 4(b). If wecan increase the electron beam current several times and/or use a detector with higherefficiency and lower noise, semi-real-time imaging with a frame rate of 1 /s may bepossible in this condition.4. – Computed tomography based on the DEI methodSince the image blur is suppressed and the available X-ray yield from the double-crystal system increases using the wedge-shaped target, the exposure required by obtain-ing the phase-contrast image by the DEI method is also reduced to several ten seconds.Figure 5(a) explains the DEI experiment using the LEBRA-PXR source, and the typical258 Y. HAYAKAWA, K. HAYAKAWA, M. INAGAKI, ETC.Fig. 6. – The tomograms reconstructed from 90 DEI projections obtained as shown in fig. 5.The total exposure was estimated to be 90min.DEI images of a biological sample are shown in fig. 5(b). Since DEI images provide theinformation about the X-ray refraction according to the analyzer angle, one can sepa-rate the absorption-contrast and the phase-contrast by calculating 2 DEI images [15,16].Figure 5(c) shows the sum and the difference of these DEI images, corresponding tothe absorption-contrast and the phase-contrast images, respectively. Here, the exposuretime of DEI images using an X-ray CCD camera was 30 s, and the total measurementtime to obtain one phase-contrast image was 60 s. Since the image blur due to themulti-beam effect seriously disturbs the separation of phase-contrast from absorption-contrast, the use of a wedge-shaped target significantly improved the efficiency of suchexperiments.In principle, computed tomography (CT) experiments based on the DEI method canbe performed by rotating the sample. The reduced exposure required to obtain phase-contrast images makes such experiments practically possible within a machine time of theLEBRA linac. Actually, the DEI-CT experiment was carried out by a 2◦ angular step forthe sample rotation, and the resulting tomograms reconstructed from 90 DEI projectionsare shown in fig. 6. Each projection was obtained in the same condition as fig. 5, andthe total net measurement time was estimated to be 90min. Although the artifact noisestill remains in the tomogram, the differential images were actually obtained excludingthe X-ray absorption. Unfortunately, the measurement system for the CT experimentshas not yet been automatized, and the efficiency of the experiment is restricted by themanual work of data taking. It is expected that higher-quality tomograms for the samemachine time could be obtained if an automatic measurement system were developed forthe DEI-CT experiment.5. – ConclusionUsing crystal plates with a wedged-shaped edge as the PXR target, the PXR in-tensity was improved suppressing the image blur due to the multi-beam effect of PXRemitted from the target edge. Due to this improvement, phase-contrast images withoutabsorption contrast could be obtained from DEI images taken with an exposure of sev-eral ten seconds. The reduction of the exposure time made it possible to carry out CTexperiments by DEI within a practical machine time, and phase-contrast tomograms ofIMPROVEMENT OF PXR PERFORMANCE USING A WEDGE-SHAPED TARGET CRYSTAL 259a biological sample were achieved at the PXR energy of 17.5 keV. To our knowledge, thisis the first case of successful phase-contrast CT using PXR.∗ ∗ ∗This study on radiators of PXR was supported by by MEXT.KAKENHI (21686088).Studies on the imaging technique were also supported in part by MEXT.KAKENHI(21560055) andNihonUniversityMultidisciplinaryResearchGrant for 2009 (Sogo 09-024).REFERENCES[1] Hayakawa Y., Sato I., Hayakawa K. and Tanaka T., Nucl. Instrum. Methods B, 227(2005) 32.[2] Sakae T., Hayakawa Y., Mori A., Kuwada T., Sakai T., Nogami K., Tanaka T.,Hayakawa K. and Sato I., J. Miner. Petrol. Sci., 101 (2006) 10.[3] Inagaki M., Hayakawa Y., Nogami K., Tanaka T., Hayakawa K., Sakai T., NakaoK. and Sato I., Jpn. J. Appl. Phys., 47 (2008) 8081.[4] Hayakawa Y., Sato I., Hayakawa K., Tanaka T., Mori A., Kuwada T., Sakai T.,Nogami K., Nakao K. and Sakae T., Nucl. Instrum. Methods B, 252 (2006) 102.[5] Hayakawa Y., Hayakawa K., Inagaki M., Kuwada T., Mori A., Nakao K., NogamiK., Sakae T., Sakai T., Sato I., Takahashi Y. and Tanaka T., in Proceedings ofSPIE Vol. 6634: International Conference on Charged and Neutral Particles ChannelingPhenomena II (Rome), edited by Dabagov S. B. (SPIE, Washington) 2007, p. 663411.[6] Sakae T., Takahashi Y., Hayakawa Y., Tanaka T., Hayakawa K., Kuwada T.,Nakao K., Nogami K., Inagaki M., Sato I., Fukumoto M., Makimura M. andYamamoto H., J. Hard Tissue Biol., 19 (2010) 131.[7] Fitzgerald R., Phys. Today, 53 (2000) 23.[8] Takahashi Y., Hayakawa Y., Kuwada T., Sakai T., Nakao K., Nogami K., InagakiM., Tanaka T., Hayakawa K. and Sato I., in AIP Conference Proceedings 1221 “X-RayOptics and Microanalysis”, edited by Denecke M. and Walker C. T. (AIP, New York)2010, p. 119.[9] Feranchuk I. D. and Feranchuk S. I., Eur. Phys. J. Appl. Phys., 38 (2007) 135.[10] Blazhevich S. V. and Noskov A. V., Nucl. Instrum. Methods B, 266 (2008) 3777.[11] Lobko A. S., Nasonov N., Park H., Piestrup M. and Zhukova P., in Proceedings ofSPIE Vol. 6634: International Conference on Charged and Neutral Particles ChannelingPhenomena II (Rome), edited by Dabagov S. B. (SPIE, Washington) 2007, p. 663417.[12] Hayakawa Y., Hayakawa K., Inagaki M., Kuwada T., Nakao K., Nogami K.,Sakai T., Sato I., Takahashi Y. and Tanaka T., in Proceedings of the 51st Workshopof the INFN Eloisatron Project “Charged and Neutral Particles Channeling Phenomena”Channeling 2008, edited by Dabagov S. B. and Palumbo L. (World Scientific, Singapore)2010, p. 677.[13] Tanaka T., Hayakawa K., Hayakawa Y., Kuwada T., Sakai T., Nakao N.,Takahashi Y., Nogami K., Inagaki M. and Sato I., in AIP Conference Proceedings 1234“SRI09 (The 10th International Conference of Synchrotron Radiation Instrumentation)”,edited by Garrett R., Gentle I., Nugent K. and Wilkins S. (AIP, New York) 2010,p. 587.[14] Hayakawa Y., Hayakawa K., Inagaki M., Kuwada T., Nakao K., Nogami K., SakaeT., Sakai T., Sato I., Takahashi Y. and Tanaka T., Nucl. Instrum. Methods B, 266(2008) 3758.[15] Davis T. J., Gao D., Gureyev T. E., Stevenson A. W. and Wilkins S. W., Nature,373 (1995) 595.[16] Ando M., Sugiyama H., Maksimenko A., Pattanasiriwisawa W., Hyodo K. andZhan X., Jpn. J. Appl. Phys., 40 (2001) L844.

Improvement in the performance of the X-ray source based on

parametric X-ray radiation using a wedge-shaped target crystal

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Improvement in the performance of the X-ray source based on parametric X-ray radiation using a wedge-shaped target crystal

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