Kyoko Nogami

Wavelength Dispersive X-ray Absorption Fine Structure Imaging by Parametric X-ray Radiation

The parametric X-ray radiation (PXR) generator system at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University is a monochromatic and coherent X-ray source with horizontal wavelength dispersion. The energy definition of the X-rays, which depends on the horizontal size of the incident electron beam on the generator target crystal, has been investigated experimentally by measuring the X-ray absorption near edge structure (XANES) spectra on Cu and CuO associated with conventional X-ray absorption imaging technique. The result demonstrated the controllability of the spectrum resolution of XANES by adjusting of the horizontal electron beam size on the target crystal. The XANES spectra were obtained with energy resolution of several eV at the narrowest case, which is in qualitative agreement with the energy definition of the PXR X-rays evaluated from geometrical consideration. The result also suggested that the wavelength dispersive X-ray absorption fine structure measurement associated with imaging technique is one of the promising applications of PXR.

Observation of intense terahertz-wave coherent synchrotron radiation at LEBRA

We observed intense coherent synchrotron radiation (CSR) in the terahertz region using an S-band linac at the Laboratory for Electron Beam Research and Application at Nihon University. The evolution of the CSR power was measured, and the CSR reflected in the vacuum chamber of the bending magnet could be extracted through the quartz window for a few tens of picoseconds. The long wave packet of the delayed CSR in the autocorrelation suggests that the delayed CSR was the non-resonant ring-down of the vacuum chamber of the bending magnet. To design a high-energy accelerator, it is necessary to decrease high-energy photons resulting from Compton backscattering with intense CSR.

Phase Contrast Imaging of Biological Materials using LEBRA‐PXR

Phase contrast x‐ray imaging is an important technique for investigation of materials consisted of light atoms, such as soft biological tissues. The tunable monochromatic x‐ray source based on Parametric X‐ray Radiation (PXR), which was developed at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University, provides x‐rays with a high spatial coherence which is an essential property required for phase contrast imaging. In preliminary experiment, refraction contrast images for leaf tissues of a tree and animal specimen have been obtained successfully with the LEBRA‐PXR x‐rays. In the imaging system, the x‐ray that passed through the sample once reflects off the silicon perfect‐crystal x‐ray analyzer at the Bragg angle, and then enters the imaging plate. The bright‐field and the dark‐field phase contrast images have been obtained by infinitesimal rotations of the analyzer, showing the evidence of contrast reversal. Although the conventional radiograph by absorption contrast was also taken with the LEBRA‐PXR, significant differences are found between the radiograph and the phase contrast images.Phase contrast x‐ray imaging is an important technique for investigation of materials consisted of light atoms, such as soft biological tissues. The tunable monochromatic x‐ray source based on Parametric X‐ray Radiation (PXR), which was developed at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University, provides x‐rays with a high spatial coherence which is an essential property required for phase contrast imaging. In preliminary experiment, refraction contrast images for leaf tissues of a tree and animal specimen have been obtained successfully with the LEBRA‐PXR x‐rays. In the imaging system, the x‐ray that passed through the sample once reflects off the silicon perfect‐crystal x‐ray analyzer at the Bragg angle, and then enters the imaging plate. The bright‐field and the dark‐field phase contrast images have been obtained by infinitesimal rotations of the analyzer, showing the evidence of contrast reversal. Although the conventional radiograph by absorption contrast was also ...

Tunable Monochromatic X‐ray Source Based on Parametric X‐ray Radiation at LEBRA, Nihon University

The monochromatic X‐ray source based on parametric X‐ray radiation (PXR) was developed by using the electron beam from the 125‐MeV linac at Nihon University. The X‐ray generating system consists of two silicon perfect‐crystal plates to offer a wide tunability. The system has actually been providing the energy dispersive monochromatic X‐ray beam in the region of 6 to 20 keV, using Si(111)‐plane for the target and the second crystals. Since the X‐ray beam from the PXR generator has rather high energy resolution and coherency, X‐ray absorption fine structure (XAFS) measurement and phase‐contrast imaging are possible applications of PXR. Actually, preliminary experiments on energy dispersive XAFS measurement and refraction‐contrast imaging have been successfully carried out using the PXR beam.

Phase‐contrast imaging with a novel X‐ray source

A novel X‐ray source based on Parametric X‐ray radiation (PXR) has been employed for phase‐contrast imaging at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, Japan. The PXR X‐rays were generated by the 100 MeV electron beam passing through a Si single crystal. The X‐rays in the 16∼34 keV range were chosen for imaging of biological samples. The quasi‐monochromatic, tunable, and coherent X‐ray source is appropriate for this application. In addition, the large X‐ray beam irradiation field of approximately 100 mm in diameter, which was achieved without special optics, suggests that the PXR is applicable to imaging for medical diagnostics.

Millijoule terahertz coherent transition radiation at LEBRA

We developed an intense coherent transition radiation (CTR) at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. A rectangular titanium screen with dimensions of 80 × 60 mm2 was used as the target, and the backward CTR generated on the screen was extracted through a crystal quartz window to air. We observed an intense terahertz (THz) radiation and confirmed it to be the CTR by measuring the spatial distribution and the dependence of the power on the electron charge. The CTR spectrum measured using a Martin–Puplett-type interferometer showed a maximum at a frequency of 0.3 THz and was emitted up to 1.6 THz. The CTR energy and peak power of a micropulse were approximately 80 nJ and 100 kW, respectively. The CTR energy during a 4.5 µs macropulse was approximately 1 mJ, indicating that this broadband THz light source is one of the most powerful coherent radiation sources in normal conducting linac facilities.

Performance and Application of FEL and PXR Sources at Nihon University

The infrared free electron laser (FEL) and the parametric X‐ray radiation (PXR) developed on the basis of the 125 MeV electron linac at Nihon University have been applied to studies in a variety of scientific fields. Primary users so far are the faculty members in the university, approximately 2000 hr/year of the machine time having been dedicated to the experiments since 2004. Currently the wavelength range of the FEL served for users’ experiments covers 1500 to 6000 nm at the optical power level of 10 to 30 mJ/macropulse. Combination of the fundamental infrared FEL with BBO non‐linear optical crystals yielded higher harmonics with good conversion efficiencies, which has extended the available wavelength range as short as approximately 400 nm. The PXR generator has employed a double‐crystal system so that the monochromatic X‐ray beam is available at a fixed output port independently of the X‐ray center energy. By using a Si(111) crystal as the PXR target the energy variable monochromatic X‐ray beam from ...

Development of ionization chamber for in-line intensity monitoring of large profile parametric X-ray beam

An in-line ionization chamber has been developed for the real-time measurement of the absolute intensity of the pulsed parametric X-ray (PXR) beam during irradiation experiments. The quasi-monochromatic PXR generating system was developed at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. In contrast to typical narrow X-ray beams in synchrotron radiation facilities, the PXR beam profile is as large as approximately 100 mm in diameter with rather uniform flux distribution at the X-ray output port in the experimental hall. The energy of the PXR beam ranges from 5 to 34 keV, which is specified by the PXR target crystal plane and its geometrical condition. The ionization chamber is of a plane parallel type employing 6-μm thick double-sided aluminum vapor-deposited polyester films for the plane electrodes through which the X-ray beam passes. The plane bias electrode has been placed at an equal distance of 25 mm from the two plane earth electrodes that act as the beam windows with an aperture diameter of 120 mm. Due to the pulsed property of the PXR beam and the geometrical configuration of the ionization chamber, the charge-sensitive preamplifier output pulse height represents an integral of the fast electron current, corresponding to a half of the total ionization charge produced by the beam. The intensity of the PXR beam has been measured for various X-ray energies by using nitrogen and argon, respectively, as the filling gas.

Simulation for THz coherent undulator radiation from combination of velocity bunchings

We study the effect of a combination of velocity bunchings and its application to THz coherent undulator radiation at LEBRA, Nihon U. by simulations. The velocity bunching is a technique that is commonly used to make the bunch length shorter at lower energies. However, since one velocity bunching has a correlation between bunch energy and length, we may not have so much room to change energies to obtain different coherent radiation wavelengths. Hence we propose a combination of velocity bunchings that relaxes the restrictive correlation. We have three 4 m traveling-wave accelerator tubes at LEBRA, Nihon U. The undulator is installed after the acceleration tubes and 2 × 45 degree bending magnets. Since the design of current undulator requires less than 25 MeV beam energy to obtain the radiation in THz region, the velocity bunching is reasonable for coherent radiation. We show the simulation results of a combination of velocity bunchings of the three tubes and the magnetic bunching at bending magnets, suitable for coherent undulator radiation.