Mitsuru Uesaka

Dual-Energy X-Ray CT by Compton Scattering Hard X-Ray Source

We are developing a compact Compton scattering hard X-ray source by the X-band linac and YAG lasers at Nuclear Professional School, University of Tokyo. The compact hard X-ray source can produce tunable monochromatic hard X-rays for 10 - 40 keV. The monochromatic hard X-rays are very useful in large fields of medical and biological sciences. We are planning to carry out dual-energy X-ray CT, which enables us to obtain 3D distribution of effective atomic number Zeffand electron density ρein a matter. The hard X-ray source has an advantage in the dual-energy X-ray CT. The X-ray energy can be changed quickly by introducing a fundamental-frequency and a second-harmonic-frequency lasers. It is indispensable to change the X-ray energy quickly for medical imaging, but it is very difficult to achieve the quickness with a large SR light source and others. The information on the atomic number and electron density will be used for radiation treatment planning as well as for identification of materials in a nondestructive test. We examined applicability of the dual-energy X-ray CT for low to medium Z elements (Z ≤ 38) by considering the X-ray energy profile generated by the Compton scattering hard X-ray source.

Numerical study of dielectric laser acceleration of nonrelativistic electrons with colonnade structure

Dielectric laser acceleration of electrons has been demonstrated recently with the potential to miniaturize accelerators. Here, we present results of the numerical investigation of a silicon colonnade structure that consists of two rows of pillars for the acceleration of nonrelativistic electrons. The dual-sided structure is expected to produce a maximum ratio of 0.52 between the acceleration gradient and the incident electric field for 50 keV electrons.

Laser Driven Dielectric Accelerator in the Non-relativistic Energy Region

Laser-driven dielectric accelerator (LDA) is suitable for delivering a submicron-size ultra-short electron beam, which is useful for studying basic processes of the radiation effect in a biological cell. Both the oblique incidence and the normal incidence configurations of LDA were studied. The oblique incidence configuration of LDA relaxes the synchronization condition as ve = ±cLG/ (λ + LGn sin θ) and is somewhat suitable for accelerating the non-relativistic electrons. The required energy to accelerate electrons in the oblique incidence configuration is smaller than that in the normal incidence configuration by a factor of cos θ, where θ is the incidence angle of the laser beam. Two gratings each were made of different material structure of silica (SiO2) were fabricated by the electron beam lithography. When a crystal silica was adopted, many large humps of several hundred nm size were observed in grooves of the grating. On the other hand, a glass silica had smoother grooves.

X-Band Linac Beam-Line for Medical Compton Scattering X-Ray Source

Compton scattering hard X-ray source for 10-40 keV are under construction using the X-band (11.424 GHz) electron linear accelerator and YAG laser at Nuclear Engineer ing Research laboratory, University of Tokyo. This work is a part of the national project on the development of advanced compact medical accelerators in Japan. National Institute for Radiological Science is the host institute and U. Tokyo and KEK are working for the X-ray source. Main advantage is to produce tunable monochromatic hard (10-40 keV) X-rays with the intensities of 108-109photons/s (at several stages) and the table-top size. In addition, dual energy monochromatic X-ray source can be realized that generate two monochromatic hard X-ray by turin with high (up to 10 pps) repetition rate by one X-ray source. The X-ray yield by the electron beam and Q-switch Nd: YAG laser of 2.5 J/10 ns is 107photons/RF-pulse (108photons/sec in 10 pps). X-band beam line for the demonstration is under commissioning. We also design to adopt a technique of laser circulation to increase the X-ray yield up to 108photons/pulse (109photons/s).