Hideaki Ohgaki

Slow Positron Pulsing System for Variable Energy Positron Lifetime Spectroscopy

A positron pulsing system has been constructed for variable energy positron lifetime spectroscopy. The system consists of a reflection type chopper, a sub-harmonic prebuncher, and a double harmonic buncher. By operating the system with an intense slow positron beam generated by an electron linac, positron lifetime spectra have been successfully measured in an extended time range of more than 45 ns with a good time resolution (250 ps). Furthermore, Doppler broadening profiles of annihilation radiations can be obtained simultaneously with the lifetime measurements.

First lasing of the NIJI-IV storage-ring free-electron laser

Abstract The first lasing at around 590 nm of a free-electron laser (FEL) in the storage ring NIJI-IV was achieved on August 18, 1992, though just above threshold. The NIJI-IV is a racetrack-type ring dedicated to FEL, which was completed in December 1990. Though the ring is compact, it has two 7.25-m straight sections. The electron beam was stacked for the first time in February 1991. After a 6.3-m optical klystron was installed in one of the straight sections, FEL related experiments were started at the end of April this year, and oscillation experiments have been carried out since the beginning of August. The electron-beam energy during the lasing was about 240 MeV, and the current was 1.1−0.2 mA/bunch. The laser wavelength ranged from 594.5 to 588.7 nm, and the bandwidth was below 0.4 nm.

Measurement of laser-induced Compton backscattered photons with anti-Compton spectrometer

Quasi-monochromatic photons of energies of 1.6-8.7 MeV have been generated by the Compton backscattering of laser light on relativistic electrons in the TERAS storage ring. The spectra of the backscattered photons have been measured with an anti-Compton spectrometer system. The present system has a 155-cm/sup 3/ a coaxial-type pure-Ge detector as the central detector and a well-type NaI(Tl) scintillator of 8-in phi *8-in as the outer one. With a usual anticoincidence technique, clear photopeak spectra were obtained with a Compton suppression ratio of 2-4. The maximum energy and the energy spread of photons show reasonable agreement with numerical calculations. The divergence and energy spread of the electron beam in the storage ring are estimated from the data. >

Generation and application of Laser-Compton gamma-ray at ETL

Abstract Laser-Compton gamma-ray facility has been developed at Electrotechnical Laboratory. Generation of the Laser-Compton gamma-ray and its applications for the establishment of the standard field of high-energy gamma-rays, for the nuclear physics research and for the beam diagnostic of the electron beam circulating in the storage ring is presented.

Nondestructive Detection of Heavily Shielded Materials by Using Nuclear Resonance Fluorescence with a Laser-Compton Scattering γ-ray Source

We perform a proof-of-principle experiment for a nondestructive method for detecting the elemental and isotopic composition of materials concealed by heavy shields such as iron plates with a thickness of several centimeters. This method uses nuclear resonance fluorescence (NRF) triggered by an energy-tunable laser-Compton scattering (LCS) γ-ray source. One-dimensional mapping of a lead block hidden behind 1.5-cm-thick iron plates is obtained by measuring an NRF γ-ray of a lead isotope 208Pb. We observe a 5512-keV γ-ray from 208Pb excited by the quasi-monochromatic LCS γ-rays with energies up to 5.7 MeV. The edge position of the lead block is consistent with the exact position within the uncertainty.

Simultaneous measurement of the photodisintegration of He-4 in the giant dipole resonance region

We have performed for the first time the simultaneous measurement of the two-body and three-body photodisintegration cross sections of

Linearly polarized photons from Compton backscattering of laser light for nuclear resonance fluorescence experiments

^{4}\mathrm{He}

Characterization of Hydrogenated Amorphous Silicon Films by a Pulsed Positron Beam

in the energy range from 21.8 to 29.8 MeV using monoenergetic pulsed photons and a 4\ensuremath{\pi} time projection chamber containing

Positronium formation in SiO2 films grown on Si substrates studied by monoenergetic positron beams

^{4}\mathrm{He}

Lasing in visible of a storage-ring free electron laser at ETL

gas as an active target in an event-by-event mode. The photon beam was produced via the Compton backscattering of laser photons with high-energy electrons. The