Hideki Maezawa

Synchrotron radiation beamline to study radioactive materials at the Photon factory

Abstract Design and construction of a new beamline have been described. The beamline is housed in a specially designed area controlled for radioactive materials at the Photon Factory (PF) in the National Laboratory for High Energy Physics (KEK). The beamline system consists of a front-end and two branchlines. One of the branchlines is used for X-ray photoelectron spectroscopy and radiation biology in the energy range of 1.8-6 keV and the other for X-ray diffractometry and XAFS studies as well as radiation biology in the range of 4–20 keV. The former was particularly equipped for the protection against accidental scattering of radioactive materials both inside and outside of the vacuum system.

Current status of 10‐m GIM for soft x‐ray undulator at the Photon Factory

The current performance of a 10‐m grazing incidence monochromator (GIM) is described. A resolution of 51, 95, and 220 meV (FWHM) has been achieved at 287, 401, and 867 eV, respectively, inferred from the linewidths for the K‐shell resonances of gaseous CO, N2, and Ne. A photon flux of ≂1012 photons/s is obtainable at the first harmonic of undulator radiation with a 1200‐l /mm grating and 50‐μm slit openings, which correspond to Δλ=0.04 A.

A 10 m grazing incidence monochromator for high resolution soft X-ray spectroscopy at the photon factory

Abstract A description of a novel 10 m grazing incidence monochromator is given on the optical and the mechanical design features as well as on its performance achieved. The monochromator was designed and constructed at the Photon Factory for high resolution spectroscopic studies in the soft X-ray region.

F-K XANES Studies of Alkaline-Earth Fluorides

F-K X-ray absorption near edge structure (XANES) spectra of alkaline-earth fluorides have been measured with a high energy resolution using synchrotron radiation. Calculations for the observed XANES spectra have been also carried out by use of the short-range order multiple scattering theory. By comparing the observed spectra with the calculated results, we can estimate the effective anion charge distribution of -0.6, -0.65 and -0.795 for MgF 2 , CaF 2 and SrF 2 , respectively. These calculated F K-edge XANES spectra of alkaline-earth fluorides are more sensitive to the charge distribution than cation K-edge XANES.

X‐ray detection characteristics of microchannel plates using synchrotron radiation in the energy range from 0.06 to 0.6 keV

The characteristics of microchannel plates (MCPs) for x‐ray detection have been investigated with continuous x‐ray energy variation using synchrotron radiation in the XUV and soft x‐ray region (from 60 to 600 eV). The current response data have shown x‐ray absorption fine structure (EXAFS or XANES) near the oxygen K absorption edge as well as a jump structure near the silicon L edge; these structures are explained by the surface composition of channel walls (SiO2). The data show that the surface layer of a microchannel is essential for x‐ray detection by MCPs in this energy range. The precise current response curve has been completed for the wide x‐ray energy range from 0.06 to 82 keV combined with the previously reported data [Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988); Cho et al., ibid. 59, 2453 (1988); Yamaguchi et al., ibid. 60, 368, 2307 (1989)].

SiC mirror development at the Photon Factory (invited)

Several large‐size mirrors coated with a thin layer of CVD‐SiC for intense synchrotron radiation have been fabricated and commissioned at the Photon Factory. Substrates of these mirrors are high‐purity graphite, recrystallized SiC and sintered SiC. Detailed properties of mirror‐materials are described. First test of exposure of high‐power mirrors to intense radiation from the 53‐pole permanent‐magnet wiggler are briefly reported.

X‐ray detection characteristics of microchannel plates in the energy range from 1.8 to 8 keV

The characteristics of microchannel plates (MCPs) for detection of x rays have been investigated using synchrotron radiation in the energy range from 1.8 to 8 keV. The current response curve of MCPs is measured with approximately continuous x‐ray energy variation, which is added to the previous data [T. Kondoh et al., Rev. Sci. Instrum. 59, 252 (1988)]. It is confirmed that there is a minimum in the current response at the x‐ray energy of about 4 keV. The precise current response curve has been completed for the wide x‐ray energy range from 0.6 to 20 keV. A transition in the incident angle dependence of current response is found from the feature based on single cylindrical photocathode model for soft x rays to that based on multiple channel activation due to the penetration of x rays through channel walls for hard x rays. In the current response of MCPs the structure similar to that in EXAFS is observed near the Si K edge.

F-K XANES studies of alkali fluorides

F–K X-ray absorption near edge structures (XANES) of alkali fluorides, Lid, NaF, KF and RbF are measured by a photoelectric yield method. Na–K spectrum of NaF is also measured. The short-range order multiple scattering calculations for each K spectrum of LiF and NaF are performed. From comparison of the observed spectra with the calculated results, the effective cation charges are estimated with q =0.70±0.05 and 0.74±0.04 for LiF and NaF, respectively. These calculated F–K XANES spectra of alkali fluorides are not so sensitive to the charge distributions as cation K XANES. These results are in contrast with the case of alkaline-earth fluorides.

Observation of Undulator Radiation. : I. Operation Studies and Visual Observation

A 19-pole permanent magnet undulator has been tested by inserting it into a straight section from outside the vacuum chamber of the SOR-RING, a dedicated synchrotron radiation source operated between 0.2 and 0.38 GeV. It was confirmed that the undulator field did not seriously disturb stable operation by observing the shift of the closed orbit and the shift of the betatron numbers. Some results of visual observation of the radiation are presented. The polarization character was studied on the rainbow circle with a polarizer and some theoretical results by Kitamura were confirmed. It was found that the interfering synchrotron radiations along the straight section of the storage ring make a series of rainbows even without the undulator field.

Ionic fragmentation of SiH4 following the K-shell excitation

Ionic fragmentation of SiH4 has been studied in the vicinity of the Si: K-edge in the photon energy range 1800-1900eV. Ionic fragments observed at photon energies above the Si: ls → σ* excitation are mostly atomic ions Siq+ (q = 1-3) and H+. Ratios of the abundances for Si+, and Si2+ and Si3+ are roughly 4:4:1, and the abundance of H+ is much higher than the sum of the Si+, Si2+ and Si3+ abundances. The averaged kinetic energy release given to H+ is estimated to be about 12eV. This complete decomposition of SiH4 with the ejection of energetic H+ is interpreted as Coulomb explosion of the multiply-charged (mainly +4 or +5) parent ion produced via the vacancy cascade (successive Auger and/or Coster-Kronig transitions).