Chu Nan Chang

Energy shift of the K-absorption edge of Mn and Fe compounds

The relative position of the K-absorption edge of Mn and Fe in different chemical states has been measured using an improved version of a single-crystal high-angle goniometer. Six different compounds of Mn and seven different compounds of Fe were measured and compared. Using the HFS model, the binding energies of the 1s electron in Mn and in Fe were calculated for the neutral and the ionised atoms. The structures on the high-energy side of the K-absorption edge were observed, and some of the studied absorption edges were found to be not the usual smooth arctangent functions.

SOFT X-RAY SPECTROSCOPY BEAMLINE 6 M HIGH ENERGY SPHERICAL GRATING MONOCHROMATOR AT SRRC : OPTICAL DESIGN AND FIRST PERFORMANCE TESTS

The layout and first data on the performance of the soft x‐ray bending magnet beamline 6 m high energy spherical grating monochromator (6m‐HSGM) at SRRC are described. The 6m‐HSGM beamline, which covers photon energies from 110 to 1500 eV, is based on the Dragon concept with spherical gratings, and a movable exit slit. During the first performance tests, core‐excitation thresholds of Ar and Ne, and K thresholds of N and O for gas phase CO, N2, and O2 have been recorded with resolutions which rank among the best reached so far in the soft x‐ray region.

Performance of the 1 m Seya-Namioka monochromator beam line at SRRC

The performance of the 1 m Seya–Namioka monochromator (1 m‐SNM) beam line at SRRC has been measured and reached the designed goal. The beam line throughput (photon flux) has been measured by a calibrated silicon photodiode and is close to the theoretical values. The resolving power of this beam line has been measured from the studies of the core absorption of Ar and Ne and the Rydberg states of Mg vapor gas, and has reached the theoretical values. The improvement of the cooling system of the first mirror is also described.

Total cross section measurements by X-ray detection of electron-capture residual activity☆

Abstract A method is presented for measuring total cross-sections for reactions producing final nuclei which decay by electron capture. The method involves the detection of the X-rays from the atom produced by the electron capture, by use of a Si(Li) detector. As an example, results are presented for the total cross section of the reaction 48Ti(α, n)51Cr in the bombarding energy range 5.0 to 11.0 MeV.

The optical system for a 1 m Seya-Namioka monochromator in the SRRC beam line

Abstract The matching optics for the 1 m Seya-Namioka monochromator were designed for the ARC synchrotron radiation of the proposed TBA lattice of SRRC. The methods of aberration control in synchrotron radiation beam lines for a Seya-Namioka monochromator were examined, and the limit imposed by using a spherical mirror as a prefocus mirror will be shown. A comparison of using a toroidal mirror and an ellipsoidal mirror for prefocusing was made. Some detailed descriptions of the choice of the mirrors and their coating materials and the geometrical arrangement will be presented. Also, the final output of the wavelength range, throughput, resolution and polarization of this VUV beam line will be shown.

Current status of the 6 m low‐energy spherical grating monochromator beamline at SRRC

The 6 m low‐energy spherical grating monochromator (6 m‐LSGM) beamline at SRRC is at its commission stage. The 6 m‐LSGM beamline, which covers photon energies from 15 to 200 eV, is based on Dragon concept with spherical gratings and movable exit slit. Some of the commission data will be presented in this paper. The photoabsorption spectra of Ar, He, and Kr have been recorded with resolution so far unattained in the vacuum ultraviolet region.

Monochromator alignment technique

A simple and high precision technique is developed for the monochromator alignment. The alignment setup is composed of two He/Ne lasers, a penta‐prism, a flat mirror, and other common alignment aids. The alignment principle and the setup is described. An example of how to align Synchrotron Radiation Research Center 1‐m‐Seya monochromator is presented as well.

Apparent dependence of α-particle induced L-subshell ionization on outer-electron configurations

Abstract Measurements are reported for positive-ion induced L-subshell ionization cross sections ratios. For α-particle projectiles, the L III /L II low-energy behavior for Au and Pt differs dramatically from that for Ta and Bi. Correlation with the outer electron configurations of these atoms is suggested.

Optical design of a 200 eV–2.5 keV cylindrical element monochromator for the 1.3‐GeV storage ring of SRRC

Separate focus‐function mirrors in combination with a simple‐scanning spherical/cylindrical grating are to be used for an extreme grazing‐incidence beamline design in the photon energy range of 200 eV–2.5 keV at the ARC synchrotron radiation of the TBA lattice of SRRC. Three mechanically ruled gratings are used to cover the spectral wavelength range of the extreme VUV and soft x rays. Both the throughput and the resolution of this optical system have been carefully calculated and compromised against the grazing angle, arm length, grating size, etc. The proper parameters of the optical elements as well as their geometrical arrangements are proposed. A resolving power of at least 2000 is obtainable at the high‐energy end of the spectrum around 2 keV. At the low‐energy end, the resolving power can be as high as 8000, comparable to a grazing‐incidence Rowland circle type of monochromator. The overall resolving power has been found to be superior to that of either the plane grating monochromator (PGM) or the 1...

The characteristics of the initial three synchrotron radiation beam lines at SRRC

Abstract The design of three beam lines has been finished at Synchrotron Radiation Research Center (SRRC), Taiwan, by the SRRC staff. The 1-m Seya-Namioko monochromator (SNM). 6-m spherical grating monochromator (SGM), and 6-m cylindrical-element monochromator are used for these beam lines. A brief description of the concept behind the design of each beam line will be made. The choice of the demagnification of the vertical focus mirror for both SGM and CEM beam lines was found important for low-emittance machines. The degradation of beam quality due to imperfections in the mirror surface was found crucial for prefocus mirrors.