Search

To establish systematic guidelines for accelerator decommissioning, a large-scale activation survey was conducted at representative synchrotron radiation facilities in Japan. The neutron flux during accelerator operation was measured with various dosimeters. A Monte Carlo simulation was conducted for some facilities to verify the special neutron distribution and their spectra. Beam loss points, reflected as high-dose-rate areas, were identified by a whole-beamline survey with a survey meter, and the generated radionuclides and their activity were determined with a lanthanum bromide (LaBr3) scintillation spectrometer. In all facilities, the activation level was quite low. Whole-beamline tunnels made of concrete were not activated, and no radionuclides were detected except for natural nuclides. In addition, almost all beamline components were either not or minimally activated. Although the acceleration energy is very high for radiation synchrotron facilities, the generation of radioactive waste would be very low.

Hiroshima Synchrotron Radiation Center (HSRC) is a common facility for research and education in the field of synchrotron radiation science in Japan. The major role of the facility is to promote nationwide SR research activities in materials science, especially in solid state physics, and education in the related fields simultaneously. HiSOR is a compact synchrotron radiation source of HSRC constructed in 1996 as a typical VUV — soft X-ray source (0.87 keV critical photon energy) similar to Helios in Singapore. Because of a compact racetrack-type ring, its natural emittance 400π nm · rad is not so small as the other standard-sized rings. There are two undulators, one linear for 26–300 eV range and the other helical/linear for 4–40 eV. The most outstanding feature of the facility lies in the good combination with beamlines to attain high-resolution (below 1 meV) for photoemission spectroscopy. It is routinely operated from 09:00 to 20:00 on weekdays at the stored current starting from 350 mA with 8 h lifetime at 300 mA. HiSOR has been running over 10 years, thus, it is time to think about the future improvements of the facility. The motivation is to pursue the leading position in the field of materials science (solid state physics) using SR for high-resolution photoemission spectroscopy. Some candidates for the upgraded HiSOR are presented.

A simple method to monitor the motion of photon beams using the visible component of synchrotron radiation (SR) is proposed, in which visible SR diagnostics are effectively extended. A preliminary test of the measurement principle was performed. We obtained a reasonable position response from photon beam fluctuation due to electron beam instability. With the aim of beam monitoring in user's beamlines of small storage rings, we discuss appropriate monitor assembly along with the advantages of the extension of visible diagnostics because the conventional photo–current method in VUV and X-ray regions is not applicable at the beamlines.

The efficiency of positron production by a 1.2-GeV electron beam incident on a tungsten single crystal oriented in an axially channeling condition has been experimentally studied. Positron yields from a 1.2-mm-thick crystal have been measured to be ,2.5 3.0 times larger than those from amorphous targets with the same thickness. A simple model simulation of the positron production process shows that coherent bremsstrahlung, as well as channeling radiation, contributes to the enhancement of the positron yields. [S0031-9007(98)05357-5]

An experiment to investigate the positron production efficiency by electrons moving in axially oriented tungsten and silicon single crystals has been conducted. The electron energy was 1.2 GeV. The positron yield from the aligned crystal ∼0.35 r.l. in thickness was 2.8 times that from the randomly oriented crystals for tungsten and 1.8 times higher for silicon. A simple model has been designed to simulate positron production by coherent bremsstrahlung (CB) photons. Comparison of the calculation with the experiment has shown that most contribution to the positron production in thick crystals comes from CB.