Improvements on water-cooled and doubly bent crystal monochromator for Compton scattering experiments

Improvements on the water-cooled and doubly bent crystal monochromator, which has been installed at the KEK, PF-AR NE1 beamline for Compton scattering experiments, are described. An as grown Si crystal is replaced by an annealed Si crystal (950° C for 24 h in air) in order to get a much higher flux. As a result, the obtained flux for 60 keV monochromatic X-rays has become four times higher. The focused beam size has not changed. The energy resolution is 90 eV, which is 1.5 times worse than the previous value, but it is acceptable for high resolution Compton scattering experiments. Two Si crystals whose directions of the surface normal are (1 1 1) and (1 0 0) were successfully mounted. With this, the beamline now covers the energy ranges of the monochromatized X-rays: 40–70 keV by Si (1 1 1) and 90–160 keV by Si (4 0 0).