Scanning x-ray spectrometer for high-resolution Compton profile measurements at ESRF

A scanning-type crystal spectrometer for high-resolution Compton profile me asurements has been constructed at the High Energy Inelastic Scattering Bea mline (ID15B) of the ESRF Radiation from a seven-period asymmetrical perman ent-magnet wiggler or from a superconducting wavelength shifter is focused horizontally onto the sample by a bent-crystal monochromator. Typical energ ies are 30, 50 and 60 keV, the flux on the sample is 10(12) photons s(-1), and the relative energy bandwidth is 3 x 10(-4). The spectrometer operates in the Rowland circle geometry, where the sample is fixed and the cylindric ally bent analyser crystal and the detector move on the focusing circle by synchronized translations and rotations. The main detector is a large-diame ter NaI scintillation counter, the incident beam is monitored by an Si diod e, and scattering from the sample is detected using a Ge detector. The reco rded spectrum is corrected for the energy-dependent response of the spectro meter, background and multiple scattering, and converted to the momentum sc ale. The resolution of the spectrometer is calculated from the geometrical factors and the reflectivity curve of the analyser crystal, and the result is checked against the widths of the elastically scattered line and fluores cent lines. So far, 0.1 a.u. resolution in electron momentum has been achie ved. The typical average count rate over the Compton profile is about 1000 counts s(-1) from a weakly absorbing sample.