IN20 – The ILL high-flux polarised-neutron three-axis spectrometer

The three-axis spectrometer IN20 has been upgraded to enhance significantly its performance in experiments using polarised neutrons in the (higher) thermal energy range. The neutron-source diameter was increased from 100 mm to 170 mm, and a new double-focusing Heusler monochromator with an active surface of 230×150 mm2, illuminated through an input slit of adjustable width, has been installed. The maximum monochromatic polarised flux is close to 108 cm-2 s-1 and, in combination with the horizontally focusing analyser of a similar design, the data-collection rate has increased by a factor of 30–50 as compared to the original IN20.