The RITA spectrometer at Risø - Design considerations and recent results

In the new cold triple axis spectrometer RITA at Risø we have improved the front end by extensive use of state of the art optical elements and better shielding material. The analyser system is situated in one large open tank and consists of seven individually orientable PG(002) crystal analyser blades, and a 170mm by 120mm² area sensitive micro-strip detector. In comparison to the old TAS6 spectrometer we have obtained a factor 2-5 gain in intensity on the sample, a substantially lower background, much more flexibility for optimising the instrument and the possibility to go beyond simple point-by-point inspection. The excellent performance of RITA in the standard TAS mode is exemplified by a study of the dynamics of ≈ 15 nm hematite (α-Fe₂O₃) nano-particles, and utilisation of horizontal and vertical focusing modes to study two dimensional systems is illustrated by a study of the spin fluctuations in the high Tc superconductor La_1.83Sr_0.17CuO₄.