The neutron guide upgrade of the TOSCA spectrometer

The primary flightpath of the TOSCA indirect geometry neutron spectrometer has been upgraded with a high-m 14.636 m (including 0.418 m of air gaps) neutron guide composed of ten sections in order to boost the neutron flux at the sample position. The upgraded incident neutron beam has been characterised with the help of the time-of-flight neutron monitor; the beam profile and the gain in the neutron flux data are presented. At an average proton current-on-target of 160 mu A and proton energy of 800 MeV (ISIS Target Station 1; at the time of the measurements) we have found that the wavelength-integrated neutron flux (from 0.28 angstrom to 4.65 angstrom) at the position of the TOSCA instrument sample (spatially averaged across a 3.0 x 3.0 cm(2) surface centred around the (0,0) position) is approximately 2.11 x 10(7) neutrons cm(-2) s(-1) while the gain in the neutron flux is as much as 46-fold for neutrons with a wavelength of 2.5 angstrom. The instrument's excellent spectral resolution and low spectral background have been preserved upon the upgrade. The much improved count rate allows faster measurements where useful data of hydrogen rich samples can be recorded within minutes, as well as experiments involving smaller samples that were not possible in the past.