TOSCA neutron spectrometer: The final configuration

The forward and backward scattering parts (phase 11) of the new neutron spectrometer, TOSCA, replacing the old TFXA and TOSCA (phase 1), have been successfully installed at the ISIS pulsed neutron source. The results show a significant enhancement in the counting rate due to the larger detector area. The improved resolution (to 1.5%-3% of the energy transfer) as compared with the previous instruments (TXFA: 2.5%-3.5%; TOSCA-I: 2%-3.5%) has been achieved by increasing the primary flight path from 12 m to 17 m. A chopper has been added in order to avoid neutron frame overlap and to reduce the fast neutron background. Additional diffraction capability will be installed in the near future. An example of the high resolution that is routinely available is provided by the spectrum of potassium hydrogen phtalate at 20 K.