The IN6 chopper unit comprises two cylindirical choppers.

A so-called Fermi chopper, located as close as possible to the sample position (39.5 mm), forms the neutron pulses and determines, thus, the energy resolution of the instrument. The neutron pulses are shaped by a rotating slit collimator consisting of a sequence of 200 neutron transmitting aluminum (0.2 mm thick) sheets separated by neutron absorbing gadolinium (0.025 mm thick) foils. A full width at half maximum of 1.4 degrees has been established experimentally for the transmission function of the slit collimator. Depending on the experimenal condition chopper frequencies of 60-250 Hz are applied.

A so-called suppressor chopper is located between the berylium filter and the Fermi chopper. Its function is to clean the monitored sample signal from frame overlap effects, i.e., to suppress the spill-over of signals stemming from subsequent neutron pulses. The extent of spill--over effects is dependent on different conditions. It can be enhanced by the instrumental setup (e.g. high chopper frequencies for high resolution experiments), the physics of the sample (materials with a rich and extensive spread of excitations covering a wide range of energies) as well as by experimental requirements (materials at very high temperatures). The speed of the suppressor chopper is given by f/n with f the Fermi chopper frequency and n = 1, 2, 3, ..., thus, cutting out none of the pulses n = 1 (maximum flux), every second pulse n = 2, every third n = 3, etc.