On the origin of spurious peaks in pseudorandom time-of-flight analysis

The pseudorandom time-of-flight analysis overcomes the classic trade-off between resolution and transmission and has become a standard tool in inelastic low-energy neutron and atom scattering. However, systematic errors in the machining of the chopper slots as well as the finite thickness of the chopper disk can lead to the appearance of spurious peaks in the time-of-flight spectrum. These spurious peaks are mirror images of the real time-of-flight distribution shifted in the spectrum by a constant number of channels which is uniquely determined by the nature and length of the chopper-slot sequence. These effects can easily be corrected for and will in general not impede the actual time-of-flight analysis. We report a systematic study of the origin of the spurious peaks and show how one can discriminate between the effects stemming from machining errors or from the finite thickness of the chopper disk.