ON THE ORIGIN OF SPURIOUS PEAKS IN PSEUDORANDOM TIME-OF-FLIGHT ANALYSIS

The pseudorandom time-of-flight analysis overcomes the classic trade-o ff between resolution and transmission and has become a standard tool in inelastic low-energy neutron and atom scattering. However, systemat ic 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 p eaks in the time-of-flight spectrum. These spurious peaks are mirror i mages of the real time-of-flight distribution shifted in the spectrum by a constant number of channels which is uniquely determined by the n ature and length of the chopper-slot sequence. These effects can easil y be corrected for and will in general not impede the actual time-of-f light analysis. We report a systematic study of the origin of the spur ious peaks and show how one can discriminate between the effects stemm ing from machining errors or from the finite thickness of the chopper disk.