Without a filter in the reactor beam, there is a substantial amount of higher order wavelength contamination in the beam onto the sample. This has the effect that the beam monitor will count to it's preset value before the proper number of lambda neutrons strike the sample, thus reducing the observed signal. This correction is strongly energy dependent, and the data need to be corrected for this. The plot gives the proper correction factor by which to multiply your signal, to correct for the fact that not enough lambda neutrons were incident on the sample.
For example, at 14 meV the flux of lambda neutrons and lambda/2 neutrons is approximately equal. The beam monitor efficiency is proportional to the wavelength, so the lambda/2 neutrons are only counted with half the efficiency, but this still leads to quite a large correction.
Last modified 11-February-2004 by website owner: NCNR (attn: Jeff Lynn)