Recoil peak

Because of the high transfers of energy and momentum applied on VESU-VIO, the recoil peaks of H and other heavier atoms (like D, Li, or La) in the TOF spectra are well separated for a wide range of scattering angles. 

Figure 1 a - Experimental setup the neutrons leave the moderator, are scattered by the sample under an angle and give a signal in the detector. The analyzer foils are periodically cycled in between sample and detector, b - A typical TOF spectrum of a 20 80 H2O - D2O mixture in an Al can (error bars) together with the corresponding fit (full line). The H and D recoil peaks are well separated from each other and from the joint O / Al peak. 

Recently, we have investigated liquid benzene and various G), //< - G) Dp mixtures at T = 20°C [Chatzidimitriou-Dreismann 2002 (a)]. In order to achieve a well defined separation between the carbon and metallic recoil peaks (Fig. 5), the liquids were put in a sample container made of Nb (heavy metal). 

Figure 5 Examples of measured TOF spectra from liquid 6V, Hi, in a Nb can, at T 295 K. The error bars are due to counting statistics only. The full lines denote the fitted TOF spectra. For the scattering angle 0 = 65°, the C- and 7V6-recoil peaks overlap. For 0 = 132°, however, these two peaks are well resolved, thus facilitating a reliable determination of the C- and Nb-peak intensities.

Having thus determined the joint intensity of the C and O recoil peaks relatively to that of the AA-pcak, the validity of the conventional theoretical expectation can be tested as follows. First, from the NCS spectra in the "forward" scattering direction we determine the ratio Ah/(Ac + Ao + Ani>)- Second, having determined the ratio (Ac + Ao)/ANb from the "backward" direction, we can straightforwardly determine the ratio... 

Figure 11. ECS energy-loss spectrum of a formvar film taken using 25 keV electrons, resulting to a mean momentum transfer hq to protons with q = 61.8 A-1. Inset the fit of the //-recoil peak (about 8 eV) with a Gaussian, before and after subtraction of the background taken from [Chatzidimitriou-Dreismann 2003 (a)].

Ratios of recoiling peaks for N and H and scattering peaks for Ga were used in calculating both the experimental and simulated ASEA values. 

The high ratio [N]/[Ga] = 6.3 from Table I provides compelling evidence that the surface is terminated in a layer of N atoms and that the Ga atoms occupy the second layer. Termination in a nitrogen layer may result from the method of cleaning, i.e, sputtering in N2. The intense H recoil peak was present under all conditions that gave rise to the clear (1x1) LEED pattern, indicating that the H concentration on the (1x1) surface is comparable to the N concentration. 

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