Backscattering spectrometer

The QNS experiments were carried out on three different spectrometers at the high flux reactor at the Institut Laue Langevin, Grenoble the high resolution backscattering spectrometer INlO, the multichopper time of flight (t.o.f.) spectrometer IN5 and the time foccussing t.o.f. spectrometer IN6 which are described in ref (6, lO). The experimental conditions are summarized in table 1. 

Thus we have observed 1) a long range diffusive motion but only for about 50 7o of the hydrogen atoms in the lattice 2) a rapid localized motion with a small spatial amplitude. It is clear that the other hydrogen atoms should also diffuse but, at the measured temperature, this diffusion is probably too slow to be observed on the backscattering spectrometer. 

Three high-resolution inelastic instruments are nearing completion at the NIST Center for Neutron Research (NCNR) (1) a disk chopper time-of-fiight spectrometer (2), a backscattering spectrometer (3), and a neutron spin echo (NSE) spectrometer. All three instruments will be available to researchers through reviewed proposals (4). Both the NSE and Backscattering spectrometers will be operation in early 1999 and the Disk Chopper Spectrometer shortly thereafter. 

The Disk Chopper and Backscattering spectrometers, like most other inelastic neutron spectrometers, measure the scattering function S(Q,w), where Q is the wave-vector transfer and w is the energy transfer of the scattering. The scattering function is the Fourier transform (in both time and length) of the... 

Flin PA (1975) Mossbauer backscattering spectrometer with full data processing capability. In Gmverman IJ and Seidel CW (eds) Mossbauer Effect Methodology, Vol 9, pp 245-250. New York Plenum Press. 

The Implementation of a backscattering spectrometer is somewhat different at a reactor than at a spallation source. Figure 5 shows a schematic view of the spectrometer IN 10 at the ILL and Figure 6 shows the equivalent spectrometer IRIS at ISIS. 

Figure 6 Schematic cf the cold-neutron backscattering spectrometer IRIS at ISIS. Reprinted from Physica, 182B, Carlile CJ and Adams MA, 431-440, 1992, with kind permission of Elsevier Science - NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Fig. 3.16 Schematic drawing of the MIMOS II Mossbauer spectrometer. The position of the loudspeaker type velocity transducer to which both the reference and main Co/Rh sources are attached is shown. The room temperature transmission spectrum for a prototype internal reference standard shows the peaks corresponding to hematite (a-Fe203), a-Fe, and magnetite (Fe304). The internal reference standards for MIMOS II flight units are hematite, magnetite, and metallic iron. The backscatter spectrum for magnetite (from the external CCT (Compositional Calibration Target) on the rover) is also shown...

Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode...

Because instrument volume and experiment time must both be minimized for a planetary Mossbauer spectrometer, it is desirable in backscatter geometry to illuminate as much of the sample as possible with source radiation. However, this... 

Cosine smearing. Because instrument volume and experiment time must both be minimized for a planetary Mossbauer spectrometer, it is desirable in backscatter geometry to illuminate as much of the sample as possible with source radiation. However, this requirement at some point compromises the quality of the Mossbauer spectrum because of an effect known as cosine smearing [327, 348, 349] (see also Sects. 3.1.8 and 3.3). The effect on the Mossbauer spectrum is to increase the linewidth of Mossbauer peaks (which lowers the resolution) and shift their centers outward (affects the values of Mossbauer parameters). Therefore, the diameter of the source y-ray beam incident on the sample, which is determined by a... 

Ti content in the polymer films was measured with a Princeton Gamma Tech System 4 x-ray Fluorescence Spectrometer. The conditions employed were Cr target, 50 keV source operating at 3 mA, 0.75 mm aperture, 4.8 mm beam stop, helium atmosphere and 100 sec. counting time. A calibration curve was constructed by plotting the fluorescence counts versus the amount of Ti in HB-HPR 206 films determined by Rutherford Backscattering Spectroscopic (RBS) analysis. 

Thomas, W., E. Hegels, S. Slijkhuis, R. Spurr, and K. Chance, Detection of Biomass Burning Combustion Products in Southeast Asia from Backscatter Data Taken by the GOME Spectrometer, Geophys. Res. Lett., 25, 1317-1329 (1998). 

All Mars rovers to date have carried alpha-particle X-ray spectrometer (APXS) instruments for chemical analyses of rocks and soils (see Fig. 13.16). The source consists of radioactive curium, which decays with a short half-life to produce a-particles, which then irradiate the sample. Secondary X-rays characteristic of specific elements are then released and measured by a silicon drift detector. The Mars Pathfinder APXS also measured the backscattered a-particles, for detection of light elements, but the Mars Exploration Rovers measured only the X-rays. 

Raman spectra were taken on a home built system, composed of Spectra-Physics 2020 series lasers, coupled with a Dilor XY-800 triple spectrometer and a Whight Instruments nitrogen cooled CCD. All samples were measured at room temperature in a backscattering configuration, with 514.53 nm Ar+ laser excitation. The laser power was tuned between 1 mW and 30 mW. UV-VIS diffuse reflectance spectra were taken on a Varian Cary 5 spectrophotometer, equipped with a specially designed Praying Mantis diffuse reflectance attachment of Harrick. 

FT-Raman spectra are measured at room temperature on a FT-IR spectrometer (Bruker IFS66) equipped with an FT-Raman accessory (Bruker FRA 106) using a Nd-YAG laser (emission wavelength 1064 nm). The data are collected in the backscattering mode (180° excitation resolution 4 cm- 256 scans 19 mW). 

This instrument concept was developed and resulted in the SBUV (Solar Backscatter Ultraviolet) and TOMS (Total Ozone Mapping Spectrometer) being launched aboard Nimbus 7 (Heath et al., 1975). The second generation SBUV instrument (SBUV-2) was further improved and has been flown by NOAA on a series of satellites (Frederick et al., 1986) (Table 1). 

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