Neutron spectrometer

The aim of an INS experiment is to measure the scattering intensity S(Q,co) as a fimction of (Q,co). This requires knowledge of both the energy transfer and the momentum transfer Q  

For INS spectroscopy there are three main types of spectrometer in use triple axis ( 3.4.1), which is rarely used to study hydrogenous materials more relevant are instruments that fix the final energy which are known as indirect geometry instruments and those that fix the incident energy which are known as direct geometry instruments. Examples of indirect geometry ( 3.4.2, filter and analyser) spectrometers and direct geometry ( 3.4.3, chopper) instruments are discussed in turn. 

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The Lunar Prospector orbiter carried a gamma-ray/neutron spectrometer (GRS) that made precise measurements of the concentration and distribution of thorium (Lawrence et al., 1998) and hydrogen (Feldman et al., 2001). Subsequent spectral deconvolutions (Prettyman et al., 2006) have produced analyses of iron, titanium, potassium, magnesium, aluminum, calcium, and silicon. The principles of these analytical techniques are explained in Box 13.1. 

Feldman, W. C., Mellon, M. T, Gasnault, O., Maurice, S. and Prettyman, T. H. (2008) Volatiles on Mars Scientific results from the Mars Odyssey Neutron Spectrometer. In The Martian Surface Composition, Mineralogy, and Physical Properties, ed. Bell, J. F. Cambridge Cambridge University Press, pp. 125-148. 

Usui, T. and McSween, H. Y. (2007) Geochemistry of 4 Vesta based on HED meteorites prospective study for interpretation of gamma-ray and neutron spectrometer for the Dawn mission. Meteoritics and Planetary Science, 42, 255-269. 

A neutron spectrometer separates detected neutrons into different energy ranges (thermal, epithermal, fast). Proportional counters containing 3He are commonly used for... 

Figure 1. Schematic of a triple-axis inelastic neutron spectrometer. The thermal-ized beam from the reactor is monochromated by Bragg reflection from crystal M. Neutrons that scatter from the sample S are energy analyzed by Bragg reflection from crystal A and enter detector D.

Before discussing the adsorbed butane vibrational spectrum, we first describe the inelastic neutron spectrometer used in this experiment. 

Various types of neutron scattering can be utilized to extract data on structure and dynamics for novel catalytic materials. By selectively deuterating an SSZ-13 zeolite, Cheetham and others" used ND performed on the Dual Beam Neutron Spectrometer (DUALSPEC) diffractometer at the Chalk River Laboratories and found that two acid sites are present in the unit cell of the zeohte. INS can be used to probe the mechanism of the catalytic reaction by looking at the change in the vibrational modes of the adsorbed molecules on the surface. Lennon et alP found that the interaction of HCl with a ]-alumina catalyst results in the dissociative adsorption of HCl, in which the hydroxyl groups terminally bound to A1 are replaced by chlorine. INS spectra reveal an in-plane deformation mode, 5 (OH), that can be resolved into two bands located at 990 and 1050 cm. ... 

As in the case for benzene in ZSM-5, the translational motion of p-xylene in ZSM-5 was too slow to be measured on the IN6 neutron spectrometer... 

Lunar Prospector s two most important geochemical mapping sensors were designed for gamma-ray spectrometry (GRS) and neutron spectrometry. The neutron spectrometer, a matched pair of He gas proportional counters, was mainly designed to map the global... 

Elphic R. C., Lawrence D. J., Feldman W. C., Barraclough B. L., Maurice S., Binder A. B., and Lucey P. G. (2000) Lunar rare earth element distribution and ramifications for FeO and Ti02 Lunar Prospector neutron spectrometer observations. J. Geophys. Res. 105, 20333-20345. 

Z.A. Dowden, M. Celli, F. Cilloco, D. Colognesi, R.J. Newport, S.F. Parker, F.P. Ricci, V. Rossi-Albertini, F. Sacchetti, J. Tomkinson M. Zoppi (2000). Physica B 276 98—99. The TOSCA incoherent inelastic neutron spectrometer progress and results. 

The INS spectroscopy of water ice is particularly demanding of the current world-wide suite of neutron spectrometers. Excellent energy transfer resolution is required, to provide data capable of discriminating between competing dynamical models. However, low Q values are also needed, to reduce the impact of the Debye-Waller factor from this very light molecular species (H2O has a Sachs-Teller mass about 2 amu). 

The SCANS is used in conjunction with an analytical system such as a portable Raman spectrometer or a portable isotopic neutron spectrometer to identify the agent inside a vial or bottle so the correct reagent can be selected to neutralize it. A 4-liter bottle of reagent is placed in the reactor case,... 

A neutron spectrometer based on LiF consists of a thin slice of LiF ( 30 X 10 kg/m = 30 /ig/cm ) sandwiched between two surface-barrier silicon detectors. When neutrons strike the LiF, charged-particle pairs ( He- H) are produced and are detected simultaneously by the two detectors. The pulses from the detectors are amplified and then summed to produce a single pulse, which is proportional to the energy of the neutron plus the Q value of the reaction. 

One type of helium neutron spectrometer consists of two surface-barrier silicon detectors facing each other, with the space between them filled with helium at a pressure of a few atmospheres (this is similar to the LiF spectrometer described in Sec. 14.2.3). 

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