Neutron guides

An example of crystal monochromator instrument on a continuous source is IN4 [31] at the ILL, shown in Fig. 3.30. IN4 sits at the end of a short thermal neutron guide, thus the lack of hot neutrons effectively restricts the energy transfer range to less than 800 cm". ... 

Figure 8.13 Schematic view of a back-scattering spectrometer. The neutrons incident from the neutron guide are back-scattered by the monochromator mounted on a Doppler drive, deflected by a graphite crystal to the sample, scattered to the analyzers and then back-scattered again to the detectors located close to the sample. The chopper interrupts the beam and makes it possible to discriminate the neutrons scattered directly into the detectors.

Figure 2 Layout of the Institute Laue Langevin (Grenoble, France) Research Reactor Instrumentation including two cold neutron guide halls...

An extensive experimental programme has been carried out with the aim of precisely defining the values of the different control rods and their interaction effects. The measurements have been performed with the reactor in a sub-critical state by using counters placed at the centre of the reactor and at 3 different locations under the reactor vessel. The responses of these last 3 counters were amplified by neutron guides. This type of sub-critical measurement requires correction factors to account for the fact that the counters see a different perturbation depending on their position in the reactor. These correction factors have been calculated using different methods and data and show no dispersion in their results and so these corrections have therefore not been recalculated. 

However, even this minute deviation from one gives the possibility of making use of the critical mirror angle (see O Sect. 29.5.2.2) for the fabrication of neutron guides. Another important application is neutron reflectometry, used extensively for the investigation of (solid and liquid) surfaces (see Sect. 29.4.4). Neutron reflection can also be used for the accurate determination of the scattering length (Maier-Leibnitz 1962 Koester et al. 1991). 

Epithermal and fast neutrons can be eliminated entirely by using diffraction to extract a narrow range of wavelengths from the beam (Byun et al. 2002). Several orders of diffraction can be summed to increase the flux. The best beams are those from neutron guides, which operate by total internal reflection in a narrow channel. Neutrons incident on a surface at... 

Yonezawa C, Wood AKH, Magara M, Sav ata S, Hoshi M, Ito Y, Tachikawa E (1993) Prompt gamma-ray analysis using JRR-3M cold and thermal neutron guide beams. In Proceedings of the 5th international symposium advanced nudear energy research (JAERI-M 93-228), Mito, Japan, vol 2. JAERI, Tokai, pp 854-861... 

A guided beam of cold neutrons will provide the highest intensity neutron beam with the lowest background at the sample position. Therefore, the use of a neutron guide is desirable. In addition, a pair spectrometer or a Compton suppression system is a desirable option, although this need is decreasing due to better detectors, MCAs and analysis software. 

Neutron guides made from borated glass and Ni mirrors, about US 1000 per meter. 

A research reactor of thermal power larger than 20 MW is always considered as having a cold neutron source (CNS) and neutron guide tubes. 

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