Neutron backscatter technique

The neutron backscatter technique is best performed with hydrogen-containing products. Both the source of a slow neutron and the receiver are located in the same box. The slow neutrons bounce off of protons (hydrogen ions) and are reflected back. The rate at which these neutrons are reflected back is measured, and corresponds to the hydrocarbon density in the vessel. This measurement is not affected by steel components inside—or outside—the vessel. 

Using nucleonic level detectors These usually employ gamma ray absorption or neutron backscatter techniques, but may also use gamma ray backscatter (Sec. 14.5). A case where a gamma ray absorption indicator solved a level control problem at the base of a column has been described (71). 

Neutron backscatter techniques are suitable for locating the interface between two materials that have different hydrogen atom concentrations. Figure 14.16 shows a typical ex unple of such an application. The probe is positioned near the wall of the vessel and is moved up and down along the surface. The signals show where the interface exists. 

The most common applications of this technique in distillation and absorption columns is for liquid level and liquid level interface detection, especially when normal level-measuring techniques suffer from plugging. Neutron backscatter techniques have also been used for froth height measurements on trays and downcomers, and for measuring the top and bottom of packed beds. One case history has been described (71) where downcomer froth height measurements using the neutron backscatter technique led to a detection of downcomer deposits which caused premature flooding of the column. The author is familiar with one case where this technique successfully detected overflow of a packed tower distributor. 

Neutron backscatter techniques can detect a liquid interface far... 

Rgura 14.16 Level and interface measurement using a neutron backscatter technique (From J. S. Charlton and M. Polarski excerpted by special permission from Chemical Engineering, February 21, 1983 copyright by McGraw-Hill, Inc., New York, NY 10020.)... 

Typical profile using the neutron backscattering technique, obtained for a storage tank filled with various liquid and vapour phases, is given in Figure 3-2 (IAEA, 2002). 

In this chapter we present the three major techniques used in petrochemicals. Gammascanning is a very effective non-invasive technique used for on-line troubleshooting of distillation columns and pipes. Neutron backscattering is applied for level and interface detection in storage tanks and other reservoirs. Radiotracers are employed to establish the residence time distribution which is an important mean of analysis of the petrochemical units. 

The economic benefits that may be derived from the use of radioisotope technology in petrochemical industry are large. In this chapter we tried to present the state-of-the-art in major techniques used in petrochemicals such as gamma-scanning as a diagnostic tool for distillation columns and pipes, neutron backscattering for level and interface detection in... 

Figure 7 This figure maps out the length and energy scales that are accessible with the different inelastic neutron scattering techniques. In the text, we have limited our discussion to the time-of-flight (TOF) spectrometers, backscattering (BS) spectrometers, and spin echo spectrometers.

There are two basic ways to look for explosive material. They differ in their point of focus. Some sensors seek the mass of explosive material within a device. These are particularly useful when the device is well sealed and its surface is well cleaned of stray explosive molecules, or when the explosive being used is nonaromatic, that is, it does not readily release molecules from its bulk. We will refer to these as bulk sensors. They include X-ray techniques, both transmission and backscatter neutron activation in several techniques y -ray excitation, in either transmission or backscatter modes and nuclear resonance techniques, either nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR). Bruschini [1] has described these thoroughly. They are also described by the staff of the Jet Propulsion Laboratory [2], The following forms a very brief synopsis. 

The X ray diffraction technique is widely used in structural characterization of materials and serves as an important complement to electron microscopy, neutron diffraction, optical methods and Rutherford backscattering. 

Thus rapid motions require relaxed resolution, while slower motions require high resolution. Note that these are relative terms typically an energy resolution of better than 1% AE/E and 100 peV is required. The timescale to be probed can be separated into three regimes, each of which uses a different technique for r 10" s, AE is 10-100 peV and direct-geometry time-of-flight is used, for t 10" s, AE is 0.3- 20 peV and a backscattering crystal analyser is used, for t 10" s, AE is 0.005-1 peV and neutron spin echo is used. Examples of each type of spectrometer will be considered. 

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