Neutron backscatter

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. 

The neutron backscatter uses a neutron radiation source that is focused on a sample, and the neutron backscatter is measured and correlated to the moisture content. The energy of the neutron after the impact is a function of the mass of the impacted atom. If the mass of the impacted nucleus is equal to the mass of the neutron, all of the neutron s kinetic energy is transferred... 

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.)... 

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. 

Fig. 3-1. Neutron backscatter level measurement principle (Hills, 2001).

Neutron backscatter gauge clearly indicates solid/liquid and liquid/liquid boundaries and, with careful interpretation of the data, foam levels. 

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). 

Neutron backscatter gauge can be used to measure level and interface of transpwrted liquids... 

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 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.

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