Pulsed neutron beams

A pulsed neutron beam can penetrate the casing of munitions and identify the filler contents, be it explosive, chemical agent, incendiary, or smoke. This is a one-sided device, unlike an x-ray, and requires a minimum of disturbance to the item. In fact, the item does not need to be dug to the point of being visible. It is absolutely necessary for any ordnance remediation work, and it should be part of any health and safety plan. 

The first experiments with the TOF method were accomplished on stationary reactors, obtaining a pulsed neutron beam by mechanical choppers. The real potential of the method was realized after the building of pulsed neutron sources, such as pulsed reactors, electron linear accelerators and proton synchrotrons - spallation sources. In electron linear accelerators (LINAC) and proton synchrotrons, targets from 239 j heavy atoms are used. Slowing-... 

Resonance parameters are determined from one or several cross-sectional measurements with high resolution, usually by the so-called area analysis. In the past few years, the experimental techniques to measure neutron cross sections in the resonance region have improved considerably. High-intensity sources for pulsed neutron beams and advances in neutron spectroscopy allow measurements with ever-increasing energy resolution, and thus it has been possible to identify resonance levels and to determine resonance parameters over extended energy ranges and with better accuracy. 

It is clear that although the exponential pile and criticality experiments would be required ultimately in any large-scale reactor development program, it would be desirable to obtain some preliminary experimental verification of reactor calculations by means of other more modest tests. One experiment which appears to be eminently suited to this purpose is based on the pulsed neutron-beam technique. This technique has been applied by several investigators to the determination of the thermal-diffusion coefficient and macroscopic absorption cross sections of reactor materials.More recently, it has been used by E. C. Campbell and P. H. Stelson in the study of short-lived isomers and for the measurement of reactor parameters of multiplying media. The experiment con-... 

This case obviously corresponds to the critical system, since the time-dependent function in the expression (9.70) now vanishes. Thus a second important fact to be obtained from the pulsed neutron-beam experiment is the critical dimensions of a given geometry. Another fact to be learned from the experiment is the diffusion coefficient of the mixture and the absorption cross section of the fuel, since for small specimens... 

It is perhaps evident from these observations that the relatively modest and inexpensive pulsed neutron-beam experiment can yield a great deal of information about a particular reactor material. The outstanding... 

An alternative method in which of variable wavelength is used, has neutron diffraction studies. This vantageous for pulsed neutron beams driven sources since time-of-f1ight to define the neutron velocity and The initial work has been conducted tota1-scatter i ng spectrometer (TSS)... 

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