Neutron radiography

The neutron radiography (short Neutrographie ) is an analog of Radiology method for nondestructive material testing, especially in the hydrogen-containing materials ( eg, numerous plastics) can be applied.

Physical Basics

Neutrons have high penetrating through matter because of the lack of electric charge, in contrast to the electrons and protons. While X- rays pass mainly with the electron shells of the atoms in the interaction and their absorption in the material, therefore, is steadily increasing with the atomic number of the element, the interaction of neutrons with nuclei and has no correlation with the ordinal number, however, the total cross -section ( to absorption and scattering ) of thermal neutrons, which is a measure of the strength of the interaction, for light elements such as hydrogen, lithium, boron, carbon, significantly higher than for heavy elements. This essential difference makes the neutron radiography to a supplementary method of non-destructive testing of materials for components made of light elements. However, the application of neutron radiography by the limited availability is shining strong neutron sources limited.

Technology

Neutron sources radioactive sources ( neutron production through nuclear reactions ), particle accelerators, research reactors and spallation neutron sources are possible, which generally only offer the latter two sufficient neutron flux. The possible well collimated jet from a thermal neutron beam is pointing to enforce the sample under a spatially varying intensity distribution, which is registered by suitable detectors. When detectors are movies and spatially resolving Neutronenzählrohre and semiconductor detectors in conjunction with electronic image intensifiers in question. In connection with films and other detectors that are permeable to neutrons, a neutron absorbing converter must be used, which converts by nuclear reactions in the neutron radiation registerable.

Demonstration examples

The figures show two examples of demonstration Neutronenradiographien taken on now decommissioned research reactor FRY -1 of the Research Center Jülich. The simple experimental setup schematically shows figure 1. The exiting from a beam tube of the reactor thermal neutron beam ( neutron flux density is about 10 x exp6 neutron / cm ² energy ca.0, 04 eV) impinges on a sample, passes through the unobstructed film c and is absorbed or scattered in the film D converter. The changes brought about in the converter foil flashes of light blacken the back lying with the photosensitive layer to the film converter film. Film and slide converter lie flat against each other in a Polaroid film cassette b; they are drawn in the figure for reasons of clarity apart. The converter consists of a mixture film of LiF as neutron absorbers and scatterers and silver sensibiliertem ZnS as a scintillator, which is bound in a plastic film. Figure 2 shows the recording of a pencil sharpener neutrographische plastic as compared with a X-ray. While Neutrographie only the plastic parts are again - to the point at which is located the mounting bolt for the blade, only the threaded hole can be seen - shows the X-ray mainly the metal blade. Neutrographie and radiograph complementary. Figure 3 shows three polyamide gears inside a blechgekapselten washing program switching mechanism and demonstrates the possibility of visualization of lightweight, water -containing plastic parts by sheet steel through it, which is not possible with such a radiograph. It should be noted also here, the gear axes do not visible.

Applications

The limited accessibility of sufficiently high intensity neutron sources restricts the application of neutron radiography course a strong. Are conceivable following applications:

• Nondestructive testing of metal joints ( aircraft )
• Examination kunststoffvergossener components for cavities ( Transformers )
• Level examination of opaque containers ( oils )
• Investigation of radioactive nuclear fuel rods ( Hydridansammlungen )

At sufficiently strong neutron sources and sensitive detectors is also an observation of dynamic processes possible.