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The existence of some 100 million active mines threatens human life and curtails substantially the economic base in over 70 countries. Humanitarian demining is tedious and it currently only employs metal detectors, prodders, dogs and armoured mechanical vehicles.
Achieving a world free of mines within a period of 10 years as stipulated in international treaties requires safer and more efficient technologies. In response to this challenge the Working Group 5 of the European Federation for Non-Destructive Testing (EFNDT WG5) was founded in Berlin in March 1999. The subject of this working group now consisting of 50 members from 17 countries is the detection of antipersonnel mines (APMD). The basic idea was to investigate existing NDT methods into their ability to aid mine detection. The scope of activities ranged from collecting available information, setting up links to related organisation, defining terminology and standards to selecting dedicated research projects. Since some of these tasks are already conducted by other organisations on an European and international level the attention of the working group has been focused mainly on two R&D areas and on reliability assessment studies. Otherwise, EFNDT WG5 APMD nevertheless remains open to novel approaches in mine detection. Aim of all activities is to provide deminers with safer and more efficient tools than merely with prodders and metal detectors currently used for their dangerous task.
Radiography is a helpful method to identify the inherent structure of unexploded ordnances (UXOs). Portable Computed Radiography (CR) systems on the basis of phosphor imaging plates , have attracted attention for NDT-applications during the last few years. A portable IP system ACR 2000 has been tested for X-ray inspection of UXO's in the field. Digitised radiographs are presented to explain the needs and demands for a reliable characterisation of UXO's. Computed radiographs of UXOs are compared with film radiographs exposed in the same way, to evaluate the reliability and to identify advantages and disadvantages of the CR system for UXO inspection. Film based and CR systems provide sufficient information for identification of chemical warfare agents in UXO's, which is an essential problem for explosive ordnance disposal. The advantages and the potential of the portable CR system is discussed on the basis of experiences gathered during different field trails.
Ability of Non-Destructive Testing to Contribute to Humanitarium Mine Detection and Clearance
(2002)
Human perception of images
(2005)
Throughout human history, wood has been used for various purposes: for
building shelters, houses and bridges, for manufacturing furniture and
household or agricultural appliances (from ploughs to spoons), as burning
material or simply as walking sticks. Contemporarily, vast amounts of wood
are going into paper production. As a consequence, different qualities of
wood are selected appropriately for the various applications. Beams incorporated
into buildings and constructions have to be sturdy and durable;
boards for furniture are supposed to be free of knots or are expected to have
certain ornamental structures. As long as wood is not simply destined for
burning it should be free of undesired knots or internal damages such as rot
or worm holes. Particularly in cases of infestation with wood destroying
fungi that definitely impairs mechanical strength and even may generate
hollows such damages are frequently invisible from the outside. Radiographic
methods are capable to detect internal damages as well as hidden
knots without the need of drilling holes or cutting a specimen to pieces.
The most thoroughly method to visualise the interior of a wooden specimen
is tomography which shows annual growth rings in their complete circumference
and all the knots or damages that might be included. However, some
of them as well as patterns of annual rings suitable for dendrological investigations
are recognisable with a less laborious method that might be applicable
even in the field, i.e. contemporary digital radiography combined with
image processing. Samples of lumber shall be presented showing the typical
annual ring structures and some infested areas.
The preservation of human achievements and progress is undoubtedly a pillar of our society. This includes detecting threats in time to prevent disasters that may occur from forces of nature, defective technology, human failure or malicious intent. In this respect, there is arguably no difference between safety and security, though different institutions are involved in the regulation and control of them. However, the unifying rationale ought to result in the building of bridges between them. This is the Working Group's mission.
Neutrons are absorbed particularly by hydrogen containing materials so
they can be used as a tool for visualising heterogeneous density distributions of organic materials. Penetration limits are set by the layer thicknesses and the neutron energies applied. In case of specimens with a flat shape the situation may be encountered that the object only could be penetrated in selected directions. In addition, the overall size may exceed the beam diameter and thus the viewing window if a certain region of interest should be studied by tomography without destroying the integrity of the specimen.
This study shows the capabilities and limits of thermal and fast neutrons to investigate flat wooden specimens such as boards and girders by neutron tomography under such circumstances. Taking projections was impaired either by the limits of penetrability or by the total size of the object. As a consequence, projections were included for reconstruction only from a limited angular range of 90°. It could be shown that an approach based on the slice theorem was capable to visualise structural features along the beam directions while simply omitting the perpendicular ones without causing additional artefacts.
Small samples with a thickness of up to 2 cm but several times broader could be studied with the ANTARES facility of the FRM II neutron source in Garching providing thermal neutrons while larger objects required a beam of higher energy as available in the NECTAR facility of the same institution. The fast (fission) neutrons (1.5 – 2 MeV) of this site allowed investigating an area of interest inside a girder with a cross section of 23.5 x 49 cm². Internal features such as inclusions could be detected as well as a heterogeneous density distribution in glue layers.
An algorithm has been developed to remove reliably dotted interferences impairing the perceptibility of objects within a radiographic image. This particularly is a major challenge encountered with neutron radiographs collected at the NECTAR facility, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II): the resulting images are dominated by features resembling a snow flurry. These artefacts are caused by scattered neutrons, gamma radiation, cosmic radiation, etc. all hitting the detector CCD directly in spite of a sophisticated shielding. This makes such images rather useless for further direct evaluations.
One approach to resolve this problem of these random effects would be to collect a vast number of single images, to combine them appropriately and to process them with common image filtering procedures. However, it has been shown that, e.g. median filtering, depending on the kernel size in the plane and/or the number of single shots to be combined, is either insufficient or tends to blur sharp lined structures. This inevitably makes a visually controlled processing image by image unavoidable. Particularly in tomographic studies, it would be by far too tedious to treat each single projection by this way. Alternatively, it would be not only more comfortable but also in many cases the only reasonable approach to filter a stack of images in a batch procedure to get rid of the disturbing interferences.
The algorithm presented here meets all these requirements. It reliably frees the images from the snowy pattern described above without the loss of fine structures and without a general blurring of the image. It consists of an iterative, within a batch procedure parameter free filtering algorithm aiming to eliminate the often complex interfering artefacts while leaving the original information untouched as far as possible.
The effective high neutron scattering absorption coefficient of hydrogen (48.5 cm²/g) due to the scattering allows neutrons to reveal hydrocarbon structures with more contrast than X-rays, but at the same time limits the sample size and thickness that can be investigated. Many planar shaped objects, particularly wood samples, are sufficiently thin to allow thermal neutrons to transmit through the sample in a direction perpendicular to the planar face but not in a parallel direction, due to increased thickness. Often, this is an obstacle that prevents some tomographic reconstruction algorithms from obtaining desired results because of inadequate information or presence of distracting artifacts due to missing projections. This can be true for samples such as the distribution of glue in glulam (boards of wooden layers glued together), or the course of partially visible annual rings in trees where the features of interest are parallel to the planar surface of the sample. However, it should be possible to study these features by rotating the specimen within a limited angular range. In principle, this approach has been shown previously in a study with fast neutrons [2]. A study of this kind was performed at the Antares facility of FRM II in Garching with a 2.6×107/cm² s thermal neutron beam. The limit of penetration was determined for a wooden step wedge carved from a 2 cm×4 cm block of wood in comparison to other materials such as heavy metals and Lucite as specimens rich in hydrogen. The depth of the steps was 1 cm, the height 0.5 cm. The annual ring structures were clearly detectable up to 2 cm thickness. Wooden specimens, i.e. shivers, from a sunken old ship have been subjected to tomography. Not visible from the outside, clear radial structures have been found that are typical for certain kinds of wood. This insight was impaired in a case where the specimen had been soaked with ethylene glycol. In another large sample study, a planar board made of glulam has been studied to show the glued layers. This study shows not only the limits of penetration in wood but also demonstrates access to structures perpendicular to the surface in larger planar objects by tomography with fast neutrons, even with incomplete sets of projection data that covers an angular range of only 90° or even 60°.
Reducing risks and confining them to an acceptable level can be regarded as an essential commitment of technical applications for safety purposes and the public security measures.
Rating the efficiency of such measures requires an assessment of the risk that is supposed to be reduced. However, approaching this subject means to face a plethora of existing literature and an ongoing discussion if and how this can be achieved. On one hand, it remains a rather uncertain estimate particularly if it comes to rare interrupting events. On the other hand, making a decision responsibly requires a certain rational base. Several approaches exist for assessing risks, from verbal to quantitative, depending on the individual case. The frequently quoted Delphi technique represents the verbal one, others such as the Bayesian statistics a quantitative one or the consequence/probability matrix in-between.
A problem remains with understanding probability. Even if an event is highly unlikely it may happen right now.
The ultimate purpose of digital image filtering is to support the visual identification of certain features expressed
by characteristic shapes and patterns. Numerous recipes, algorithms and ready made programs exist nowadays
that predominantly have in common that users have to set certain parameters. Particularly if processing is fast
and shows results rather immediately, the choice of parameters may be guided by making the image 'looking
nice'. However, in practical situations most users are not in a mood to 'play around' with a displayed image,
particularly if they are in a stressy situation as it may encountered in security applications. The requirements for
the application of digital image processing under such circumstances will be discussed with an example of automatic
filtering without manual parameter settings that even entails the advantage of delivering unbiased results.
Safety and security both entail freedom from danger, i.e. unacceptable risk, whatever the cause might be. This
entails an understanding of the term 'risk' that is broadly used in areas such as economics, health, insurance etc.
According a rather popular definition used in the economical sciences for a long time (KNIGHT), risk has a lot
in common with uncertainty while the former is regarded quantifiable and the latter one is not. However, it has
to be taken into account that there are other understandings of 'uncertainty'. Particularly encountering rare
events never experienced before and recent contemporary definitions are weakening Knightfs differentiation.
This is reflected in some recent standard definitions. Attempts have been made to define a risk as common as
possible covering not only societal, ecological and financial areas but also natural and technical, ones. This is of
particular concern in non-destructive testing. This raises the question how far this can be achieved in a common
understanding, i.e. the discussion on this term seems not at all finished yet.
It is a common ambition to lower the risk by several actions including detection technologies. This entails that a
risk could be estimated somehow. The existence of numerous approaches indicates the complexity of this question.
The EFNDT (European Federation for Non-Destructive Testing) Working Group 5 took a commitment
also to tackle this central aspect of safety and security in its understanding as a bridging forum between these
two areas.
Stochastic artefacts are frequently encountered in digital radiography and tomography with neutrons. Most obviously, they are caused by ubiquitous scattered radiation hitting the CCD-sensor. They appear as scattered dots and, at higher frequency of occurrence, they may obscure the image. Some of these dotted interferences vary with time, however, a large portion of them remains persistent so the problem cannot be resolved by collecting stacks of images and to merge them to a median image. The situation becomes even worse in computed tomography (CT) where each artefact causes a circular pattern in the reconstructed plane. Therefore, these stochastic artefacts have to be removed completely and automatically while leaving the original image content untouched. A simplified image acquisition and artefact removal tool was developed at BAM and is available to interested users. Furthermore, an algorithm complying with all the requirements mentioned above was developed that reliably removes artefacts that could even exceed the size of a single pixel without affecting other parts of the image. It consists of an iterative two-step algorithm adjusting pixel values within a 3 × 3 matrix inside of a 5 × 5 kernel and the centre pixel only within a 3 × 3 kernel, resp. It has been applied to thousands of images obtained from the NECTAR facility at the FRM II in Garching, Germany, without any need of a visual control. In essence, the procedure consists of identifying and tackling asymmetric intensity distributions locally with recording each treatment of a pixel. Searching for the local asymmetry with subsequent correction rather than replacing individually identified pixels constitutes the basic idea of the algorithm. The efficiency of the proposed algorithm is demonstrated with a severely spoiled example of neutron radiography and tomography as compared with median filtering, the most convenient alternative approach by visual check, histogram and power spectra analysis.
The detection of defects in aircraft components or parts of a power plant or mines in the ground is connected with the task to distinguish between signals caused be the item searched for and noisy signals from other sources. The reliability of the system is the better the better the system is in detecting the wanted signal and avoiding false alarms caused by noise. It is usual to measure the reliability of diagnostic systems in terms of ROC-curves (Re-ceiver Operating Characteristics) and POD-curves (Probability of Detec-tion). The ROC curves describe the POD versus Probability of False Alarm with growing system sensitivity along the curve. POD curves describe the Probability of Detection for a fixed sensitivity for a variation of item sizes or depths. Reliability of the whole system is always a composition of the physics
and technique, application influences and the human factors. For the scien-tific understanding and possibilities of improvement, decomposition accord-ing to a modular model is helpful. The authors present their experiences with the reliability evaluation of metal detectors for humanitarian demining and an NDT system of mechanized ultrasonic phased array testing of copper welds. The special concern in demining is the influence of soil types, detec-tors and the experiences of human beings.
Wood is the material that has accompanied the whole development of mankind in various applications, for manufacturing tools and weapons, for buildings and constructions and also as fuel. It has various appearances and is subjected to decomposing changes, so there are sufficient arguments for non-destructive testing of wooden objects in the same way as is common practice with other technologically used materials. However, even today wood is rarely tested. Moreover, artefacts of cultural heritage containing wood are rare and delicate, so dismantling these for studying purposes is undesirable. Radiological inspection technologies are the methods of choice to provide a non-destructive insight. Interrogations of a specimen with various kinds of radiation provide different answers about their internal structures. High-quality detailed images are achievable with X-rays or gamma radiation in cases where heavy metals or other dense materials are not involved. Neutrons behave complementarily; they are avidly absorbed by light elements such as hydrogen on the one hand and yet are capable of easily penetrating heavy metals on the other. This provides an alternative for X-ray radiography and tomography when material characteristics are of primary interest rather than structural details, or when shielding with plates or sleeves of heavy metal severely impedes inspections with X-ray or gamma radiation technologies. However, due to the moderating effect of wooden samples it is essential to use fast neutrons for radiography and tomography of voluminous objects. Some typical examples described here will show the difference between neutron and X-ray photon-based radiographic technologies.
Some of the most perfidious remnants of war are mines threatening not
only combating parties but also innocent civilian lives. Moreover, they make large
areas inaccessible that otherwise could be used economically. This threat exists
even long after cessation of hostile actions. Up to now, the range of tools for humanitarian
demining is confined to mine detection dogs, metal detectors, prodders,
manual excavation tools and mechanical clearance machines (flails and tillers). In
1999, this gave rise for the Board of Directors of the EFNDT to suggest whether
detection methods commonly applied may also be helpful in detecting mines and the
like. It was proposed to transfer existing NDT technology to these areas. As a consequence,
Working Group 5 Antipersonnel Landmine Detection (APLD) was
founded to support this concept. As soon as the group became aware of the fact that
mines were encountered not only in the soil but also elsewhere the name was
changed to Antipersonnel Mine Detection (APMD).
It now is becoming more and more obvious that vicious devises such as mines
and bombs threatening lives everywhere represent an increasing risk to everybody.
In contrast, the particular interest in antipersonnel mine detection is decreasing in
favour of general security and safety. However, all these problems have in common
that such devices need to be detected in time, i.e. before they become effective. This
gives reason to extend the scope of the existing Working Group 5 accordingly. It is
of advantage to exchange existing knowledge and there is a chance to keep the
awareness of the mine problem alive by this way.
Industrial Radiology
(2006)
For the radiographic investigation of large cargo Containers the energies of conventional Xray tubes are inadequately for certain layer thicknesses. In that case the high energy radiation sources like electron accelerators and gamma radiators (60CO) are adequate for the non invasive inspection of large Containers because of the high penetration through thick materials. Multiple imaging even enables to distinguish between different materials. The main challenging task in air and sea cargo Container inspection is to improve the detectability of contraband and dangerous materials which are hidden in the heterogeneously packed Containers by detailed analysis of cluttered radiographic images. So it is to be expected that objects of organic substances like certain explosives or their precursors are hard to identify behind thick walls of heavy metal objects such as engine-blocks with flat bottom holes. The primary aim here is to investigate the detectability of dangerous materials (typically of light elements) in cargo Containers using high energy X-ray digital radiography.
Radiological inspections, in general, are the nondestructive testing (NDT) methods to detect the bulk of explosives in large objects. In contrast to personal luggage, cargo or building components constitute a complexity that may significantly hinder the detection of a threat by conventional X-ray transmission radiography. In this article, a novel X-ray backscatter technique is presented for detecting suspicious objects in a densely packed large object with only a single sided access. It consists of an X-ray backscatter camera with a special twisted slit collimator for imaging backscattering objects. The new X-ray backscatter camera is not only imaging the objects based on their densities but also by including the influences of surrounding objects. This unique feature of the X-ray backscatter camera provides new insights in identifying the internal features of the inspected object. Experimental mock-ups were designed imitating containers with threats among a complex packing as they may be encountered in reality. We investigated the dependence of the quality of the X-ray backscatter image on (a) the exposure time, (b) multiple exposures, (c) the distance between object and slit camera, and (d) the width of the slit. At the end, the significant advantages of the presented X-ray backscatter camera in the context of aviation and port security are discussed.
Threat detection and imaging
(2007)
Digital detectors such as phosphor imaging plates (IP) and digital detector arrays (DDA) allow radiographic inspection with higher efficiency and improved image quality in comparison to the classic film technique. Mobile X-ray flash tubes are used routinely for veterinarian and security applications. New high sensetive IPs and DDAs enable to apply them for inspection of light materials with low X-ray attenuation as in aluminium, plastics and composites. A versatile computed tompgraphy (CT) system was developed for in situ inspection of large aircraft components under production conditions. A gate based planar computed tomograph wsa developed and testes for inspection of integrety of the stringer incorporation. Successful test trials were performed to prove the detection rate of cracks in embedded stringers. Honey comb structures of aircrafts have to be inspected for water inclusions during in-service inspections. Thermography is a powerful method for in house inspections when variations in temperature caused e. g. by sunshine can be excluded. A new X-ray diaphragm was developed for mobile back scatter measurements of large components. This method is insensitive to heat alterations in the field and thus can be applied also outdoors.
As a matter of fact, avoiding unexpected events with an undesired outcome is an element of survival strategies.
Such events are encountered unexpectedly mainly because they occur rarely. Both, safety and security measures are the main pillars to prevent them by appropriate inspections. Common tools in both areas e.g. are radiological technologies enabling an insight into objects to detect suspicious features without even touching them. Since any of these measures is linked to efforts, costs or even obstructions of ongoing processes, it needs a rationale to invest into an appropriate activity. A putative objection to take action in this direction always could be the question 'when and how often it could happen'. This gave rise to find approaches how to define 'rare events' and how to deal with them. Since they entail both, the frequency of occurrence and the unpleasantness of the possible outcome make them to have something in common with the definition of risk: a combination of the probability of occurrence of harm and the severity of that harm. Tackling putative consequences is one side of the coin whereas understanding the rareness of an event is the other, an aspect that worries but not always fully understood.
As a first step in approaching the subject 'rare events', the putative occurrence rate is considered in terms of probability distribution functions or their cumulative ones, resp. The problems of estimating an incidence of such an event will be tackled subsequently with the problem of assessing the reliability of diagnostic measures.
Any numeric approach of dealing with rare events inevitably remains an ill defined or 'ill-posed' problem that needs additional information for a reasonably satisfying solution. Ways to ease this situation can be found in utilizing additional information, also commonly called prior knowledge, that might be introduced via the Bayesian inference or by regularization algorithms. Simplified models will demonstrate how to apply such tools.
As a consequence, there are ways helping to avoid unexpected ad 'surprises' by taking adequate measures in due time upon the correct perception of certain indications.
EFNDT working group 5 'NDT technology for public security and safety', two areas with the same aim
(2014)
It is a quite common and understandable wish to make the world a safer place. This entails both freedom from danger, and thus encompasses both, safety and security. However, it is a trivial fact that public security and technical safety are commitments to distinct social entities that might be quite understandable due to the various kinds of threats. On the other hand, it is a common justifiable interest to have effective methodologies to detect them in time, i.e., before something disastrous might happen. It is rather obvious that particularly non-destructive inspection technologies, namely radiological methods, are applied in both areas. As a logical consequence, sharing the technical knowledge and experiences could be of benefit for both of them. However, the different areas of activities cleave the information exchange between them. In order to overcome this gap, the EFNDT Working Group 5 'NDT Technology for Public Security and Safety' (EFNDT WG 5) has taken an initiative to bring together actors of both areas of activities, symbolized as building a 'bridge'. The activities of the EFNDT WG 5 range from identifying features exhibiting certain threats that are detectable with available NDT technologies, adapting and improving them according to their specified applications and to search for alternative technologies or ways of applications where deemed to be applicable. Successful exchanges of information and experiences have been achieved in recent workshops, where also new ideas have been raised for future common projects. This kind of work is far from being completed; it is more or less at its beginning. In future workshops it is intended to follow up these ideas and to pave the way for future common interdisciplinary projects. Therefore, all groups involved in such projects are welcome, not only researchers and NDT-specialists, but also all endusers of the respective technologies as well as theoreticians for risk assessment, performance evaluation, modelling, statistics etc. All the addressed areas are deemed to play an important role in making the world a safer place, cooperatively.
Wooden artworks residing in churches for centuries inevitably suffered from decaying processes such as Wood worm infestation. About 100 years ago, this process was ceased with a polluting coal tar extract 'Carbolineum', a treatment usually applied to railway sleepers. Nowadays, this lead to undesired effects not only of causing dark stains on the surface of the treated sculptures but also in unimpaired release of traces of harmful substances into the atmosphere perceptible as the typical smell of coal tar oil. To resolve this problem, the knowledge of the internal structure could provide a support for this effort. As an example, sculptures from an epitaph in a church in northern Germany were subjected to X-ray and neutron computed tomography (CT). The purpose of using neutrons was to get information about the distribution of the impregnant Carbolineum. It consists of a mixture of polycyclic aromatic hydrocarbons which should increase the absorption of neutrons. In contrast, X-rays are rather poorly absorbed by such substances as compared to the wood matrix. All radiographic approaches
revealed traces of previous conservation measures that were not always documented in detail. Comparing the neutron images with those from the X-ray interrogation some differences became obvious indicating varied material compositions. Nails e.g. were clearly visible in the X-ray images rather than in the neutron ones. Some less visibly stained parts of the sculptures correspond with obviously replaced materials in the inside. These results will be used to identify ways how to treat the infested artworks.
The objects of this investigation were sculptures taken from a ca. three hundred years old baroque epitaph of a church in Tonning, a town in Northern Germany. Around 1900 it was found in a disastrous state heavily damaged by wood-worm. At that time, the whole artwork was treated with the tar extract carbolineum as a remedy. Nowadays, this substance has been identified as carcinogenic, and its presence can be perceived by its stench and visually at certain spots on the surface where it has penetrated the covering paint.
A gold-painted sculpture of a massive wooden skull was interrogated with X-rays and fast neutrons to investigate the internal distribution of the carbolineum. The X-ray tomography, with its excellent spatial resolution revealed galleries left over from the worm infestation in the outer areas and cracks in the central region. The golden color coating appeared as a thick and dense layer. In comparison the tomography with fast neutrons, though being of lower resolution and yet unresolved artefacts revealed sections of slightly different densities in the bulk of the wood. These differences we attribute to the differences in the distribution of the impregnant in the wood, visible due to its higher hydrogen content making it less transparent for neutrons.
Rare events are understood to be events occurring once in a while but with dramatic consequences. Their occurrence cannot be predicted precisely, only a probability might be estimated, for example from past experiences. However, it might be rather misleading to attempt to describe them by distribution curves that apply for frequent or repeated observations, such as the Gaussian bell shape. Alternative distributions have been introduced to characterise the intervals at which a certain event may occur. It is the aim of technical safety and public security to prevent adverse events. Detectable indications that are typical for their course and are observable have to be identified before an incident occurs. Since they should be characteristic for such cases, they themselves also constitute rare events. The problem encountered in any detection system is that nothing is perfect. As in medical diagnostics, true indications may be missed or false test responses may pretend to be something that does not exist. Balancing missed indications with false positive calls is achieved with the aid of the so-called receiver operating characteristics (ROC). However, with the aid of Bayes’ inference it can be shown that identifying signs of a rarely occurring indication is like looking for a needle in a haystack, even with an excellent detection Approach with a low miss rate and an even lower probability of false calls. The inclusion of additionally available information may lead to a more effective search strategy. When employing imaging methods for detecting flaws or illicit items, the identification of rare indications can be impeded by blurring noise or overlapping items. The identification of the features sought can be supported by including information on their typical characteristics
by regularisation algorithms. The strategy of such an approach is demonstrated in a simplified example with a plain geometric figure (circle) corrupted with structural noise. The shape of the original figure was clearly recovered. In general, search strategies should aim at an indication typical for the event to be prevented; otherwise, alternative approaches have to be considered, including, perhaps, serendipity.
While the absorption of X-rays and gamma radiation is determined by the Z-number of the elements a specimen is composed of, it is the hydrogen making an effective contrast with neutron imaging. As a consequence, interrogating with neutrons presents a suitable tool to study the distribution of organic consolidants in materials such as wood as encountered in impregnated wooden artworks.
Four different examples of objects are presented here to demonstrate the potential of neutron CT: 1) small wooden pieces of ship wrecks (< 2 cm thickness) interrogated with cold neutrons (0.5 meV at the ANTARES facility of the FRM II in Garching) to demonstrate the potential and the limitation of using low energy neutrons, 2) a wooden statue soaked with carbolineum (fission neutrons 1.8 MeV at the NECTAR facility of the FRM II), 3) a smaller wooden figure of a skull heavily soaked with carbolineum so it was too tight for the fission neutrons used before with accelerator neutrons (broad range about 5.5 MeV at the PTB in Braunschweig) and 4) pieces of charred wood to study the impregnation with a consolidant (NECTAR, FRM II). With the exception of the last example, all results have been combined with X-ray tomography (BAM 8.3 in Berlin). In the case of the charred wood specimens (example 4) the density histograms of the neutron tomography results were compared with those obtained from untreated references. The observed gain in specific density of the soaked specimens corresponded with an increase of specific weight. All results obtained so far showed distinct distribution patterns attributable to structural peculiarities or organic consolidants providing valuable support for subsequent restoration works.