Neutron Computed Tomography for Concepts in Decontaminating Biocidally Treated Wooden Artefacts

Abstract

The preservation of wooden artwork using pesticides or carbolineum some hundred years ago raised new problems over the years. They consist not only of aesthetic ones such as darkening of pigmentations but also of environmental ones by the persisting release of polluting substances. Approaches of resolving these problems should be preceded by a vision into the inside situation of the infested objects. Radiological methods with fast neutrons were chosen as appropriate measures for this purpose since imaging with neutrons is sensitive to reveal density distribution patterns of hydrocarbons inside of an object. It was expected that the treatment with carbolineum hadincreased the hydrogen content of the wooden matrix. Fast neutrons were demonstrably essential to penetrate the interrogated specimens. Imaging problems encountered with fast neutrons have been successfully resolved, metal shielding did not impair the detection of structural details, and the ultimate penetration limit in wood has been reached at a layer thickness of 50 cm. Two sculptures taken from an epitaph in a church in Northern Germany were studied in detail, one of them additionally with X-rays. It was shown that computed tomography (CT) was much more conclusive than straight forward radiography. While X-ray techniques remained the measures of choice to investigate structural details neutron CT reflected the hydrogen content that may give a clue to the distribution of the impregnant the objects were treated with. It is suggested to use a combination of both technologies to support the preservation work on wooden artworks infested with the described problem.