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AN IN SITU RADIOGRAPHIC SYSTEM FOR IMAGING MARINE SEDIMENT

This paper introduces a radiographic system for imaging marine sedimentary structures in situ, as an alternative to the currently used intrusive and tedious process of imaging extracted core samples in the laboratory. The system consists of a small isotopic source and a film incorporated into a device that can penetrate the sediment. The design of the device is introduced, and the results of mock-up experiments conducted to demonstrate the feasibility of the concept are presented. Introduction: Extracted cores of marine sediments are x-rayed in the laboratory [1], to facilitate the analysis of its properties, sedimentary structure (formation mechanism), and biological content. Sediment cores are typically shaped as rectangular or cylindrical columns, extracted from marine sediment floors by a suitable coring technique [2]. These cores are then sliced into thin sections suitable for radiography. The quality and reliability of x-ray radiography of extracted cores depend to a large extent on the physical integrity of the collected sediment samples and on the precision of extraction. Extracted cores are frequently stored for long periods before slicing or radiography, which increases the probability of desiccation (drying), alteration and contamination of core [3]. Saw marks might also remain in the sliced sample, obscuring structural details [2]. This intrusive and tedious process can be overcome by performing in situ imaging. Obviously, in situ imaging cannot be performed with a conventional x-ray machine, but can be readily conducted with a small radioisotopic source. We, therefore, conceived the system shown in Figure 1, which consists of a mechanism to hold the source and a radiographic film in place, and enable their insertion into (and removal from) the sediment, in a manner similar to that used in oil well-logging devices employed in petroleum exploration [4]. To our knowledge, this concept of in situ radiography of sediment was not explored before. As Figure 1 shows, the introduced system employs a mechanism similar to that used in existing coring mechanisms. A radioisotopic source capsule is mounted at the end of a source guiding rod that enables its insertion into the sediment. The small size and self-powered nature of radioisotopes, and their ability to sustain underwater conditions of marine sediment, makes them particularly suited for this application. A waterproof film holder is to be positioned on the periphery of the device to hold the film during radiation exposure. In order to reduce image geometric-unshaprness, it is necessary to maintain some distance between the source and the object. This can be accommodated in the confined space of the in situ device by creating a vacated core between the source and the imaged section, while keeping the source at the periphery, as shown in Figure 2.