2-D PRECISE AUTORADIOGRAPHY OF SEDIMENTARY CORE USING IMAGING PLATE

The Imaging plate (IP) is a storage film coated with photostimulated phosphor (BaFBr: Eu2+), and the latent images produced by irradiation of the imaging plate are read by superficial scanning with stimulation light and are reconstructed as two-dimensional dot images on a computer display. It has excellent performance for radiation detection, and its advantages include the ease of use, a high position resolution (up to 25μm), a large detection area (up to 35×43cm2), a high detection sensitivity with high signal-to-noise ratio, an extremely wide dynamic range of dose, sensitivity to several kinds of radiation, and an erasing capability for reuse (Hareyama et al., 2000). Therefore, in order to develop nondestructive, precise and large area evaluation method of sedimentary structure, application of autoradiography using IP is attempted to marine sediment.

IP (BAS-MS2040 Fujifilm Co. Ltd., 20×40 cm2) was cut into rectangular five pieces (4×40 cm2). Whole round marine sedimentary cores were divided into two half for duplicate and they were covered with a plastic wrap. The rectangular IP were put along the center line of plane side of half round. The exposure in the low temperature was for 48 hours in a shield box. The latent images produced by irradiation of the IP were read out by using the BAS-2500 imaging analyzer (Fujifilm Co. Ltd.). Radiation dose of IP is output as PSL value, that is unique dose units and quantities of IP system. Position resolution was set to 50μm.

Marine sedimentary cores including volcanic ash layer were measured using IP and Natural Gamma Logger (NGL), which is measuring instrument for marine sediments in practice use, to compare their measuring ability. The content of radiation source in volcanic ash layer is expected to be high compared with other layers because minerals tend to have more potassium, uranium and other radioactive elements than other layer components, for example, organic materials and biotic shells. As a result of experiment, it becomes clear that high dose distribution is found at volcanic ash layer with IP, meanwhile it can’t be found with NGL. It is considered that IP has high position resolution and detection sensitivity to figure out the dose distribution from volcanic ash layer.