IDENTIFIKASI MUTIARA BERDASARKAN KOEFISIEN ATENUASI LINIER MENGGUNAKAN MIKRO TOMOGRAFI KOMPUTER SINAR-X; PEARL IDENTIFICATION BASED ON LINEAR ATTENUATION COEFFICIENT USING X-RAY MICRO COMPUTED TOMOGRAPHY

Santoso, Pande Putu Agus, N

2015 | Disertasi | FMIPA

Pearls are the only type of gemstone, which is grown in the living organisms, that is pearl oyster. Based on the pearls formation process, it can be classified into three, seawater pearls, freshwater pearls and imitation pearl (from shell or from resin). It is hard to distinguish pearls when using conventional method. Solutions offered through this research is using linear attenuation coefficient (?) of pearl, which was obtained by an x-ray micro Computed Tomography, as a basis for identification. t-test were applied to distinguish the ? value of each pearl, so it can use for the identification parameter. The results from line profil analysis show that cross-section image from four kinds of pearl in each pearl is relatively homogen. Based on this homogenity, the ? analysis by taking into account of 4 points (top, left, botton, and right) in every slice image and 150 slices from each sample was done. The result of ? analysis using DRCT software show that the ? of freshwater pearl is (7,3 ± 0,6) x 10-3 cm- 1, the resin pearl ? is (4,7 ± 0,4) x 10-3 cm-1, the shell pearl ? is (4,0 ± 0,3) x 10-3 cm-1, and the seawater pearl ? is (2,9 ± 0,3) x 10-3 cm-1. The result of density analysis show that freshwater pearl ? is (3,6 ± 0,1) g/cm3, resin pearl ? is (2,9 ± 0,3) g/cm3, shell pearl ? is (2,6 ± 0,2) g/cm3 and seawater pearl ? is (2,5 ± 0,1) g/cm3. This case show that if pearls density increase so its ? increases too. Statistic analysis (t-test) showed that there are differences between each kind of ?, at the 95% confidence level. So it can be concluded that the linear attenuation coefficient can be used as an indicator in identifying pearls scientifically.

Kata Kunci : pearl identification; linear attenuation coefficient (?); X-ray; computed tomography