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Experimentsfor the Analysis of Ash and Sulphur of Low-ash Coal with Radioisotope 55Fe.Hiroshi KAMADA, Keiji MOTOMIYA and Jiroh ONODERAFor the purpose of the automation of the coal preparation process , experiments for the rapid analysis of ash and sulphur of low-ash coal were carried out at the Miike Coal Preparation Plant using radioisotope 55Fe, 80 mCi, including automatic sampling , drying and preparation of samples.Mn KX ray from this RI was irradiated to the surface of coal powder samph; back-scattered X-ray was detected by Xe-sealed proportional counter; the energy analysis was made by filters and pulse-height analyzers and finally the analy tical values of ash and sulphur were calculated with the established regression equations. Results obtained are as follows:1) It takes approximately 25 minutes from the automatic sapling of clean coal (about 10 kg, minus 35 mm in size and about 10% moisture content) to the display of the calculation results. 2) Accuracies of the regression equations for clean coal of Miike (ash; 8%, sulphur; 2%) are 0.200for ash and 0.1% for sulphur, respectively. 3) This method is also applicable to low-ash coals other than Miike; but in the case of extremely low sulphur coals, the regression equations for ash should be establi shed separately by the rearrangement of these low-sulphur coals. 4) The optimum X-ray analysis can be conducted when coal powder samples have 85 to 95% weight of passing at 0.25 mm and moisture content less than 1% . 5) The higher the Ca content in ash, the larger the O/C atomic ratio in coal , then the higher the analytical value of ash. This can be attributed to the higher mass absorption coefficient of Ca than AI or Si, etc., and that of 0 than C, to Mn KX-ray . 6) When applying this measurement system to the same group of coal samples, accuracy of the analysis is of good satisfaction even to the high-ash region up to about 50% . Therefore, if a certain interval of allowable error is provided , X-ray analysis at the high-ash region can be successfully made.