An on-line enrichment monitor has been designed and developed which is applied to measure the enrichment of UF6 gas flowing through the processing pipes in uranium enrichment plant, and a set of corresponding software has been set up. It uses a sodium-iodide detector to measure the rates of 186 keV An on-line enrichment monitor has been designed and developed which is applied to measure the enrichment of UF6 gas flowing through the processing pipes in uranium enrichment plant, and a set of corresponding software has been set up. It uses a sodium-iodide detector to measure the rates of 186 keV