Studies on the Detection of Surface Contamination by Electron Capture Emitters

Contamination in German nuclear power plants often contains the nuclides 51Cr, 54Mn, 55Fe, 58Co and 65Zn. These nuclides decay principally by electron capture and contamination containing these nuclides is not easy to detect. It will be shown that with the large-area proportional counters generally used for contamination detection it is possible to detect surface contamination of less than 5 Bq.cm-2 generated by electron capture emitters if argon-methane is used as the counter gas. Contaminations of even less than 0.5 Bq.cm-2 can be detected by using suitable pulse height discrimination.