Workplace monitoring of swipes and air filters for 55Fe

⁵⁵Fe has been identified as a possible contaminant found around nuclear reactors. Possible suspension and dispersion of the radioactive-iron during planned repairs could result in intakes by the workers. The weak 5.9 keV X-ray from ⁵⁵Fe is difficult to detect in the presence of other radionuclides like ¹⁴C, ⁵¹Cr, ⁵⁴Mn, ⁶⁰Co, ⁹⁵Zr/Nb ¹⁶⁰Tb and plutonium. The low-energy X-rays from iron are stopped by the windows of most common detectors and are not detected by normal routine measurements. This paper describes a monitor, based on a sealed, xenon-filled (3% CO₂) proportional counter with a 25 mm by 50 mm thin (0.05 mm) beryllium window. Detector is located in a lead castle with a shuttle mechanism for swipe media or air filters. Signal amplification, conditioning and display of results is achieved with Nuclear Instrumentation Modules (NIM) electronics. A single channel analyzer (SCA) was used instead of a multichannel analyzer (MCA) for simplicity and ease of operation. The detection limit for a distributed source and 100 second count time is about 10 Bq