SURVEY TECHNIQUES FOR MEASURING URANIUM-235

This paper discusses a survey technique for U-235 using a portable stabilized gamma ray meter with a 5 cm by 1.3 cm AM-241 doped Nal detector. Surveys of ventilation ducts, filter housings, and miscellaneous items are described. The survey technique is calibrated relative to standards fabricated to represent the holdup in cylindrical ducting and large filter housings. Miscellaneous items are surveyed using a calibration based on adding a source with known U-235 content to the unknown being surveyed. Since thorium is present, the technique includes procedures for eliminating the thorium background interference. Data are presented showing the accuracy of the survey technique which was determined by comparing survey results with assays of the material aftT cleanout.