RAPID DETAILED CHARACTERIZATION OF CONCRETE SHIELDING BLOCKS UTILIZING INTERNAL NATURAL RADIONUCLIDES FOR CALIBRATION

Following many years of productive research, the 184-inch Cyclotron, t he SuperHILAC, and the BEVALAC accelerators at the Berkeley Laboratory were closed, leaving thousands of concrete shielding blocks available for reuse, recycling, or disposal. The process history of these block s precludes free release pending radiological characterization. This p aper describes a procedure whereby a high efficiency shielded germaniu m spectrometer is used to rapidly characterize natural and man-made ac tivity within the blocks. The spectrometer is moved up to the block an d 5 minutes of data are collected at the point on the block that regis ters highest on a micro-R meter. Sensitivity is better than 1 pCi/g (0 .037 Bq/g) for Co-60 and Eu-152, the prominent man-made activities obs erved. One-time calibration of the detector system is obtained from a sample of concrete, drilled with a hammer drill, counted in our low-ba ckground facility, and compared to crushed rock with known U, Th, and K activity. A simple relationship exists between the counts/minute obs erved in a characteristic gamma-ray peak and the activity in the block .