HIGH-ACCURACY DETERMINATION OF THE SHAPE OF THE EFFICIENCY CURVE OF THE HPGE DETECTOR IN THE ENERGY-RANGE 900-KEV TO 1300-KEV

A method for high accuracy characterization of the shape of a High Pur ity Germanium (HPGe) detector efficiency curve has been developed. Rad ionuclides with decay schemes having at least two gamma lines, for whi ch the yield ratio can be calculated accurately, are used to establish the shape of the detector efficiency curve. Measurements using Co-60 and Sc-46 sources show that the behavior of the efficiency curve of th e detector on a log-log scale is indistinguishable from that of a stra ight Line with a slope of -0.828 +/- 0.004. Measurements using a Na-24 source show that above 1368 keV this behavior no longer holds due to pair production and escape effects. The measured value of the slope in that case is -0.951 +/- 0.002. The proposed method is to be used in m easurements requiring the minimum calibration bias in the determinatio n of the reaction rate ratios, such as reactor dosimetry applications, integral cross section measurements and k(0) determination for neutro n activation analysis.