A new assembly dedicated for the low-level ψ-ray spectrometric measurements of environmental samples have been installed recently
at the International Atomic Energy Agency's Laboratories, Seibersdorf. Calibration of the detection efficiency was performed
by a set of 14 IAEA Certified Reference Materials, a standardized solution of134Cs, solutions of 2 pure potassium salts, and 2 mixed radionuclide gamma reference standard solutions. These materials, in
1.3 liter Marinelli beakers, were measured by a large HPGe detector. The high precision and accuracy of the calibration procedure
is shown by the high significance achieved in the linear fits of the efficiency results, which are traceable to certified
and standard reference materials. Small biases between some calibrands were detected. A new corrected result is the 1.37±0.05
Bq/kg activity concentration of137Cs in IAEA-A-14 Milk Powder.