A new experimental procedure for determination of photoelectric efficiency of a NaI(Tl) detector used for nuclear medicine liquid waste monitoring with traceability to a reference standard radionuclide calibrator.

To determine photopeak efficiency for (99m)Tc of the NaI(Tl) detector used for liquid waste monitoring at the Nuclear Medicine Unit of IRCCS Paediatric Hospital Bambino Gesù in Rome, a specific experimental procedure, with traceability to primary standards, was developed. Working with the Italian National Institute for Occupational Prevention and Safety, two different calibration source geometries were employed and the detector response dependence on geometry was investigated. The large percentage difference (almost 40%) between the two efficiency values obtained showed that geometrical effects cannot be neglected.