Iridium-192, Cobalt-60, Ytterbium-169 and Thalium-170 have been used in gamma radiography throughout the last decades, with Co-60 and Ir-192 being the most common isotopes. For weld inspection in a very large range of material thicknesses Ir-192 has been the first choice among the isotopes. Recently the isotope Selenium- 75 has been made available for industrial gamma radiography including a gammagraphic apparatus optimized for the use with Se- 75.

The isotope Se-75 provides radiation energies considerably lower than the Ir-192 spectrum, which results in largely improved quality of weld radiographs. Sources of 3 TBq (80 Ci) at a physical size of 3 x 3 mm and a halflife of approximately 120 days are most interesting aspects for practical applications in gamma radiography. The working and transport container, has been designed in compliance to new draft of ISO 3999 and offers an incredibly low weight of 7 kg at a maximum load of 3 TBq Se- 75.

The paper discusses the properties of this new isotope and its applications in gamma radiography. The radiographic parameters of Se-75 have been measured using different film types and lead screens. These results have been taken into account with the proposal for the new European standard EN 1435 for radiographic inspection of weldments and the draft of ISO5579.