Gamma radiography using Selenium-75 is now generally acknowledged throughout the world to provide performance benefits relative to Iridium-192 in the working range of 5-30mm steel. Selenium-75 has a softer gamma ray spectrum than Iridium-192 and it has a significantly longer half-life. For these reasons Selenium-75 provides real performance benefits and working life advantages. The general features and benefits of these sources and their performance relative to other techniques has been thoroughly researched and published elsewhere [1,2].

Selenium-75 provides advantages of longer half-life, improved operator safety, smaller exclusion zone and high image quality, particularly in the 5-30mm steel working range. The advantage of the longer half-life reduces decay loss due to transportation and minimizes the costs associated with managing frequent source exchanges of other isotopes. This is particularly beneficial when sources are used in remote geographical regions and most particularly in offshore applications. Safety compliance, operator dose and storage logistics are made easier using Selenium-75. The operational exclusion zone for Selenium-75 is reduced relative to that of Iridium-192 due to the softer emission spectrum and lower gamma ray constant. Sources can be used in more restricted areas, affording considerable operational and safety advantages. The half-life of Selenium-75 is 120 days; this is almost double that of Iridium-192 and four times Ytterbium-169.