The standard deals with leakage test methods on sealed radioactive sources in the context of production and prototype testing related to DIN 25426 part 1 or part 2. The test methods have the purpose to guarantee that only leaktight sealed sources can be circulated.
DIN 25426-3:1991 history
2021DIN ISO 9978:2021 Radiation protection - Sealed sources - Leakage test methods (ISO 9978:2020)
1991DIN 25426-3:1991 Sealed radioactive sources; leakage test methods as part of production and prototype testing