For the International Monitoring System (IMS) to be effective, it is vital that nuclear explosion signals can be distinguished from natural and man-made radioactivity in the atmosphere. The International Data Centre (IDC) applies standard event screening criteria, with the objective of characterizing, highlighting, and thereby screening out, events considered to be consistent with natural phenomena or non-nuclear, man-made phenomena. This presentation looks back to the initial understanding of possible screening methods in the early years of CTBT negotiations, summarizes the development of the categorization schemes and screening flags applied in the IDC reports for each particulate and noble gas sample, and reviews new proposals and open issues for discriminating nuclear explosion signals from normal radioactivity background in the atmosphere. There is still high need and ample room for enhancing radionuclide screening methodologies. This presentation sketches out what methods that were already demonstrated can be enhanced and implemented in the coming years, which novel methods appear promising to be developed and it creates a vision of highly effective screening for the longer future.
Much has been achieved in developing methods for radionuclide screening, but future developments will make the detection of radionuclide signals of nuclear explosions much more effective.