ActiWiz – a tool to reduce activation levels in CERN’s accelerators even further
CERN operates accelerators to deliver high-energy particle beams for physics. This requires extremely precise beam steering, and tremendous efforts are invested to keep beam losses at the absolute minimum.
However, it is inevitable that some particles escape from their ideal path and, furthermore, the beam is sometimes even intentionally directed to hit equipment like targets or collimators. This results in the creation of radioactive nuclei in the matter with which the beam interacts. The physical processes driving this phenomenon are quite complex and the level of activation depends on a multitude of parameters like the location of the material with respect to the beam loss, the length of the irradiation period and potentially the chemical composition of the irradiated material. Sometimes the presence of chemical elements that are found only in traces, even fractions of weight-percent, can cause considerable differences when it comes to the beam-impact-driven production of radioactivity.
The decay process of the radioactive nuclei generates a radiation field to which workers are exposed during maintenance and repair. Consequently, the level of radioactivity has direct consequences for the operation of the accelerators and experiments as it imposes constraints in terms of accessibility and the safe handling of equipment. On the other hand, it also has an impact on CERN’s environmental footprint due to the creation of potentially radioactive waste. Optimising the choice of materials not only for mechanical properties but also with respect to the radiological hazard clearly has a safety benefit as well as operational and financial benefits. It should be seen as a prudent investment into the future, especially in view of new projects striving for even higher beam intensities and energies.
In order to support the accelerator and high-energy physics communities to meet those challenges, a unique piece of software called ActiWiz has been developed by the Radiation Protection (RP) group in the HSE Unit. This tool is based on calculations using the FLUKA Monte Carlo code, which is widely used for RP studies at CERN and is the most appropriate code for activation calculations up to LHC energies. ActiWiz provides rankings for materials whose chemical composition can be freely defined with respect to their radiological hazard. It comes with a graphical user interface and consequently allows for a simple first comparison of materials without any need for expertise in radiation sciences. Based on this tool and thanks to a fruitful collaboration with CERN's material science experts in the EN-MME group, the HSE Unit has issued a catalogue ranking the most common raw materials that are used in our accelerators. The software has also been used to provide input for the Raw Material Working team, headed by the EN-MME group, who are currently updating CERN’s material specifications. Although the current release of the tool mainly focuses on CERN’s accelerators, several institutes (e.g. PSI in Switzerland, KEK in Japan, etc.) have asked to use the software. With the support of the Knowledge Transfer group, the RP group is now able to provide the tool to interested parties via appropriate licences. Work on the next generation has started in order to respond to the need for such a tool for other CERN facilities, including the LHC experiments as well as future installations, and to the large number of requests from outside CERN. This future version should allow users to evaluate the creation of radioactivity in all relevant radiation fields.
The radiological material hazard catalogue and the software are available for internal use within CERN and can be found at: www.cern.ch/actiwiz
by HSE Unit
