Comparison of Design and Practices for Radiation Safety among Five Synchrotron Radiation Facilities

There are more and more third-generation synchrotron radiation (SR) facilities in the world that utilize low emittance electron (or positron) beam circulating in a storage ring to generate synchrotron light for various types of experiments. A storage ring based SR facility consists of an injector, a storage ring, and many SR beamlines. When compared to other types of accelerator facilities, the design and practices for radiation safety of storage ring and SR beamlines are unique to SR facilities. Unlike many other accelerator facilities, the storage ring and beamlines of a SR facility are generally above ground with users and workers occupying the experimental floor frequently. The users are generally non-radiation workers and do not wear dosimeters, though basic facility safety training is required. Thus, the shielding design typically aims for an annual dose limit of 100 mrem over 2000 h without the need for administrative control for radiation hazards. On the other hand, for operational and cost considerations, the concrete ring wall (both lateral and ratchet walls) is often desired to be no more than a few feet thick (with an even thinner roof). Most SR facilities have similar operation modes and beam parameters (both injection and stored) for storage ring and SR beamlines. The facility typically operates almost full year with one-month start-up period, 10-month science program for experiments (with short accelerator physics studies and routine maintenance during the period of science program), and a month-long shutdown period. A typical operational mode for science program consists of long periods of circulating stored beam (which decays with a lifetime in tens of hours), interposed with short injection events (in minutes) to fill the stored current. The stored beam energy ranges from a few hundreds MeV to 10 GeV with a low injection beam power (generally less than 10 watts). The injection beam energy can be the same as, or lower than, the stored beam energy. However, the stored beam power (product of stored beam current and energy), which is one of the key parameters in determining the production and hazards of gas bremsstrahlung (GB) and SR in beamlines, is quite high (MW to GW levels). Because of the similar design and dose control goals as well as similar beam parameters and operation modes among SR facilities, it is highly desired and useful for SR accelerator community to have the design and practices for radiation safety of the storage ring and SR beamlines that are professionally sound and consistent. On the other hand, it can be understood that a SR facility may need to have its specific policies and practices, due to its own technical, practical, economical and/or political considerations