Safe Working Distance for Radiography

  • Safe Working Distance for Radiography

    Posted by arsal on 27/11/2021 at 2:30 pm

    Can someone help me out? I am trying to figure out how do radiographers calculate the safe working distance from a source. We are in a shutdown and have maintenance crews working in the same areas as RT crews. I know the inverse square law gives us that information, but that is theoretical. What about if they are using a collimator and the pipe is 1/2″ thick with a double wall exposure. What would be the actual distance? And what about the direction of the radiation?
    Thanks in advance for your help.

    lucas replied 5 months, 4 weeks ago 2 Members · 1 Reply
  • 1 Reply
  • Radiography


    27/11/2021 at 10:47 pm
    2 Points

    You must have a physical barrier at 7.5 ìSv/hr. How do you achieve this? Let’s say you use 250 kV and 4 mA in your example. If no object is in the way for the radiation this gives 6 Sv/hr at 1 metre. If you then use the inverse square law the safety distance is 895 m. For steel and 250 kV the half value layer is 12 mm. So if the incoming radiation is 6 Sv/hr the radiation out is approx. 3 Sv/hr, then you need a safety distance of… 632 m. –Wow. This is how to calculate the safety distance for the central beam of radiation, but in the real life you have other objects around you that absorb the radiation (pipes, valves, etc.), so if don’t want to set up a barrier around half the world you need to measure the radiation level with a dose rate meter.