Dose rate through a small aperture widget

Source: Design & implementation by Dr Chris Robbins (Grallator) / Facilitated by Ionactive radiation protection resource

The scenario description and mathematical  / physics analysis upon which this widget is built can be found at the following resource: 'Radioactive source holders - Dose rate through an aperture' (opens in a new window). 

The widget is reasonably self explanatory,  and whilst the above referenced article uses some real data based on Cs-137, radionuclide and shielding material is not important since the widget uses scaled dose rates and TVT / HVT (10th value thickness and 1/2 value thickness).  The geometry is set up such that the activity of the shielded radioactive source increases with source shielding diameter, such that the surface dose rate away from the aperture is always 5 micro Sv/h (typical for the outer surface of a radioactive source holder on a nuclear gauge). 

Have a play by:

  • altering the shielding diameter
  • changing the aperture diameter
  • changing distance by dragging ion man closer to, or further way, from the aperture. 

Some observations  / discussion 

For given values of shield and aperture diameter, and position of ion man (distance), note in particular the following:

  • Maximum dose rate (to any part of the body)
  • Fractional (%) of trunk exposed at given distance from the aperture
  • The distance required between the open aperture and ion man where full trunk (effective dose) exposure can be assumed.  

Of particular interest (to Ionactive) is that headline dose rates (either calculated or measured near the aperture) are a poor indicator of whole body exposure. Furthermore, whilst whole body dosimetry would be worn during such scenarios, a modest exposure recorded on a dosimeter might significantly underestimate the equivalent dose to a part of the body (including hands and eyes).

Physics is, hopefully, simple. Physicists are not

– Edward Teller -