Reduce Shielding Design Cycle Time From Over a Week to Several Cycles per Day

CHALLENGE

Design cycle time for new shielding configurations or modifications to existing configurations was simply too long. Typically 2 weeks or more.

SOLUTION

Automate the existing analysis process.  Use finite element structure to convey configuration geometry to a custom built program. Further improve the automated process by reducing the computational time.

Linear accelerator based x-ray sources generate x-rays in all directions.  The “forward” direction (the direction the electrons were going before they were stopped) is stronger and these are the useful x-rays, but unwanted x-rays are also generated that go sideways and even directly backwards.  Shielding is added to the system to attenuate the x-rays in unwanted directions.   The tradeoff is weight.  In some situations, this may be a critical factor (a crane mounted system, for example).

When my current employment began, I recall watching this iterative design process.  Designers would print out full size section drawings, manually measure distances, and put these numbers into an excel spreadsheet.  Completing this process required a week, so a full design cycle typically took 2 or 3 weeks.

I developed a computational code that automated this process.  I could take CAD geometry, in the form of a finite element mesh from a structural code, and analyze it directly to get shielding effectiveness.  This code performed the same types of calculations as the manual process, calculating distances along various paths from the target, but of course automatically and in more detail.

The code I developed performed the calculations correctly, but because of the number of elements involved and the solution of 4 sets of three equation in three unknowns for each, for each direction, the solution time was still on the order of 2 days.  I also developed a method to speed this up, by a factor of 1000. This made the program a very useful tool reducing design cycle time from weeks, to several cycles per day.

Further improvements have been recently realized by enabling the code to operate on ”.STL” files that can be directly generated from CAD.  This eliminates the need for a finite element code to generate the mesh and results in further execution speed improvements.

Below is a typical plot of the results that can be easily inspected for weak areas in the shielding.

Data visualization through Excel

The end result is easy inspection for both under and over shielded regions. In this plot the vertical scale is the logarithm of the ratio of the radiation emitted in a particular direction to the 0° (main beam) radiation.