Answer to Question #4702 Submitted to "Ask the Experts"

I am working with a wide spectrum of radionuclides. I need to know how much lead shielding is needed for each radionuclide since the HLV (half-value layers) vary with emitted gamma energy. Is such a list available?

You have essentially answered your question. Since each radionuclide has a different array of gamma-ray energies, each radionuclide has a certain half-value layer (HVL). If you are going to store all of your radionuclides in the same general area, you will want to provide enough shielding to shield gamma rays from the radionuclide with the highest HVL value.

A 3.33 HVL corresponds to one-tenth value layer (TVL) and may be adequate for small quantities of radionuclides. This may not be enough for higher activities (you did not specify radionuclides or activities that you are using).

The driving factor will be the dose rate measured with a survey meter outside the shielded area and what survey trigger levels you have set up for your facility. In most regulatory jurisdictions, the maximum exposure in an unrestricted area cannot exceed 2 mrem in any one hour and 100 mrem in one year. Note that occupancy must be factored into the calculation. These numbers will be higher for radiation workers in controlled or restricted areas.

You should work with the radiation safety officer for your facility to determine if the amount of shielding that you use is adequate to protect workers and members of the public from unnecessary radiation exposure.

Ken "Duke" Lovins, MS, CHP