Answer to Question #11104 Submitted to "Ask the Experts"

Category: Accelerators — Radiation shielding

The following question was answered by an expert in the appropriate field:

Q

In order to calculate the shielding requirements for a static industrial electron boron plant linear accelerator, what does radiation leakage mean?

Which standard would you recomend using since National Council on Radiation Protection and Measurements (NCRP) 151, Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities is for medical equipment?

How do you suggest doing the calculations?

A

Basically, radiation leakage is the radiation that leaks out of the shielding. If you are referring to the language used in NCRP 151, Structural Shielding Design and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities, it distinguishes between the sources of the leakage radiation. Any radiation from the source/linear accelerator that gets through the shielding/barrier is called leakage radiation. Then any radiation that is scattered from the patient under treatment (or object being irradiated in your case) that leaks through the barrier downstream of the patient is called scattered leakage radiation.

The goal of your shielding design should be to reduce the dose rates from all leakage radiation to levels at or below what is required by the regulations. Depending on the linear accelerator's beam energy and current, you will need a combination of iron and concrete to provide the required attenuation of the radiation produced in the accelerator and the target area. If space is tight, you may have to use other material such as lead and polyethylene or a combination of the four for shielding.

I suggest using NCRP 144, Radiation Protection for Particle Accelerator Facilities, for the shielding parameters, especially section 3.3 and chapter 4. NCRP 51 is an older version of NCRP 144, but since you have a relatively low energy linear accelerator, you can use NCRP 51 as well. The information provided in NCRP 151 can also be used to achieve the level of shielding that you require.

Kamran Vaziri, PhD

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