Radiation measurements at the site boundary for the MOLLER Experiment Vassu Doomra (for the MOLLER Collaboration)

For the safety of the personnel working at Jefferson Lab, it’s important to ensure that the shielding around the experiment is reducing the radiation levels to an acceptable limit set by the DOE/JLab (100/10 mrem/year). Absorbed Dose is a crucial parameter in quantifying these radiation levels. However, for discussing biological effects, the nonspecificity of the absorbed dose proves to be inconvenient. Studies have shown that the biological damage caused by irradiation is a strong function of the specific radiation type. To account for this effect, the absorbed dose is multiplied by a quality factor measuring the relative biological effectiveness (specific for each radiation type) and that gives the equivalent dose (measured in rem).

The monitors measuring the equivalent dose at Jefferson Lab are located at the periphery of the lab ( 200 m away from the center of Hall A) and hence the name boundary dose monitors. Full GEANT4 simulations have been performed to determine the origin of particles (from within the experimental hall) contributing the most towards boundary dose. The results of these simulations suggest that neutrons are the largest contributors to the boundary dose. And that these neutrons are mainly originating from the target and the upstream region.