Study of thermal neutron albedo for hydrogenous materials using Geant4 simulations

The medical LINACS with energies greater than 8 MeV produce photo-neutrons along with x-rays. These photo-neutrons contaminate the therapeutic beam and are of concern to the personnel working around the treatment room. Consequently, study of neutron albedo is very helpful for radiation protection purposes. In this work, the integral neutron albedo is determined as a function of thickness of target materials using parallel beam of thermal neutrons for a number of materials important in radiation protection and medical purposes, including water, aluminum, lead, iron, beryllium, graphite, skin-ICRP, soft tissue-ICRP, muscle skeletal-ICRP using Geant4 Monte Carlo simulation code. These simulations clearly show that neutron albedo rises quickly with target thickness and reaches saturation after about 15 cm. The value of neutron albedo depends upon scattering material thickness and geometry of reflector and its physical properties. The results of this work have also been compared with those obtained with other experimental results and theoretical calculated values, and found a good agreement with simulated value. These calculations will be helpful for evaluating the outcome of future clinical treatment planning in LINACS, radiation protection and radiation safety. The study of these materials demonstrates that a large proportion of neutrons are reflected at the edge of reflector from 1 to 10 cm, further increasing thickness have relatively small effect on neutron-albedo.