An experimental evaluation of effective dose equivalent for neutrons

The study is aimed at providing a technique for evaluating the effective dose equivalent based on measurements of either the ionization density (observed by TLD or small-cavity ionization chamber) or the recoil nucleus density (observed by SSNTD) in a phantom, or weighted sum of them. For a phantom composed of soft tissues, depth distribution of absorbed dose is calculated on the assumption that the incident neutrons are perpendicular to the phantom axis. The absorbed dose is divided into two components: Dγ and Dp representing the contributions in the form of capture gamma rays and recoil protons, respectively. The depth distribution calculated above are then compared with a curve which represents the energy dependence of effective dose equivalent per unit fluence to determine the appropriateness of the calculations. Next, the recoil proton density in a pohantom is actually measured by SSNTD to provide data on the dependence of the depth distribution on the angle of the incident neutrons. This makes it possible to determine the feasibility concerning the measurement technique. It is inferred from these calculations and measurements that the effective dose equivalent can be evaluated appropriately by using SSNTD to perform selective observation of recoil proton fluence at a depth of 1 centimeter in a phantom. (Nogami, K.)