## 3 Results and Discussions
### Comparison with Nominal Risk  
Effective dose is a widely used quantity to evaluate the stochastic health effects of radiation exposure for the aim of radiological protection. This quantity is not defined for an individual person but for \"Reference Person\" which represents a nominal population having typical age and sex distributions. On the basis of this concept, nominal risk coefficients for estimating nominal risks from the effective dose are given for two groups: whole  
Figure 3: Predicted integrated cancer-mortality risk induced by \(\gamma\)-rays from \({}^{137}\)Cs deposited onto ground for a female infant (0 years old) at the initial dose rate of 20 mGy y\({}^{-1}\).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Land**} & \multicolumn{3}{c}{**Integrated Cancer Risk [\%]**} \\ \cline{2-4}  & **\(\sim\)6 Years** & **\(\sim\)18 Years** & **\(\sim\)80 Years** \\ \hline Fast & 0.88 & 1.40 & 1.83 \\ Middle & 1.28 & 2.05 & 2.69 \\ Slow & 1.64 & 2.70 & 3.56 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Integrated cancer risks of a female person for three periods at the areas having different land-surface properties with the initial dose rate of 20 mGy y\({}^{-1}\).  
Figure 2: Predicted time change of the relative external dose rates from \({}^{137}\)Cs deposited onto the ground surfaces having different properties.  
population (the public) and adults (workers) [7]. Thus, the risks estimated from effective doses should be the same for all members of an intended group regardless of the different physical and physiological properties. This nature was intentionally given for avoiding unnecessarily discriminatory actions, which means that this quantity is unsuitable for the purpose of assessing individual risks [7; 13].  
If we employed the ICRP-recommended nominal risk coefficient (5.5% for cancer mortality) [7] in calculation of the cancer risk for the whole population of residents that were assumed to live in the land having an average land-surface properties (i.e., the Middle category), the nominal risks following the initial dose rate of 20 mGy y\({}^{-1}\) were calculated to be 0.45% for the preschool age (~6 years), 0.86% for up to the high-school graduation, and 1.5% for lifetime (~80 years) (Table 4). These values were much lower (35% to 57%) than those calculated for a female person of the corresponding time period (Table 3).  
The findings above imply that the currently common approach using effective dose would lead to an inappropriate judgement in the process of decision making regarding protective actions such as evacuation, relocation and decontamination following the concept for optimization in radiological protection, i.e., \"As Low As Reasonably Achievable (ALARA)\" [7; 9]. It is expected that the alternate risk-based approach presented in this study would be useful for more appropriate judgement in optimization based on the integrated risk of all hazardous materials including heavy ions and toxic organic compounds in the living environment and the different sensitivities of the respective people to those materials.  
It should be noted that difficulties still remain in the application of the presented approach to the decision making regarding protective actions. It is envisaged that many of the residents would prefer to behave as a community and they would not consider the difference in individual health status as an important matter. Moreover, the fear of radiation exposure would force them to just stay distant from the affected area, while it would not necessarily reduce the total health risk because some other effects, including psychological stress, could bring about more significant impacts on physiological status, as highlighted in the Fukushima Daiichi accident [5; 6]. More efforts are needed for practical application of the presented approach based on the firm concept of minimizing the overall risk with consideration of social, economic, and psychological factors as well as the radiological consequences.