## 1 Introduction  
After the severe nuclear accident that occurred at the Fukushima Daiichi nuclear power station on 11 March 2011, more than 160,000 people from within a 20 km zone and the area having relatively high radiation levels were forced to evacuate and, as of March 2021, more than 40,000 people are still recognized as evacuees [1]. While it is certain that those evacuation measures prevented some excessive radiation exposure of residents [2, 3, 4], it has caused severe psychological distress in evacuees who were forced to stay outside their home towns/villages for years [5, 6]. Currently, most of the evacuation orders have been lifted in the affected areas where the levels of radioactive contamination are quite low. However, it seems many residents have not returned to their previous homes partly due to persistent concerns about the possible adverse health effects of chronic radiation exposure, despite the fact authorities have tried to convince them that they are overly concerned about the radiological effects by introducing the recommendations of international authorities such as the International Commission on Radiological Protection (ICRP). This standstill is attributable to the way authorities have provided explanations by the using short-term effective dose estimates. For example, soon after the accident occurred, the national and local governments announced that the reference level for such an emergency situation was typically in the effective dose band of 20 to 100 mSv, with citation of the basic recommendations of ICRP [7]. Though updates of these reference levels have been recommended by ICRP in a recent publication [8] as shown in Table 1, the decision process based on effective dose of a certain-scale population has not essentially changed. With their own experience of risk communication with the people affected by the nuclear accident in Fukushima, the author feels that many of the residents have been suspicious of such uniformly applied, dose-based approach since they know well that every individual could have a unique consequence on his/her health from the same dose radiation and, in particular, one with a higher radiosensitivity, like a small child, could suffer from more severe damage. Actually, it has been clearly shown by many experts that the radiosensitivity of humans significantly changes depending on age and sex. In general, smaller children are more radiosensitive than adults, which is attributable to the fact that children have more actively dividing cells that could amplify radiation-induced DNA damage to a large extent compared to the adults [9; 10; 11; 12; 13]. It is also known that female people are more radiosensitive in regard to carcinogenesis, mainly because the breast is notably susceptible to radiation compared to other organs [7; 9; 11; 13]. Thus, it is desirable to answer more sincerely to their underlying question, \"how safe is safe?\", by precisely showing the health risk for the most sensitive group on a community basis, instead of just presenting an average value of effective dose for an anonymous general population. It is also desirable to show the integrated risk of all hazards, including possible effects of other toxic materials such as heavy metals and some organic compounds released into the environment, and then to enable the authorities to make more appropriate decisions through comprehensive optimization of those different-quality risks and benefits. With these considerations, the author tries to present an approach for predicting long-term radiological risk of female infants, i.e., the most radiosensitive group, under the assumption that they would live on the land contaminated by radiocesium (\({}^{137}\)Cs) with consideration of the difference in land-surface properties.