Transition of radioactive density after filtration treatment of the samples obtained in the "groundwater observation hole No.1-2" Near the Bank Protection at fukushima dai-ichi Nuclear Power station 2013-08-09 Transition of radioactive density after filtration treatment of the samples obtained in the "groundwater observation hole No.1-2" Near the Bank Protection at fukushima dai-ichi Nuclear Power station 2013-08-09