From 12/6/2011 to 12/20/2011, Japanese self defense force went to Fukushima to decontaminate.
900 members were sent to the town halls of Narahamachi, Tomiokamachi, Namiemachi, and Iidatemura.
As expected, they successfully proved decontamination is meaningless.
Self defense force struggled to decontaminate the flags of the Iidatemura town hall on 12/20/2011.
Between the stones of the path, dead leaves were already put.
Even Asahi newspaper reported like this below.
Experts and house makers are warning about high-pressure washing to decontaminate the roofs because it may hurt the roof but doesn’t decrease the radiation level. Some of the local governments are starting to remove it from the decontamination options.
Fukushima local government tried to decontaminate the roof of a house in Oonami Fukushima, 8/2011.
However, the radiation level of 1cm above the roof (Concrete) only decreased by less than half.(2.4 microSv/h→1.6 microSv/h).
When it comes to slate, it was only 2.4 microSv/h → 2.0 microSv/h, and in the case of tiled roof, it was only 1.2 microSv/h → 1.1 microSv/h.