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Radioactivity and Air Dose Rate


Does the effect of air dose rate reduction vary between different decontamination methods?

Air dose rate reduction effects of three farmland decontamination methods (surface soil stripping, reversal tillage, and upside-down plowing) were analyzed and compared with the experimental results obtained in the decontamination model project to verify the effectiveness of decontamination.
The study also clarified issues such as the distribution of radioactive cesium in depth and the relationship between the depth of decontamination and decontamination effects, and indicated the possibility that the effectiveness of decontamination may decline with the depth of migration of radioactive cesium.

  • Surface soil stripping (A1)

    Fig.1 Surface soil stripping (A1)

  • Upside-down plowing (A3)

    Fig.2 Upside-down plowing (A3)

  • Reversal tillage (A4)

    Fig.3 Reversal tillage (A4)

Table 1 shows, for each of the decontamination methods, a comparison of the measurement results from the decontamination model project entrusted to JAEA by the government in 2011 and calculation results obtained by using ADRET, an air dose rate evaluation model.
The fact that the calculated values are close to the measured values indicates the accuracy of the calculations performed. Surface soil stripping shows the highest effectiveness of decontamination.

Table 1 Comparison of simulation results and measured values

Decontamination method Effectiveness of decontamination (dose rate reduction rate)
Measured value (decontamination model project) Analyzed value (center)
Surface soil stripping (A1) 40~70% 73%
Upside-down plowing (A3) ≤ 65% 68%
Reversal tillage (A4) 30~60% 54%

Figure 4 shows how much the air dose rate decreases depending on the depth of cesium penetration into the soil and on the depth of decontamination.
The deeper the soil is decontaminated, the more the dose rate decreases. The figure also shows that the shallower the distribution of cesium is, the more effective decontamination is.

Depth distribution of cesium and estimated effectiveness of decontamination

Fig.4 Depth distribution of cesium and estimated effectiveness of decontamination


  1. Malins et al. Proc Int Symp Rad Issues Fukushima (2015)