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Air Radioactivity Concentration

Measuring Device and the Unit of Measured Value of Air Radioactivity Concentration

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 Air radioactivity concentration is measured with the airborne dust continuous analyzer (dust monitor).
 The shown data is the concentration of radionuclide in the airborne dust which emits beta ray.
 As radon daughter, which is natural radioactive nuclide, emits beta ray even in the normal state, the data shall not be detected as 0, and it fluctuates between 0.1 and dozens of Bq/m3. (Bq (Bequirel) is a unit to express strength of radioactivity.)

Monitoring Station and Data Display

 Air Radioactivity Concentration is measured at 11 spots among the monitoring stations in Fukui Pref.
The monitoring stations are locating at, Urasoko, Tateishi, Shiraki, Shirakitouge, Nyu, Takenami, Hitsuhama, Miyadome, Ogurui, Otomi, and Kounoura.
 The air radioactivity concentration data measured at those stations are shown in this website by the trend graph of “one hour value”, “four hours value”, and “daily value”.

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How to Measure Air radioactivity Concentration

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 In the measurement of air radioactivity concentration, fine particles are caught with a filter from the outdoor air absorbed with a pump, and then alpha ray and beta ray emitted from them are measured.
 Airborne dust continuous analyzer (dust monitor) absorbs and measures the fine particles in the air, exchanging the filter at a certain interval.
 As iodine and cesium released in a nuclear power plant accident are radioactive material emitting beta ray with gamma ray, this website displays the concentration of the fine particles which emits beta ray contained in the air.

Example of the Change of Air Radioactivity Concentration

  •  The change of the air radioactivity concentration is affected by the weather change as well as the air radiation dose rate.
     Radon daughter in the air originated from the natural uranium 238 in the soil, and the air radioactivity concentration rises from midnight to dawn while the fine weather continues, as the radon daughter migrated to the air stays near the surface. This status is resolved when the sun rises, the surface gets warmed and the air diffusion begins.
     However, when the moisture content of the earth surface increases by the rainfall, the air radioactivity does not increase in concentration as the radon migrating rate from the earth to the air decreases.
  •  As radon daughter derives from the earth, when the air mass which has high radon daughter density flows from the continent, all of the monitoring stations may detect higher value. On the other hand, lower value may be detected when the maritime air mass of the Pacific Ocean which has low radon daughter density flows in by typhoons.

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