Between becquerels millisieverts per hour, the grays and other curies, it is sometimes difficult to navigate. The activity can be expressed in curie (Ci), but the unit most commonly used is the becquerel (Bq). Equivalence: 1 Bq = 27 picocuries (27 millionth of a millionth of a curie). To determine a level of internal contamination, it is reported the activity to the mass or volume considered (Bq / kg or Bq / l).
For example, in Japan, the permissible limit of 131 in drinking water is 100 Bq / kg (or liter, since one liter of water weighs 1 kg). Thus, the alpha and beta particles have very low penetrating power in the air - a sheet of paper can stop helium nuclei, aluminum foil electrons - but they may have an impact on contact with cells If ingested or inhaled.
X-rays and gamma rays travel several hundred meters and you have very thick lead and concrete to protect themselves. In practice, it is expressed in dose equivalent rate (in sievert per hour, for example) to set exposure limits. In France, for the public, the limit is one thousandth of a sievert per year (one mSv per year, 1 mSv / year), while it is 20 mSv / year for workers under ionizing radiation (nuclear industry , radiology medical ...).
In Fukushima, a rate equivalent dose of 400 mSv / h was recorded at the site. It must of course take into account in this assessment, the initial concentration. For iodine, the contamination may have virtually disappeared in 80 days, but it takes 300 years for cesium and 240 000 years for plutonium 239.
In animals, the period may be shorter, since some radionuclides can be eliminated by natural means. In cattle, the concentration of cesium decreases by half in 70 days, it still 1000 times less then in about two years. Reminder of multipliers: 1 kilo (k) = 1000 000 milli (m) = 1 billion micro (μ).
Hervé Morin 
For example, in Japan, the permissible limit of 131 in drinking water is 100 Bq / kg (or liter, since one liter of water weighs 1 kg). Thus, the alpha and beta particles have very low penetrating power in the air - a sheet of paper can stop helium nuclei, aluminum foil electrons - but they may have an impact on contact with cells If ingested or inhaled.
X-rays and gamma rays travel several hundred meters and you have very thick lead and concrete to protect themselves. In practice, it is expressed in dose equivalent rate (in sievert per hour, for example) to set exposure limits. In France, for the public, the limit is one thousandth of a sievert per year (one mSv per year, 1 mSv / year), while it is 20 mSv / year for workers under ionizing radiation (nuclear industry , radiology medical ...).
In Fukushima, a rate equivalent dose of 400 mSv / h was recorded at the site. It must of course take into account in this assessment, the initial concentration. For iodine, the contamination may have virtually disappeared in 80 days, but it takes 300 years for cesium and 240 000 years for plutonium 239.
In animals, the period may be shorter, since some radionuclides can be eliminated by natural means. In cattle, the concentration of cesium decreases by half in 70 days, it still 1000 times less then in about two years. Reminder of multipliers: 1 kilo (k) = 1000 000 milli (m) = 1 billion micro (μ).
Hervé Morin
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