Today the Japanese government ordered four prefectures to stop selling spinach and leeks after levels of radiation above the legal limit were picked up in them. The affected prefectures were Fukushima, where the nuclear plant damaged by the tsunami is based, and the nearby Ibaraki, Tochigi and Gunma prefectures. Traces of radioactive iodine were discovered in Tokyo tap water on Sunday. Lastly, officials have discovered iodine in three milk samples from Kawamata, a town in Fukushima prefecture. Radioactive caesium also appeared in one of the samples, but at levels below the legal limit.
As a precaution, the government has asked farmers in the prefecture to stop selling raw milk. So how dangerous were the levels found?
Not very — at least, so says Yukio Edano, the chief cabinet secretary. He is quoted in the Japan Times as saying that the contaminated milk from Kawamata contained up to becquerels of iodine per kilogram, about five times the legal limit for milk. But to put this in perspective, he pointed out that if someone on a typical Japanese diet drank this milk for a whole year, the accumulated radiation would equal that from a single CT scan.
Medical procedures account for about 1. It is also worth noting that this figure varies from person to person, depending on the number of radiological diagnosis and treatments. The 0. Canadian provinces have control over the regulations for the quality of the drinking water, including setting limits for tritium levels.
Provincial authorities and municipalities have monitoring programs to control water quality, including tritium levels. Nuclear power plant operators, as well as AECL's facility in Chalk River, have monitoring programs in place to sample and report tritium concentrations in drinking water. Other nuclear facilities, such as tritium processing facilities, have their own environmental monitoring programs to keep tritium levels under control.
Some provinces, such as Ontario, have adopted this value as a legal standard. Tritium levels in the municipal drinking water of these communities vary between 6.
A terabecquerel TBq represents one million, million 10 12 becquerels Bq. A Bq is a measure of the amount of radioactivity but has little to do with the weight or volume of the material. For example, a Bq of tritium has the same activity as a Bq of uranium. This is because tritium has a much shorter half-life than uranium A Bq of tritium weighs 2. Of course, one never gets pure tritium.
Tritium's most common form is HTO, or tritiated water. Here are some examples:. In underground uranium mines, as well in some other mines, radiation exposure occurs mainly due to airborne radon gas and its solid short-lived decay products, called radon daughters or radon progeny.
Radon daughters enter the body with the inhaled air. The alpha particle dose to the lungs depends on the concentration of radon gas and radon daughters in the air. The concentration of radon daughters is measured in working level WL units this is a measure of the concentration of potential alpha particles per litre of air.
Such estimates are subject to error because the ratio of radon to its decay products radon daughters is not constant. Equilibrium factor is the ratio of the activity of all the short-lived radon daughters to the activity of the parent radon gas.
Equilibrium factor is 1 when both are equal. Radon daughter activities are usually less than the radon activity and hence the equilibrium factor is usually less than 1. Add a badge to your website or intranet so your workers can quickly find answers to their health and safety questions.
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Search all fact sheets: Search. Type a word, a phrase, or ask a question. Ionizing radiation is measured in terms of: the strength or radioactivity of the radiation source, the energy of the radiation, the level of radiation in the environment, and the radiation dose or the amount of radiation energy absorbed by the human body.
Radioactivity or the strength of radioactive source is measured in units of becquerel Bq. An old and still popular unit of measuring radioactivity is the curie Ci. Table 1 Radioactive Decay Number of half-lives elapsed Percent radioactivity remaining 0 1 50 2 25 3 Examples of these controls include: Education and training Reducing exposure time Increasing the distance from the radiation source Using a physical barrier that modifies the pathway between worker and source of radiation e.
One sievert is a large dose. The diagram above shows the range of activities different substances — from a litre of water up to the spent fuel extracted from the core of nuclear reactors — can have. Historic units such as curies and millicures have also been indicated.
Evolution of the activity of caesium in the human body The activity of caesium in the human body has been measured near the Mol laboratory in Northern Belgium for more than half a century.
Despite the laboratory large distance from nuclear tests bomb sites and Chernobyl, the peaks of activity due to these tests and the Chernobyl accident four times weaker can be seen. In these two cases, the decay of caesium in the human body takes place much more quickly than the natural decay, which has a half-life of 30 years.
Though caesium is absorbed slowly by the soil, the rapid decay of its activity in the human body means that no soil decontamination using, for instance, Prussian blue , is needed in Belgium. Learn more : Activity. About the site Glossary Site Map Contact.
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