Half-life is a term used to express the rate at which a given radionuclide gives up its radioactivity. With time, the radioactivity comes down, but not the mass. More or less, the mass of the radioactive material remains the same even after very many years of radioactive decay. And Specific Activity is the term used to express the quantity of radioactivity per gram of a material.
Take an example of a source of Cobalt-60 (Co-60). The source is generally used in gamma irradiators/chambers used in industry and medicine. The half life of Co-60 is 5.27 years. This means, in 5.27 years the radioactivity of the source reduces by one-half. The mass of the source remains the same. A typical irradiator source of strength 1000 Curie (Similar to sources recovered in Mayapuri, Delhi) will give gamma radiation dose rate of 13.25 Gray per hour. After say, 25 years of decay, the dose rate of the source will reduce to 0.4 Gray per hour. If some one is exposed to this source (the so-called decayed source) for about 10 hours, the person is likely to get dose of 4 Gray which is in the range of Lethal dose -50 (LD-50).
Lethal dose – 50/60 means, if 100 people are exposed to the dose of 4 to 5 Gray, 50 persons will die in 60 days’ time after the exposure.
That is precisely the reason why the “decayed sources” just lying in some cup-boards in laboratories or in hospitals for over 25 to 30 years can still be dangerous and can deliver fatal doses if the sources are not properly shielded, or not handled with care. The decayed sources should be disposed off by strictly following the procedure suggested by the national regulators. In India, the regulator is Atomic Energy Regulatory Board (AERB), located at Anushaktinagar, Mumbai, 400094.
Handle radioactivity carefully and not fearfully.
Monday, January 10, 2011
Handle radioactivity carefully and not fearfully
Half-life is a term used to express the rate at which a given radionuclide gives up its radioactivity. With time, the radioactivity comes down, but not the mass. More or less, the mass of the radioactive material remains the same even after very many years of radioactive decay. And Specific Activity is the term used to express the quantity of radioactivity per gram of a material.
Take an example of a source of Cobalt-60 (Co-60). The source is generally used in gamma irradiators/chambers used in industry and medicine. The half life of Co-60 is 5.27 years. This means, in 5.27 years the radioactivity of the source reduces by one-half. The mass of the source remains the same. A typical irradiator source of strength 1000 Curie (Similar to sources recovered in Mayapuri, Delhi) will give gamma radiation dose rate of 13.25 Gray per hour. After say, 25 years of decay, the dose rate of the source will reduce to 0.4 Gray per hour. If some one is exposed to this source (the so-called decayed source) for about 10 hours, the person is likely to get dose of 4 Gray which is in the range of Lethal dose -50 (LD-50).
Lethal dose – 50/60 means, if 100 people are exposed to the dose of 4 to 5 Gray, 50 persons will die in 60 days’ time after the exposure.
That is precisely the reason why the “decayed sources” just lying in some cup-boards in laboratories or in hospitals for over 25 to 30 years can still be dangerous and can deliver fatal doses if the sources are not properly shielded, or not handled with care. The decayed sources should be disposed off by strictly following the procedure suggested by the national regulators. In India, the regulator is Atomic Energy Regulatory Board (AERB), located at Anushaktinagar, Mumbai, 400094.
Handle radioactivity carefully and not fearfully.
Take an example of a source of Cobalt-60 (Co-60). The source is generally used in gamma irradiators/chambers used in industry and medicine. The half life of Co-60 is 5.27 years. This means, in 5.27 years the radioactivity of the source reduces by one-half. The mass of the source remains the same. A typical irradiator source of strength 1000 Curie (Similar to sources recovered in Mayapuri, Delhi) will give gamma radiation dose rate of 13.25 Gray per hour. After say, 25 years of decay, the dose rate of the source will reduce to 0.4 Gray per hour. If some one is exposed to this source (the so-called decayed source) for about 10 hours, the person is likely to get dose of 4 Gray which is in the range of Lethal dose -50 (LD-50).
Lethal dose – 50/60 means, if 100 people are exposed to the dose of 4 to 5 Gray, 50 persons will die in 60 days’ time after the exposure.
That is precisely the reason why the “decayed sources” just lying in some cup-boards in laboratories or in hospitals for over 25 to 30 years can still be dangerous and can deliver fatal doses if the sources are not properly shielded, or not handled with care. The decayed sources should be disposed off by strictly following the procedure suggested by the national regulators. In India, the regulator is Atomic Energy Regulatory Board (AERB), located at Anushaktinagar, Mumbai, 400094.
Handle radioactivity carefully and not fearfully.
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