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He presents data showing that "it takes about seven times as long for the dose rate to decay from 1000 roentgens per hour (1000 R/hr) to 10 R/hr (48 hours) as to decay from 1000 R/hr to 100 R/hr (7 hours)." [47] This is a rule of thumb based on observed data, not a precise relation.
The range for significant levels of initial radiation does not increase markedly with weapon yield and, as a result, the initial radiation becomes less of a hazard with increasing yield. With larger weapons, above 50 kt (200 TJ), blast and thermal effects are so much greater in importance that prompt radiation effects can be ignored.
The exposure to 4.5 Gray of penetrating gamma rays has many effects that occur at different times: In 24 hours: [10] vomiting; diarrhea; These will usually abate after 6–7 days. Within 3–4 weeks there is a period of extreme illness. [10] severe bloody diarrhea, indicating intestinal disorders causing fluid imbalance; extensive internal bleeding
It typically takes about 750 millisieverts (mSv) of exposure over several hours or less to make a person sick, or roughly 100 times the amount of background radiation an American receives each year.
The 1.4 Mt total yield 1962 Starfish Prime test had a gamma output of 0.1%, hence 1.4 kt of prompt gamma rays (the blue 'pre-ionisation' curve applies to certain types of thermonuclear weapons, for which gamma and X-rays from the primary fission stage ionize the atmosphere and make it electrically conductive before the main pulse from the ...
[100] [193] Experts said exposure to this amount of radiation for 6 to 7 hours would result in absorption of the maximum level considered safe for one year. [193] On 16 March Japan's ministry of science measured radiation levels of up to 330 μSv/h 20 kilometers northwest of the power plant. [194]
The Fukushima Daiichi nuclear accident was originally rated as INES 5, but then upgraded to INES 7 (the highest level) when the events of units 1, 2 and 3 were combined into a single event and the combined release of radiological material was the determining factor for the INES rating.
Above 7.5–10 Sv (7.5–10 Gy) to the entire body, even extraordinary treatment, such as bone-marrow transplants, will not prevent the death of the individual exposed (see radiation poisoning). [29] Doses much larger than this may, however, be delivered to selected parts of the body in the course of radiation therapy .)