Tokyo Radiation Levels
Posted by
JAC on 3/17/2011, 9:35 pm
http://metropolis.co.jp/quake/quake-2011-03/tokyo-atmospheric-radiation-levels/
Due to concerns about radiation in Tokyo from a number of our readers, Metropolis will publish daily radiation levels (sometimes multiple times daily if relevant). This is a log of background radiation levels in Tokyo from March 15 2011. Measurements will be taken daily at different times. Levels are measured in micro-roentgens and micro-sieverts.
2011-03-17 11:34: 9 micro roentgens (0.14 micro sieverts per hour). Normal
2011-03-16 15:25: 10 micro roentgens (normal). (0.2 micro sieverts per hour). Normal
2011-03-16 08:30: 17 micro roentgens. Twice normal but fine
2011-03-15 22:35: 21 micro roentgens (2x normal). Twice normal but fine
2011-03-15 10:00: 218 micro roentgens (22x normal). Elevated but not harmful.
2011-03-15 08:30: 9 micro roentgens (9-10 micro R = normal baseline). Normal
What does this compare too?
1 sievert for 1 hour will kill 50% of people exposed. This is a
deadly
400 milli sieverts per hour = conditions in the Fukushima Daiichi plant. 2 hours at this level will burn skin like a sunburn and produce nausea and radiation sickness.
50 milli sieverts per hour = maximum allowed exposure by personnel working in nuclear facilities.
5 milli sieverts per hour = 1 chest xray equivalent per hour. Not deadly. 5 milli sieverts = 0.005 sieverts (5/1000 sieverts)
0.2 micro sieverts per hour = Average normal background radiation for most cities in the world. 0.2 micro sieverts = 2 / 10,000,000 sievert or 2,000,000 times below deadly dose. 40,000 time below maximum allowed dose).
0.14 micro sieverts = Tokyo background radiation on March 17th 2011, 6 days after the earthquake and nuclear plant crisis.
What do the units mean?
Roentgens are measure of the amount of radiation required to liberate charge of one electrostatic unit of charge (esu) in 1 cm of dry air at standard temperature and pressure. It's a useful unit for legacy reasons because many people understand the Roentgen unit and the dose equivalent; Roentgen Equivalent Man (rem).
Sieverts are the biological dose. 1 Sievert = 1 Joule per Kilogram. Or the (damaging) energy imparted on the body by ionizing (nuclear) radiation.
*Disclaimer: We are not qualified experts in the field of nuclear science and nuclear medicine. Metropolis owns a Geiger counter and we are just giving a daily reading of exactly what we see on the screen of the Geiger counter. Geiger counter readings are taken outside, in an open area after the device has had 2 minutes to get an average reading of the background radiation level.
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Bryan Norcross on TWC talking on Dispersion Models -
BobbiStorm,
3/17/2011, 9:17 pm- Tokyo Radiation Levels - JAC, 3/17/2011, 9:35 pm
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