Online Radioactivity Measurements in Japan
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Author:  t00fri [ Fri, 18-03-11, 16:09 GMT ]
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Reiko wrote:
Where exactly you need translations?

Well, Reiko,

fortunately, there are now an increasing number of translations coming in (e.g. by Japanese students).

I rather thought that I'd leave this to your own judgement: if you think you read some relevant info in the japanese material collected here, you might just leave a comment in English about it.
Just anything you find relevant for us to know...

Here is something specific

On the site from which I took the above radiation monitoring plot,

there are also two dials at the top that have something to do with the speed and direction of the wind. There are some explanations in Japanese that might be interesting...

Thanks for your help,

Author:  t00fri [ Fri, 18-03-11, 16:50 GMT ]
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Hi all,

meanwhile the Japanese authorities have also added plots to their tables with the actual radiation levels.

The two most relevant files for us seem these containing mainly plots of the radiation in
the usual units of μSv/h = (micro-Sievert / hour)

March 18th

p5-Iwate, p6-Akita, p7-Yamagata, p8-Niigata, p9-Tochigi, p10-Ibaraki, p11-Saitama, p12-Chiba, p13-Tokyo

March 17th

p1-Iwate, p2-Akita, p3-Yamagata, p4-Niigata, p5-Tochigi, p6-Ibaraki, p7-Saitama, p8-Chiba, p9-Tokyo

p1, p2,... denote the plot numbers referring to the various Japanese prefectures (cities). Tokyo is always last. Ibaraki is somewhat north of Tokyo, for example. There are also locations at the west coast of Japan.

As an example, here is the radiation in μSv/h for Tokyo as function of date/time (including March 18th). You see the characteristic series of spikes between March 15 and March 16. The radiation level in Tokyo rose to something around 0.5 μSv/h.


So now compare what happened during the same period of time near the Fukushima nuclear plant: Here is a plot as taken from the German Spiegel-online site ( The data have been measured by TEPCO.


You can clearly now associate the peaks with various events at the Fukushima I plant.
However, take a look at the scale of radiation!!! The peak values here are around 12000
μSv/h! This is to be compared with a maximum of 0.5 μSv/h measured in Tokyo.

In order to appreciate the effects on peoples' health, note first that it is not the radiation rate in μSv/h but the sum (integral) over time that counts.

If you have an X-ray taken of your spine, you absorb a dose of around 1.2 mSv (milli=1000 * micro). A computer tomography of your entire body amounts to 10 mSv.
An anual dose of 100 mSv triggers cancer with 1 % of the exposed people. Accute radiation illness is caused by 250 mSv. Finally a dose of 4000 mSv is considered lethal.


Author:  t00fri [ Fri, 18-03-11, 17:21 GMT ]
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Here is a live-radiation monitor in cpm = counts-per-minute from West-LA / US

++++++++++++++++++++++++++++++++++++++++++++++++++ ... om-west-la
A range of normal background radiation has been determined to be between 40 to 46 CPM.

More info about this monitoring station you find on the homepage: ... n-station/

The arrival of the radiation plume in south California was forcast for March 18...
Actually, on March 19, minuscule traces of radiation have indeed been measured in Sacramento. But there is absolutely no associated health risk (so far).

Here are some recent 10-minute averages of the measured rates

2:17 pm 10-minute average: 41.9 Counts Per Minute NORMAL
10:45 am 10-minute average: 39.8 Counts Per Minute NORMAL

11:50 pm 10-minute average: 41.9 Counts Per Minute NORMAL
8:30 pm 10-minute average: 41.4 Counts Per Minute NORMAL
5:05 pm 10-min average: 42.7 Counts Per Minute NORMAL
1:00 pm 10-min average: 44.8 Counts Per Minute NORMAL
9:10 am 10-minute average: 44.2 Counts Per Minute NORMAL
1:42 am 10-minute average: 45.1 Counts Per Minute NORMAL


Author:  t00fri [ Fri, 18-03-11, 18:20 GMT ]
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The originally linked Geiger-Mueller counter in Tokyo went offline a few days ago. Here is another one, I suppose also in Tokyo

EDIT: again now we see yet another one with rates agreeing reasonably well with the above GM-10 monitored radiation (average count: <cpm> = 16.52 +- 3.8 ) ...


Author:  fenerit [ Fri, 18-03-11, 19:58 GMT ]
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Yesterday were 16 cpm, today 22. Moreover, through the Spiegel data is clear that TEPCO is hiding the real situation. Even the IAEA play an obscure role:

Japan Earthquake Update (18 March 2011, 10:15 UTC)

Japanese authorities have informed the IAEA that new INES ratings have been issued for some of the events relating to the nuclear emergency at the Fukushima Daiichi and Daini nuclear power plants.
Japanese authorities have assessed that the core damage at the Fukushima Daiichi 2 and 3 reactor Units caused by loss of all cooling function has been rated as 5 on the INES scale.
Japanese authorities have assessed that the loss of cooling and water supplying functions in the spent fuel pool of the Unit 4 reactor has been rated as 3.
Japanese authorities have assessed that the loss of cooling functions in the reactor Units 1, 2 and 4 of the Fukushima Daini nuclear power plant has also been rated as 3. All reactor Units at Fukushima Daini nuclear power plant are now in a cold shut down condition.

Author:  t00fri [ Fri, 18-03-11, 20:09 GMT ]
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unfortunately yesterday's Geiger counter (now offline, service?) is a different instrument from today's. The two had somewhat diffrent readings. There are various possible reasons: position in the house (wood, concrete? window?) or efficiency of instrument which is a material constant varying between instruments. These cheap Geiger counters only serve as relative indicators of radiation.

Yes we have heard that today the overall INES rating went up from 4 to 5. The rest of the made statements I am not sure I fully understand...


Author:  fenerit [ Fri, 18-03-11, 21:03 GMT ]
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Citations in black are mine. Before is said that the INES scale has been rated from 4 to 5 in two and three reactor Units, then is said that ALL the reactor Units are "in a cold shut down condition". If the condition is as such, why to rise the INES scale? At least it should have been costant or diminuishing.

Author:  t00fri [ Sun, 20-03-11, 15:46 GMT ]
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Official update of radiation at posts around Fukushima Dai-ichi for March 20 (local date)


The data are from
as always.


Author:  t00fri [ Sun, 20-03-11, 16:02 GMT ]
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Radiation in drinking water for some locations including Tokyo (yellow). Units are Bq/kg

Some non-dangerous amounts of contamination in the drinking water have now been found

The first number in the table refers to I-131, while the second one refers to Cs-137.

According to the Nuclear Safety Commission of Japan", upper limits for intake are: I-131:More than 300Bq/kg, Cs-137:More than 200Bq/kg


Author:  fenerit [ Sun, 20-03-11, 22:17 GMT ]
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Just my attempt to make some calcolus with the unities of measure. I'm unable to find the direct conversion amongst microSv and Bequerel.

From the converter found here:

I've take up the microSv in Tokyo between the 15 - 16 March, that is 0.5 microSv and converted in Rontgen.
0.5 microSv = 0.00000419 Rontgen.
Then I've converted Rontgen to milliCurie:
0.00000419 Rontgen = 5e-7 millicurie.
From milliCurie I've got the Bequerel:
5e-7 milliCurie = 18.5 Bequerel.

The question is: how the atomkraft physicist accounts for the hours and the kilograms into the relevants contest? Are 18.5 Bequerel the disintegrations of 18.5 radioactive nucleii (either Iodine 131 or Cesium 137) per kilogram of water? If yes, why such water's radioactivity has been found just now and not before?

No Nuke!

Author:  t00fri [ Mon, 21-03-11, 15:26 GMT ]
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while I am NOT a nuclear physicist, I still remember these somewhat tricky issues about units in radioactivity from my University lectures a long time ago.

The main point is that one has to be very careful not to mix up units that serve different puposes in radioactivity. Otherwise you try to convert "apples" into "pears"...

Also, one should focus on the modern SI (international) units throughout.

Let's only consider ionizing radiation and the 3 groups of units describing
1) the radioactive activity of substances and 2),3) for quantifying the amount of radiation striking other objects, particularly people.

1) Activity of a substance
Here one frequently uses decays per minute[dpm] or Becquerel [Bq] with

1 Bq = 1 / 60 dpm = 1 dps

since 1 Bq = 1 decay per second [dps]. Curie[Ci] is the old unit rarely used today.

Next in 2) and 3) I turn to radiation units that focus on the absorbed dosage e.g. by people

2) Absorbed radiation dose

Here we need units that denote basically absorbed [radiation energy/weight]. The standard SI unit is

1Gray [Gy] = 1 joule of absorbed radiation energy / Kg = 100 rad

X-ray and gamma-ray exposure is often expressed in units of roentgen [R]. The roentgen [R] unit refers to the amount of ionization present in the air.

3) Dose equivalent
The dose equivalent is a measure of the biological effect of the irradiation on the whole body.

The dose equivalent is equal to the product of the absorbed dose (Gray) and the "penalty" Weight factor W. For X-rays, Gamma rays, or beta radiation: W = 1. However, for the harmful alpha rays, W = 20!!

The modern SI unit here is sievert [Sv]. The older one is rem.

1 Sv = 1Gy * W = 100 rem

Hence again a conversion factor depending on the type of radiation particle...


To illustrate the typical conversion problematics, let us consider a Geiger-Müller counter (e.g. GM-10) that is a standard instrument for measuring ionizing radiation activity.

The crucial hardware part is a tube filled with inert gas that becomes briefly conducting when a ionizing particle of radiation from some source passes through it. These conductivity 'blips' are expressed in counts per minute [cpm] (see my posts above). But the entrance window of a Geiger counter has a certain limited geometry and thus will not catch ALL decays. So there is an unknown efficiency factor < 1 if you want to convert

cpm <-> dpm or Bq

That efficiency factor will depend strongly on the type and energy of the radiation ( particle), the window geometry etc. Hence there is NO single conversion factor e.g. from cpm to μSv/h. In addition, not all Geiger counters can sense the (dangerous) alpha particles (He^2+) besides beta radiation (e^-, e^+) and gamma rays (photons).

Many radiation meters are calibrated to Cs137 or Co60. Here is a table for GM-10 showing the empirical conversion factors from cpm <-> μSv/h in case of Cs137 and Co60:

.................mR/h........ μSv/h..........mR/h........... μSv/h
GM-45....0.000333....0.00333.....0.000277.....0.00277 ... _mRhr.html

The GM-45 is a more sensitive model than the GM-10, illustrating the completely different model-dependent conversion factor...

Unfortunately, most relevant radiation in Japan for now is I-131, where I didn't find the GM-10 conversion factor yet.

I hope this was somewhat useful,


Author:  t00fri [ Mon, 21-03-11, 15:46 GMT ]
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Please have a look to the online Geiger--Müller counter (GM-10 in Tokyo) that I linked in above.

Here are the exact data of the counter from the original site:

Nuclear radiation detector:Black Cat Systems GM-10 Geiger-Müller Counter
Radiation detected: Alpha - Above 3 MeV , Beta - Above 50 keV , Gamma / X-Ray - Above 7 keV
Location: Latitude: N 35 ° 39 ' 28 '', Longitude: E 139 ° 24 ' 5 ''  
Altitude: 101m Hitoshi Minami 2-chome, Hino, Tokyo,
two-story wooden house, location near the window.

120CPM = about 1 μSv/h
Reload every 10 minutes.

First, note the wind direction displayed above the GM-10 output.

Wind direction, wind speed & weather (Tokyo):
ImageImage Image

In agreement with weather forecasts (for Mon, March 21 and Tue, March 22) the wind direction now ranges between NW .... E directions, implying that the chances for an influx of radiation from the Fukushima region into Tokyo will increase. Fortunally the wind speed is still low.

Indeed, one can see a clearcut rise in the radiation rate [cpm] for today, March 21!...
Until yesterday the average radiation level was quoted as

<cpm> = (16.52 +- 3.8 )

Today the average rose to

<cpm> = (23.61 +- 5.38 )

as is printed on the online GM-10 output below.

For your convenience, here is a redisplay of the online output. A clear rise on the right is obvious:



Author:  t00fri [ Mon, 21-03-11, 21:13 GMT ]
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For comparison with the previous evidence of increased radiation in Tokyo, here is again the official plot from . Units are again μSv/h with x-axis being date/time.


You can clearly see the rise of the radiation on the right hand side of the plot.

An analogous, but much more dramatic effect you see in today's official plot of the radiation in the town of Mito (Ibaraki prefecture) North of Tokyo. According to Google maps, from Mito to Tokyo it's about 2 hours South and from Mito to the Fukushima plant it's about 3 hours North...


Presumably is is all due to the changed wind direction as of today, Monday March 21?


Author:  t00fri [ Tue, 22-03-11, 11:38 GMT ]
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The contamination of the tap water has further increased (cf my previous display)! Here is the latest comparison with official measurements taken on March 21. Units are again Bq/Kg. The first value in the table refers to I-131, while the second one refers to Cs-137.


The I-131 contamination in the more northern prefecture Ibaraki is more then 10 times that of Tokyo! The contamination in Tokyo has almost doubled (2.9 -> 5.3 Bq/Kg) since March 19.

As noted before, the limits are:

According to the Nuclear Safety Commission of Japan", upper limits for intake are: I-131:More than 300Bq/kg, Cs-137:More than 200Bq/kg

The water in the sea has been found to be strongly contaminated (fish!): e.g. the value of I-131 has been found to be 127 times the legal uper limit! Nevertheless, TEPCO continues to argue that this high value is not harmful to human health...

Author:  fenerit [ Tue, 22-03-11, 13:38 GMT ]
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Thank you Fridger, for dedicating yourself in these matters. I rely on you about the smashing of "softened" data eventually argued by TEPCO.

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