Time Plot

The graphs below show the results of radiation data collected in Sapporo by the author with four different measuring instruments.

System A:


summaryA_2013asummaryA_2013bsummaryA_2013csummaryA_2013dsummaryA_2014asummaryA_2014bsummaryA_2014csummaryA_2014dPlease compare the above picture with the readings from one year before, and you’ll see that they are slightly lower. The conclusion of course is that last year readings were above normal, most certainly due to the Fukushima accident. In fairness, this trend doesn’t appear to be confirmed by the readings from my other measuring device: system B below.

System B:

  • Geiger tube: J305ß
  • Instrument: Arduino + Cooking Hacks shield
  • Assumption: 123 CPM = 1 μSv/h
  • Detected Radiation: Beta plus Gamma







System C:

  • Geiger tube: LND712
  • Instrument: Arduino + Cooking Hacks shield
  • Assumption: 123 CPM = 1 μSv/h
  • Detected Radiation: Alpha + Beta + Gamma

System D:

  • Geiger tube: LND712
  • Instrument: Arduino + Cooking Hacks shield
  • Assumption: 123 CPM = 1 μSv/h
  • Detected Radiation: Alpha + Beta + Gamma

In Sep 2013 I started recording with this tube again:

summaryD_2013cSystem E:

  • Geiger tube: SBM20
  • Instrument: Ecotest Terra-P MKS-05
  • Conversion Factor: 160 CPM = 1 μSv/h
  • Detected Radiation: Beta + Gamma

Disclaimer: I am not claiming that the data is accurate, I am merely reporting what my instruments indicate. The scale on the right side gives the average daily reading in counts-per-minute (CPM) and it reflects unequivocally what the instruments read. The scale on the left side is subject to an assumption about the conversion factor for that particular tube. I have been searching for an authoritative reference on the conversion factor, but all I have been able to find so far is not always consistent: different people use different factors, leading to discrepancy in the results, when compared to other web sites reporting similar data.


  • System A: data is missing for some days due to malfunctioning of the probe. I suspect the circuit generating the high voltage for the Geiger tube sometimes stops operating. It seems to be an intermittent fault: the system is not able to run for more than 3 days straight, then it “recovers” after one day of being left switched off.

6 Responses to Time Plot

  1. Check out http://www.sapporo-now.com to see if Hokkaido milk is safe to drink

  2. What have you used to calibrate your sensors?

    • paguyu says:

      Well, that’s a good point. The short answer is “nothing”.
      Please suggest what I should be doing about that, but let me explain something first.
      By calibrating, I guess you mean making sure that the value reported in μSv/h is accurate enough. Each graph has two scales. The one on the right gives the CPM range and the graphs are 100% accurate for that scale. It is after all what I am directly measuring: events per minute (averaged), and the microprocessor logging all those events does a decent job. The issue of calibration comes into play when I try to express those readings into different units, like μSv/h, on the left scale range. Unfortunately the conversion factor, the one thing that should be calibrated, is not even well defined. I intend to make a separate post on this blog to show how different people use wildly different factors for the same tube. As far as my graphs are concerned, I think the results (in μSv/h) are not even in the correct “ball park”, so there is no need to worry about accuracy, as yet. In summary, you can rely on the CPM values: I guarantee that they are quite accurate. Anybody with a good knowledge of how they should be converted, they can do so and hopefully they will also post a message about it. (Read the “About” page on this blog for some more insight on the LND 712 tube)

  3. Should you be eating oysters? Check out this radiation report for Hokkaido Oysters at http://www.sapporo-now.com

  4. Matt says:

    Paguyu, you should contact the people at http://blog.safecast.org/ for info on conversions, they seem to have it sorted.

  5. Question time (in Japanese) at last weeks talk on radiation in Hokkaido http://www.ustream.tv/recorded/17689161

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