Friday, March 18, 2011

Radiation: Geiger-Müller counter in Tokyo

Many people are worried that the radiation in Tokyo has to be elevated. Well, here you have a most up-to-date Geiger-Müller counter (wiki) from Hino, Central Tokyo:

Click to zoom in

The y-axis shows "clicks per minute", between 0 and 100 CPM (divided to five intervals with a 20 CPM spacing). In December 2010, the average number was 14 CPM. When I was posting this text, the average was 17 CPM but the increase isn't necessarily due to Fukyshima.

Note that 1 CPM (count per minute) is equal to 0.01 microsievert for hour (for gamma rays, electrons, muons...) or up to 20 times more for heavy nuclei etc. So 20 CPM is 0.2 microsieverts per hour.

Note that the standard deviation of the distribution is 3.79 CPM, which is close to sqrt(17)=4.12, close to the statistical expectations. In fact, the variations are slightly smaller than the noise. That's a big hint that there is actually no significant variable source of the radiation.

Get sound effects & royalty free music at AudioMicro.

Press the Play button to detect the ionizing particles above your mouse. You can see that you're safe, too. ;-) Just to remind you, these clicks occur randomly which means that their spacings are determined by the Poisson distribution. Popcorn obeys the same clicking law. The clicks are much less regular (periodic) than most people expect - there's nothing that prevents two clicks from occurring a very short time after one another.

I understand that some of the readers don't speak Japanese. It's easy for us whose names are Fujimoto, Akimoto, Lubošmoto, Iwamoto, Motl etc. Just to be sure, "Moto" means "origin" or "base". So Fujimoto means "base of Mount Fuji", Akimoto means "originating in the land of [beautiful] autumn", and "Lubošmoto" means "fundamental Luboš". ;-)


  1. This is a massive disaster whose true dimensions are obscured because thankfully the wind is blowing the radiation plume from the overheating spent fuel out to sea.
    The destruction of the spent fuel from the loss of coolant in their storage pools represents a risk many times worse than the Chernobyl explosion, which only involved 1 reactor, rather than decades worth of spent fuel for several.
    Pray the winds do not change soon.

  2. the wind is "probably" blowing the radiation plume

    but the japs are incorrectly feeding data....the economic prospects are very bad

    the governement renewed its pressure to incorporate " good radiation data"
    and exclude several sets of abnormal data

    ate least some say so....
    i do not believe in Vorhidin false prophets