Background radiation can be emitted from a number of sources. The most newsworthy is man-made such as nuclear weapons testing and waste from nuclear power generation. In reality, the natural background radiation is far more interesting.

Radon gas is found in geological formations such as granite and permeates the ground emitting alpha particles which in some area's of the Southwest and Scotland are a major concern. Radon is colourless, odourless and is present because of the decay of naturally occurring uranium in the earth, one of the most abundant geological formations on earth. Radon has a 3.8 day half life, so has a short lifespan in nuclear terms.

Other sources in the home are smoke detectors, containing Americum-241 but this is at a negligible level and safely contained.

Incorrectly, a number of people believe that microwave ovens contain ionising radiation, which could damage your health. This is not true, Microwave energy is non-ionising and therefore not a radiation issue.

Alpha, Beta and Gamma Radiation

  • Alpha - these are fast moving helium atoms. They have high energy, typically in the MeV range, but due to their large mass, they are stopped by just a few inches of air, or a piece of paper. (e.g Uranium, Thorium)
  • Beta - these are fast moving electrons. They typically have energies in the range of a few hundred keV to several MeV. Since electrons are might lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals. (e.g )
  • Gamma - these are photons, just like light, except of much higher energy, typically from several keV to several MeV. X-Rays and gamma rays are really the same thing, the difference is how they were produced. Depending on their energy, they can be stopped by a thin piece of aluminum foil, or they can penetrate several inches of lead.

Our current equipment cannot sense which of the three are being counted, although the sensor has a higher sensitivity for alpha than gamma particles.

Our monitoring station

We have added a radiation sensor to the station to monitor the background radiation in the local area. Whilst the likelihood of an issue like the one in Fukushima, Japan is extremely unlikely in the UK just by the sheer fact that we are not on a major fault line, the other sources of radiation that are present in the environment are of interest.

A Geiger Counter from BlackCatSystems is connected to a Serial port and CPM's are calculated and stored within a mySQL database. The recording time interval is 10 seconds = 6 measures per minute. Data is extracted in real time and displayed below and on the module on the front page of the site.

Whilst this solution is quite accurate, it should not be a source of calibrated data. All sensors are supported without traceable calibration.

Data output to Twitter is in CPM and μSv. The μSv value is not directly related to CPM, however is based on the calibration values of the Geiger-Muller tube used when calibrated with Caesuim 60. This is 1μSv = 108 CPM.

The average background radiation level is 0.15 μSv in Ottery St Mary, which is normal for UK geology.

Symptoms of acute radiation (dose received within one day):

  • 0 – 0.25 Sv (0 – 250 mSv): None
  • 0.25 – 1 Sv (250 – 1000 mSv): Some people feel nausea and loss of appetite; bone marrow, lymph nodes, spleen damaged.
  • 1 – 3 Sv (1000 – 3000 mSv): Mild to severe nausea, loss of appetite, infection; more severe bone marrow, lymph node, spleen damage; recovery probable, not assured.
  • 3 – 6 Sv (3000 – 6000 mSv): Severe nausea, loss of appetite; hemorrhaging, infection, diarrhea, peeling of skin, sterility; death if untreated.
  • 6 – 10 Sv (6000 – 10000 mSv): Above symptoms plus central nervous system impairment; death expected.
  • Above 10 Sv (10000 mSv): Incapacitation and death.

Data Output


Graph of the last hour, with rolling average. Due to the randomness of the emission of radioactive particles, a single count does not indicate anything which is relevant. The graph clearly shows a 10 sec period can have 0 counts and another up to 45.


Monthly readings, averaged over the day for comparison. Readings taken every 6 seconds from GM-10 Geiger Counter.