Direct evidence of radiation falling on Canada in the rain, as far east as Toronto. 20,000 CPM is equivalent to a highly targeted dose of radiation used for cancer radiotherapy.

The radiation one typically encounters is one of four types: alpha radiation, beta radiation, gamma radiation, and x radiation. Neutron radiation is also encountered in nuclear power plants and high-altitude flight and is emitted from some industrial radioactive sources.

Alpha Radiation

Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus. Some characteristics of alpha radiation are:

1. Most alpha radiation is not able to penetrate human skin.
2. Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.
3. A variety of instruments has been designed to measure alpha radiation. Special training in the use of these instruments is essential for making accurate measurements.
4. A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.
5. Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or other material, because alpha radiation is not penetrating.
6. Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard.
7. Alpha radiation is not able to penetrate clothing.

Examples of some alpha emitters: radium, radon, uranium, thorium.

internet site reference: http://theagoranational.ca/index.php/content/health/item/322-extremely-high-radiation-20000-cpm-in-ontario-after-rainfall