Radiation is Everywhere and Always Has Been

Most radiation in the world is caused naturally through cosmic and terrestrial sources.  Most of our exposure to natural radiation comes from radon in the rocks and soil and the largest man made source of radiation comes from coal-fire power plants. The radiation dose actually was a lot higher thousands of years ago than it is today and life still flourished.

The worldwide average background radiation dose is 2.4mSv per year and the average in the United States is 4.0mSv. A typical person is hit by 15,000 particles of radiation per second from natural sources (totalling 500 billion per year, or 40 trillion in a lifetime), and an average X-ray involves being hit by 100 billion. However, this is not dangerous because the probability for a particle of radiation to cause a cancer or a genetic disease is only one chance in 30 million billion (30 quintillion).  Grand Central Station in New York City is made from granite, which contains uranium,  and if you spent a whole year there you would get a dose of 6msv.  

Average Annual Dose (mSv)
Average  Range of Annual Dose (mSv)
Inhalation (Radon Gas)
External Terrestrial
Cosmic Radiation
Total Natural

Natural radiation causes approximately 1% of all cancers and radiation from nuclear technology will increase the cancer risk by 0.002% which reduces our life expectancy by less than one hour.  If you live within 75 kilometers from a nuclear reactor, you’d get an estimated trace exposure of 0.009 millirem a year, which is smaller dose than eating one banana, which contains the radioactive isotope potassium-40.

                                            Ionizing and non-ionizing Radiation

There's ionizing radiation and non-ionizing radiation. Ionizing radiation is dangerous and has enough energy to damage cells, your DNA and cause cell mutation.  Ionizing radiation is everywhere including in minerals in the soil that emit alpha and beta particles as well as some gamma rays. Sunlight also has ionizing ultraviolet radiation.   Non-ionizing radiation is mostly harmless. 

Then there are two kinds of radiation: Particle and Electromagnetic.

                                         Particle Radiation (Ionizing Radiation)

There are also two kinds of particle radiation called alpha and beta particles. Neither is very strong and don't travel far from their source.

Alpha Particles  (Ionizing Radiation)

Alpha particles are too weak to penetrate skin, although if you ingest them they can cause damage. The most common source of alpha radiation is radon, which exists naturally everywhere. More than half of the average persons radiation exposure comes from radon in soil. Uranium oxide,  or Yellowcake, emits mostly alpha particles and you could hold plutonium metal in your hand with only  a sheet of paper as protection  and you will be completely safe.

Beta Particles  (Ionizing Radiation)

Beta particle emitters like iodine-131 are often found in certain medical treatments. Beta particles are fast moving electrons and are dangerous when you're close to them because they can penetrate skin at close range.  They can travel long distances,  one metre or more.  Potassium-40 in salt substitute is 90% beta emitter but has a half life of over a billion years so is only slightly radioactive.

      Electromagnetic Radiation  (Mostly Non-Ionizing Radiation)

Electromagnetic radiation  is all around us and comes from lots of different places and most is non-ionizing.  Around the home you'll find a lot of sources of electromagnetic radiation such a lamp, computer monitor or candles you have burning as visible light is radiation.   Your microwave oven and radio are also examples of electromagnetic radiation.

Gamma Rays (X-Rays)

Gamma rays have no charge like the alpha and beta particles and therefore have greater penetrating power and travel longer distances through most materials.  Because of its deep and uniform penetrating ability, gamma radiation is used for X-rays of the human body and for food preservation,  killing parasites and bacteria. 

Alpha,  beta and gamma radiation that have the same energy will ionize the same number of molecules and only differs in the distance travelled to ionize those numbers of molecules.

                                                 Radiation penetration (CX = Alpha,  B = Beta,  y =Gamma)                                                               Source: http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/radact.html