Natural Background Radiation

Natural background radiation (NBR) comes from naturally occurring radioactive materials (NORM) in our environment which come from radioactive minerals and ores within the earth which contain radioactive elements such as uranium, thorium, radium, radon, potassium-40, etc. This includes carbon-14 and a small amount of tritium produced as nuclear activation products created by collisions of high energy cosmic rays/particles with the components of our atmosphere. Some of these particles also come from our sun via the solar wind, in addition to those which originate in deep space. NBR also includes the direct action of cosmic rays/particles on our bodies where they deposit their energy directly into our cells, tissues and organs.

The Nuclear Regulatory Commission (NRC) sets the “acceptable” exposure limit to man-made radiation at 500 mR/yr for members of the general public. This is more than five times the NBR. And is all this extra radiation exposure supposed to be “acceptable?” To whom? This extra radiation creates additional risk and shortens life expectancy, so why should we accept this exposure as a given. The NRC calls it a “dose,” but is shortening everyone’s life really a gift? Using the word “dose” in connection with radiation exposure is inappropriate both scientifically and semantically. In fact, the use of “acceptable dose” needs to be seriously reconsidered when talking about radiation since such language creates the appearance of harmlessness when caution actually needs to be exercised.

Nuclear apologists simply repeat, without thinking, the nuclear industry propaganda that the natural background radiation is 350 mR/yr. Based on this figure the NRC has set an “acceptable” exposure limit of 500 mR/yr to man-made sources of radiation for members of the general public and it assumes this amount to be harmless. If the NRC has included internal radioactive emitters such as radon in this 350 mR/yr total, then it must take into account micro-exposures to cell components and biomolecules. These exposures are typically very high in very small volumes/masses of tissue so they can not be legitimately combined with external whole body radiation measurements. Exposure to radionuclides such as uranium, plutonium and tritium, (byproducts of nuclear weapons tests), as well as fission products such as strontium-90, cesium-137 and iodine-131 (from the nuclear fuel cycle as well as weapons tests), and neutron activation products such as carbon-14 are internalized in the body and cause damage from within. These radioactive isotopes are clearly not natural and should not be included in the NBR total. Exposures from medical procedures should also not be included in this total.

Occasionally in its public relations documents the NRC speaks of an even higher NBR of 640 mR/yr. Since the NRC regulates the reactors, it is in their vested interest to keep alive the public impression of a high level of “harmless” natural radiation. Clearly there is considerable confusion about this actual number. In point of fact, the natural background radiation is between 80 and 90 mR/yr. Using a hand-held Geiger counter one can verify that an average reading is around 10 counts per minute (cpm) at sea-level and mid-latitudes where most of us live. This translates to about 0.01 mR/hr. Since there are 24 hours in a day and 365 days in a year, there are 8760 hours in a year. If one multiplies this number by 0.01 one gets 87.6 mR/yr of external radiation from cosmic rays and radionuclides in the soil, at least from those radiations with enough energy to penetrate a Geiger tube or interact with its membrane. At the altitude of Denver (about 1 mile) NBR is about 120 mR/yr. The 640 mR/yr NRC value is completely inaccurate and can only be perceived as a blatant attempt to label their “permissible,” excessive radiation exposure level as lying within a fictional “safe” level. Both natural and man-made radiation cause harm and are additive.

In an attempt to diminish radiation exposure concerns among the general public, many nuclear industry apologists mistakenly, or even purposefully, compare the NRC’s 500 mR/yr “acceptable” limit of  exposure to man-made sources of radiation from all-sources to:  (1)  Taking an airline flight from New York to Los Angeles; (2) Living at a higher altitude; (3) Eating a few bananas; (4) Sleeping with another person in the same bed because their bones, as well as your own contain radioactive elements; and/or (5) Watching TV for a few hours. I will address each claim individually.

(1)  The NBR actually does increase with altitude above sea-level. If one carries a hand-held Geiger counter, such as a RadAlert device, onto an airplane one can discern a simple pattern of exposure versus altitude. Because the atmospheric density decreases with altitude there is less air to shield from incoming cosmic radiation the higher one goes. The background radiation is about 10 counts per minute (cpm) at sea-level and a rule of thumb says that it will double with an increase in altitude about every 7,000 feet as follows:

Sea Level 10 cpm
7,000 Feet 20 cpm
14,000 Feet 40 cpm
21,000 Feet 80 cpm
28,000 Feet 160 cpm
35,000 Feet 320 cpm
42,000 Feet 640 cpm

Since most commercial aircraft fly between 35,000 and 39,000 feet (about 7 miles high),we can assume that a flight from New York to Los Angeles, lasting about 6 hours, will expose a passenger to about 350 to 400 cpm for six hours. Since 1,000 cpm is equal to 1 mR/hr the total exposure will be about 2.0 to 2.4 mR for the entire flight. That amount translated into gray or sieverts is about 0.02 mGY or mSV. Thus it would take about 200 to 250 cross country trips, in a year, to accumulate an exposure equal to the NRC’s “allowable” limit to the general public. Most people do not fly anywhere near that much so the NRC comparison of their “acceptable exposure limit” to airline travel is deceptive. Clearly this is not a valid argument for members of the general public. Airline crew members, however, who fly more than this should be classified as radiation workers;

(2)  As for living at higher altitudes the vast majority of us live at altitudes below 7,000 feet so that is not a major issue. Living at higher altitudes exposes one to lower atmospheric oxygen partial pressures which are somewhat protective against radiation damage so that may offset the higher radiation levels;

(3)  As for the bananas argument, although there is a small amount of potassium-40 in bananas, this amount cannot even be measured without first removing the NBR. This is clearly a specious argument.

(4)  As for watching TV, most TV sets are now flat screen LCD or LED displays which emit no ionizing radiation at all. This argument is clearly bogus;

(5)  As for bones, this depends on the age and the location where the specific person lived. Bones contain some small amounts of natural isotopes of uranium and thorium but most of the incorporated radionuclides are fission products and bomb components such as strontium-90 and plutonium, which have contaminated the environment during the manufacture and testing of nuclear weapons and the operation of the nuclear fuel cycle for nuclear reactors since the 1940s. These sources are clearly not natural. These amounts are also typically too small to be measured externally relative to the natural background radiation. This is not to suggest, however, that they are harmless nor does it mean that natural background radiation is harmless.

It becomes clear that the people who claim that “low-levels” of ionizing radiation are harmless: (1) Do not understand how human cells and tissues are damaged by ionizing radiation and how such damage may or may not be repaired; (2) Do not understand that NBR is also dangerous and may limit our life spans; and (3) Do not even realize that there is no such thing as “low-level” radiation because a single nuclear disintegration with its emitted high energy photons and particles contains enough energy, in and of itself, to completely disrupt a cell or group of cells and their sub-cellular components such as the mitochondria, ribosomes, lysosomes, cellular architecture and the nucleus with its DNA.

Radon gas is found in the air all around us. It is a naturally occurring disintegration product of radium. It is sometimes said to be the largest contributor to lung cancer of any natural product. Radon itself is a large, radioactive, polarizable, lipophilic, electrically neutral atom which emits energetic alpha particles when it disintegrates. It is highly soluble in adipose (fatty) tissues such as those which make up the brain, neurons, breast and bone marrow where the alpha particles can cause considerable damage. Because of its physical properties and its solubility in fat it is also a very good anesthetic agent. If it were not for its high cost and its radioactive emissions it would probably be the anesthetic of choice in operating rooms worldwide because it is an inert gas chemically. The alpha particle emissions are unfortunately an insurmountable problem preventing this use. Fortunately, in well ventilated areas the concentration of radon in the air is not very high, not much is taken into the body and even less becomes dissolved in the fatty tissues. In underground areas with little air circulation the concentration of radon can accumulate. A particular problem is in underground uranium and thorium mines where radon can build up to dangerous levels. A very high incidence of lung and other cancers has been observed among miners who worked in these underground mines. The incidence of lung cancer among those miners who smoked was nearly 100%. This was probably due, not to radon atoms themselves, but to the progeny or radon decay – products such as lead-210 and polonium-210. These descendants of radon also emit energetic alpha and beta particles as well as gamma rays which can destroy or damage adjacent cells and tissues. When these progeny atoms of radon are produced they first appear as ionized atoms and eventually become electrically neutral by gaining or shedding electrons from/to their environment. Unfortunately for smokers, the process of burning tobacco also produces ionized smoke particles which attract oppositely charged ions of the newly emerged radon daughter products from the surrounding air. This electrostatic attraction of ionized tobacco smoke sweeps the surrounding air and accumulates all the ionized radon progeny atoms onto the ionized smoke. The smoke particles, with radioactive radon progeny ions attached, are then drawn deeply into the lungs by inhalation where they deposit their radioactive load. This can result in exposures to the smokers lungs from 20 to 30 times higher than that in the ambient air.

An easy experiment can demonstrate the electrostatic concentration of radon decay products from the ambient air. Take a thin sheet of white, opaque, Mylar plastic, about 2-1/2″ x 4″ and about 2 – 3 mm thick. Take a wood block about the same size and drill holes in each corner. Place a “swizzle” or coffee stirring stick in each hole. Take a flat piece of hardwood about the size of the Mylar sheet but about 5-6 mm thick. Wrap one end of the wood with insulating tape. Place the Mylar sheet on a non-conducting surface and rub it with the wood piece, being careful not to touch the wood, only the tape. Pick up the Mylar sheet with non-conducting tweezers, being careful not to collapse the charge by touching it to any other surface. Place it on top of the four “swizzle” sticks mounted in the wooden block. Place the entire apparatus on a window sill with free circulating air. Wait about 15 to 30 minutes and then count the Mylar sheet with a hand held Geiger counter such as a RadAlert machine. The count will be 20 to 30 times higher than the ambient background radiation of the surrounding air indicating that the electrostatic charge has attracted many radon decay products from the circulating air. Such an electrostatic concentration of radon daughters in the vicinity of electric fields and charges may also be responsible for the health effects attributed to electromagnetic fields when, in fact, these health effects are probably caused by the accumulation and concentration of radioactive radon decay products in the vicinity of these fields.