|Ionising radiation and health—risk analysis is the sixth of a series of briefing documents on the problems of power consumption, posed by the steady depletion of fossil fuels and most particularly of pumpable oil.|
|on energy||on global warming|
housing and making living systems ecological
sustainable futures briefing documents
|Tectonics: tectonic plates - floating on the surface of a cauldron|
|Them there rays|
|Food: eating is bad for you!|
|Naturally produced background radiation, with illustration|
|A comparison of the activities of selected radioactive materials|
|Risks from different types of ionising radiation exposure|
|The atomic bomb|
|High altitudes, including flight|
|Decommissioning nuclear reactors|
This document is introductory only; very much more is known about radiation and can be learnt by study. The purpose of this document is to remove irrational fears and to present basic analysis of risk. The figures given in the document are often useful examples rather than the latest figures for your country or local conditions.
You live surrounded by ionising radiation, just as you live in a world surrounded by heat. If you were transported into the sun, or even a furnace, you would not last long. Heat is a form of energy; at normal background levels it is no big deal, but you sure donít want to take up residence in the core of a nuclear reactor, any more than you would welcome living unprotected in a coal-fired furnace.
In 1902, Ernest Rutherford found that three different kinds of radiation are emitted in the decay of radioactive substances. These he called alpha, beta, and gamma rays in sequence of their ability to penetrate matter. Be aware that alpha, beta and gamma particles are named in order of reducing size, but of increasing energy. Gamma particles also penetrate matter more because they interact less with other matter.
Gamma rays In 1912, gamma rays were shown to be much more penetrating and have all the properties of very energetic electromagnetic radiation, or photons. Gamma-ray photons, when they originate from radioactive atomic nuclei, are between 10,000 and 10,000,000 times more energetic than the photons of visible light. Gamma rays, with a million million times higher energy, make up a very small part of the cosmic rays that reach the Earth from supernovae, or from other galaxies. The origin of the most energetic gamma rays is not yet known.
High energy is not highly dangerous in isolation. I would rather a drop of rain fell on my head at 50 miles per hour, than a grand piano at 10 miles per hour. These particles are incredibly small. If I am hit by a small fast moving bullet, it is likely Iíll survive the experience; whereas a slower-moving, but physically larger, blast from a shotgun is liable to inconvenience me greatly. High-energy particles have the potential to damage the cells in your body, setting off cancers. But I emphasise, you live among such radiation, you just do not welcome a surfeit.
No figures given for the thicknesses of the sheets of difference materials because the stopping ability of different materials depends on the variable energetic ability of the particular radiation.
Here are some example approximate thicknesses:
4 cm air
|beta||3 mm aluminium|
6 cm lead
1 metre concrete
The lifetime risk of cancer:
from the food you eat
from spices and flavourings
less than 0.1%
all other additives such as pesticides, drugs fed to farm animals and processes of food preparation
less than 0.05%
That is, the risk of eating at all is around 60 times the risks of all those additives that the media rattle on about. If you are really worried, perhaps you might like to starve! 
Now that is just the cancer risk from eating that dangerous stuff called food. You might also choke on the stuff, get mad cow disease (BSE), or some nasty, potentially fatal, e-coli bug like E.c. 0157:H7. Even if you donít die from eating food, it is quite likely that you will still die! Be happy, donít worry Ė well, at least not so much.
There is no such thing as a dangerous
substance or a poison,
During radioactive decay, an unstable nucleus usually emits alpha particles, electrons, gamma rays, and neutrinos.
In nuclear fission, the unstable nucleus breaks into fragments, which are themselves complex nuclei, along with other particles such as neutrons and protons. The resultant nuclear fragments are often in a highly excited state, and then reach their low-energy ground state by emitting one or more gamma rays.
Because gamma rays have no electric charge, and thus do not interact with matter as strongly as do charged particles, they have great penetrating power. Because of their penetrating power, gamma rays can be used for radiographing holes and defects in metal castings and other structural parts. At the same time, this property makes gamma rays extremely hazardous. The lethal effect of this form of ionising radiation makes it useful for sterilizing medical supplies that cannot be sanitized by boiling, or for killing organisms that cause food spoilage. More than 50 percent of the ionising radiation to which humans are exposed comes from natural radon gas, which is an end-product of the radioactive decay chain of natural radioactive substances in minerals. Radon escapes from the ground and enters the environment in varying amounts.
Naturally produced background radiation comes
from a number of sources, as shown in the illustration above.
Note that plutonium is 153,000 times more active than depleted uranium. (2,298,000/15=153200)
U238, U235 and U234 predominantly emit alpha particles (over 95% are alpha particles). The alpha activity of natural uranium amounts to about 25 kBq/g. The progeny from the alpha decay of uranium themselves continue to decay, mostly by emitting beta particles. The activity of these progeny is added to that of uranium. The beta radiation of the progeny of natural uranium and depleted uranium have practically the same intensity, amounting to about 25 kBq/g.
Uranium, together with its progeny, has an activity of 50 kBq/g (for instance, 50 000 decays take place per gram per second).
The very long half-life [read this linked section now, if you do not understand half-life] of U238 (4.5 billion years) yields a low decay rate per unit mass of uranium. Naturally occurring uranium, which mostly consists of U238, is one of the least radioactive substances containing unstable isotopes on the planet. It is classified by the International Atomic Energy Agency in the lowest hazard class for radioactive materials.
Exposure to the radiation emitted from uranium can occur if it is outside the body, or if it is ingested, inhaled or taken in by other means. It is useful to consider the exposure pathways with regard to average radiation exposure in the normal environment. As you can see in the illustration, gamma radiation can travel right through you from the environment and alpha radiation can be stopped by your skin. However, should you ingest radionucleides (radioactive materials) and they become lodged in the body, the alpha radiation will become a considerably greater problem because the radionuclides will not just wash or fall off.
Alpha rays are 20 times more effective than beta and gamma rays at causing tissue damage. To allow for this, the dose in grays is multiplied by an effectiveness factor and the new units are called sieverts (abbreviation Sv) and the dose is called the equivalent dose.
The Sievert (Sv) is the international measure of radiation expressed as a dose-equivalent. In the general population ingestion of uranium and its decay series in food and drink gives a committed effective dose of 0.11 mSv per year for adults, as compared to 0.0058 mSv through inhalation, excluding inhalation of radon (1.2 mSv).
This annual dose corresponds to 5% of the average annual dose due to internal and external exposure to natural sources of radiation (2.4 mSv). It relates essentially to progeny, Pb210 and Po210. U238 accounts only for 0.00025 mSv total dose and 0.000021 mSv for inhalation. External exposure from all natural U238 in soil is also negligible. U238 series, together with other primordial radionuclides, Th232 and K40, cause a world-average annual external exposure of about 1 mSv per year.
If I have a 1 in 1 million chance of being in an aeroplane crash and my risk doubles, I have then a 2 in 1 million chance of being in a crash. These rates are worked out by calculating, for example, how many people on average died in such crashes over the last 10 years. If none were killed in 9 of the years and 20 in the final year, that will give you an average of 2 each year.
Of course in the year that 6 die in a crash, the Daily Slime will Ďreportí as follows: ď200% more killed in ’plane crashes this year, something must be doneĒ. (2 is the 100% base average figure, 6 is three times 2 and is therefore 300% relative to the base rate, hence the rise of 200% above the base rate.) Although, knowing full well the ignorance of the reporters at the Daily Slime, they will probably say 300% because they canít count either.
The chance of being killed on the roads of America† is approximately 1:8000 each year, over 80 years that is a risk of 1 in 100. This is now becoming a serious risk compared with figures for flying! A doubling of that road-kill risk would be serious news!
The risk of being killed while flying on large commercial jets is around 1 in million, if you fly 200,000 miles a year (the risks are higher on commuter flights and higher still in a private aircraft). Clearly you will not be killed in an aircraft if you do not fly in one; but you can still worry if you like; there is even about 1 chance in 25 million that an aeroplane will fall on you sometime in your life!
It is important to
It is further important to remember that
The atomic bomb, or atom or fission bomb, is a weapon whose explosive power comes from the fission (or splitting) of atomic nuclei. When the nucleus of a heavy atom, such as uranium-235, is split, a certain amount of mass is released as an equivalent amount of energy, powering the atom bomb. On a pound-for-pound basis, the U-235 in an atomic bomb can release on the order of one million times as much energy as TNT.
Effects of an Atomic Bomb Explosion
On Aug. 6, 1945, an atomic weapon of about 15 kilotons was exploded about 1,800 feet (550 meters) over the Japanese city of Hiroshima. On August 9, a plutonium-based weapon of about 20 kilotons was exploded about 1,800 feet (550 meters) above Nagasaki. The bombs devastated both cities. About 70,000 people died at Hiroshima and about 40,000 at Nagasaki, and many thousands more were injured.
The devastation of Hiroshima and Nagasaki resulted from three main types of effects:
The blast effect of an atomic bomb is similar to that of a conventional
explosive but much more intense and far-reaching. (Note: only the blast
effect is significant for chemical high explosives.)
Among the survivors of the attacks on Hiroshima and Nagasaki, roughly equal numbers of injuries were caused by blast and thermal radiation but considerably fewer by nuclear radiation. Each of the three types of effects posed serious hazards to unprotected persons out to a distance of about a mile (1.6 km) from a point directly below the explosion.
You may find some comments and references on medical x-ray radiation here.
X-rays are a type of penetrating radiation that, depending on the dose, can reduce cell division, damage genetic material, and harm unborn children. Exposure to x-rays is measured in units of radiation absorbed dose (rad).
Cells that divide quickly are very sensitive to x-ray exposure. Unborn children are particularly sensitive to x-rays because their cells are rapidly dividing and developing into different types of tissue. Exposure of pregnant women to sufficient doses of x-rays could possibly result in birth defects or illnesses such as leukaemia later in life. With most x-ray procedures, relatively low levels of radiation are produced. However, a doctor may decide to postpone or modify abdominal or lower back x-rays in a pregnant woman unless absolutely necessary. Women who receive x-rays before realizing they are pregnant should speak to their doctors. Some pregnant women may be exposed to x-rays in the workplace, so governments may establish limits to protect unborn children from radiation exposure in work settings.
The rate of risk of cancers from X-ray exposure are calculated from atomic bombs and other exposures, extrapolating for the smaller exposures given by X-rays.
There is some theoretical effect, but empiric results do not easily detect it.
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of depleted uranium munitions [.doc format]
The person who wrote this document has a neat sense of humour. Obviously, they also have had to deal with moonbats!
You will find a great deal of hysterical nonsense about vast monetary sums and time scales involved in ‘decommissioning’. As you will see from a careful reading of this document and its companion document on nuclear power, the ‘dangers’ are great exaggerations, based mainly in ignorance.
Naturally, the nuclear industry will quote huge sums for clean-up, just as other government contractors, and their political clients, will seek enormous profits in fields like aviation, space flight and pharmaceuticals, where most people are unable to judge the technology or to make reasonable assessments of costs.
All the waste from all nuclear activities since the beginning of the development of nuclear power would fit into the space of a few football fields; and, as you will see from these documents, this nuclear waste is not the dangerous horror as represented by some lobbyists.
In fact, a major reason that no large, deep-earth depository has yet been built is that the amount of waste currently available does not easily justify the cost of dealing with it. Delays and obstruction are aggravated by constant campaigns from those seeking publicity through scaremongering, combined with the usual NIMBY (not in my backyard) syndrome. These delays are tiresome because we end up with scattered and inadequately supervised dumps in many locations.
The wastes of the nuclear industry are quite trivial when placed against the last century or two of devastation, ruined landscapes, subsidence and externalised filth, attributable to the fossil fuel industries. The difference in waste level is hardly surprising as it is estimated that something like 10 million times the energy can be extracted from an atom of uranium as can be extracted from an atom of carbon in fossil fuels!
|Danger ahead—the risks you
really face on life’s highway
by Larry Laudan, 1997, Wiley & Sons, pbk, 0471134406
|The culture of fear—why Americans are
afraid of the wrong things
by Barry Glassner, 1999, Basic Books, pbk, 0465014909
email abelard at abelard.org
© abelard, 2004, 05 february
the address for this document is http://www.abelard.org/briefings/ionising-radiation.php