by John Moore

from TyniVitalSystems Website

Terrorist Related Information ("Suitcase Nukes")

• The US produced, and for many years deployed "Atomic Demolition Munitions." The Medium Atomic Demolition Munition (MADM) produced 1-15 kilotons of yield, and weighed 400 pounds. The Special Atomic Demolition Munition (SADM) yielded .01-1 kilotons and weighed only 163 pounds.
   

• The smallest nuclear weapon the US produced was the "Davy Crockett" - a recoilless rifle round. It weighed about 51 pounds, was 16 inches long and 11 inches in diameter. It produced a variable yield of up to 1 kiloton.
   

• An excellent discussion of this issue is here.
   

• The Soviets supposedly produced "suitcase nukes" and there is no reason to doubt this assertion. Former Soviet General Ledbed has asserted that a number of these are not accounted for. There are reasons, however, to doubt his assertions given his political position. Interestingly, Ledbed was recently killed in a helicopter crash.
   

• The Soviets supposedly produced "suitcase nukes" and there is a US DOE estimate that only 4kg of Plutonium is necessary to make a fission weapon. Some believe that only 1kg is needed.
   

Basic Nuclear Weapons Engineering

• See Nuclear Weapons FAQ for primary reference material.

   

• All known nuclear weapons require the fission of Uranium (235 or 233) or Plutonium 239. An "atomic bomb" (fission weapon) uses the fission energy directly, while a "hydrogen bomb" (thermonuclear weapon) uses fission to ignite a fusion reaction, achieving much higher energy release. In theory, there is no limit to the power of a fusion bomb. There has been speculation that it is possible to create useful fusion weapons without a uranium trigger, but no reliable unclassified information indicates that this is true, and there is a difficult physical principle to overcome.
   

• Uranium consisting of unnaturally high amounts of isotopes 233 and 235 is called enriched uranium. Uranium is a common element on earth, but U-233 and U-235 constitute small percentages of it (<1%) and are always found mixed with the less useful U-238.
   

• Fission is the process whereby an atom's nucleus splits, releasing a large amount of energy. In a simple fission weapon, fission occurs when a neutron is absorbed by a nucleus, causing it to be highly unstable, at which point the nucleus splits, releasing a large amount of energy and more neutrons. This only occurs easily in a few isotopes (in Uranium, 235 or 233).
   

• A chain reaction occurs because the fission of a nucleus releases additional neutrons, which can then cause fission in more nuclei.
   

• Critical mass is the amount of fissile material needed for a chain reaction to become self-sustaining. This means that for each neutron released in the material, on average one more neutron will be released as a result. The critical mass is a factor not just of the type and amount of material, but also its instantaneous density and geometry. In other words, a mass of plutonium might not be critical until it is rapidly and highly compressed by high velocity "implosion."
   

• Fission weapons explode when the fissile material is suddenly placed in a configuration significantly greater than the critical mass - a state of supercriticality. If critical mass is reached too slowly, the weapon will explode with greatly reduced energy, possibly simply melting.
   

• When a weapon has reached supercriticality, it still may not explode unless a neutron passes into the core. Since a high explosive implosion maintains criticality for only a few microseconds, a neutron flux generator may be required to guarantee this.
   

• The easiest weapon to build uses a large amount (tens of kilograms) of enriched uranium. Because uranium releases neutrons at a very low rate, the weapon can use a relatively long "assembly time" to reach supercriticality. One design uses a sphere with a cylindrical hole in it, and a "gun" to fire a cylinder of uranium into that hole. Until the cylinder is inserted, both assemblies are well below critical mass, but when the cylinder is inserted, the mass rapidly rises to supercriticality. A neutron randomly released by the material during this process triggers the chain reaction. This weapon is so simple that the US used one against Nagasaki without ever testing the design. These weapons tend to be fairly large and inefficient, although the design was used in a US nuclear artillery shell.
   

• A plutonium based weapon cannot use the "gun" approach, because plutonium releases too many neutrons, which would cause the chain reaction to start long before the mass was supercritical enough to cause a large explosion. Hence plutonium weapons require assembly by compressing a sphere or shell of plutonium very rapidly, using high velocity explosives. This necessitates very high quality explosives, a very precise machining of all parts, and an electrical detonating system which can deliver very high energy pulses to a number of detonators with great timing precision. Hence plutonium based weapons are significantly harder to build. The US tested one at Trinity Site before deploying another against Nagasaki.
   

• A uranium weapon can also use the implosion approach, to achieve greater efficiency. However, in this case it requires a neutron flux generator to assure that enough neutrons flood the core during the maximal period of compression that the chain reaction will start and the weapon will be efficient.
   

• Uranium weapons require the production of enriched uranium (although it does not have to be as highly enriched as is used in some power reactors). This is a complex process because it requires the separation of isotopes of the same element (which means they have the same chemical behavior) and the isotopes have almost the same weight. Thus multiple stages of gas diffusion, centrifuges or electromagnetic (calutron) separation are required. This is inevitably a major industrial project, and is likely to be detectable by intelligence agencies. However, the centrifuge method can be distributed, making it hard to spot. It is believed that Saddam Hussein intended to use this approach once he was rid of UN inspectors. Laser separation has also been used. In addition, there may be new technologies that make enrichment much easier to do or at least easier to conceal. Only a ton or so of natural uranium is required to produce enough enriched uranium for a weapon.
   

• Plutonium weapons require the production of highly pure plutonium. Because plutonium is a not found in nature, it must be made in a nuclear reactor. Once made, however, it is relatively easy to extract because it is chemically different from the other elements in the mix, although the extraction process must take place in an environment made extremely radioactive by other elements mixed with the plutonium.
   

• Fusion weapons can be much more powerful than fission weapons, but require a subtle and difficult design. However, at least two different teams (Teller-Ulam and Sakarov) independently discovered the same approach. Since that time knowledge of fusion designs has spread through espionage and possibly technology trades. The details of fusion weapons will not be discussed here - see the Nuclear Weapons FAQ for vastly more information.
   

Radiation Risk - The Facts, not the Scare Stories

• Myth: Nuclear war would end human life on earth through radiation.

  Fact: If all of the nuclear weapons in stock at the height of the cold war were detonated, the average radiation dose per person is only 1/100th of a lethal dose, and well below doses which can be shown to have even long term effects (such as cancer).

   

• Myth: Chernobyl caused or will cause thousands of deaths.

  Fact: The Chernobyl disaster was the worst possible reactor disaster. It released an extremely large amount of radiation into the environment (see below). Even so, there have been no detectable increases in death rates even among the most highly exposed population (other than those who received extremely high doses fighting the fire, and many of whom died as a result). The radiation levels of the "highly radioactive" regions evacuated after the event are significantly lower than the natural radiation level in many parts of the world. Long term very sensitive genetic studies of animals in the most highly exposed region have found no abnormalities. There is no excess of three eared rabbits or 10 pound cockroaches around Chernobyl!

   

• Myth: Fallout caused deaths in Japanese nuclear bombings.

  Fact: There was no significant fallout in the vicinity of the Hiroshima and Nagasaki bombings. All radiation injuries were a result of immediate (first 1 minute) radiation.

   

• The United States Transuranium and Uranium Registries (USTUR), operated by Washington State University, reports:

  • "The health effects from plutonium, americium, and uranium intakes by humans, as determined with USTUR data can be summarized in two words, virtually none. A study of the causes of death of USTUR organ donors has been completed. The study showed that the vast majority of USTUR donors died from the same diseases that have caused the deaths of most of the U. S. population, heart disease, strokes, and cancers not necessarily associated with radiation exposure. This is in spite of the fact that the USTUR donors are a biased population in that a number of donors volunteered for the program after having been diagnosed with cancer. The average age at death of USTUR registrants is 63 years (range between 25 and 91 years). The average age of USTUR registrants who are still living is 73 years (range between 30 and 93 years)."

• The only human cases of significant fallout exposure to humans (as of 1964, and outside of the USSR) were in the Marshall Islands, after a U.S. test (CROSSROADS, Bikini Atoll, 1946). The short term effects were skin burns, nausea, and other symptoms typical of exposure to high radiation doses. Even so, there was only one cancer (leukemia) likely caused by the radiation, 18 years after exposure of a 1 year old. Of the pregnancies in progress at time of exposure, there was one miscarriage (no evidence for or against radiation relationship). The rest produced healthy children. Not surprisingly, there were a large number of cases of thyroid problems, which lead to some reduced growth in children. A study of the 40,000 military members who participated found no scientific evidence of radiation induced cancers. References are here. These results do not mean that fallout is harmless - far from it, but they show that even radiation intense enough to produce burns and nausea need not create a significantly increased risk of cancer.

   

• Almost all radioactivity in fallout - even in a ground burst - comes from the fission products themselves or transmutation of parts of the weapon. Thus air bursts and ground bursts produce approximately the same amount of radioactive products. However, ground bursts cause much more of the radioactive debris to be deposited within a fallout pattern, rather than distributed (and accordingly diluted and decayed) across the entire planet.

   

• There is evidence that radiation is beneficial and improves health (radiation hormesis) up to some surprisingly high levels..
   

Blast Effects - More Technical Information

• The blast effect is primarily determined by the "overpressure" - given in English units in PSI.

   

• This effect at any distance is proportional to the cube root of the weapons yield. Thus a 20 megaton bomb, which is large by today's standards, will affect only 10 times the radius of a 20 kiloton bomb - which was the yield at Hiroshima.

   

• In Hiroshima, there was a 50% survival rate 12 miles (200 meters) from ground zero. The bomb went off at 1850 feet above ground zero with a yield of about 20kt. Concrete structures at ground zero survived.

   

• In Hiroshima, there was only one known case of burst eardrums among the survivors.

   

• A human being can withstand up to about 35PSI of peak overpressure from a nuclear blast (1% fatality rate). Your mileage may vary. Thus a human will almost always survive the blast overpressure at approximately the following distances (slant range) from a blast according to the following table:
   

  Distance From Blast to Survive Blast Wave Yield Distance (mi) Distance (km) Comments 20 kT .35 .56 Hiroshima and Nagasaki 600 kT 1.1 1.8 Typical Strategic US Nuke 20 MT 3.5 5.6 Very Big Bomb

   

• The blast wave can, however, pick people up and throw them. For a 165 pound standing person to be thrown at 20 feet per second, the following table shows the distance from the blast:

  Distance From Blast to be Thrown at 20 fps Yield Distance (mi) Distance (km) 20kT 1.06 1.75 600kT 4.1 6.6 20MT 16.8 27

   

  Max Wind at Distance from Blast Yield 1 mi 1.6 km 3 mi 4.8 km 10 mi 16 km 30 mi 48 km 20kT 200 mph 89 mps 47 mph 21 mps 5 mph 2 mps ~0 600kT 1000 mph 447 mps 210 mph 94 mps 51 mps 23 5 mps 2 20MT off scale 1200 mph 536 mps 195 mph 87 mps 47 mph 21 mps

   

• The greatest danger from the blast wave comes from destruction of structures and the conversion of objects into missiles. The following tables gives the destruction distance from various yields for a few kinds of structures:
   

  Window Breakage Yield Distance (mi) Distance (km) 20kT 3.2 5.1 600kT 10 16 20MT 32 51 Wood-frame Building Destruction Yield Distance (mi) Distance (km) 20kT 1.5 1.9 600kT 4.8 7.7 20MT 15 19

   

  Multi-story Brick Yield Distance (mi) Distance (km) 20kT 1. 1.6 600kT 3.0 4.8 20MT 10 16 Multi-story Reinforced Concrete Offices Yield Distance (mi) Distance (km) 20kT .5 .81 600kT 1.3 2.1 20MT 5 8.1

   

• A ground burst produces a crater. The following table shows crater sizes:

   

  Crater Sizes Yield Width (feet) Width (m) Depth (feet) Depth (m) 20kT 633 193 80 24 600kT 2112 643 211 64 20MT 7392 2253 792 241

   

• Historic Radiation Releases

   

  Historic Radiation Releases (MegaCuries) Chernobyl 7.3            MCi Hiroshima 1.4            MCi Hanford (I-131 only) 0.74          MCi Three Mile Island 0.000015   MCi

Nuclear Physics Reference

• The negative effects of radiation can be divided into immediate effects (from very high dosages) and long term effects (from lower dosages). Long term effects are thought to be either the development of cancer, or genetic damage passed on to offspring. However, there is no evidence that low to moderate levels of radiation cause any long term damage in humans, and some evidence that it may be beneficial (radiation hormesis). Both long term effects would be a result of damage to DNA - most likely nuclear DNA (as opposed to mitochondrial DNA). However, the human cell experiences an average of 70 million (7x10⁷) DNA damages per year. Only 5 of these are attributable to natural radiation. Even radiation much higher than natural radiation would produce a negligible percentage of the total DNA damage. The average natural human dose is 2.2 mSv per year (see below for units). The lethal dose is typically 3000 mSv - 5000 mSv.
   

• Some elements of the following tables of miscellaneous conversion factors are excerpted from Nuclear Weapons Frequently Asked Questions by Carey Sublette.

References

• Nuclear Weapons Archive and FAQ - This is an outstanding and comprehensive resource.: http://nuclearweaponarchive.org/

• A paper disputing Linear No Threshold Theory - read below report:

Beneficial Radiation

And Regulations

by Zbigniew Jaworowski

Central Laboratory for Radiological Protection

Ul. Konwaliowa 7, 03-194 Warsaw, Poland
from UniversitéP.M.Curie Website

recovered trough WayBackMachine Website

 
Abstract

Administrative acceptance of the linear, no-threshold dose/effect relationship (LNT) for radiological protection was convenient for regulatory bodies, but is impractical, and inconsistent with observations on beneficial effects of low doses and dose rates of radiation, with a lack of increased malignancy and hereditary disorders in inhabitants of areas with high natural radiation background, and with a lack of genetic effects in progeny of Hiroshima and Nagasaki survivors. Man-made contribution to the average global individual radiation dose from all commercial nuclear power plants, nuclear explosions and Chernobyl accident, amounts now to about 0.4%, and from medical x-ray diagnostics 20% of the average natural dose of 2.2 mSv per year. The natural dose is in many regions of the world two orders of magnitude higher than the current exceedingly low dose limit for population of 1 mSv per year. act text here.


INTRODUCTION

A prompt criticality accident occurred in September last year at a nuclear plant Tokaimura, Japan. Three workers absorbed potentially lethal radiation doses of about 4500 to more than 20 000 milisieverts (mSv). One of them died on 83^rd day after the accident. Other was discharged from the hospital on 82^nd day, and the third, with skin lesions is successfully treated by skin grafts. Radionuclides produced in this accident by the short-term fission reaction, entered the atmosphere, but no significant ground contamination was found outside the plant boundary. Notwithstanding, the local authorities evacuated 150 residents and urged another 310 000 to stay indoors. . Compared with other industrial accidents occurring every day over the world, and which result in about 12 000 deaths per year in the United States alone, the Tokaimura incident does not seem to have been very serious.

Nevertheless, it was described by the media and by IAEA officials as "the world's third worst nuclear accident behind Chernobyl and Three Mile Island", and the worst nuclear accident in Japan, all of which is indeed correct. In Japan, nuclear power has been in operation since 1965. Today, 35 years later, almost 36% of its electric power is produced by 53 nuclear reactors. One fatal victim during so long time just proves the excellent safety of the vast nuclear industry in Japan. Every year during the last decade, due to fatal accidents at work, Poland suffered the loss of anywhere between 20 to 110 miners, to produce about half of Japan's electric power output, almost exclusively by burning coal.

Why then Tokaimura incident evoke such enormous media outcry? Why did it provoke such a vehement reaction from the public and from local and international authorities? Why had, for several days, the Emergency Response Center of IAEA in Vienna, given reports on the accident, sometimes five times daily, to all Permanent (national) Missions to the IAEA, and to 213 National (emergency) Contact Points all over the world? Why President Clinton ordered a safety survey of all American nuclear facilities, as if what had occurred in Japan could somehow extend to the United States?

Nothing like this occurs in any other industry when three workers get electrocuted, or flashed by a hot fumes, or die when a cloud of ammonia escapes from a factory or a railway tank. Any minor, leak of radioactivity from a broken tube in a reactor, even if completely innocent and bearing not relevance to the overall safety of the plant, is trumpeted throughout the world, and is used to direct mass emotions against the inherently safe and environmentally friendly nuclear energy. What makes people demand that nuclear industry to be a zero accident enterprise? Yet, at the same time, the same people appear to willingly accept all other kinds of man-made accidents, including the some 17 million deaths estimated to be caused by cars since their invention. What causes this paranoiac imbalance? An attempt to answer these questions is the subject of this presentation.

The Chernobyl catastrophe resulted in vast quantities of radionuclides being released into the global atmosphere, which were easy to measure even high in the stratosphere, and far away at the South Pole. It was a godsend for anti-nuclear activists. Yet according to estimates of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), one of the most distinguished international authority in matters of ionizing radiation, there were only 31 early death among the plant workers and rescue operators, and no early death among the public.

Thirteen years after the accident, apart from an increase in thyroid cancer registry (very likely due to increased screening rather than a real increase in incidence), there is no evidence of a major public health impact related to the ionizing radiation, and no increase of overall cancer incidence or mortality that could be associated with radiation exposure. There is no scientific proof of any increase in other non-malignant disorders, genetic, somatic or mental, that could be related to ionizing radiation from Chernobyl. This UNSCEAR estimate is clearly quite different from what one finds in most media, which prefer to cultivate mass radiophobia - an irrational fear of radiation and all things nuclear. But who reads UNSCEAR reports?

Chernobyl was the worst possible catastrophe of a badly constructed nuclear power reactor: complete core meltdown, followed by free dispersion of radionuclides in the atmosphere, and with an area of lethal fallout, of only 0.5 km2, reaching up to 1800 meters from the reactor. Nothing worse could happen with any reactor. It resulted in comparatively minute death toll, amounting to about half of that of each weekend's traffic in Poland. When the irrational rumble and emotions of Chernobyl finally settle down, in the centuries to come, this catastrophe will be seen as a proof that nuclear fission reactors are a safe means of energy production. Several accidents at hydroelectric, gas and coal energy production, and other industrial catastrophes in the 20^th century, each caused up to three orders of magnitude greater death toll than the Chernobyl accident (Table 1).

In the highly contaminated regions of the former Soviet Union, from which 270,000 people were evacuated and relocated, the 1986-95 average radiation doses from the Chernobyl fallout ranged between 6 and 60 mSv. By comparison, the world's average individual lifetime dose due to natural background radiation is about 150 mSv. In the Chernobyl-contaminated regions of the former Soviet Union, the natural lifetime dose is 210 mSv - in many regions of the world it is about 1000 mSv, and in the state of Kerala, India, or in parts of Iran reaches 5000 mSv. Yet no adverse genetic, carcinogenic, or any other deleterious effects of those higher, doses have been ever observed among the people, animals, and plants that have lived in those parts since time immemorial ; ; ; ; .

The forced evacuation of 270,000 people from their, presumably, poisoned homes, and other forms of overreaction of Soviet authorities (for example the famous "coffin subsidy" - a monthly financial compensation), did not result in a benefit, but instead induced some real harm: an epidemics of psychosomatic disorders observed in the 15 million people of Belarus, Ukraine and Russia, such as diseases of endocrinological system, circulatory and gastrointestinal diseases, depression and other psychological disturbances, headaches, sleeping disturbances, difficulties in concentration, emotional instability, inability to work and so on . The "coffin subsidy", which in impoverished Belarus will total $86 billion by 2015 , for millions of recipients, each time they sign a receipt, confirms that they are the "victims of Chernobyl".

The psychosomatic disorders could not be attributed to the ionizing radiation, but were assumed to be linked to the popular belief that any amount of man-made radiation - even miniscule, close to zero doses - can cause harm. This assumption, linear, no-threshold theory (LNT) was accepted in the 1950s, arbitrarily, as the basis for regulations on radiation and nuclear safety, now still in force. It was under this assumption and regulations that the Soviet government decided on the mass relocation of people from regions in which the Chernobyl radiation dose was much smaller than natural radiation background in many countries. This act of Soviet authorities demonstrated not only absurdity of LNT, but also the harmful effects of practical application of regulations based on this principle.

During the last three decades, the principles and regulations of radiation protection have gone astray and have lead to exceedingly prohibitive, LNT-derived standards and recommendations. Revision of these principles, being now proposed by many scientists and several organizations, was evoked both by an eye opening Chernobyl experience, and by recent progress in radiobiology, genetics and oncology.

Radiation carcinogenesis should no longer be perceived as a straightforward process started by a random hit by radiation to the DNA double strand in the cell. The complexity of this process precludes the use of direct proportionality even to estimate probability of the malignant cell becoming a macroscopic, clinically verifiable tumor. After a total malignant transformation, the cell has to divide some billions of times, before a cancer is formed. Such transformed cells appear to be distant from cancer by so many billions of iterative steps, that their outcome cannot be predicted, as a matter of principle .

A great radiobiologist, the late Harald Rossi summarized the situation as follows:

"It would appear...that radiation carcinogenesis is an intricate intercellular process and that the notion that it is caused by simple mutations in a unicellular response is erroneous. Thus, there is no scientific basis for the "linearity hypothesis" according to which cancer risk is proportional to absorbed dose and independent of dose rate at low doses" .

One of the factors responsible for these winds of change is recognizing by many scientists that small doses of radiation, like small doses of other physical or chemical agents, may be beneficial for organisms, and evoke a stimulatory or hormetic response, which is in direct opposition to the LNT. About 2000 scientific papers on radiation hormesis were published in the 20th century. However, when in 1982 I proposed that UNSCEAR should review and assess these papers, nobody seemed interested. Each following year I had repeated this proposal in vain, until after Chernobyl, in 1987, it finally gained support from the representatives of France and Germany. It took UNSCEAR some dozen years of deliberations before in 1994 the Committee published its fundamental report , rubberstamping the very existence of phenomenon of hormesis.

It was difficult for the Committee to overcome its own prejudices on radiation hormesis, and to produce a balanced objective report. Along the way, the Committee rejected two rather one-sided drafts of "hormesis document", but in 1990 also an excellent document on "Hereditary Effects of Radiation", prepared by a leading expert in the field, professor F. Vogel.

This last rejection demonstrated a hesitating mood of the Committee, as the Vogel's paper showed lack of genetic effects after Chernobyl accident, presented the existence of hormetic effects in children of Hiroshima and Nagasaki survivors, and the lack of any hereditary disorders both in these children, and in inhabitants of high natural background radiation areas. The draft of UNSCEAR 1994 "hormetic report" was prepared by Dr. Hylton Smith, then the Scientific Secretary of the ICRP, a body strongly supporting LNT and rejecting hormesis.

However, working for a few years on this report, Dr. Smith changed his initially negative approach to radiation hormesis, and finely produced an excellent, unbiased treatise on this yet unfathomed matter, demonstrating his scientific integrity.

This report sparked in the radiation protection community a quasi revolution, which is now gaining momentum, with some encouragement from the chairman of ICRP, professor Roger Clarke .


NATURAL AND MAN-MADE

The linear no-threshold hypothesis was accepted in 1959 by the International Commission on Radiological Protection (ICRP) as a philosophical basis for radiological protection . This decision was based on the first report of the, then just established, UNSCEAR committee. Large part of this report was dedicated to a discussion of linearity and of the threshold dose for adverse radiation effects. UNSCEAR's stand on this subject, more than forty years ago, was formed after an in-depth debate, not however without any influence of the political atmosphere and issues of the time. Soviet, Czechoslovakian and Egyptian delegations to UNSCEAR strongly supported the LNT assumption, using it as a basis for recommendation of an immediate cessation of nuclear test explosions.

The then prevailing target theory and the then new results of genetic experiments with fruit flies irradiated with high doses and dose rates, strongly influenced this debate. In 1958 UNSCEAR stated that contamination of the environment by nuclear explosions increase radiation levels all over the world, posing new and unknown hazards for the present and future generations. These hazards cannot be controlled and "even the smallest amounts of radiation are liable to cause deleterious genetic, and perhaps also somatic, effects".

This sentence had an enormous impact in the next decades, being repeated in a plethora of publications, and taken even now as an article of faith by the public. However, throughout the whole 1958 report, the original UNSCEAR view on LNT remained ambivalent. At example, UNSCEAR accepted as a threshold for leukemia a dose of 4000 mSv (page 42), but at the same time the committee accepted the risk factor for leukemia of 0.52% per 1000 mSv, assuming LNT (page 115).

Committee quite openly presented this difficulty, showing in one table (page 42) its consequences: continuation of nuclear weapon tests in the atmosphere was estimated to cause 60,000 leukemia cases worldwide if no threshold is assumed, and zero leukemia cases if a threshold of 4000 mSv exists. In final conclusions the UNSCEAR pinpointed this situation:

"Linearity has been assumed primarily for purposes of simplicity", and "There may or may not be a threshold dose. Two possibilities of threshold and no-threshold have been retained because of the very great differences they engender".

In the ICRP document of 1959 no such controversy appears, LNT was arbitrarily assumed, and serious epistemological problems related to impossibility of finding harmful effects at very low levels of radiation {later discussed by and } were ignored. Over the years the working assumption of ICRP of 1959 came to be regarded as a scientifically documented fact by mass media, public opinion and even many scientists. The LNT principle, however, belongs to the realm of administration and is not a scientific principle.

In these early years the LNT assumption did not seem very realistic, but was generally accepted because it simplified regulatory work. The original purpose was to regulate the exposure to radiation of a relatively small group of occupationally exposed persons, and it did not involve exceedingly high costs. In the 1970s, however, ICRP extended the LNT principle to exposure of the general population to man-made radiation, and in the 1980s it extended LNT limiting the exposure to natural sources of radiation . In the same document ICRP recommended restriction of radiation exposure of members of the public to 1 mSv per year, that is below the average annual global natural radiation dose of 2.2 mSv, and many tens or hundreds of times lower than the natural doses in many regions of the world.

Such an absurdly low limitation of exposure was a logical consequence of administrative LNT assumption from 1959. It made a false impression in the public that new research steadily discovers a greater harmfulness of radiation, which needs more protection, more money, and lower standards. In fact nothing like this occurred. Since introduction of rational standards in the 1930s, which were based on tolerance dose concept, and were orders of magnitude higher than now, no deleterious effects were found among those that observed them (Taylor, 1981).

This constant decreasing of standards, however, was less than palatable to many scientists associated with radiation protection, standing both on purely scientific and practical grounds. One of the important factors in changing opinion of many scientists was finding actual proportions between man-made and natural exposures. Data published in the UNSCEAR documents clearly show that the average individual global radiation dose in 1990 from nuclear explosions, the Chernobyl accident, and commercial nuclear plants combined was about 0.4% of the average natural dose of 2.2 mSv per year. In areas of the former Soviet Union that were highly contaminated by Chernobyl fallout, the average individual dose was much lower than that in regions with high natural radiation.

The greatest man-made contribution to radiation dose has been irradiation from x-ray diagnostics in medicine, which accounts for about 20% of the average natural radiation dose (Figure 1). From the medical point of view, it does not matter whether ionizing radiation comes from natural or from man-made sources: its nature is the same. We do not observe any adverse effects of irradiation from Mother Nature's sources: no increase of cancers and hereditary disorders was ever found in natural high radiation areas. The concern about large doses, such as absorbed by three workers in Tokaimura or by 28 fatal radiation victims in Chernobyl, is obviously justified. But should we spend enormous funds to protect people against radiation corresponding to tiny fractions of natural doses, only because humans make them?

Few billion years ago, when life on Earth began, the natural level of ionizing radiation was about three to five times higher than it is now . At the early stages of evolution, increasingly complex organisms developed powerful defense mechanisms against adverse effects of this radiation, and of all kinds of environmental factors, for example against toxicity of oxygen and other innumerable inorganic and organic toxins, and dangerous physical agents, including the whole range of radiation energy spectrum. Living organisms developed not only protective mechanisms against these environmental agents, but they learned how to use them to their advantage.

We see this readily in the case of visible light and UV radiation. UV radiation belongs to the ionizing part of the spectrum. It is rather doubtful that other types of ionizing radiation were excluded from this evolutionary adaptive process. The phenomenon of radiation hormesis observed in man, and in animals argues against such exclusion. On the other hand, that the evolution proceeded for so long is proof of the effectiveness of living things' defenses against environmental agents, including ionizing radiation.

The adverse effects of ionizing radiation, such as mutation and malignant change, originate in the cell nucleus, where the DNA is their primary target. Other adverse effects - which lead to acute radiation sickness and premature death in humans, also originate in the cell, but outside its nucleus. For them to take place requires radiation doses thousands of times higher than those from natural sources. A nuclear explosion or a cyclotron beam could deliver such a dose; so could a defective medical or industrial radiation source - Tokaimura and Chernobyl are two examples. An artificial distinction between these two types of effects:

(1) starting in the DNA of the cell nucleus

(2) outside the nucleus was made by introducing terms of "stochastic effects" for late malignant and hereditary changes, and "deterministic effects" for early acute changes and cataracts

Medicine does not recognize such a distinction. In fact, it was a tacit introduction of the LNT thinking template into radiation protection. By definition, stochastic (probabilistic) effect is "an all-or nothing effect, the severity of which does not vary with dose" , and which distinguishes them from "deterministic" effects, the severity of which increases with dose.

However, both notions: stochastic and deterministic effects seem rather empty and obsolete, in view of the new information on mechanisms of carcinogenesis and genetics. The lack of dose related severity in stochastic effects - the main difference between them and deterministic effects, is simply not true. As demonstrated by many radiogenic cancers in man and in experimental animals show greater histologic and clinical malignancy after high radiation doses than after smaller ones. Also latency time is shortened when the dose increases, so the malignant tumors can have more time to develop during a lifetime.

According to recent studies, by far the most DNA damage in humans is spontaneous and is caused by thermodynamic decay processes and by reactive free radicals formed by the oxygen metabolism. Each mammalian cell suffers about 70 million spontaneous DNA-damaging events per year . More recent measurements of steady state oxygen free radical damages to DNA (Helbock et al., 1998) and their repair rates (Jaruga, Dizderoglu, 1996) demonstrate about 350 million metabolic DNA oxidamages per cell per year. Only if armed with a powerful defense system could a living organism survive such a high rate of DNA damage.

An effective defense system consists of mechanisms that repair DNA, and other homeostatic mechanisms that maintain the integrity of organisms, both during the life of the individual and for thousands of generations. Among those homeostatic mechanisms are antioxidants, enzymatic reactions, apoptosis (suicidal elimination of changed cells), immune system removal of cells with persistent DNA alterations, cell cycle regulation, and intercellular interactions.

Ionizing radiation damages DNA also, but at a much lower rate. At the present average individual dose rate of 2.2 mSv per year, natural radiation could be responsible for no more than about 5 DNA-damaging events in one cell per year. Why with a background of 70 million spontaneous DNA damages per cell per year, should we protect people against 2.3 DNA damages per cell per year, expected from 1 mSv annual dose limit recommended by ICRP? Though spontaneous repairing of double strand break damages of DNA occurs rarely compared to their occurrence in radiation damage, spontaneous oxygen metabolism induces about 1000 timeas as many double strand breaks as background radiation (Stewart, 1999). In this perspective even a limit permitting for 200 DNA damages per cell per year, or 100 mSv per year, would be proper.

As compared with other noxious agents, ionizing radiation should be regarded as rather feeble. The safety margin for ionizing radiation is much larger than for many other agents present in the environment, e.g. thermal changes, plant and animal poisons, or heavy metals. For example, a toxic level of lead in blood is only 3 times higher than its "normal" level. A lethal dose of ionizing radiation delivered in one hour - which for an individual human is 3000 to 5000 mSv - is a factor of 10 million higher than the average natural radiation dose received in the same time (0.00027 mSv).

Nature seems to have provided living organisms with an enormous safety margin for natural levels of ionizing radiation - and also, adventitiously, for man-made radiation from controlled, peacetime sources. Conditions in which levels of ionizing radiation could be noxious do not normally occur in the biosphere, so humans required no radiation-sensing organ and none evolved, although all species have always been immersed in the sea of radiation ever since life began.


WHY RADIOPHOBIA?

If radiation and radioactivity, though ubiquitous, are so innocuous at normal levels, why do they cause such universal apprehension? What is the cause of radiophobia, an irrational fear that any level of radiation is dangerous? Why have radiation protection authorities introduced a dose limit for the public of 1 mSv per year, which is less than half the average dose rate from natural radiation, and less than 1% of the natural dose rates in many areas of the world? Why do the nations of the world spend many billions of dollars a year to maintain this standard ? In a recent paper I proposed some likely reasons :

• The psychological reaction to devastation and loss of life caused by the atomic bombs dropped on Hiroshima and Nagasaki at the end of World War II.

• Psychological warfare during the cold war that played on the public's fear of nuclear weapons.

• Lobbying by fossil fuel industries.

• The interests of radiation researchers striving for recognition and budget.

• The interests of politicians for whom radiophobia has been a handy weapon in their power games (in the 1970s in the USA, and in the 1980s and 1990s in eastern and western Europe and in the former Soviet Union).

• The interest of news media that profit by inducing public fear.

• The interest of "greens" that profit by inducing public fear.

The assumption of a linear, no-threshold relationship between radiation and biological effects (LNT). In addition, a very important factor was:

Complaisance of nuclear industry leadership, paralyzed by anti-nuclear propaganda. Intimidated industry accepted irrational standards, and did not develop research programs to check the validity of LNT.

During the past five decades nuclear weapons were regarded as a deterrent, and the countries that possess them wished to make radiation and radioactivity seem as dreadful as possible. Therefore, national security agencies seldom correct even the most obviously false statements, such as often voiced: "Radiation from a nuclear war can annihilate all mankind, or even all life", or (the ever authoritative International Herald Tribune) "200 grams of plutonium could kill every human being on Earth" .
The facts say otherwise. According to UNSCEAR reports, between 1945 and 1980, the 541 atmospheric nuclear tests, injected into the global atmosphere about 3000 kilograms of plutonium (that is, almost 15 000 supposedly deadly 200-gram doses), yet lo and behold: somehow we are still alive! (Try to publish this in the International Herald Tribune: no way).

According to UNSCEAR data, from all these 541 atmospheric explosions with a total energy yield of 440 megatons of TNT, we accumulated between 1945 and 1998, an average individual radiation dose of about 1 mSv, what is less than 1% of the dose from natural sources over the same period. In the heyday of atmospheric testing, 1961 and 1962, there were 176 atmospheric explosions, with a total energy yield of 84 megatons. The average individual dose accumulated from the fallout between 1961 and 1964 was about 0.35 mSv.

At its cold war peak of 50 000 weapons, the global nuclear arsenal had a combined potential explosive power of about 13 000 megatons, which was only 30 times larger than the megatonnage already released in the atmosphere by all previous nuclear tests. If that whole global nuclear arsenal had been deployed in the same places as the previous nuclear tests, the average individual would have received a lifetime radiation dose from the global fallout of about 30 to 55 mSv, a far cry from the short-term dose of 3000 mSv that would kill a human.

For several decades, humanity had lived under the gloomy shadow of imminent nuclear annihilation. This had extremely negative influence not only on public perception of radiation and nuclear energy, but induced a cultural change: an distrust of science, rejuvenation of irrational apocalyptic mythologies, and even aversive approach to civilization, the fruit of toil and sweat of ourselves and of our forefathers.
 

HIROSHIMA, NAGASAKI AND LNT

The survivors of the atomic bombing of Hiroshima and Nagasaki who received instantaneous radiation doses of less than 200 mSv have not suffered significant induction of cancers . Among 59 539 inhabitants of these two cities that absorbed doses up to 1990 mSv, 119 persons died between 1950 and 1985, due to leukemia, i.e. about 0.006% per year, and 4.319 persons died due to all other cancers, i.e. 0.2% . According to the Polish Cancer Registry data, in 1993 0.006% people died in Poland due to leukemia, and about 0.2% due to all other cancers . This comparison shows that with doses of up to near 2000 mSv we should not expect any detectable epidemic of malignances.

Among the bomb survivors irradiated with doses lower than 150 mSv mortality caused by leukemia was lower (although statistically not significant) than among the non-irradiated inhabitants of two Japanese cities . A slight, but non significant, decrease in overall non-cancer mortality among bomb survivors exposed to low and intermediate dose can also be seen in the data of Atomic Bomb Casualty Commission and the Radiation Effects Research Foundation . So far, after 50 years of study, the progeny of Japanese survivors who were exposed to these and much higher, near lethal doses had not developed any adverse genetic effects .

Until recently, such findings from the study of A-bomb survivors has been consistently ignored. In place of the actual findings has been the theory of linear no-threshold (LNT), which presumes that the detrimental effects of radiation are proportional to the dose, and that there is no dose at which the effects of radiation are not detrimental. LNT theory played an important role in effecting first a moratorium and then a ban on atmospheric nuclear tests. But otherwise its role was mostly negative, inducing worldwide fear of radiation and effective strangulation of development of nuclear energy systems in many countries, including the United States. My own country, Poland, spent billions of dollars on construction of its first nuclear power station, only to abandon the project after politically motivated manipulation of the public opinion by means of the LNT theory.
 

The mechanism of inducing fear is quite simple. For example, one calculates, very exactly, that 28 000 people would die of Chernobyl-induced cancers over the next 50 years, and news media trumpet this, or much greater values all over the world, now and again, and ad nauseam. The frightening death toll was derived by multiplying the trifling Chernobyl doses in the Northern Hemisphere, including Canada and the United States (0.0046 mSv per person) by the vast number of people leaving there and by a cancer risk factor based on epidemiological studies of 75 000 atomic bomb survivors in Japan .

But the A-bomb survivor data are irrelevant to such estimates, because of the difference in the individual doses and dose rates. A-bomb survivors were flashed within about one second by radiation doses at least 50 000 times higher than dose which US inhabitants will ever receive, over the period of 50 years, from the Chernobyl fallout.

We have reliable epidemiological data for a dose rate of, say, 6000 mSv per second in Japanese A-bomb survivors. But there are no such data for human exposure at a dose rate of 0.0046 mSv over 50 years (nor will there ever be any). The dose rate in Japan was larger by 2 x 1015 than the Chernobyl dose rate in the USA. Extrapolating over such a vast span is neither scientifically justified nor epistemologically acceptable. It is also morally suspect .

An offspring of the LNT assumption is the concept of dose commitment, introduced in the early 1960, and of collective dose. Dose commitment reflected the great concern, at that time, that harmful hereditary effects could be induced by fallout from nuclear tests. The concern was so great, that according to definition, dose commitment values were to be calculated for periods of time ending in the infinity. In later years, the individual dose commitments, and collective dose commitments, also for some truncated periods, were calculated mainly for exposures from nuclear power. For example, UNSCEAR calculated 205 000 man Sv for the next 10 000 years from power reactors and reprocessing plants, 600 000 man Sv from Chernobyl fallout in the Northern Hemisphere for eternity, and 650 000 000 mSv for the world's population from only past 50 years of exposure to natural radiation.

These large values, terrifying as they are to the general public, provide society with no relevant biological or medical information. Rather, they create a false image of the imminent danger of radiation, with its all actual negative social and psychosomatic consequences. But why to stop at 50 years calculating dose commitments for natural radiation, when for man-made radiation, one make estimates over infinite time? For example, the individual dose commitment, supposedly accumulated over the past 130 000 years of existence of the modern Homo sapiens, and calculated for now living average human, is 286 000 mSv, i.e. about hundred short term lethal doses.

Each of us is burdened with this or similar value of dose commitment. Do these values represent anything real, or are they just figments of scholastic fantasies? What are the medical effects of these enormously high doses? I proposed in a recent paper, that the intellectually invalid concepts of collective dose and dose commitment be hacked off with William of Occam's razor.
 

Acknowledgments

I am indebted to Dr. Michael Waligórski for stimulating discussion and comments.

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