Nuclear Radiation Any dose of radiation is an overdose. ~ George Wald (1906-1997) Only two things are infinite, the universe and human stupidity, and I’m not sure about the former. ~ Albert Einstein (1879-1955) CHAPTER 12 Unlike fossil fuel combustion that produces toxic air pollutants, carbon dioxide, and other greenhouse gases, nuclear energy is clean and produces no such contaminants. Nuclear energy, however, generates other products that pose far greater threats to the environment if not handled properly. The radiation released during the Three Mile Island nuclear accident in 1979, and the much greater catastrophic Chernobyl accident in 1986, catalyzed a major debate about the safety of nuclear reactors. The buildup of nuclear arsenals (primarily by the United States and Russia and, to a lesser extent, by China, France, England, Pakistan, India, Israel, and now North Korea), the threat of terrorism on nuclear stockpiles, and the issues related to storage of nuclear wastes have all raised concerns about the environmental aspects of nuclear energy and radiation. In this chapter, we will examine various sources of radiation, their effect on health, and the consequences of nuclear energy in times of war and peace. Ionizing Radiation All forms of radiation can be categorized into two types: ionizing and nonionizing. Ionizing radiation has enough energy to eject electrons from atoms and produce positively charged ions. Materials capable of emitting ionizing radiation are radioactive. Cosmic rays, gamma rays, x-rays, and high-energy UV lights are examples of ionizing radiation. Visible, infrared (heat), microwave, and radio waves do not have sufficient energy to cause ionization and thus are called non-ionizing radiation. Non-ionizing radiation was covered earlier and will not be discussed any further. Our body is largely transparent to both low-energy radar and high-energy x-rays and gamma radiations, but readily absorbs visible and infrared. Although visible and infrared absorptions are quite harmless, even small amounts of x-ray and gamma ray absorption can harm our bodies. Sources of Ionizing Radiation Ionizing radiation can come from both natural and man-made sources. Natural (background) sources of radiation are cosmic radiation and terrestrial radiation. Cosmic radiation is due to interactions between earth’s magnetic field and charged particles coming from the sun and other distant stars. Cosmic radiation is stronger at higher elevations. Sources of terrestrial radiation are uranium and products of its decay such as thorium, radium, and radon, which are found in soil. Our body also contains radioactive materials such as potassium-40, carbon-14, and lead-210 when we are born. Man-made (anthropogenic) sources of radiation come from nuclear reactors, consumer products, irradiated food, medical checkups, and radiation therapy. Precluded from this list is possible exposure due to the accidental release of nuclear radiation from nuclear reactors, testing of nuclear bombs, or nuclear wars. It is therefore reasonable to assume that the geographical location we live in, our lifestyle, and the state of our health all affect the amount of radiation to which we are exposed. Because the earth itself contains radioactive materials, the food and water we consume may also be affected. Even the materials from which our houses are made contribute. For example, stone and bricks are more radioactive than wood and aluminum. Consumer products such as televisions and computer screens, luminous watches and dials, smoke detectors, and airport x-ray machines (See box “X-ray Vision”) also contribute to the radiation doses we regularly receive. In addition to the sources mentioned above, there are other sources such as alpha particles, beta particles, and neutrons which may occur naturally in the outer atmosphere or may be produced in nuclear fission processes. Measuring Radiation Depending on whether we refer to radiation emitted by a source (activity), absorbed or deposited in an object (exposure), or the biological damage it causes (dose), different units of measurement are most commonly used (Figure 12-1). Becquerel is the unit most commonly used for ionizing radiation; it is simply the number of nuclei disintegrations per second. A larger unit is the curie, which represents the amount of radiation emitted by one gram of radium, or 3.7x107 nuclei per second. Both curie (Ci) and becquerel (Bq) are measured by an appropriate radiation detection device such as Geiger counters and are used when the amount of radiation emitted from a source is of interest. They tell nothing about the radiation dose that is actually absorbed by objects. Roentgen (R) is the measure of the radiation intensity of x-rays and gamma rays and refers to the number of ionizations produced in air. Rad (radiation absorbed dose) gives the amount of radiation absorbed and deposited in a matter (exposure) — be it bone, fat, muscle, or concrete, irrespective of the effects this deposit has on the material. For water and soft tissues, rad and roentgen are approximately equal. Another commonly used unit of absorbed dose is a gray, which is equal to 100 rads. Equal doses of different types of radiation cause different degrees of biological damage. 276 Intensity of source (roentgens) converted to dose-equivalent (rems or sieverts) Activity of radioactive source (becquerels or curies) Absorbed dose (rads or grays) Figure 12-1 Radiation units Chapter 12 - Nuclear Radiation X-ray Vision FYI ... S oon after the discovery of X-rays in 1895, scientists constructed devices that looked into broken bones and located bullets in patients’ bodies.i Critics, however, envisioned this device as a threat to privacy, fearing some might design instruments that could see through walls of houses and peek through women’s clothing. The New Jersey legislature even tried to pass a law banning x-rays from use in opera glasses so as to protect the stars’ modesty. Although the quality of x-ray images was rather poor at the time, new scanners are now being developed that reveal much more than meets the eye. Backscatter x-ray machines are being considered at airport security checkpoints. This woman appears to be carrying a gun and a grenade. The discovery of the x-ray by Roentgen brought excitement and public interest along with many speculations on its possible applications. For e xample, one proposal suggested making an invisible ink that can only be read by x-ray. Another claimed to have taken photographs of his thoughts; one company marketed anti x-ray u nderpants, while others sent the hollow eyepieces of their opera glasses to be fitted with x-ray. One customer was even seeking to buy one kilogram of x-ray. i Rem (roentgen equivalent man) is a measure of the damage caused by one rad of radiation in the human body (dose). It takes into account the effectiveness of both the source and the living tissue. Since rem values are normalized to different tissue types, one rem of any type of radiation does the same biological damage. For x-rays and gamma rays, the rem and rad are taken to be equivalent. Alpha particles have 20 times the risk of x-ray and gamma ray radiation, so one rad of alpha particle radiation is equivalent to 20 rem (both singular and plural). Since one rem of radiation is a large quantity, the unit most often used is the millirem (mrem), which is one thousandth of a rem. Another commonly used unit is the sievert, which is a measure of the biological effect of one gray of gamma ray. One sievert is equal to 100 rem. Radiation Dosimetry Individuals receive radiation from natural sources and from various activities over their lifetimes. The cumulative effect is not equivalent to the effect of an equal amount of radiation received at once or over a short time. Chronic exposure refers to relatively low doses of radiation for periods of months and years. This is typically experienced in normal daily activities such as handling nuclear materials and living next to a nuclear waste dump, or is accumulated as a result of years of radiation therapy and routine medical checkups. Acute exposure refers to a large dose of radiation received over a short time, such as that resulting from a nuclear accident or a nuclear war. Although people cannot sense radiation directly, sensitive instruments called dosimeters can measure the amount of radiation they receive. Dosimeters are small sensors that a person can carry to measure the total dose of radiation received over a period of time. Geiger counters are normally used to detect the presence of radiation. In the United States, each healthy person receives an average of 300 mrem of radiation per year. The amount can be significantly higher for those who receive radiation therapy or who work in nuclear power plants, radiology units, and some 277 research laboratories. The US Environmental Protection Agency (EPA) is responsible for setting limits on the amount of radiation humans can receive. According to these guidelines, the maximum annual permissible dosage is 500 mrem for the public. Furthermore, it has set a limit of 5,000 mrem per year, not to exceed 1,250 mrem in any given three month period, as the safety limit for adults working with radioactive materials from manmade radiation sources. The EPA guideline for the maximum one-time radiation dose for emergency workers volunteering for lifesaving work is 75 rem. You can estimate the amount of radiation you receive every year by filling in the dosimeter chart given below. Effects of Radiation on Health There are over 300 different products derived from fission of uranium and plutonium isotopes. Some have very short half-lives and practically disappear after a few seconds. Others, such as strontium-90 and cesium-137 with half-lives of about 30 years, enter the body by inhalation and the ingestion of contaminated foods and slowly decay by the continuous emission of beta and gamma radiation. Iodine-131 has half-life of only 8 days, so it accumulates in victim’s thyroid gland very fast. This is why doctors prescribe the normal (nonradioactive) iodine pills to saturate the body before radioactive isotope has a chance to be absorbed. This of course has no protective effect on other types of radioactive materials. Radiation Dosimetry Y 1 2 3 4 FYI ... ou can get a good approximation of the amount of radiation you receive every year from various sources. Here is how to estimate: Where do you live? _________ Elevation (meters) _______ Cosmic radiation at Sea level Elevation x 0.015 If you live within 10 km of a nuclear or coal power plant, add 0.3 What is your house made of? Brick or concrete (add 70), wood (add 30) Ground radiation (US average) Radon (consult EPA sources) Water, food, and air (US average) Watching TV (1 mrem/hr) Number of hours a day _____ x 1 How many miles do you fly every year? Number of miles _____ x.001 or Numbers of hours of flying ____ x 0.5 How is your health? Number of chest x-rays _____ x 10 Number of dental x-rays _____ x 5 Number of mammograms _____ x 30 Others (chemotherapy, varies) Total 28 mrem _______ _______ _______ 26 mrem _______ 28 mrem _______ _______ _______ _______ _______ _______ 5 6 278 Chapter 12 - Nuclear Radiation When molecules of living organisms are exposed to ionizing radiation, they become unstable; chromosomes and strands of DNA (deoxyribonucleic acid) break apart to form new molecules. DNA is a double helix of thousands of atoms strung along carbon-linked struts that contains all the information needed to produce and control living tissues. When mutations occur in reproductive cells (eggs or sperm), the changes can be passed on to subsequent generations.1 Effects of ionizing radiation on human health are hard to assess and are highly dependent on the dose, the duration of exposure, and the type of cells involved.2 For example, if a body receives a massive amount of radiation in a short time, such as what might occur following a nuclear Digging Deeper ... Ionizing Radiation A lpha particles are charged particles made up of two protons and two neutrons (the same as a helium nucleus). An example of alpha particle emission is the radioactive decay of uranium and radium. An alpha particle can travel only a few millimeters in the air and is easily stopped by a sheet of paper. Although alpha particles cannot penetrate human skin, they can do serious damage if swallowed. As alpha particles slow down, they encounter and attach themselves to electrons and form helium. Beta particles are electrons ejected from the nucleus of a decaying atom. Beta particles cannot be stopped by a sheet of paper or human skin, but need a thicker shield (like wood) to stop them. Gamma and x-rays are high-energy electromagnetic radiation produced by radioactive decay of unstable nuclei. Gamma rays have no charge or mass and can travel thousands of meters in air, easily penetrating the human body or even lead. X-ray is similar to gamma ray except they are 10-100 times less energetic. They can penetrate the soft tissues but are stopped by bones. Neutrons are heavy, uncharged particles resulting from nuclear fission. α - PARTICLE β - PARTICLE aluminium lead concrete γ - RAY X - RAY NEUTRONS Type Alpha Beta Gamma Neutron 1 Symbol Charge +2 -1 0 0 Composition Helium nucleus Electron Photon Neutron Penetrating Power Low (1) Medium (100) High (1000) High (1000) Shielding Guideline Stopped by paper. Stopped by aluminum, wood, or Plexiglas. Stopped by lead or concrete. Slowed by water. a b g n The Los Alamos national laboratory maintains a website that provides information on radiation health physics and a radiation exposure calculator (http://newnet.lanl.gov/dosecalc. htm). 2 US Environmental Protection Agency (http://www.epa.gov). 279 accident or an atomic blast, the effects are immediate – usually resulting in radiation sickness and death within hours or days. On the other hand, chronic exposure to low-level radiation may not be observed for many years or until future generations. Rapidly-growing cells like bone marrow and soft tissues such as ovaries, testes, and lenses of the eyes are most susceptible to destruction by radiation. Furthermore, depending on the general state of health of the individual, the same amount of radiation may result in different symptoms. It is difficult to quote a number as the threshold at which death by radiation exposure is a certainty. Most nuclear scientists, however, agree that a single radiation dose of 500 rads or higher will almost certainly result in death within hours or days. If exposed to radiation doses of 100-250 rads, symptoms will include nausea, vomiting, and diarrhea, and many may eventually die as a result. No death is expected with a radiation dose of 100 rads or less, although in future years the risk of development of cancer, leukemia, cataracts, or sterility is significantly higher. Question: Does a single 10 rem dose cause the same amount of damage as 10 doses of 1 rem spread over many years? Answer: Many believe that genetic damage is probably independent of the dose rate since all doses cause non-reversible mutations. The somatic effects of several smaller doses are less, however, because time allows for some repair between administration of small doses. Most data on high-level radiation doses are available from the two nuclear bombs dropped on Japan and the nuclear accident in Chernobyl. Over 200,000 people perished in a few days following the Hiroshima and Nagasaki bombings, and numerous others suffered from cancer, miscarriages, birth defects, and stillbirths in the years after. Even thirdgeneration offspring of bombing survivors show higher rates of leukemia, thyroid, and colon cancers. Data from the Chernobyl accident point to similar catastrophes. More than 28,000 square kilometers of prime farmland were contaminated and another 200,000 people were forced to leave their homes as a result. According to the World Health Organization (WHO)3, rates of thyroid cancer have climbed five to 30-fold depending on the indivisual’s distance from the power plant. There has also been a considerably higher rate of spontaneous miscarriages. The effect of low-level radiation is much harder to assess, as factors that can affect one’s health increase with time. However, it has been established that low-level radiation is responsible for increased rates of several types of cancer. Iodine-131, a byproduct of nuclear reactions, concentrates in the thyroid gland and ovaries. Strontium-90 attacks bone marrow, increasing the risk of leukemia and other blood diseases. Plutonium-239 is one of the most toxic substances known. If inhaled, one thousandth of 3 World Health Organization (http://www.who.int/en). 280 Chapter 12 - Nuclear Radiation a gram can cause massive fibrosis of the lungs. Another radioactive waste, cesium-137, is mostly absorbed by the liver, kidneys, and sexual organs. Useful Radiation Radiation is not always associated with ills and disaster. Radiation has many uses in diagnosis and treatment of diseases, as well as industrial applications. Radiation can be used in numerous research and diagnostic tools, such as x-rays, MRI, and CAT scanners. Radioactive solutions can be ingested by a patient as a tracer to allow mapping of the blood stream for detection of tumors and restricted blood vessels, as well as photography of a particular internal organ. Radiation therapy can also be used in the treatment of disease, primarily to kill cancerous cells. Other applications include crop improvement and protection, manufacturing of consumer products such as watches, and ionization smoke detectors, and in the sterilization of such products as cosmetics and medical supplies. Foods are also irradiated to kill germs and other microorganisms, to aid in preservation, and to increase their shelf life. Radiation is a convenient tool for dating art and antiques, even dating such things as the age of the earth or a meteorite. Industrial uses of radiation include process monitoring, desalination, welding, detection of cracks and seams, and numerous others. Question: R adiation therapy involves irradiating and killing the cancerous cells without damage to the healthy cells. How does radiation distinguish normal cells from cancerous cells? Answer: Patients will be subjected to crossed beams of radiation that pass through the cancerous region. Alternatively, the patient can be rotated as he is radiated by a single beam of radiation. This way, the normal, non-cancerous, cells are exposed to much less radiation than the damaged cells that receive continuous exposure. Nuclear Wastes Uranium undergoes several changes as it is mined, processed, burned, reprocessed, and eventually discarded and stored in a repository. Along the way, uranium fuel leaves a footprint by producing and leaving behind various levels of radioactive waste. Depending on the amount and type, radioactive waste can be classified as low level, intermediate level, or high level. Low- level nuclear wastes are those with relatively short halflives. They come from hospitals, medical and research laboratories, x-ray machines, and contaminated clothing and equipment. Many commercial products such as watches, ionization smoke detectors, eyeglasses, dental porcelain, luminescent products, instrument dials, signs, and markers contain some radioactive materials. Low-level wastes do not need any casks and are suitable for shallow depth burial or incineration. The sources of intermediate-level nuclear waste are nuclear fuel processing, 281 FYI ... Healthy Radiationi A i small but growing number of studies suggest that very low doses of ionizing radiation may actually have some health benefits due to stimulation of certain enzymes. Radon treatments have been used in treating severe pain in joints and rheumatic arthritis. This phenomenon is termed radiation hormesis. It has even been suggested that a significant fraction of cancer deaths are preventable by increasing our low dose radiation exposure. Luckey, T.D., “Hormesis with Ionizing Radiation,” CRC Press, Baca Raton, 1980. enrichment plants, nuclear weapons facilities, and contaminated parts of nuclear power plants before decommissioning. Intermediate-level wastes are usually solidified in concrete and, depending on their type, buried in shallow or deep underground repositories. High-level nuclear wastes are spent fuel and other products from the reactor core and, if it has been decommissioned, the reactor itself. A typical power plant generates about 20-30 tons of high-level radioactive wastes each year, mainly cesium-137, strontium-190, and technetium-99. Plutonium-239 is the most serious byproduct of breeder reactors. Disposal of Nuclear Wastes Waste management is one of the most controversial and pressing issues tarnishing the image of the nuclear industry. Nuclear waste has not only presented challenges for the present generation, but has also endangered the welfare of future generations for many tens of thousands of years. Example 12-1: The concentration of strontium-90 in high-level liquid wastes is about 1 curie (Ci) per gallon. If the concentration is to be dropped to 10-9 curie per gallon for it to become safe, how long do we need to wait? Solution: Stronium-90 has a half-life of 30 years. In 10 half-lives (300 years), the concentration drops by 1000; in 20 half-lives (600 years), the concentration drops by a million, and in 30 half-lives (900 years), the concentration drops by a billion to an acceptable level. Examples like this help us understand the concern environmentalists have for the storage of nuclear waste. As of yet, there is no completely reliable method of permanently disposing of nuclear waste. All current methods are only interim measures. In addition, there is no reliable information on the total amount of nuclear waste we have produced so far. No matter how small or large a role nuclear energy plays in meeting future energy needs, developing technologies that can safely dispose of the intensely radioactive byproducts remains a top priority. Here are some promising ideas. Permanent subterranean storage – The most commonly favored method for disposal is the placement of waste into deep geological repositories. Factors affecting this determination are soil stability, proximity to large 282 Chapter 12 - Nuclear Radiation water reservoirs and run-offs, seismic activity, and the local population. An ideal site must be completely dry, with no possibility of moisture percolating through the cracks and corroding the alloys. Salt has been shown to be an effective barrier to radiation; therefore lands with large salt deposits located in geographically stable landmasses are believed to be the best choice. The US government has considered many sites and has decided on a repository near Yucca Mountain. This Nevada desert site, with its thick section of porous volcanic rock, will serve as the US’s first permanent underground repository for more than 40,000 metric tons of nuclear waste that has already been accumulated. The plan includes processing the spent fuel in steel canisters and inserting them into holes drilled in the rock floor of caverns hundreds of meters below the surface. Residents of nearby communities have vehemently opposed this construction (Figure 12-2). Some jokingly refer to Yucca Mountain as “ Yucky Mountain” or “Yuck-a-Mountain.” Other opponents charge that the government has overlooked seismic and volcanic activity and other potential dangers in the area in the rush to find a location. Still others claim that since the Department of Energy has set its mind on Yucca as the permanent repository and has already spent billions of dollars on the Yucca project, they are unwilling to consider other sites or other storage alternatives. As a result, incentives for seeking more innovative solutions and better options have been gradually diminishing. In the meantime, nuclear wastes are piling up across the nation. Waste levels are getting so high that even if the Nevada facility were constructed, it would not be large enough to house all of the waste. Originally planned to open by 1998, the date has now been pushed back to 2010, although many experts doubt that even this date is realistic. Entombment under the seabed – This plan is similar to the plan outlined above, but in this case, canisters are dropped from ships and allowed to come to rest on the deep ocean floor far below. The advantage of this plan is the use of seafloors, which are far away from the shore and from FYI ... Figure 12-2 Yucca Mountain, the site of the permanent US nuclear waste disposal facility. Source: Thinkquest.com Alchemists and Transmutation T ransmutating metals to gold has been the aspiration of alchemists for over 4,000 years and independently by ancient Egypt and China. The origin of the word alchemy is “khem” which means fertility. The Egyptians’ original desire was to find a way to preserve bodies in anticipation of the eventual return of their dead to life. Khem was the technique used for mummification. The prefix -al was added to the word when Arabs occupied Egypt in the 7th century. The Arabs believed that all metals were made up of mercury and sulfur in different proportions, and gold was the “purest” of all metals. So it was ideal to turn (transmute) metals from their lowest form to the most perfect form: gold. The interest in alchemy eventually led to the discovery of new elements and the start of the science of chemistry. Alchemists tried to achieve their goal through various chemical reactions. What they did not have was an understanding of the structure of atoms and a nuclear reactor! 283 people. However, the potential leakage could be catastrophic, and there are international treaties that bar the disposal of radioactive wastes at sea. Nuclear transmutation – This method converts (transmutes) the radioactive waste materials with very long half-lives to short-lived or nonradioactive products by bombarding them with elementary particles such as neutrons. For example, by absorbing a neutron, technetium-99 (T1/2= 210,000 years) becomes technetium-100, which then rapidly decays to rubidium-100. The Ru-100 isotope is non-radioactive, with a half-life of only 17 seconds. Another example is the transmutation of iodine-129 (T1/2 = 17 million years) into the stable element xenon-130. An intense beam of fast-moving protons produced by a linear accelerator hits a lead or tungsten target and knocks out a large number of neutrons which then attacks the radioactive waste. In the process, additional energy is released, a portion of which is used to run the accelerator; the remainder would be fed into the regional power grid. Figure 12-3 On January 28, 1986, America was shocked by the destruction of the space shuttle Challenger and the death of its seven crew members. If nuclear material were being carried on-board, the scope of the catastrophe would have been far greater. In addition to these, there have been other proposals that are considered impractical. Among the less serious proposals are: Taking nuclear waste into space or to the moon – The major concern in regards to this method is an explosion during the launch of the rocket containing nuclear waste. In light of the explosions of the space shuttles Challenger in 1986 (Figure 12-3) and Columbia in 2003, this fear seems ever more relevant. As space launch technology becomes more and more reliable, it may become possible to find a nearly fool-proof method to send the waste products into orbit around the sun or bury them on the moon and other planets. Storage under polar icecaps – The concern surrounding this proposal is that a large amount of heat generation would result in melting of major icecaps with irreversible environmental consequences. “We knew the world would not be the same. A few people laughed, a few people cried, most people were silent. I remembered the line from the Hindu scripture, the Bhagavad-Gita. Vishnu is trying to persuade the Prince that he should do his duty and to impress him takes on his multi-armed form and says, ‘Now, I am become death, the destroyer of worlds.’ I suppose we all felt that one way or another.” ~ Robert J. Openheimer, Physicist and Director of the Manhattan Project (1904-1967). Nuclear Weapons Alarmed by the military advances of Hitler’s army, and fearing that Germany was developing its own nuclear weapon, Einstein wrote a letter to President Roosevelt in 1939 informing him of possibility to “set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated.” 4 In response to Einstein’s letter, Roosevelt ordered a team of physicists to initiate research on uranium fission and whether a bomb could be built in a short time. The task proved to be difficult as researchers soon found that uranium-238 could not sustain a chain reaction; uranium-235 was a possibility, but only if it was enriched to very high concentrations; separating the two isotopes was extremely difficult as they were chemically identical, and their masses differed by a mere 1%. L ater in his life Einstein admitted that signing the letter to Mr. Roosevelt was the most tragic mistake in his life, and that he had never believed that the President would ever use the atomic weapon. 4 284 Chapter 12 - Nuclear Radiation As the work continued, a second possible path to building the bomb was suggested by scientists at Lawrence Radiation Laboratory at Berkeley who produced a new man-made element, first identified as element-94 and later named plutonium, that fissioned more easily and could be produced easily in large quantities; it is formed when uranium-238 captures a neutron, becoming neptunium-239, which is unstable and rapidly decays to plutonium-239. On December 2, 1942, researchers headed by Italian-émigré Enrico Fermi of the University of Chicago achieved the first self-sustaining chain reaction in a graphite and uranium pile. Soon thereafter, Robert Oppenheimer, a professor of physics at the University of California at Berkeley led a team of nuclear physicists in what became to be known as the “Manhattan Project” to develop the atomic bomb. The effort eventually succeeded in the first nuclear explosion test named Trinity in Alamogordo Bombing range near Los Alamos, New Mexico. The test conducted on July 16, 1945 used plutonium and had a yield of 21 kilotons of TNT (Figure 12-4). Less than a month later, at 8:15 on the morning of August 6, 1945, the United States detonated the first atomic bomb on Hiroshima, Japan, which leveled the city and killed 140,000 people instantly. Germany was not a target, as it surrendered earlier in May. In addition, many tens of thousands of people died from cancer in the years that followed.5 That bomb, nicknamed “The Little Boy,” (allegedly named after US President Roosevelt) used uranium-235 and had the destructive power of 13,000 tons of TNT (Figure 12-5).6 Three days later a bigger bomb, nicknamed “The Fat Man,” (allegedly named after British Prime Minister, Winston Churchill) was dropped over Nagasaki, killing another 75,000. It was fueled by plutonium-239 and had the destructive power of 21,000 tons of TNT.7 Shortly thereafter, Japan surrendered and WWII was officially ended. Following Trinity test, and bombing of Hiroshima and Nagasaki, the US conducted numerous other tests over Marshall Islands in the Pacific and underwater. In 1946, then US President Truman suggested establishment of an international agency that oversaw all nuclear activity. Not surprisingly, the Soviet Union, a non-nuclear power objected, arguing that all atomic weapons must be abolished before such agency would have the legitimacy. Three years later, in August 1949, the Soviets tested their first fission bomb. The Cold War had begun. As the Cold War intensified, so did the demand for bigger and more deadlier nuclear bombs. The advent of the Soviet bomb had reduced “The Atomic Bombings of Hiroshima and Nagasaki: The Manhattan Engineer District, The Manhattan Engineer District ,” 1946, The World Wide School, 1997. Copies can be downloaded f rom http://worldwideschool.org/library/books/hst/northamerican/TheAtomicBombingsofHiroshimaandNagasaki/legalese.html. 6 Tri-nitro-toluene (TNT) is a chemical compound used commonly in road construction and for demolition. It is non-radioactive and its explosion does not result in the release of any nuclear products. Nuclear destructive power is often expressed in terms of kilograms or tons of TNT. One ton of TNT=4.18x10 9 J. 7 I n comparison, the destructive power of the planes that flew into and destroyed New York’s Twin Towers in 2001 was equivalent to only 1 kiloton of TNT. 5 Table 12-4 The “Trinity” Figure 12-5 The “Little Boy,” Hiroshima Japan, August 6, 1945. The bomb was fueled by U-235 and had a yield of only 13 kilotons. 285 the US absolute superiority to only a numerical advantage. The Hungarian émigré physicist Edward Teller promoted the development of thermonuclear (hydrogen) bomb. In 1950, Truman ordered accelerated development of the bomb. On November 1, 1952, US detonated “Mike,” the first H-bomb at Eniwetok in the Pacific. Three years later, the Soviet Union followed suit and detonated its first hydrogen bomb with a force equivalent to 1.6 megaton of TNT. Uncontrolled Nuclear Fission: The A-Bomb As we discussed before, the difference between a nuclear explosion and a nuclear reactor is in the ability to control the chain reaction in the fission process. Unlike a nuclear reactor, where the rate of neutron production must be carefully controlled, there is no such effort in a nuclear bomb. Critical Mass A small mass of pure fissile material, such as uranium-235 or plutonium-239, would not sustain a chain reaction. Too many neutrons leak out through the large empty volume surrounding nuclei. A large enough mass of these materials is needed to ensure that enough neutrons are generated to compensate for the loss through the void. This mass is dependent upon the size, shape, and purity of the isotopes being used. The minimum amount of fissile material (of a given shape) required for maintaining a chain reaction is known as the critical mass. In an atomic bomb, a mass of fissile material greater than the critical mass must be assembled and held together for about a millionth of a second to permit the chain reaction to propagate and the bomb to explode. Plutonium has a very small critical mass, whereas uranium must be enriched substantially before it can serve as a weapons-grade material. Naturally occurring uranium has only 0.7% of the fissile uranium-235 isotope and must be enriched to a minimum 90% before it qualifies as weapons-grade. For this reason, plutonium is favored over highly enriched uranium (HEU). Building weapons with HEU is, however, easier, as no reprocessing facility to separate plutonium from spent reactor fuel is needed. The critical mass necessary to construct a bomb using Pu-239 is only the size of a baseball. Construction of a plutonium bomb is more difficult, however, as a byproduct of plutonium processing operation, Plutonium-240 is highly unstable and cause predetonation which reduces the effectiveness of the bomb. It is far easier for countries to develop secret weapons using enriched uranium fuel; the necessary facilities can be disguised as ordinary chemical plants, and they do not produce signatures that can be readily identified. Plutonium, on the other hand, requires waste-reprocessing facilities that, unlike the uranium enrichment plants, cannot be easily hidden. 286 Chapter 12 - Nuclear Radiation Weapon Design To make detonation possible, the mass of the fissile material must become critical. This is accomplished by bringing two or more subcritical masses together. The simplest mechanism for assembling a supercritical mass is to shoot one piece of the material against another in a gun tube. A heavy material, called a tamper, surrounds the fissile mass. The tamper (also called neutron reflector) reduces the number of neutrons that can escape and prevents the bomb’s premature explosion (Figure 126a). An alternative method (called implosion method) is to detonate a conventional explosive that surrounds the fissionable material. The rapid increase in pressure compresses the fissile mass, preventing neutrons from escaping through the void and reducing the critical mass necessary to initiate the fission reaction (Figure 12-6b).The implosion device is very difficult to build, as the implosion has to be highly symmetrical. The Little Boy was a gun-type; the Fat Man was of the implosive design. In addition to the A-bomb, which is a result of fission reactions, radioactive materials can be used in conventional bombs and warheads. Two examples are dirty bombs and depleted uranium warheads. Dirty Bombs Figure 12-6 Construction of A-Bombs a) In the gun method (top), a conventional propellant is used to shoot a subcritical mass of fissile material (uranium-235) into another subcritical mass, making the combined mass supercritical. b) In the implosion method (bottom), a conventional explosive compresses a fissile material (plutonium-239) releasing more neutrons and starting the fission. The term “dirty bomb” usually refers to any device that generates a significant amount of radioactive waste without actually undergoing a fission reaction. These may include conventional weapons which, upon explosion, spread radioactive, biological, or toxic materials and may be delivered as an aerosol or simply by wrapping the materials around dynamite. These weapons do not require weapons-grade materials and even the relatively common materials used in radiological medical equipment would be enough to cause catastrophic results and an extensive loss of life. Depleted Uranium Depleted uranium (DU) is the byproduct of the reprocessing of spent nuclear fuel that has been enriched for use in nuclear reactors or weapons-essentially pure uranium-238. Much like natural uranium, depleted uranium is both toxic and radioactive and, because of its long half-life (4.5 billion years), it is practically indestructible. DU is 1.7 times denser than lead and, when turned into metal and used to make shells, it penetrates heavy steel and concrete with relative ease. The search for more effective weapons has led to the development of armor-piercing shells made of depleted uranium. These weapons were used for the first time in the 1991 Gulf War after the Iraqi invasion of Kuwait. Since then, they have been used extensively in other regional conflicts in areas including the Balkans (1994, 1999), Afghanistan (2001), and again in Iraq (2003). The use of this material in ammunitions has remained highly controversial (Figure 12-7).8 W hen a DU round hits its target, as much as 70 percent of the 8 Catalinotto ,J. Metal of Dishonor-Depleted Uranium : How the Pentagon Radiates Soldiers & Civilians with DU Weapons , 2nd. Ed., Independent Publishers Group, Chicago, 1995. 287 projectile burns on impact and forms an aerosol of radioactive particles. The uranium dust can then be spread by the wind and may become part of the food chain. Studies by the United Nations have concluded that DU is at least partially responsible for the increase in the rate of cancer among Iraqi children and in the number of spontaneous abortions among pregnant Iraqi women.9 DU may even be linked to the Gulf War Syndrome that is affecting US veterans of the 1991 Gulf War.10,11 Figure 12-7 A reporter using a radiation detector examines an Iraqi tank destroyed by depleted uranium bullets. Uncontrolled Nuclear Fusion: The H-Bomb Hydrogen or thermonuclear bombs are probably the most deadly of all nuclear weapons. The large energy release per unit mass of fuel makes H-bombs very efficient. This allows for the building of bombs with much greater yields than fission bombs. The Soviet scientist Andrei Sakharov first proposed the idea in 1948, but it was the Americans who detonated the first H-bomb, code named Ivy Mike, on November 1, 1952. The bomb used liquid deuterium as fuel and had a yield of 10.4 MT, about 700 times more powerful than the A-bomb dropped on Hiroshima. A second 15MT bomb, code named Bravo, was tested on the island of Bikini near the Marshall Islands in 1954. Since then, several hydrogen bomb tests have been conducted. The Soviet Union conducted tests in 1953 and 1961; the British detonated an H-bomb in 1957. France conducted a test in 1960, as did China in 1964. Fortunately, hydrogen bombs have never been used in a military conflict. An H-bomb is essentially a three-stage weapon (Figure 12-8). In the first stage or trigger, a small amount of plutonium is detonated (explosion), as in a conventional A-bomb. In the second stage, the immense energy in the form of x-ray-radiation compresses and heats up a solid mixture of lithium deuteride (a source of tritium) and deuterium12 located in the center of the bomb to millions of degrees (implosion), triggering the thermonuclear reaction. The fusion reaction produces an ample supply of neutrons so powerful they can initiate fission (explosion) of otherwise unfissionable casing of depleted uranium. This is the third stage and the one that produces most of the radioactive fallout. Question: W hy doesn’t the sun blow up like a hydrogen bomb? Answer: The main difference between the sun and the hydrogen bomb is that the sun contains very few heavy hydrogen isotopes. The proton-proton reaction that results from normal hydrogen atoms proceeds about a billion times more slowly than a strong deuteriumtritium reaction at the same temperature and pressure. Neutron Bombs Figure 12-8 A modern warhead carrying a hydrogen bomb. Neutron bombs are small (less than one kiloton) thermonuclear bombs Fifty-sixth Genral Assembly, Uniteed Nation Press Release GA/SHC/3639, 2001. Peterson, S., “Remains of toxic bullets litter Iraq,” Christian Science Monitor, May 15, 2003. H astings, D., “Is an Armament Sickening U.S. Soldiers?,” A ssociated Press, August 12, 2006. 12 The first device used liquid helium at cryogenic temperatures. 9 10 11 288 Chapter 12 - Nuclear Radiation designed to produce a high-intensity burst of radiation over a relatively small area. Instead of absorbing the neutrons inside the weapon, the neutrons are allowed to escape into the environment. Because neutrons are absorbed by the air, neutron bombs have limited yields, and so are effective over relatively small areas. Since heat and blast effects are minimal, they work primarily on biological systems and are dubbed as anti-personnel bomb. Because of this many consider these weapons as highly immoral that could be used prematurely in regional conflicts which can lead into full-scale nuclear war. Effects of Nuclear War Nuclear bombs can result in a wide range of destruction in any of the following ways:13,14 1. Blast: Blast damage from a nuclear weapon comes from the overpressure in the air and from winds which result from the pressure. Right after the bomb detonates, a shock initiates at the center and moves outward at a rate several times faster than the speed of sound, and a large overpressure develops across the shock wave.15 Depending on the yield and distance from the blast, the blast wind can reach several thousand kilometers per hour and overpressure can exceed several atmospheres. Most buildings suffer moderate to severe damage when subjected to only 35 kilopascals (0.35 atmospheres). As for the human body, the shock causes a pressure wave to travel through the body, with the most damage occurring in junctions between materials of different densities, such as the interface between bones and muscles or between tissues and air. Most eardrums rupture at around 100 kPa (one atmosphere), and lungs are damaged at around 70 kPa (0.7 atmospheres) overpressure. Roughly, 50% of the energy of the low-altitude atmospheric detonation is released in the initial shockwave. 2. Heat: Depending on yield, fireballs as large as one mile in diameter, with temperatures of several thousand degrees, are possible immediately after the explosion. Such fireballs practically vaporize everything near ground zero and causes extensive, rapidly spreading fires. As the weapon explodes, it produces a brilliant flash of light and a heat wave beyond the tolerance of the human retina, causing severe eye injuries, including blindness. 35% of the energy of the nuclear blast is in the form of heat, and visible radiation. 3. Radiation: Both short and long term effects of ionizing radiation are important. Shortly after the blast, the heat of the fireball vaporizes weapon residue into small particles that are quickly drawn up into Glasstone, S. “The Effect of Nuclear Weapons,” US Atomic Energy Commission, 1962. A good sorce of information on nuclear weapon effects is the Federation of American Scientists. See http://www.fas.org/nuke/intro/nuke/effects.htm For a 10-megaton fission bomb, overpressure can reach one thousand atmospheres close to ground zero (GZ), but drops to about 15 atmospheres when it becomes a fireball about one m ile in radius. The wind speed can reach 1700 mph (2700 km/hr). The overpressure becomes negligible at around 20 miles from ground zero, where wind has slowed down to about 55 mph (90 km/hr). 13 14 15 I do not know with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. ~ Albert Einstein 289 the stratosphere. Larger particles settle and contaminate the earth, while smaller particles are carried by the stratospheric wind across the globe, eventually showing up as radioactive fallout. If detonation occurs over water, sea salts will act as condensation nuclei to seed the clouds, causing highly radioactive rainout. In addition, the large flux of neutrons released during the first few seconds after detonation travels outward and is absorbed by the soil, air, water, and other materials, making them radioactive. In turn, these radioactive materials release gamma and beta radiation over an extended period of time. 4. Electromagnetic pulse: In addition to various radioactive isotopes, nuclear blasts emit a significant amount of x-rays into the atmosphere. X-rays can ionize the air at high altitudes and produce large numbers of fast-moving electrons. The moving electric charge produces a pulse so powerful that long metal objects would act as antennae and electrify all electronic devices on its path. The resulting voltage and the associated high current could destroy unshielded electronics and interfere with electric signals, resulting in failures of critical medical and transportation equipment. The ionized air also disrupts radio traffic that would normally bounce from the ionosphere. Ionizing radiation and EMP account for the remaining 15% of the detonation energy. Nuclear Arms Treaties and International Conflicts Following WWII and the explosion of the two powerful nuclear bombs on Hiroshima and Nagasaki, the Allies, mainly the United States and Soviet Union, engaged in a rapid buildup of nuclear weapons. So many weapons were amassed that if one country decided to use its nuclear option, the entire planet could have been destroyed many times over in a matter of hours. At the peak of the nuclear weapons stockpile in 1967, the US and USSR (Union of Soviet Socialist Republics or Soviet Union) maintained over 40,000 active warheads.16 The rapid proliferation of the nuclear arsenal, and with it the escalation of Cold War rhetoric, required a new way of thinking and bold initiatives to save the world by preventing an accidental nuclear war.17 Figure 12-9 Boeing B-52 Stratofortress is a long-range heavy bomber capable of carrying multiple nuclear or precision guided conventional ordinances. In 1970, the five great nuclear powers (the US, USSR, UK, France, and China) signed a non-proliferation treaty which mandated that those countries would “pursue negotiations in good faith on effective measures relating to the cessation of the nuclear arms race at an early date and to nuclear disarmament.” In exchange, nations without nuclear weapons pledged never to acquire them and, as signatories, open their nuclear facilities to the Vienna-based International Atomic Energy Agency (IAEA), to monitor nuclear program activities and assure no nuclear weapons are being developed. Nuclear Notebook, Bulletin of Atomic Scientists, March/April 2000. 17 A n excellent website on nuclear arm treaties can be found at http://www.nautilis.org/library/security/natotreaty. html. 17 A good reference on the history of nuclear arms treaties can be found at http://www.nautilis.org/library/security/natotreaty.html . 16 290 Chapter 12 - Nuclear Radiation In the years that followed, the US and the Soviet Union negotiated the Strategic Arms Limitation Treaty (SALT-I, 1971 and SALT-II, 1979). These treaties aimed at limiting the number of strategic offensive weapons on each side.18 Furthermore, the Anti -Ballistic Missile Treaty (ABM) constrained the numbers of launchers and interceptors available to each country. The underlying assumption prevalent during this time was that if each country had enough nuclear power to survive an enemy’s first strike and was still able to retaliate with overwhelming nuclear response, then neither country would undertake such madness. The policy commonly referred to as Mutually Assured Destruction (MAD) left no doubt that both countries would be destroyed in the event of any nuclear attack. In 1983, US President Ronald Reagan announced his intention to initiate a program for research and development of a space-based system to defend the nation from attack by strategic ballistic missiles. The Strategic Defense Initiative (SDI), popularly referred to as “Star Wars,” would supposedly eliminate the threat of a nuclear arms confrontation by installing lasers and other space-based defensive systems that detected and destroyed all incoming missiles. The critics charged that this would be in violation of the ABM treaty and would encourage the militarization of space and destabilize the nuclear balance of power. Furthermore, SDI was based on untested technologies and was unable to defend against cruise missiles, airplanes, and several other possible delivery systems. Following the dissolution of the Soviet Union in 1991 and the end of the cold war, the selection of a new administration temporarily put the SDI program on hold. The reality of the new world order and the demise of communism provided a unique opportunity not only to limit the nuclear arsenal, but also to actually reduce it. The STrategic Arms Reduction Treaties (START-I, II, and III) are the first comprehensive arms-control agreements that require a reduction of offensive nuclear weapons. Under these treaties, the United States, the former Soviet Union, and its successor states (Russia, Ukraine, Belarus, and Kazakhstan) had to cut down their nuclear warheads and delivery systems that included intercontinental bombers and land-based and submarine-launched ballistic missiles. Based on these treaties, the US and Russia agreed to reduce the total number of strategic nuclear warheads to about 2,000-2,500 warheads each by 2007. Although some progress has been made in reducing the size of nuclear arsenals, talks have reached impasse as NATO announced plans to build a missile defense system in Poland and Czech Republic. There are new proposals by the Obama administration to restart talks to reduce the size of nuclear stockpiles. Nuclear arsenals can be divided into either strategic or tactical categories. Strategic nuclear weapons are weapons designed to target cities and other large areas. Tactical nuclear weapons are smaller weapons used to destroy specific military targets. Depending on delivery method, weapons are classified as bombs, ballistic missiles, cruise missiles, artillery shells, or hand-held. Ballistic missiles are long-range missiles that use ballistic orbital trajectories, whereas cruise missiles use low altitude trajectories and are suitable for short range and smaller payloads. Artillery shells and hand-held devices are purely for tactical use. 18 291 Terrorism The end of the Cold War and the resulting reduction in tensions between the Former Soviet Union and the United States brought about a new spirit of cooperation. This resulted in a number of treaties which have reduced the number of nuclear warheads each country possesses, and with them, the threat of nuclear war. The end of the Cold War also raised a new threat: terrorism. As nuclear warheads are dismantled, an abundant amount of weapons-grade nuclear fuel and accessories which must be disposed of accumulate. In addition, thousands of tons of uranium have been refined and converted to plutonium or enriched to weapons-grade material. Less than 8 kg of plutonium is all that is needed to make a Nagasaki-sized bomb. The possibility exists that terrorist groups with no access to reprocessing plants could steal or buy enriched uranium and plutonium fuels on the black market and disperse them throughout cities and other population centers or use them in making crude and dirty bombs. Equally important is the danger of attack on or accidental spillage of nuclear waste en route to a proposed permanent repository site. Nuclear reactors themselves could also be the subject of sabotage and therefore must be designed with many layers of safety in the event of a loss of coolants, damage to the containment structure, or the possibly of the reactor control rooms being taken over by terrorists and their internal collaborators. The key defense against large radioactive leaks to the outside is to keep the containment intact. The containment dome is shaped such that it can withstand internal pressure resulting from the buildup of gas pressures. Unfortunately, existing containments may not withstand external overpressures that may result from major rocket attacks or car bombs.19 In light of the September 11 terrorist attacks on New York and Washington D.C.,20 nuclear reactors may be particularly vulnerable. Summary Nuclear radiation has found many uses and, depending on its application, can be either the deadliest enemy known to mankind or a source of hope in diagnosing and treating many formerly incurable diseases. If operated safely, nuclear reactors generate electricity with practically none of the adverse environmental consequences of fossil power plants. The waste, however, could have tremendous environmental impact for many thousands of years. The obvious solution is not to keep radioactive waste for such long times, but to find solutions to rid us of these wastes within the next few decades. In the meantime, natural radioactive decay has cooled the waste, making it easier to handle. For an excellent overview of nuclear terrorism risks see: Leventhal, P. L., and M. M. Hoenig, “Nuclear Terrorism: Reactor Sabotage and Weapons Proliferation Risks,” Contemporary Policy Issues, July 1990, V. 8, No. 3, pp.106-121. 20 E arly in the morning of September 11, 2001, Al Qaeda terrorists hijacked four commercial jets and crashed three of them into the World Trade Center in New York and the Pentagon i n Washington D.C. The fourth aircraft was heading toward the White House, but crashed in Pennsylvania. Over 3,000 innocent lives were lost, 265 aboard the airplanes and the rest in t he buildings that collapsed as a result of the tragic incident. 19 292 Chapter 12 - Nuclear Radiation Additional Information Books 1. Petty, G. W., A First Course in Atmospheric Radiation, Sundog Publishing, 2006. 2. Wagner, H., and Ketchum, L., Living with radiation: the risk, the promise, The Johns Hopkins University Press, 1989. 3. Glasstone, S. The Effect of Nuclear Weapons, US Atomic Energy Commission, 1962. Periodicals 1. Journal of Radiological Protection; the official journal of the Society for Radiological Protection and publishes articles on all aspects of radiological protection, including non-ionizing and ionizing radiation. 2. Nuclear Instruments and Methods; Elsevier Science Direct. papers on design, manufacturing and performance of scientific instruments with an emphasis on large scale facilities. Government Agencies and Websites 1. US Environmental Protection Agency (http://www.epa.gov) is responsible for issuing standards and guidance to limit human exposure to radiation. 2. US Nuclear Regulatory Commission (http://www.nrc.gov) is responsible for implementing the EPA’s exposure standards through regulation of nuclear power reactors. It also oversees licensing of facilities that posses or dispose nuclear materials. 3. US Department of Energy (http://www.doe.gov) is responsible for disposal of nuclear waste from civilian power plants. 4. US Department of Defense (http://www.dod.gov) is responsible for the safe handling and storage of nuclear weapons. 5. US Department of Transportation (http://www.dot.gov) is responsible for the packaging and transport of radioactive materials. 6. US Food and Drug Administration (http://www.fda.gov) regulates medical procedures that use radiation. Non-Government Organizations and Websites 1. International Atomic Energy Commission (http://www.iaea.org) is the United Nation’s agency responsible for promoting peaceful applications of nuclear science and technology for critical needs in developing countries. 2. Nuclear Energy Institute (http://www.ne.doe.gov). 3. World Nuclear Association (http://www.world-nuclear.org). 293 Exercises I. Essay Questions 1. What is the difference between isotopes of U-235 and U-238? Which one is more stable? Which one has a longer half-life? 2. Which types of electromagnetic radiation are ionizing? Which kinds are non-ionizing? 3. Name three sources of natural background radiation. 4. Name three sources of man-made radiation. 5. What are the risks involved in the decommissioning of a nuclear plant? 6. What is depleted uranium, what is it used for, and why is it dangerous? 7. What are the differences between an A-bomb and an H-bomb? 8. What are some of the hazards radiation poses to human health? How can radiation help in improving human health? 9. How does a nuclear bomb work? Draw a schematic of a nuclear bomb. 10. What is a dirty bomb? 11. What are similarities between fission and fusion bombs? How are they different? 12. What is transmutation? What are its applications? II. Multiple Choice Questions: 1. Which of the following is considered to be ionizing radiation? a. Microwaves b. RF c. Visible d. Infrared e. High frequency UV 294 2. What percentage of human radiation exposure comes from natural sources? a. More than 99% b. About 80% c. About half d. Less than 10% e. Less than 1% 3. The amount of radiation damage to a living tissue is expressed in a. Roentgen b. Rad c. Curie d. Rem e. Becquerel 4. Which of the following units is usually used to express the strength of an x-ray source? a. Roentgen b. Rad c. Rem d. Curie e. Becquerel 5. Radiation emitted by a microwave oven is a. Ionizing b. Extremely dangerous c. Visible d. Radio waves of very high frequency e. Absorbed by nonmetallic substances like glass, ceramics, and paper products 6. What is (are) the mechanism(s) responsible for major destruction and loss of life following a nuclear attack? a. Shock b. Heat of the fireball c. Short term immediate radiation d. Long term, low-level radiation e. All of the above 7. The maximum permissible occupational dose for nuclear industry workers in the US is _______ per year. a. 5000 mrem b. 1250 mrem c. 500 mrem Chapter 12 - Nuclear Radiation d. 500 rads e. 500 curies 8. The maximum permissible occupational dose for the general public in the US is ________ per year. a. 500 mrem b. 125 mrem c. 0.5 rads d. 500 rads e. 500 curies 9. Alpha particles are a. The same as nuclei of helium b. The same as electrons c. Electromagnetic radiation with no electric charge and no mass d. The same as protons e. None of the above 10. Gamma radiation is a. High energy electrons b. High energy neutrons c. High energy protons d. High energy helium nuclei e. High energy electromagnetic wave 11. The beta particle is a. The same as proton b. The same as electron c. The same as positron d. The same as neutron e. High-intensity electromagnetic rays 12. Lab coats and gloves provide shielding from a. Alpha radiation b. Alpha and beta radiation c. Alpha, beta, and gamma radiation d. Neutrons e. None of the above 13. Which of the following have the highest penetrating power? a. Electrons b. Neutrons c. Alpha particles d. Beta particles e. Gamma rays 14. The agency responsible for setting the standards for safe radioactive exposure in the United States is a. The Nuclear Regulatory Commission b. The Department of Energy c. The Environmental Protection Agency d. The International Atomic Energy Agency e. The White House 15. The agency responsible for enforcing the safe operation of US nuclear reactors is a. The Nuclear Regulatory Commission b. The Department of Energy c. The Environmental Protection Agency d. The International Atomic Energy Agency e. The White House 16. The reason that alchemists could not transform mercury and other metals into gold was that a. They had no knowledge of the structure of atoms b. They did not use the right chemicals c. They did not have the right catalysts for making the necessary reactions possible d. The cost was extremely high e. All of the above 17. Consider a substance with a half-life of 30 years; what fraction remains after 90 years? a. 1/16 b. 1/8 c. 1/4 d. 1/3 e. 3/4 18. A nuclear physicist measures the nuclei disintegration of a substance. His detector counts 8x106 integrations in the first hour, but drops to 1x106 in the second hour. What is the half-life of the radioactive source? a. 8 hours b. 30 minutes c. 20 minutes d. 7.5 minutes e. Cannot determine 295 19. The best solution for disposing of nuclear waste is a. Sell it to other countries b. Dispose it in the landfills c. Reuse them as nuclear fuel d. Store and monitor the waste e. All of the above 20. What is currently being done with US nuclear waste? a. It is reused as nuclear fuel. b. It is enriched to make more bombs. c. It is disposed in nuclear landfills. d. It is sold. e. It is held in temporary storage facilities. 21. What was the name of the project to develop nuclear weapons? a. The Little Boy b. The Fat Man c. Manhattan d. Trinity e. Mike 22. What was the name of the bomb dropped on Nagasaki? a. The Little Boy b. The Fat Man c. Manhattan d. The Peacemaker e. The Last Resort 23. The fuel used in the nuclear bomb dropped on Hiroshima was a. TNT b. Hydrogen c. Uranium d. Plutonium e. None of the above 24. Who was the US president who authorized the dropping of the nuclear bomb on Japan? a. Harry Truman b. Franklin Roosevelt c. Dwight Eisenhower d. John F. Kennedy e. Winston Churchill 296 25. Who was the scientist in charge of design and fabrication of the atomic bomb dropped on Japan? a. Albert Einstein b. Enrico Fermi c. Robert J. Oppenheimer d. Glean Seaborg e. Edward Teller 26. In what form is most energy from a nuclear blast released into the atmosphere? a. Shock b. Heat c. Prompt radiation d. Radioactive fallout e. All of the above 27. Plutonium is of concern in proliferation of nuclear weapons because a. It is cheaper to construct a bomb using plutonium than uranium b. Plutonium bombs are much more destructive than uranium bombs c. Plutonium has a much smaller critical mass than uranium d. Plutonium is much more abundant than uranium e. Enriching plutonium is much easier than enriching uranium 28. An electromagnetic pulse generated by nuclear explosions is most effective in a. Killing people b. Destroying other nuclear weapons c. Damaging building d. Harming the environment e. Damaging electrical equipments and communication devices 29. START nonproliferation treaty stands for a. START arms reduction now. b. STrategic Arm Reduction Treaty c. STop Arm Restructuring Treaty d. STop ARming the Terrorists e. None of the above 30. Background radiation levels a. Are constant world-wide Chapter 12 - Nuclear Radiation b. Decrease with elevation c. Are nearly zero except when in proximity of nuclear reactors d. Depend on altitude and type of rock or soil in the area e. Are highest in snow and ice III. True or False 1. Infrared and visible radiations are the primary sources of ionizing radiation. 2. Ionization radiation refers to those electromagnetic waves with enough energy to eject electrons from atoms. 3. The range of electromagnetic radiation with wavelengths slightly shorter than those of visible light is called infrared. 4. Rad is an abbreviation for radiation. 5. Alpha particles are much potent source of ionizing radiation than x-rays and gamma-rays. 6. The human body is naturally radioactive. 7. The three types of radiation in order of decreasing penetrating power are alpha, beta, and gamma. 8. An alpha particle has the atomic mass of four. 9. Relative to the surrounding areas, coal mines have elevated level of radiation. 10. All nuclear materials remain highly toxic for thousands of years 11. The main factors affecting the choice for a proper, permanent nuclear waste repository are soil stability, seismic activity, and proximity to large water reservoirs. 12. Up to now, most nuclear waste has been disposed of by nuclear transmutation. 13. Because of their enormous destructive powers, atomic weapons are commonly referred to as dirty bombs. 14. Depleted uranium is uranium depleted of all its harmful radiation. 15. The best way to get rid of nuclear waste is to use it as nuclear fuel. 16. Strategic nuclear weapons refer to weapons designed to target cities and other large installations. 17. There are no major differences between a reactor meltdown and a nuclear bomb explosion. 18. The main consequence of electromagnetic pulse emission from nuclear blasts is the rapid increase in the number of brain cancers. 19. X-rays are produced when a target is bombarded with an electron beam. 20. Unlike tactical nuclear weapons, strategic weapons are designed to inflict maximum casualties. IV. Fill-in the Blanks 1. Alpha, beta, and gamma radiation can physically dislodge a/an ___________ from atoms in their path. 2. _____________ are the least penetrating of all ionizing radiations. 3. The most penetrating type of radiation is ____________. 4. The radiation emitted from a source is measured in __________ or ___________. 5. Any radiation dose less than ______ millirem is considered an acceptable level for general public. 6. A radiation exposure of over _________ rads will certainly cause death. 7. A _________________ is used to detect radiation. 297 8. Electromagnetic radiation in the frequency range just higher than x-rays is called ____________. 9. Uncontrolled nuclear fusion is the basis for manufacturing the ______________bomb. 10. Neutron bombs are small ___________ bombs designed to produce a locally intense bust of radiation. IV. Project I - Radiation Dose To estimate the annual radiation dose your body receives, fill out the radiation dosimetry questionnaire in page 282 and answer the following questions: 1. What is the annual radiation dose you receive? 2. Do you receive considerably more radiation during any particular season? If so, why? 3. Do you meet the radiation exposure limit set by the regulatory agencies in your country of residence? Explain. 4. Is there any reasonable way to reduce the level of your radiation exposure? Project II - Energy Alternatives (Group project) There is a ballot on whether a nuclear, a fossil, or a solar power plant is to be built near the city you are living in. You are asked to assume one of these roles and act either as a proponent (pro) or opponent (con) in the following list and address the issues from that point of view. Pro as the parent oil company person electric utility scientist economist business person consumer regulatory agency electric utility Con as the child conservationist stockholder economist scientist consumer business person electric utility consumer 298