Niels Bohr, the Danish physicist who founded quantum mechanics, almost waited too long to escape from Europe during World War II. The German Army overran and occupied Denmark in April 1940, but Bohr felt fairly safe in spite of his Jew­ish heritage. He was head of the Institute of Theoretical Physics at the University of Copenhagen, and it would have seemed unusually severe if the Germans had arrested him. Denmark essentially collaborated with the German Army, maintain­ing an uneasy peace. However, in 1941, Bohr was visited by Werner Heisenberg from Berlin. They had a long walk and a private conversation that left Bohr with a feeling of dread that scientists in Germany were working on an atomic bomb. Although he would deny it after the war, Heisenberg seemed to hint at atomic weapons research back in Berlin, while probing Bohr for indications as to what the British and Americans were up to.

By 1943, the situation in Denmark had worsened, and on September 28 Bohr learned from the Swedish ambassador that he was to be arrested and deported to Germany within three days. Wasting no time, Bohr and his family walked through Copenhagen to the seaside and hid until nightfall in a gardener’s shed. A motorboat then ran them out to a fishing boat, which avoided minefields and German patrols and took them across the Oresund Channel to Limhamn, Sweden.

Sweden was relatively safe, but it was crawling with German agents, and there was real fear that Bohr would be assassinated now that he had escaped German con­trol in Denmark. He wanted to get to Britain, at least, where he could warn the Allies of an impending German nuclear weapon. He was flown out in a British Mosquito

to have miraculous qualities. The activation was much more intense when the experiment was performed on the wooden table.

It was a mystery worth further study. Fermi set up an experiment with a carefully machined piece of lead separating the neutron source and the silver target, but at the last moment, on a vague hunch, he substituted a scrap sheet of paraffin for the lead. The activation level increased dramati­cally over all previous experiments, and Fermi immediately knew what was taking place. The neutrons, barreling out of the neutron source at high speed, were slowed down to a crawl by elastic collisions with the hydrogen nuclei in the paraffin. Neutrons running slowly had more time to interact with the silver nuclei as they passed by, increasing the probability of being

twin-engine fighter-bomber, stripped of armaments but equipped with a compartment for a person to ride in a prone position where the bombs were normally kept. Bohr was strapped into a flight suit, with a parachute, a flight helmet with audio hookup, oxygen mask, and a handful of flares. They would be flying high, above 20,000 feet (6,100 m), to avoid German antiaircraft guns in Norway, and if they were caught by a fighter plane they were to open the bomb bay and drop Bohr into the ocean, in which case his flares would come in handy.

Unfortunately, Bohr had an unusually large head, and the standard issue flight helmet did not fit properly. He did not hear the pilot through the built-in headphones when he was told to turn on his oxygen after the plane made high altitude, and he passed out somewhere over Norway. The pilot could tell that something was wrong when he could get no verbal response from Bohr, and as soon as they were clear of Norway he dropped altitude and flew low over the North Sea. When they landed in England, Bohr was in fine shape, commenting that he had slept well during the flight.

From England, Bohr was flown to the United States, where he was taken to the top-secret atomic bomb laboratory in Los Alamos, New Mexico. Here he would add guidance, encouragement, and assistance to the theoretical work, as an expert in quantum mechanics. “An expert,” he commented, “is a person who had made all the mistakes that can be made in a very narrow field.” Upon seeing the extent of the American operation at Los Alamos, he was deeply impressed. Nothing of this magnitude had seemed possible anywhere in Europe. Although welcomed as a revered elder statesman of nuclear physics at the laboratory, he later confided to a friend, “They didn’t need my help in making the atom bomb." They seemed to have it well in hand.

captured by the target. In the original experiments, neutrons bouncing off the wooden table had been slowed down, again by collisions with hydro­gen nuclei in the wood. Hitting the heavy marble table top, the neutrons had not been slowed noticeably. To varying extents, the probability of neutron interaction would be increased as the speed of the particles was decreased, and this effect would apply to both absorption and fission. Fermi won the Nobel Prize in physics in 1938 for this discovery. Although he came very close to discovering fission, the Nobel Prize for that finding would go to Otto Hahn after World War II had ended.

At the subatomic level, all interactions of matter with matter are prob­abilistic in nature. If a freely traveling neutron flies close to a standing uranium atom, it does not necessarily do anything with the uranium, but there is a probability that it will be captured by its nucleus. The magni­tude of the interaction probability depends entirely on the speed of the neutron as it passes. Although an interaction can occur at any speed, it seems that the slower a neutron is traveling, the higher is its probability of interaction.

Neutrons set free in uranium fission events are most likely traveling with an energy of about 1 MeV. (Neutron speed is expressed as neutron energy, which is always expressed in electron volts. An MeV is a million electron volts.) There is a probability that a fast neutron can produce an additional fission by hitting a nearby uranium nucleus, but it is a low chance. Slow the neutron down to thermal speed, or 0.025 eV (electron volts), and the probability of fission increases 1,000-fold. The term thermal speed means the speed at which air molecules normally move at room temperature. To consider building a machine that will operate as a nuclear fission reactor using natural uranium, as it is mined, then all favorable probabilities must be maximized. All probabilities unfavorable to fission, such as unproductive neutron absorption or leakage, must be minimized.

In his experiments on a wooden table and with paraffin wax, Fermi had found that if a high-speed neutron hits a hydrogen atom at room tempera­ture, then the neutron and the hydrogen nucleus exchange momentum. The neutron slows to thermal speed and the hydrogen nucleus, which weighs about the same as a neutron, takes off at the speed of the original incoming neutron. This exchange between the energetic neutron and the room temperature hydrogen nucleus, or proton, would prove very impor­tant, as it is the mechanism by which the energy of fission can be trans­ferred to a working fluid and exploited as power. Use water as the working fluid in a reactor, and the fast neutrons slowing down in it make steam.

Fermi, a Roman Catholic, had married Laura Capon, the daughter of a Jewish officer in the Italian navy, and he felt that anti-Semitic laws being enforced by the Fascist government of Italy were threatening his family. He took his wife and children to Stockholm, Sweden, to accept the pres­tigious Nobel Prize, and they never returned to Italy, slipping away and shipping instead to New York City for a new life in the United States. The United States gained a Nobel laureate, and Europe lost one. Fermi began work at Columbia University upon his arrival, and in 1942 he transferred his work to the University of Chicago. At this carefully selected location in the Midwest, under strictest secrecy, Fermi and his team of scientists built the first working nuclear reactor, Chicago Pile 1, and physics and the world would never be quite the same.

Two definite milestones in the history of nuclear power were the manufacture of plutonium, the first man-made element, in 1941, and the first sustained nuclear reaction in 1942. Both milestones were modified in 1972 when it was discovered that there had been an operating nuclear power reactor 1.5 billion years ago, and that it had produced 3,300 pounds (1,500 kg) of plutonium. There were actually 16 reactors, which ran for a few hundred thousand years, breaking all run-time records and producing energy at an average rate of 100 kilowatts, in the Oklo uranium mine, in Gabon, Africa.

This remarkable discovery was made at the Pierrelatte Uranium Enrichment Facil­ity in France. Output from uranium mines was routinely analyzed by a mass spec­trometer, to insure that every atom of uranium fuel was accounted for and none were being diverted for weapons production. In May 1972, samples from the Oklo mine showed a curious discrepancy. Particular attention was given to the fissionable isotope U-235. The normal concentration of U-235 in raw uranium is 0.7202 percent. The Oklo samples showed only 0.7171 percent, and the difference was significant. The French Commissariat a I’energie atomique launched an immediate investigation, finding con­centrations of U-235 as low as 0.440 percent in the Oklo uranium.

Clues from a detailed analysis of the mineral content of the mine led to a startling conclusion. On September 25,1972, the Commissariat announced their finding: Self — sustaining nuclear chain reactions had occurred at the Oklo uranium mine about 1.5 billion years ago, producing 12,000 pounds (5,400 kg) of fission waste products and depleting the fissionable uranium in the ore.

The natural reactors formed in uranium-rich mineral deposits when groundwater inundated the ore. The water acted as a neutron moderator, bringing the concentrated uranium deposits to criticality, raising the temperature of the ore to a few hundred degrees Celsius, and boiling the water. As the water boiled away, a natural reactor would shut down, resulting in a pulsed action, over an interval of about 2.5 hours, as water once again collected in the ore, repeating the process for 100,000 years. At the time, more than a billion years ago, the U-235 concentration in the ore was about 3 percent, which is comparable to the fuel used in some power reactors today. Since the U-235 component decays away faster than the remainder of the uranium ore, the concentration of U-235 in natural uranium has dropped to about 0.7 percent since the natural reactors last powered up.

By 1864, the concept of electromagnetism in space was reconsidered by a Scottish mathematician and theoretical physicist named James Clerk Maxwell (1831-79). Faraday’s knowledge of algebra had been weak, and he could not formulate a mathematical argument for his idea, but Maxwell was a genius at calculus and had earned the Second Wrangler of Math­ematics degree at Trinity College, Cambridge. Maxwell was interested in everything scientific. He wrote an original essay in college, “On the Stability of Saturn’s Rings,” in which he concluded that the rings were not completely solid, nor liquid, but were composed of “brickbats.” He did

some important work on color and color blindness and took the world’s first color photograph in 1861, of a Scottish tartan. He studied Faraday’s work on magnetic lines of force, and with that as an inspiration, he for­mulated a set of 20 differential equations, in 20 variables describing the magnetic and electrical fields in both static and dynamic conditions.

The equations were complicated and difficult to fathom, but in these equations was a perfect, mathematical prediction that there exist waves of oscillating electric and magnetic fields that travel through empty space at a predictable speed. The speed predicted happened to be the speed of light, and Maxwell jumped to the conclusion that light is an electromagnetic wave, vibrating in a frequency band that we can detect with our eyes. Maxwell would be proven correct.

The implications of Maxwell’s equations remained an elegant but unap­plied theory until Heinrich Rudolf Hertz (1857-94), a German mathema­tician and physicist, made an accidental discovery in 1887. Hertz earned his Ph. D. in 1880 at the University of Berlin and became a full professor at the University of Karlsruhe in 1885. He had dabbled in the investiga­tion of many subjects, including meteorology and elasticity, but in 1887 he was working with a newly invented piece of high-tech equipment. It was a high-voltage coil, producing sparks a half-inch long, with a buzzer built into the end of the coil to sustain the spark. Hertz was fascinated by the effect of light on the spark. He noticed that the spark seemed to dim when ultraviolet light hit it. The light was apparently knocking electrical charge off the spark gap, and this was an exciting finding.

Of even greater importance than this photoelectric effect was an unex­pected by-product of the high-voltage spark. As Hertz turned off the lights to get a better look at his spark under ultraviolet, he noticed something out of the corner of his eye. There was another spark occurring in the room, in the gap between the ends of a loop of wire that was not connected to the apparatus. To his amazement, the spark produced by his high-voltage coil was somehow perceived and replicated by another spark gap, sitting on another table in the room. This concept of action at a distance seemed profoundly strange. There were no electrical wires connecting the two pieces of equipment, and yet if he threw the switch on his spark coil, a spark would occur on a loop of wire on the other side of the room. He was affecting the loop of wire, the antenna, by generating Maxwell’s electro­magnetic wave. Hertz had discovered radio, and he had confirmed Max­well’s vision of radiating waves.

Wilhelm Roentgen (1845-1923), a German physicist, was also fas­cinated by the high-voltage coil and its novel effects. Roentgen had

graduated from the University of Zurich in 1869 with a Ph. D. and was named the physics chair at the University of Wurzburg in 1888. He was studying the effects of a high-voltage coil connected to an evacuated glass tube. Study of the newly discovered cathode rays was popular in Europe in the 1890s, and it seemed as if everyone on the leading edge of science was experimenting with some form of vacuum tube. The cathode ray would soon be identified as a stream of electrons, or small components of atoms stripped off by high voltage, but in 1895 the ray was only known to travel from one end of the tube to another, from the negative to the positive high-voltage electrodes, causing the glass to fluoresce. Roentgen wanted to find out if he could cause the rays to leave the tube and enter the air surrounding it. In the late afternoon of November 8,1895, he tried a special tube, built by a colleague, having a thin, aluminum window on the end. The cathode rays might penetrate the aluminum, and he would use a piece of cardboard painted with barium platinocyanide as a detector.

Being careful, Roentgen devised a cardboard shield to fit over the tube so that no fluorescent light would escape and spoil his measurement, but as he dimmed the lights in the laboratory to test his shield with the tube running at full power, he noticed something out of the corner of his eye. Just as Hertz had noticed his sparks, Roentgen noticed that his piece of cardboard, on a lab bench more than a meter away, was shimmering with yellow-green light. He had hoped to get cathode rays out of the tube, but he knew that they could not have enough energy to bore through the air and hit the barium screen that far away. He had discovered a new type of ray. When the cathode rays hit the aluminum window at the positive electrode end of the tube, they were stopped, and the sudden deceleration produced high-energy rays, invisible and streaming out the end of the tube, just as Maxwell’s equations had predicted. Experiments over the next few days proved that these new rays were more powerful than light and could penetrate solid objects. Needing a quick, temporary name for his discovery, Roentgen called them X-rays.

By 1896, atomic science was progressing rapidly, with physics journals having trouble keeping up with the rate of discovery. Antoine-Henri Bec — querel (1852-1908), a French physicist, was caught up in the excitement and was investigating the work of Wilhelm Roentgen. Although he had studied physics at the bcole Polytechnique, there were practical consider­ations for getting a paying job, so he also studied engineering at the bcole des Pont et Chaussees and became chief engineer in the Department of Bridges and Highways.

Practical work did not keep him from his fascination with Roentgen’s work, which was very successful, with immediate applications in medi­cine, but not completely understood. The composition of cathode rays was unknown. It was known only that something would stream from the negative electrode, or cathode, at one end of a glass tube, with the air removed, to the positive electrode at the other end of a glass tube, when 30,000 volts were applied to the electrodes. When the cathode rays hit the glass at the positive end, they caused the glass to glow, but, aside from that, the cathode rays were invisible in a hard vacuum. Roentgen still did not realize that his X-rays were produced by electrons hitting his big, alu­minum, positive electrode, because the electron had yet to be discovered. Becquerel went to the weekly meeting at the museum national d’Histoire naturelle in Paris on January 20, 1896, to hear a report on Roentgen’s work in Germany. Roentgen was convinced that his powerful X-rays, which

would penetrate light-shielding and fog photographic plates, were pro­duced by the induced fluorescence in the end of the tube.

It occurred to Becquerel that if the weak fluorescent glow at the end of a cathode-ray tube produced X-rays, then he could produce a greater flux of X-rays by using a material that would give a bright, robust fluores­cence under ultraviolet light. He immediately bought all the fluorescent materials he could find and began experimenting, using the ultraviolet component of sunlight to excite fluorescence and using sealed photo­graphic plates to record his X-ray production. Although his experiments were carefully assembled, he was getting no results. In 10 days of experi­menting, he could not fog any film with fluorescence-induced X-rays. On January 30, he read an article on X-rays, and it encouraged him to keep trying.

Becquerel bought some uranium salt, uranyl potassium sulfate, the most strongly fluorescent substance available, sprinkled some atop a sealed photographic plate and exposed it to sunlight for several hours. The experiment was immediately successful, or so he thought. When he devel­oped the plate, he could see the black silhouette of the sprinkled uranium salt on the negative. Obviously, he had found the right fluorescent mate­rial to make X-rays using sunlight. The commercial possibilities of the discovery were wonderful. He could manufacture a simple medical X-ray machine that would require no electricity and no fragile glass tubes and could be used in remote locations.

Just to make sure of the results, on February 26, Becquerel prepared another photographic plate, wrapped in thick, black paper, with a small amount of uranium salt on top. Unfortunately, the weather in Paris had turned cloudy. With no sunlight, he slipped his experiment into a dark drawer in his desk. The next day was cloudy as well. On March 1, for some odd, serendipitous reason, Becquerel decided to go ahead and develop the plate, without any ultraviolet light having excited the fluorescent uranium.

To Becquerel’s amazement, the plate was clouded, as if the light-shield had been defective, but the shape of the dark cloud was a perfect replica of the irregular scattering of uranium salt. Furthermore, the clouding on a plate abandoned in a dark drawer for three days was much darker than he had achieved in sunlight for a few hours. He started putting the evidence together, and he realized that the sunlight and the fluorescence had noth­ing to do with the effect. It was something in the uranium that was cloud­ing the plates. Henri Becquerel had discovered some kind of force that

could cloud a photographic negative, through the light-tight cover, requir­ing no high-voltage tube to produce it. It was something that could not be felt, seen, heard, tasted, or smelled. He gave it a name: Becquerel rays.

In a few years, Becquerel’s important discovery would be given a new designation by Marie Curie (1867-1934), radioactivity.

and the soviET uNioN

The German secrecy structure was as airtight as the Manhattan Project, and there was no word as to what nuclear work was transpiring in the Axis countries. Only after the Allies were able to occupy major territory in Germany in early 1945 were investigators able to evaluate the status of the German atomic bomb effort. A special project, known as the Alsos Mis­sion, was formed by General Groves to capture nuclear personnel, plans, and equipment from the defeated country and discover why no nuclear weapons had been implemented. The project had to work quickly and with maximum priority to beat the Soviets in the last-minute rush to col­lect German assets.

The Alsos Mission eventually found that the Germans had given up on a full-scale atomic bomb effort in early 1942. The Minister of Armaments and War Production had been killed in a plane crash, and Albert Speer (1905-81), an architect working directly for Adolf Hitler, was named to replace him. Speer immediately took charge of the armaments budget, and in examining the expenditure books he noticed money disappear­ing into a project labeled “uranium.” Curious, Speer arranged a meeting with the principal scientists to find out the nature of this effort. Speer was not impressed. When he asked how long it would take to complete this uranium weapons project, Speer was given the realistic estimate of four or five years. He knew that they did not have four or five years. Germany

After starting off with a firm lead in the race for an atomic bomb, this modest experiment in a cave in Haigerloch, Germany, is all that the Germans had to show for seven years work. Cubes of uranium oxide hanging by wires were lowered into an aluminum pot of heavy water. A self- sustaining fission reaction was never achieved. (Atomkeller-Museum Haigerloch)

would run out of fuel to run tanks, airplanes, and trucks in 12 months, and the ability to wage war would come to a stop, so it made no sense to have a war production effort that would take longer than a year to complete. Nuclear research was given appropriately low priority for the remainder of the war.

Imperial Japan seemed less capable of a practical atomic bomb devel­opment than Germany, but two such projects were underway when the war ended in 1945. Dr. Yoshio Nishina (1890-1951) established a nuclear research laboratory at the Riken Institute for Physical and Chemical Research in 1931, and by 1937 he had built two cyclotrons, copies of the large machines at Berkeley that were used to transmute uranium-238 into plutonium-239. In 1938, he was able to purchase a new cyclotron from Berkeley. In 1939, the potential for nuclear fission in uranium became clear to physicists all over the world, and in July 1941 Nishina became the director of the Japanese army nuclear program. The mis­sion was to build an atomic bomb for use in conquering territory in the Pacific Ocean.

A small Japanese team managed to build gaseous diffusion appara­tus for the critical U-235 separation, but only on a laboratory level and nothing approaching the enormity of the K-25 plant at Oak Ridge, Ten­nessee. Another limiting problem was the lack of uranium. It was only available through the black market in China and by trade with Germany, but there was no usable transport system between Germany and Japan. Attempts were made to ship uranium to Japan by way of submarine, with no success.

Soviet Russia was ideologically opposed to anything as impractical as nuclear research in the decades leading to World War II, but when nuclear fission was discovered in Germany in 1939 official interest picked up. Most Soviet scientists reasoned that nuclear power production was theoretically possible, but development would take decades. The first work in nuclear research was performed in 1940, confirming that multiple neutrons were released in the debris following a fission of uranium.

By April 1942, it was obvious to the Soviets that the United States had launched a nuclear weapons project because suddenly the American phys­ics journals stopped publishing nuclear research papers. Joseph Stalin (1878-1953), general secretary of the Communist Party, saw this as an ominous development, but the USSR was not in a good position to mount a large-scale scientific industrial project. Stalin chose the next-best option, to thoroughly infiltrate the Manhattan Project with spies.

In 1801, Thomas Young (1773-1829), an English polymath with a doctorate in physics from the University of Gottingen, decided to prove that light was a wave phenomenon, such as sound. He set up an opaque screen, in which two vertical slits were cut and spaced about an inch apart. He directed a beam of light into the slits on one side of the screen, and on the other side he observed the result­ing pattern of light on a piece of white paper.

The experiment was entirely successful, showing an interference pattern of alter­nating light and dark lines projected onto the paper. From this simple setup, there is no doubt that light travels as a wave. The wave front encounters the screen, where it is divided into two sub-waves, which recombine in space and then hit the paper with a predictable interference pattern. The experiment has been rerun innumerable times, using all known types of electromagnetic radiation and even beams of high-speed particles. In 1961, the experiment was run using a beam of electrons, and in 1989, it was run successfully using a single electron aimed at the screen between the two slits. The results are always the same.

In 1913, Niels Bohr confirmed the theories of Planck and Einstein, that light is not a wave but a particle, with his quantum theory of the orbital mechanics of

Bohr modeled the ground energy state of an electron as a sphere of hypothetical altitude above the central nucleus. These ground energies occur in integral steps, of course, and as the ground energy becomes higher, the sphere has a larger simulated diameter and can accommodate a larger number of electrons. It is possible for the first ground state to have as many as two electrons in it. Hydrogen has this ground state, but it contains only one electron, as there is only one positive charge in the hydrogen nucleus to counteract one negative charge. This ground state is only half filled. Helium had two protons in the nucleus and could accom­modate two electrons, so its ground state is filled. Higher ground state energies, or shells, can accommodate eight electrons, 18 electrons, then 32 electrons, and so on as the shells grow larger around the nucleus.

With Bohr’s orderly arrangement of electrons in an atom, the physi­cal meaning of the periodic table of the elements, as invented in 1869 by

atomic electrons. Furthermore, Arthur Compton (1892-1962), head of the physics department at Washington University in St. Louis, proved in 1922 that photons lose energy when they crash into something solid and exchange momentum with elec­trons. Waves do not do that. Only solid particles exchange momentum and scatter like balls on a billiard table. From Compton’s experiments, there is no doubt that light travels as particles. In the single-electron experiment of 1989, however, an electron, which is a particle, apparently divided in half and interfered with itself on the other side of the slit screen.

Scientists found, and still find, these experimental results profoundly baffling. Light can be a particle or light can be a wave, but it cannot be both. Set up both experiments, in tandem. First, divide the wave with the double slits, and then determine that the light coming out of one of the slits is a particle. When the light is detected as a particle, the interference pattern from the two slits disappears. The light can be determined to be a particle or a wave, but not both simultane­ously, and the nature of the measurement determines what it shall be. It seems as if light knows how it is being perceived and adjusts its identity according to the experiment.

Niels Bohr summed up the physical meaning of these findings: "Nothing exists until it is measured.” Quantum mechanics is considered counterintuitive, or outside normal perceptions of reality, for these and other reasons.

The double-slit experiment, showing a most vexing paradox of quantum mechanics: Light can be a particle or a wave, depending on how the experiment is set up. (GIPhotoStock/Photo Researchers, Inc.)

the Russian chemist Dmitry Mendeleev (1834-1907), became clear. Alkali metals, such as lithium, sodium, and potassium, are arranged in a column in the periodic table, as they all seem to have a similar chemical charac­teristic. They have this common characteristic because all elements in this column have a single electron in the outermost energy shell. It is the outer shell that determines an elements chemical interaction, and any lower ground state electrons do not contribute at all to compounding. The inert gases, such as helium, neon, argon, and krypton, all have a completely filled outer shell. With no unfilled electron stations in this uppermost ground state, there is no way one of these gases can bind with another element. Bohr went so far as to predict that when element number 72 was discovered, it would have four electrons in its outer shell and therefore behave chemically like zirconium.

The Chernobyl disaster may have marked the end of the long period of nuclear exuberance, in which experimental reactors were assembled in the desert, bolted into boats, shot into orbit, buried in arctic ice, and built to test exotic ideas. Every nuclear power reactor that was built in the United States was experimental. There was no standard design, and no two reactors were exactly alike. Even in a plant with two, identical-look­ing reactors, built by the same manufacturer, the two units were not exactly the same, requiring unique operator training and different spare parts. It was a massive engineering experiment in which much was learned, by trial, error, and accident investigation.

A point that was definitely learned was how not to build a nuclear reactor. So many designs that now seem obviously flawed had to be tried, and from all the large and small failures came a condensation of wisdom, pointing toward inherently safe, accident-free nuclear reactor designs. The path to a safe reactor is not necessarily coincident with a path to the least expensive reactor, and that is the hardest lesson of all to learn. The cheapest, simplest construction may also be the best construction, although not necessarily, and in nuclear power the path of success must follow the safety path.

Nuclear power has been in a holding mode for the past 30 years, nei­ther moving forward nor receding. As it has remained dormant, the needs of the industrial world have changed. Atmospheric chemistry and general environmental pollution have become factors in power generation deci­sions. Global warming and air pollution are larger issues now than they were 30 years ago, and burnable materials such as coal, oil, and natural gas are now seen as finite resources. Because of all these factors, nuclear power generation is being given a second look.

On March 11, 2011, the expansion of nuclear power was once again challenged when the biggest earthquake in the history of Japan occurred off the northeast coast of the main island, Honshu. Minutes later, a power­ful tsunami struck, wiping out entire towns and killing tens of thousands of people. Although designed for the maximum expected seismic activity, nuclear plants located on the beach faced the full force of the quake and tsunami. Closest to the quake, Onagawa, Tokai, and Fukushima II suf­fered complete automatic shutdowns. Fukushima I also shut down three reactors that were running but lost the use of its emergency diesel genera­tors in the tsunami. There was no power to run coolant pumps, and the situation slowly progressed over days from serious to destructive. Reac­tor cores, still hot from having run continuously for years at full power, melted, and reactor buildings exploded from hydrogen gas buildups. Fis­sion products escaped and polluted Japan and the Pacific Ocean. Reper­cussions and rebuilding from this massive human and economic disaster will continue for years.

Japan is recovering, and the need for nuclear power in this island nation and the world are still there. Expansion of nuclear power proceeds, using better and stronger reactors, designed for safe cooldown even when all power, including emergency generators, has been lost. Over the past 30 years, the nuclear industry has been refining and implementing safety procedures and systems, improving training, and always learning from mistakes and acts of nature, small, large, and calamitous.

Read More 26.08.2015   POWER AN EXODUS FROM EUROPE In the 1930s, Germany and Europe in general suffered a depletion of a resource that they had nurtured for decades. Starting in 1932, laws con­cerning the employment of people of Jewish heritage in universities and research organizations began to have serious effects. Germany began to lose the core of its valuable cache of theoretical and experimental scien­tists as they packed up and left the country. It was an inopportune time to have the number of available nuclear physicists reduced. Hans Bethe (1906-2005) was a loyal German, reared in a Christian household, who became known as one of the few scientists who produced significant work for 60 years. He lost his job at the University of Tubin­gen in 1933 because his mother was Jewish. He then moved to the United States, joined the faculty of Cornell University, in New York, and became head of the theoretical division at the Los Alamos Laboratory during the atomic bomb project of World War II. Bethe calculated the critical mass of the weapons and did theoretical work on the implosion method used in the plutonium-based bombs. Edward Teller (1908-2003) was a Hungarian Jew who moved to Ger­many for his education in chemical engineering and nuclear physics, earning a bachelor’s degree at the University of Karlsruhe and a Ph. D. studying under Werner Heisenberg at the University of Leipzig. His job at the University of Gottingen was cut short in 1933, and he was invited to become a professor of physics at George Washington University in Washington, D. C. He joined the atomic bomb team at Los Alamos, New Mexico, during the war and went on to develop the hydrogen bomb and to be one of the founders of the Lawrence Livermore National Laboratory in California. Another Hungarian Jew who immigrated to Germany to escape com­munism was Eugene “E. P.” Wigner (1902-95). Wigner is the originator of most nuclear reactor theory as it is now practiced, and he won the Nobel Prize in physics in 1963 for his theories of symmetry in quantum mechan­ics. He studied at the Technische Hochschule in Berlin and worked at the University of Gottingen before he left Germany in 1930, seeing a dete­rioration of his fortunes as the Nazi regime coalesced. He was hired by Princeton University in New Jersey, and during the war he was named director of research and development at the Clinton Laboratory in Oak Ridge, Tennessee. His colleagues considered him the intellectual equal of Albert Einstein, and he was instrumental in convincing the U. S. govern­ment to begin the atomic bomb project. These are only a few examples of the European scientists who fled to the United States because of repressive government policies. The United States had not been on the leading edge of nuclear research, but it would quickly become the world’s center of it as these refugee scientists con­verged from Europe. In Britain, scientists had conducted research on a dignified, noncommercial scale, trying not to be extravagant or make out­rageous predictions. The scientists in the United States may have been a second tier behind the Europeans, but they would not be held back by fear of extravagance. In the United States during World War II, a new type of science would be created. It would be science on a large scale, or “big sci­ence,” with a direct connection to engineering and industrial processes. Billions of dollars would be diverted into some very risky research. The expatriate Europeans would be given anything they needed to continue their quest for the energy in the atomic nucleus. The large outpouring of effort and funding under war priorities would give nuclear power a push that would not have occurred under peaceful conditions with research conducted on an academic level. Read More 26.08.2015   POWER PROOF THAT ATOMS CAN BE BROKEN Sir Joseph John “J. J.” Thomson (1856-1940) was born in Manchester, England. Showing early interest in technical matters, he studied engineer­ing at the University of Manchester in 1870 and then moved to Trinity Col­lege, Cambridge, in 1876 to study mathematics. In 1880, he earned a B. A. degree (Second Wrangler) and an M. A. in 1883. In 1884, he became Caven­dish Professor of Physics, in 1890, he married the daughter of the Regius Professor of Physics at Cambridge, and in 1897, he analyzed the atom into component parts, sending atomic science bounding in new directions. Thomson was interested, as were many of his fellow physicists, in the mystery of the cathode rays. He built more sophisticated, more compli­cated glass tubes, in which he electrically accelerated the ray from the tube’s negative electrode through holes drilled in positive electrodes, sending the beam gliding through the deep vacuum beyond the electrodes and to the far end of the tube, where it would hit a fluorescent screen and cause a small spot to glow. He found that he could deflect the thin cathode ray streaming through the hole in the positive electrode using a magnet at the side of the tube. To investigate the nature of the cathode rays, Thomson devised three, sequential experiments. The cathode rays obviously involved a negative charge, as they originated at the negative electrode and vanished into the positive electrode, and for his first experiment Thomson wanted to know whether the negative charge could be separated from the rays. He built a special variant of his tube, blowing a thin, wide beam of cathode rays through a slit in the positive electrode. This beam would traverse the tube, unencumbered by air molecules, and hit a third electrode at the end of the tube. He connected an electrometer to the electrode to measure the charge from the cathode rays and confirmed that there was an elec­trical current flowing between the negative electrode origin of the rays and his target electrode. The target electrode had a slit cut in it, off the straight axis of the beam. With the tube operating at full power, Thomson adjusted a horseshoe magnet across the length of the ray’s flight path, % throwing the beam into a downward turn. He aimed it for the hole in the third electrode. The rays missed his electrode and hit the wall of the tube, causing fluorescence. At that point, the electrical current stopped register­ing on his electrometer. Thomson concluded that the electrical charge and the rays were one and the same, and that one could not be separated from the other. Thomson suspected that he knew the nature of the mysterious rays, but he set up experiment number two for a stronger case. If the rays were purely electrical charge in motion, then he should be able to bend the rays with a stationary electrical charge. He set up another tube, this time with a thin beam established at one end of the tube and shot through a couple of parallel metal plates, against a fluorescent screen at the far end of the tube. This experiment had been tried several times by others with no results, but Thomson thought he knew why. The ray must have been crashing into gas particles left in the tubes, because of imperfect vacuums. Thomson made certain that his tube was pumped all the way down. He put the 30,000 volts on the negative and positive electrodes, turned down the lights, and observed his bright spot on the end of the tube, as he charged the parallel plates from a battery. Just as he had thought, the beam deflected away from a negative electrical charge and toward a positively charged plate. He could not see the beam itself, but he could watch as the spot of light changed position on the end of the tube. Knowing the angle of deflection of the beam and the voltage required to do it, he was able to calculate the ratio of charge to mass of the particle he suspected made up the beam. There was one more experiment needed. Thomson repeated the beam- deflection measurement using a magnetic field instead of an electrical field to bend the beam, and again he calculated the ratio. He was then prepared to make a bold, sweeping conclusion: The cathode rays were composed of tiny negatively charged particles he called “corpuscles,” which were stripped-off atoms in the negative electrode and thrown down the length of the tube. He went further, to propose that, because matter was naturally without electrical charge, the rest of the atom, with the electrons stripped off, had to be positively charged, so that it would cancel the negative charge of his corpuscles. He imagined that the tiny lightweight electrons were stuck in a relatively large, soft ball of positive charge. It was called the “plum pudding” model of the atom, and it would do nicely for the time being. J. J. Thomson’s corpuscles would later be named electrons, and he would be awarded the Nobel Prize in physics in 1906 for this important discovery. Read More 26.08.2015   POWER THE TRINITY TEST The uranium-based atomic bomb design, “Little Boy,” was so foolproof there was no question that its use would result in a full nuclear explosion. The only problem was producing the purified U-235, but it looked as though a full bomb load would be ready by August 1945. The configura­tion was straightforward. A stack of nine rings of U-235, 6.25 inches (15.9 cm) in diameter, were to be shot down a 6.5-inch (16.5-cm) gun barrel using four two-pound (1.8-kg) bags of cordite canon propellant. The four — inch (10-cm) hole in the center of the stack of rings would slide perfectly over a stack of six U-235 disks bolted to the end of the gun and centered in the bore. The stack of rings and the stack of disks would come together quickly as the rings reached the end-of-travel in the gun barrel, slamming into a tungsten-carbide anvil, with the two combined uranium shapes forming the equivalent of four supercritical masses. Instantly, the nose of the bomb would convert into a ball of superheated, radioactive plasma, "Little Boy" Nuclear Weapon   6.5-inch (16.5-cm) gun tube   U-235 Target rings Tamper plug   U-235 projectile rings   Projectile tungsten-carbide disk   Polonium-beryllium Rod holding initiators target components   Gun breech   © Infobase Learning   “Little Boy” brought two masses of uranium-235 together to form a hypercritical mass, using a gun barrel.   "Fat Man" Nuclear Weapon   Fast explosive Slow explosive Tamper/pusher   Spherical shockwave compresses core   Plutonium core   Neutron initiator   © Infobase Learning   “Fat Man” imploded a ball of plutonium-239 using a surrounding larger ball of chemical explosive.   1.25 miles (two km) in radius, as the uranium underwent unimpeded, prompt fission on the high end of the neutron energy spectrum. There was no need to even test this version of the atomic bomb. The plutonium bomb, Fat Man, to be detonated by the implosion method, was another matter. There were too many unknowns, too many bits and pieces of technology that had never been tried before, and there was too much surplus Pu-239 not to test it. After several configuration changes in early 1945, the final production design, designated Model 1560, was frozen by April 3,1945. At the center of the 10,265-pound (4,656-kg) bomb was a 14-pound (6.4-kg) ball of plutonium, to be crushed into a hyperdense, hypercritical mass. The ball, or core, 3.62 inches (9.2 cm) in diameter, was surrounded by a shell of U-238, to act as an inertial weight to keep the core together for a few microseconds as it fissioned, sur­rounded by a thin layer of boron-10 to hold down spontaneous neutrons reflecting back into the core, surrounded by a thick layer of aluminum, to hold it in place. The chemical explosives surrounded the metal core pieces in two layers. The inner layer was 32 close-fitting segments, made of a slow-burning explosive called baratol-70, precision cast like parts of a plastic puzzle. Surrounding the baratol layer were another 32 segments of a fast-burning explosive called Composition B. On the inner surface of each segment of the outer explosive was a depression, backfilled with baratol. These were the explosive “lenses” that would direct the detonation into a shrinking spherical shock wave, imploding the core and starting the fission. Each outer segment of the explosive was equipped with two Model 1773 bridge-wire detonators, all wired to go off at once. A replica of the bomb to be dropped by airplane over Japan was assem­bled, having all parts except the outer steel armor plating, and was tested in the desert of New Mexico, early in the morning on July 14, 1945. The test was code-named Trinity, or TR. The test site was a lonely patch of desert named Alamogordo. On it was erected a 60-foot (18-m) steel tower, bought as surplus from the U. S. Forestry Service, and the bomb was winched into position on a wooden platform at the top. Scientists from the lab were invited to the test, and they could watch from a spot 10 miles (16 km) away from the blast. They were cautioned against looking into the darkness at the point where the explosion was expected to occur, because it was expected to be an unusually bright flash. Most looked in the opposite direction, some just closed their eyes, some looked through welder’s goggles, and Richard Feynman (1918-88), an American theorist from MIT and Princeton, decided to sit in a truck and look through the windshield. He reasoned that the ultraviolet rays from the light would be shielded from his eyes by the glass. Oppenheimer, scientific director of the project, watched the 25-minute countdown at the 10-mile point, while General Groves observed from a more discrete 17 miles (27 km). There was a pool of bets on the strength of the blast, ranging from a bet that nothing would hap­pen to a bet that the atmosphere would catch fire and the entire world would be destroyed. The countdown had to be stopped at 20 minutes, as a rainstorm blew across the test site, with lightning. There was fear that a lightning strike would set off the bomb, but the storm left, and at 5:10 a. m., the countdown resumed. At 5:29:45 a. m., the first atomic bomb exploded. It lit up the darkness like instant noon. Feynman, staring directly at the blast, was temporarily blinded as the brilliant white light overloaded his retinas. The light was visible on the horizon 150 miles (241 km) away, and the shock wave rattled windows at a distance of 200 miles (322 km). Performance of the gadget exceeded most expectations, with an energy yield equivalent to 20,000 tons (18,143.7 mt) of TNT, or 84 trillion joules. Read More 26.08.2015   POWER Nuclear Fission Is Discovered In the 1920s, theoretical physics seemed to flourish and move forward, while experimental physics was stalled and making no headway. Niels Bohrs creation of quantum mechanics led to new and deeper insights into forces and structures that were too small to be detected using the available experimental equipment. Excellent theoretical work could go only so far without experimental results to back it up, and there was ongoing work in England, France, and Germany to analyze the construction of the atomic nucleus as the new theories grew in acceptance and importance. On June 3, 1920, Sir Ernest Rutherford gave the Bakerian Lecture at the Royal Society of London, on the successful transmutation of the nitro­gen atom using alpha particles. Out of character, Rutherford diverted off the topic of his nitrogen experiment into speculations concerning the constitution of the nucleus. It was known by this time that atoms were composed of a fixed number of electrons clouding a nucleus that is com­posed of a like number of protons. The negative charges of the electrons perfectly cancel the equal positive charges of the nucleus, leaving an elec­trically neutral atom. The majority of the atomic weight is due to the pro­tons, which are heavy particles, jammed closely together, making a dense nucleus. It was a workable model of the atom, and quantum mechan­ics would come to explain how chemical reactions work given no more detail than this. However, there was a serious problem. Hydrogen has one electron and one proton. Helium has two electrons and two protons. A helium atom should weigh exactly twice what a hydrogen atom weighs. It does not. A helium atom weighs four times what a hydrogen atom weighs. If hydrogen has an atomic weight of one, then helium is four. Moreover, nitrogen has seven protons, but an atomic weight of 14, and the disparity grows worse as the atoms grow heavier. Barium has 56 protons but weighs 138. Uranium has 92 protons and weighs 235 or 238, depending on which isotope of uranium is weighed. In his now famous lecture, Rutherford proposed a solution to this puz­zling aspect of nuclear structure. Nuclei above hydrogen are heavier than is explicable. There must be another particle at work in the nucleus. It is a particle with no measurable electrical charge, but it has all the weight of a proton. It is electrically neutral, and it should be called the neutron. Such a particle would have interesting properties. Because it has no electrical charge, it would be free to go in and out of matter without being stopped by electron clouds covering atoms. It could not be contained by any solid walls, such as in a glass tube, or even by blocks of lead, and it would be free to enter the atomic cloud, penetrate cleanly to the center of the atom, and crash into the nucleus without being stopped. Having no charge, it would not leave an ionized trail as it flew through gas, liquid, or solid, and therefore it could not be detected with any known method of particle measurement. It was indeed an interesting particle for these reasons, but it was pure speculation. Nobody had ever seen even indirect evidence of a neutron beyond the observations of atomic weight. In 1932, a research assistant of Rutherford’s would finally find the neu­tron, in a skillful interpretation of experimental results. From his work, experiments with the newly found particle led to the discovery of nuclear fission, and from there experimental physics took the lead in the system­atic development of nuclear power. Read More 26.08.2015   POWER Conclusion

For hundreds of thousands of years, mankind has released stored energy by burning hydrocarbons, such as wood, natural gas, and oil. Heat is pro­duced, as are chemical compounds such as water and carbon dioxide. This is a simple chemical process, employing the weak forces that hold together the electron structures of atoms. In the case of all energy conver­sion, there is direct matter-to-energy conversion. The products of com­bustion weigh less than the original components, but the effect is so slight it is not measurable. A much more obvious matter-to-energy conversion employs the forces that bind together the atomic nucleus and not just the atom. The nuclear forces are a million times greater than the electron forces, and the energy release is accordingly larger on an atom-by-atom basis.

Anything that will burn in air will give a combustion energy release, but to get a nuclear energy release is not so simple. The Sun and stars release energy by nuclear conversion, but the stellar process is difficult to scale down. One way that nuclear energy can be released with practical effect is to use fissile materials. Only a few special species, or isotopes, of a few elements are fissile, meaning that they have nuclei that will blow in half upon capture of a passing neutron, and further that the process of fission releases multiple neutrons. The neutron is a special, subnuclear particle, and its presence can affect nuclear properties. The products of

a nuclear fission definitely weigh less than the original components, and the effect is measurable. Uranium-235, a rare isotope of uranium, is fissile.

The fission process releases energy at a very efficient level, more than a million times greater per atom than the best chemical process, and it is sustainable. Each fission is initiated by the capture of a free neutron, and each fission releases more than two new neutrons. These neutrons can then cause further fissions in other U-235 nuclei, and there are neutrons left over to waste. If there were only one neutron released for every neu­tron captured, then nuclear fission would never sustain. Out of trillions of fissions per second, if only one neutron were lost then the process would become nonsustaining and shut down. The existence of excess fission neu­trons allows some to be lost by nonproductive capture and leakage from the assembly of uranium.

Energy release by fission uses a plentiful fuel, uranium. Using advanced fuel-breeding technology, there is enough uranium in the Earth’s crust to supply the energy needs of mankind for thousands of years. An important advantage of nuclear energy release is that it results in no greenhouse gases, and the volume of the waste product is millions of times less than the waste product of any technology that involves combustion. An impor­tant disadvantage to nuclear energy release is that the waste products are dangerously radioactive. The elements produced by the splitting of a ura­nium nucleus are unnaturally neutron heavy. They tend to revert to a more natural state, and in doing so they release heat and ionizing radia­tion. These materials must be handled with unusual care and attention.

The special handling of waste and the extraordinary detail with which every aspect of this new energy conversion process must be conducted have taken time to work into the industrial culture. Becoming accustomed to the cost of such a fastidious process has been a challenge, but this is a new century with modified expectations, requirements, and anticipations. As mankind and civilization have matured, so has the concept of energy conversion and its relationship with the biosphere.