First fission

Shortly after Japan s December 7,1941 attack on Pearl Harbor, the U.S. became more driven to expedite its timetable for developing the first fission weapon because of fear that the U.S. lagged behind Nazi Germany in efforts to create the first atomic bomb. On December 2, 1942 at 3 49 p.m., Enrico Fermi and Samuel K. Allison achieved the world s first controlled, self-sustained nuclear chain reaction in an experimental reactor using natural uranium and graphite. 

For the Noddack controversy, see T. Hopper, She was Ignored, master s thesis, Stanford University, 1990 P. van Assche, Ignored priorities First fission fragment (1925) and first mention of fission (1934), Nuclear Europe 6-7 (1988) 24-25 Segre, Enrico Fermi, 76 F. Krafft, Im Schatten der Sensation Leben und Wirken von Fritz Strafimann (Weinheim, 1981), 314-17. 

Scientists who worked on the first fission (atomic) bomb during World War II were aware of the potential for building an even more powerful bomb that operated on fusion principles. Here is how it would work. 

Release of this energy in a large-scale way is a possibility because of the fact that in each fission process, which requires a neutron to produce it, two neutrons are released. Consider a very great mass of active material, so great that no neutrons are lost through the surface and assume the material so pure that no neutrons are lost in other ways than by fission. One neutron released in the mass would become 2 after the first fission, each of these would produce 2 after they each had produced fission so in the nth generation of neutrons there would be 2" neutrons available. 

Fermium was discovered in 1952, among the products formed during the first hydrogen bomb test at Eniwetok Atoll, Marshall Islands, in the Pacific Ocean. For security reasons, this discovery was not announced until 1955. Credit for the discovery of fermium goes to a group of University of California scientists under the direction of Albert Ghiorso (1915-). The element was named for Italian physicist Enrico Fermi (1901-1954). Fermi, who made many important scientific discoveries in his life, was a leader of the U.S. effort to build the world s first fission (atomic) bomb during World War II. 

It was clear from the time of the first fission product studies that the mass spectrometer would eventually be used in separation problems, mass identification, and isotope abundance measurements. However, the early work on fission products involved very small samples of material and only radiochemical methods were considered sensitive enough to identify and follow the radioactive isotopes. In 1945, Thode and Graham (104) succeeded in obtaining mass spectrograms of the xenon and krypton isotopes formed in the thermal neutron fission of U23B. 

Fusion bombs have been oohstructed and exploded with thousands of tim fee destructive potential of the first fission bombs that destroyed two cities in Japan. A single large fusion bomb could destroy utterly even the greatest city, and if all the fusion bombs now existing were exploded over various cities, it is possible that all life would be destroyed by direct blast and fire, and by scattered radioactivity (fallout). 

The flux (j)yjj is the first-generation flux distribution developed in the perturbed reactor starting from the fission-neutron density distribution in the unperturbed reactor. The calculation of 4)pQ takes into account all the interactions the fission-neutron can undergo up to the first fission event. Thus, p, accounts for perturbations in all nuclear parameters except in the fission cross section. Whereas p (and (/> [,) includes effects of single collision events in the perturbed system, 0pp includes effects of multiple collisions. Consequently we expect that, for many problems, Pid[0fd> ] will be more accurate than Pid[0fl> 0 ]-... 

Cyclotron made possible the first ever synthesis of technetium and fission reactor allowed the chemists to produce kilograms of technetium. But even before the first fission reactor started operating Segre in 1940 found the technetium isotope with a mass number of 99 in uranium fission products in his laboratory. Having found its new birthplace in a fission reactor technetium started to turn into an everyday (paradoxical as it may be) element. Indeed, fission of 1 g of uranium-235 gives rise to 26 mg of technetium-99. 

Nuclear Fusion Modem nuclear weapons are fusion bombs with 1000 times the power of the first fission bombs. Nuclear fusion is being explored as a way to generate electricity but has not yet proven successful. 

Plutonium would not be the only material to be produced in the piles. Another material that would be needed for the first fission bomb was polonium 210, which could be produced by irradiating bismuth with neutrons. Later, tritium, which is an isotope of hydrogen, would also be needed. In addition the opportunity was taken to produce a wide variety of isotopes for industrial and commercial purposes. The major problem with this was that all these substances would absorb neutrons and so reduce the reactivity of the pile. One way round this would be to use slightly enriched uranium in the fuel cartridges. 

The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

When an aromatic compound having an aliphatic side chain is subjected to oxidation, fission of the side chain occurs between the first and second carbon atoms from the benzene ring, the first carbon atom thus becoming part of a carboxyl ( -COOH) group. For example ... 

Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

In the above examples the size of the chain can be measured by considering the number of automobile collisions that result from the first accident, or the number of fission reactions which follow from the first neutron capture. When we think about the number of monomers that react as a result of a single initiation step, we are led directly to the degree of polymerization of the resulting molecule. In this way the chain mechanism and the properties of the polymer chains are directly related. 

The chronology of the development of nuclear reactors can be divided into several principal periods pre-1939, before fission was discovered (12) 1939—1945, the time of World War II (13—15) 1945—1963, the era of research, development, and demonstration (16—18) 1963—mid-1990s, during which reactors have been deployed in large numbers throughout the world (10,18) and extending into the twenty-first century, a time when advanced power reactors are expected to be built (19—23). Design of nuclear reactors has been based on a combination of theory, measurement of basic and derived parameters, and experiments with complete systems (24—27). 

The First Reactor. When word about the discovery of fission in Germany reached the United States, researchers thereafter found that (/) the principal uranium isotope involved was uranium-235 (2) slow neutrons were very effective in causing fission (J) several fast neutrons were released and (4) a large energy release occurred. The possibiUty of an atom bomb of enormous destmctive power was visualized. 

The Model 412 PWR uses several control mechanisms. The first is the control cluster, consisting of a set of 25 hafnium metal rods coimected by a spider and inserted in the vacant spaces of 53 of the fuel assembhes (see Fig. 6). The clusters can be moved up and down, or released to shut down the reactor quickly. The rods are also used to (/) provide positive reactivity for the startup of the reactor from cold conditions, (2) make adjustments in power that fit the load demand on the system, (J) help shape the core power distribution to assure favorable fuel consumption and avoid hot spots on fuel cladding, and (4) compensate for the production and consumption of the strongly neutron-absorbing fission product xenon-135. Other PWRs use an alloy of cadmium, indium, and silver, all strong neutron absorbers, as control material. 

In the startup of a reactor, it is necessary to have a source of neutrons other than those from fission. Otherwise, it might be possible for the critical condition to be reached without any visual or audible signal. Two types of sources are used to supply neutrons. The first, appHcable when fuel is fresh, is califomium-252 [13981-174-Jwhich undergoes fission spontaneously, emitting on average three neutrons, and has a half-life of 2.6 yr. The second, which is effective during operation, is a capsule of antimony and beryUium. Antimony-123 [14119-16-5] is continually made radioactive by neutron... 

Uses of Plutonium. The fissile isotope Pu had its first use in fission weapons, beginning with the Trinity test at Alamogordo, New Mexico, on July 16, 1945, followed soon thereafter by the "Litde Boy" bomb dropped on Nagasaki on August 9, 1945. Its weapons use was extended as triggers for thermonuclear weapons. This isotope is produced in and consumed as fuel in breeder reactors. The short-Hved isotope Tu has been used in radioisotope electrical generators in unmanned space sateUites, lunar and interplanetary spaceships, heart pacemakers, and (as Tu—Be alloy) neutron sources (23). 

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