The fission of uranium

Krypton and Xenon from Huclear Power Plants. Both xenon and krypton are products of the fission of uranium and plutonium. These gases are present in the spent fuel rods from nuclear power plants in the ratio 1 Kr 4 Xe. Recovered krypton contains ca 6% of the radioactive isotope Kr-85, with a 10.7 year half-life, but all radioactive xenon isotopes have short half-Hves. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

The isotope molybdenum-99 is produced in large quantity as the precursor to technetium-99y, a radionucleide used in numerous medical imaging procedures such as those of bone and the heart (see Medical imaging technology). The molybdenum-99 is either recovered from the fission of uranium or made from lighter Mo isotopes by neutron capture. Typically, a Mo-99 cow consists of MoO adsorbed on a lead-shielded alumina column. The TcO formed upon the decay of Mo-99 by P-decay, = 66 h, has less affinity for the column and is eluted or milked and either used directly or appropriately chemically derivatized for the particular diagnostic test (100). 

Fission reactions produce vast quantities of energy. For example, when one mole of uranium-235 splits, it releases 2.1 x 10 J. By contrast, when one mole of coal hums, it releases about 3.9 x 10 J. Thus, the comhustion of coal releases about five million times fewer joules of energy per mole than the fission of uranium-235. 

Modern nuclear power is based on harnessing the energy released in a fission reaction. The development of atomic energy started in the 1930s with the discovery that atoms could be split with neutrons. This discovery laid the foundation for building the first atomic bombs during World War 11. A basic reaction representing the fission of uranium can be represented as ... 

The first scientific attempts to prepare the elements beyond uranium were performed by Enrico Fermi, Emilio Segre, and co-workers in Rome in 1934, shortly after the existence of the neutron was discovered. This group of investigators irradiated uranium with slow neutrons and found several radioactive products, which were thought to be due to new elements. However, detailed chemical studies by Otto Hahn and Fritz Strassman in Berlin showed these species were isotopes of the known elements created by the fission of uranium into two approximately equal parts (see Chap. 11). This discovery of nuclear fission in December of 1938 was thus a by-product of man s quest for the transuranium elements. 

Nuclear reactors harness the energy from the fission of uranium-235. Nuclear fission occurs when the unstable nucleus of a radioactive isotope splits up, forming smaller atoms and producing a large amount of energy as a result. Scientists believe that the energy comes from the conversion of some of the mass of the isotope. 

In 1945, Marinsky, Glendenin, and Coryell first identified isotopes of element 61, promethium (Pm), which was the last member of the lanthanide series of rare-earth elements to be discovered. Isotopes of this element were obtained both as products of the fission of uranium and as products of several different types of nuclear reactions, most of which involve suitable bombardment of isotopes of neodymium for example ... 

Hiroshima exploded with energy equivalent to about 20,000 tons of TNT.18 But where does all of this energy come from Unlike ordinary chemical reactions, nuclear fission does not involve breaking and forming chemical bonds. Instead, the energy comes from the loss of mass that accompanies the fission reaction. Most, if not all, of the students will be familiar with Einstein s famous equation, E = me2, but few are likely to understand what it means.19 In 1939, Lise Meitner and her nephew Robert Frisch reported their discovery of nuclear fission.20 They realized that the energy that accompanied the fission of uranium nuclei could be accounted for by using Einstein s equation. 

Since the neutron proton ratio for relatively stable nuclei having atomic numbers in the 90 s is greater than the ratio for those having atomic numbers in the 3G , 40 s, or 50 s, the fission of uranium yields products whicli would be too neutron rich for stability unless extra neutrons were emitted also. Some neutrons are indeed ejected (an average of about 2.5 neutrons per fission) thus, in a typical fission ... 

In addition to the black spot contrast, most crystals of neutron-irradiated amethyst quartz showed black lines, which were subsequently identified as the tracks of particles produced by the fission of uranium impurity atoms (see Section 8.13.3),... 

Second, the release of neutrons during fission makes it possible for a rapid and continuous repetition of the reaction. Suppose that a single neutron strikes a one gram block of uranium-235. The fission of one uranium nucleus in that block releases, on an average, about two to three more neutrons. Each of those neutrons, then, is available for the fission of three more uranium nuclei, hi the next stage, about nine neutrons (three from each of three fissioned uranium nuclei) are released. As long as more neutrons are being released, the fission of uranium nuclei can continue. 

Another potential use for holmium is a result of its very unusual and strong magnetic properties. It has been used in alloys with other metals to produce some of the strongest magnetic fields ever produced. Holmium also has some limited use in the manufacture of control rods for nuclear power plants. Control rods limit the number of neutrons available to cause the fission of uranium in nuclear reactors, thus controlling the amount of energy produced in the plant. 

In these steps, each reactive intermediate used up causes the generation of two others. This leads to rapid growth in the number of reactive species, speeding the rate further and possibly causing an explosion. Branching chain reactions are critical in the fission of uranium (see Chapter 19). 

The operation of the first atomic bomb hinged on the fission of uranium in a chain reaction induced by absorption of neutrons. The two most abundant isotopes of uranium are and whose natural relative abundances are... 

Hahn began a 30-year collaboration with Dr. Lise Meitner, who came to Berlin from Vienna. They worked on investigations on beta rays, discovered protactinium, and Hahn discovered the fission of uranium and thorium. In 1944 he was awarded the Nobel Prize in chemistry for his discovery of the fission of heavy nuclei. ... 

Reductive metabolism captures free energy ultimately produced by the fission of uranium, thorium, and potassium-40 in the earth s mantle, but makes no use of the richer free energy stress from solar fusion reactions, other than exploiting liquid water as a solvent in the habitable zone. Photosynthesis captures this independent fusion energy source, but appears to have become accessible only with the molecular complexity of modem cells. It therefore evolved to be self-supporting by artificially... 

During a chain reaction, each step produces a reactant for the next step. In the fission of uranium, a neutron enters a uranium-235 nucleus. As a result, the nucleus breaks into two smaller nuclei. At the same time, it releases more neutrons, which are absorbed by other uranium-235 nuclei, and the reaction continues. 

Objective 41 To sustain a chain reaction for the fission of uranium 235, an average of at least one... 

Cesium, on the other hand, is toxic to plants in anything but trace amounts, whereas indications are that Cs+ ions impair the activity of potassium-binding sites in proteins. Excess cesium can be found in the air and in soils as a by-product of nuclear testing and spent nuclear fuels. Radioactive cesium 137, which results from the fission of uranium 235, decays by emission of a... 

Strontium-90 is one of the products of the fission of uranium-235. This strontium isotope is radioactive, with a half-life of 28.1 yr. Calculate how long (in yr) it will take for 1.00 g of the isotope to be reduced to 0.200 g by decay. 

The fission of uranium-235 producing a chain reaction. Note that the number of avaiiabie neutrons, which "trigger" the decomposition of the fissionabie nuciei to reiease energy, increases at each step in the "chain." in this way the reaction buiids in intensity. Controi rods stabiiize (or iimit) the extent of the chain reaction to a safe ievei. 

Is the fission of uranium-235 an example of natural or artificial radioactivity ... 

With the discovery of the neutron as a fundamental particle, many paradoxes of physics and chemistry were finally resolved, and new areas of research evolved. Prior to the discovery of the neutron as a fundamental particle, scientists generally believed that the nucleus was comprised of protons and nuclear electrons. However, one could not explain, for example, the spin of nuclei with that model. Now, at last, theory could predict the properties of the nucleus quite well. Also, since neutrons are not repelled by the charge on the atomic nucleus, they interact easily with nnclei. Nen-tron scattering enables the determination of crystal stmctnres by probing the positions of nuclei in a sample. Neutrons can also catalyze fission reactions, for example, the fission of uranium nuclei that led to the creation of nuclear power plants and the atomic bomb. 

Leo Szilard determined that the formation of neutrons occurs during the fission of uranium. This is crucial to sustaining a chain reaction necessary to build an atomic bomb, the first of which he helped to construct in 1942. Shortly thereafter, realizing the destructive power of the atom bomb, Szilard argued for an end to nuclear weapons research. 

Estimate if fusion of deuterium into helium releases more or less energy per gram of material consumed than the fission of uranium. 

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