Nuclear fission spontaneous

Some heavy nuclei will fission spontaneously. Others can be induced to fission through interaction with a neutron. In both spontaneous nuclear fission and induced nuclear fission the pool of neutrons and protons is conseiwed. For example, the nucleus "" Cf (Californium) fissions spontaneously. The 98 protons and 154 neutrons in the nucleus of Cf are reconfigured into other nuclei. Usually a few neu-... 

Uranium-235 and U-238 behave differently in the presence of a controlled nuclear reaction. Uranium-235 is naturally fissile. A fissile element is one that splits when bombarded by a neutron during a controlled process of nuclear fission (like that which occurs in a nuclear reactor). Uranium-235 is the only naturally fissile isotope of uranium. Uranium-238 is fertile. A fertile element is one that is not itself fissile, but one that can produce a fissile element. When a U-238 atom is struck by a neutron, it likely will absorb the neutron to form U-239. Through spontaneous radioactive decay, the U-239 will turn into plutonium (Pu-239). This new isotope of plutonium is fissile, and if struck by a neutron, will likely split. 

FIGURE 17.21 In spontaneous nuclear fission, the oscillations of the heavy nucleus (a) in cffccl tear the nucleus apart, thereby forming two or more smaller nuclei of similar mass (b). Here, two neutrons are released. 

Spontaneous nuclear fission takes place when the natural oscillations of a heavy nucleus cause it to break into two nuclei of similar mass (Fig. 17.21). We can think of the nucleus as distorting into a dumbbell shape and then breaking into two smaller nuclei. An example is the spontaneous disintegration of americium-244 into iodine and molybdenum ... 

Californium is a synthetic radioactive transuranic element of the actinide series. The pure metal form is not found in nature and has not been artificially produced in particle accelerators. However, a few compounds consisting of cahfornium and nonmetals have been formed by nuclear reactions. The most important isotope of cahfornium is Cf-252, which fissions spontaneously while emitting free neutrons. This makes it of some use as a portable neutron source since there are few elements that produce neutrons all by themselves. Most transuranic elements must be placed in a nuclear reactor, must go through a series of decay processes, or must be mixed with other elements in order to give off neutrons. Cf-252 has a half-life of 2.65 years, and just one microgram (0.000001 grams) of the element produces over 170 mhhon neutrons per minute. 

Figure 11.4 Spontaneous fission half-lives of even-even ( ) and even-odd (O) nuclides as a function of fissionability parameter, x. (From R. Vandenbosch and J. R. Huizenga, Nuclear Fission. Copyright 1973 Academic Press. Reprinted by permission of Elsevier.)...

Table 5.4. Partial half-lives of spontaneous fission (values from R. Vandenbosch, J. R. Huizenga, Nuclear Fission, Academic Press, New York, 1973).

Neutrons are emitted by spontaneously fissioning heavy nuclei. They play an important role in nuclear reactions, in particular in nuclear fission (chapter 8). High fluxes of neutrons are available in nuclear reactors (chapter 11). 

Nuclear Fission. Ordinary uranium contains two isotopes, (99.3%) and ( 7%). When a neutron collides with a nucleus it combines wdth it, forming a U- nucleus. This nucleus is unstable, and it immediately decomposes spontaneously by splitting into two large fragments, plus several neutrons. Each of the two fragments is itself an atomic nucleus, the sum of their atomic numbers being 92, the atomic number of uranium. 

Nuclear Fission and Nuclear Fusion. The instability of the heavy elements relative to those of mass number around 60, as shown by the packing fraction curve, suggests the possibility of spontaneous decomposition of the heavy elements into fragments of approximately halfsize (atomic masses 70 to 160, atomic numbers 30 to 65). This fission has been accomplished. A brief statement has been made about it in Chapter 25, in the discussion of uranium. 

When nuclei are very proton-deficient or very neutron-deficient, an excess particle may boil off, that is, be ejected directly from the nucleus. These decay modes are called neutron emission and proton emission, respectively, and move nuclides down or to the left in Figure 19.1. Finally, certain unstable nuclei undergo spontaneous fission, in which they split into two nuclei of roughly equal size. Nuclear fission will be discussed in more detail in Section 19.5. 

Some isotopes of uranium (Z = 92) and elements of higher atomic number, the transuranium elements, also decay by spontaneous nuclear fission. In this process a heavy nuclide splits into nuclides of intermediate mass and neutrons. 

Lise Meitner, the codiscoverer of nuclear fission and an equally keen observer of human nature, was struck by the contrast between Haber and another prominent member of Berlin s scientific establishment, Adolf von Harnack. Harnack, she wrote, possessed an inner stability that made him seem remote and detached. Haber was the opposite, divided within himself, and extremely passionate, which as you can imagine sometimes made things difficult for himself and for others. His spontaneous reactions could be very violent and not always objective. But in the long run his generosity and reason always triumphed. ... 

After the discovery of uranium radioactivity by Henri Becquerel in 1896, uranium ores were used primarily as a source of radioactive decay products such as Ra. With the discovery of nuclear fission by Otto Hahn and Fritz Strassman in 1938, uranium became extremely important as a source of nuclear energy. Hahn and Strassman made the experimental discovery Lise Meitner and Otto Frisch provided the theoretical explanation. Enrichment of the spontaneous fissioning isotope U in uranium targets led to the development of the atomic bomb, and subsequently to the production of nuclear-generated electrical power. There are considerable amounts of uranium in nuclear waste throughout the world, see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendelevium Neptunium Nobelium Plutonium Protactinium Rutherfordium Thorium. 

In addition to the extinct isotope discussed above, the very heavy isotopes Th, U and U all undergo spontaneous nuclear fission and remain in existence. In... 

Nuclear fission involves the splitting of the nucleus into two nuclei of roughly equal mass. Uranium-235 and uranium-238 naturally undergo a type of fission (known as spontaneous fission) in which the uranium nucleus, without assistance, breaks up into two nuclei and produces a neutron, but this process is incredibly slow - even slower than the radioactive decay of these radioisotopes by alpha emission. 

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