Radioactive decay spontaneous fission

There are four modes of radioactive decay that are common and that are exhibited by the decay of naturally occurring radionucHdes. These four are a-decay, j3 -decay, electron capture and j3 -decay, and isomeric or y-decay. In the first three of these, the atom is changed from one chemical element to another in the fourth, the atom is unchanged. In addition, there are three modes of decay that occur almost exclusively in synthetic radionucHdes. These are spontaneous fission, delayed-proton emission, and delayed-neutron emission. Lasdy, there are two exotic, and very long-Hved, decay modes. These are cluster emission and double P-decay. In all of these processes, the energy, spin and parity, nucleon number, and lepton number are conserved. Methods of measuring the associated radiations are discussed in Reference 2 specific methods for y-rays are discussed in Reference 1. 

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. 

State whether the following statements are true or false. If false, explain why. (a) The dose equivalent is lower than the actual dose of radiation because it takes into account the differential effects of different types of radiation, (b) Exposure to 1 X 1 ()x Bq of radiation would be much more hazardous than exposure to 10 Ci of radiation, (c) Spontaneous radioactive decay follows first-order kinetics, (d) Fissile nuclei can undergo fission when struck with slow neutrons, whereas fast neutrons are required to split fissionable nuclei. 

ISOTOPES There are a total of 23 isotopes of neptunium. None are stable. All are radioactive with half-lives ranging from two microseconds to 2.144xl0+ years for the isotope Np-237, which spontaneously fissions through alpha decay. 

The most stable isotope of plutonium is Pu-244, with a half-life of S.OOxlO+ years (about 82,000,000 years). Being radioactive, Pu-244 can decay in two different ways. One way involves alpha decay, resulting in the formation of the isotope uranium-240, and the other is through spontaneous fission. 

ISOTOPES There are a total of 21 isotopes of californium. None are found in nature and all are artificially produced and radioactive. Their half-lives range from 45 nanoseconds for californium-246 to 898 years for californium-251, which is its most stable isotope and which decays into curium-247 either though spontaneous fission or by alpha decay. 

The transactinide series of elements (Z-104 to Z-113) are those elements that follow the actinide series (Z-89 to Z-103) and proceed to the superactinides, some of which are yet to be discovered. (Note Z is the symbol used to represent the atomic numbers [protons] of elements in the transactinide series, as well as of other elements.) All elements of the transactinide series are radioactive, heavy metals that are unstable, and they usually decay by spontaneous fission or alpha decay into smaller nuclei of elements with less mass. 

ISOTOPES There are a total of 15 Isotopes for rutherfordlum, ranging from Rf-253 to Rf-264. Their half-lives range from 23 microseconds to 10 minutes. They are all artificially made, radioactive, and unstable. Their decay modes are a combination of alpha decay and spontaneous fission (SF). 

ORIGIN OF NAME Named after and in honor of the nuclear chemist Glenn T. Seaborg. ISOTOPES There a total of 16 Isotopes of unnilhexium (seaborgium) with half-lives ranging from 2.9 milliseconds to 22 seconds. All are artificially produced and radioactive, and they decay by spontaneous fission (SF) or alpha decay. 

Browne, E. and R. B. Firestone. Table of Radioactive Isotopes, Wiley, New York, 1986. An authoritative compilation of radioactive decay properties. Do note that the spontaneous fission half-lives are missing for several heavy nuclei. 

He and 3He 4He, not only in the crust but also in the Earth, is essentially radiogenic, and has been produced from radioactive decay of U, Th series elements. Only a significant source for nucleogenic 3He in the crust is a reaction 6Li(n, Cf) H( 7 , 2 = 12.3 a) —> 3He, where neutrons are derived from a spontaneous fission of 23SU and from reactions of light elements such as Na, Mg, Al, and Si with a particles emitted from U, Th decays. However, in a very shallow surface region (less than a few meters), the secondary cosmic ray neutrons would be more important. 

All isotopes of Tc are unstable toward fi decay or electron capture, and traces exist in nature only as fragments from the spontaneous fission of U. Thus, while it is not a member of the actinide series, it is radioactive and, therefore, the role of photocatalysis in control of its valence state will be briefly considered here. 

Detection of these elements relies on studying their radioactive decay, which is usually either a-emission or spontaneous fission. A time-correlation process is used in this, a solid-state detector monitors both the time and position of arrival of fusion products. Subsequent decay events at this position give not just the decay information of the atom (half-life, O -particle energy) but also the corresponding information for its decay products, which are recognizable and thus known nuclei. This therefore gives a history of stepwise decay of the initial product. 

Spontaneous fission (symbol sf) was found in 1940 by Flerov and Petrzhak at Dubna, after fission by neutrons had been discovered in 1938 by Hahn and Strassmann in Berlin. Spontaneous fission is another mode of radioactive decay, which is observed only for high mass numbers A. For the ratio of the probability of spontaneous fission to that of a decay is about 1 10 . It increases with the atomic number Z and the number of neutrons in the nucleus. For Fm the probability of spontaneous fission relative to the total probability of decay is already 92%. 

The major difficulty with synthesizing heavy elements is the number of protons in their nuclei (Z > 92). The large amount of positive charge makes the nuclei unstable so that they tend to disintegrate either by radioactive decay or spontaneous fission. Therefore, with the exception of a few transuranium elements like plutonium (Pu) and americium (Am), most artificial elements are made only a few atoms at a time and so far have no practical or commercial uses. 

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