|
Plutonium-242
Plutonium-242 (242Pu or Pu-242) is one of the isotopes of plutonium, the second longest-lived, with a half-life of 375,000 years. The half-life of 242Pu is about 15 times that of 239Pu; so it is one-fifteenth as radioactive, and not one of the larger contributors to nuclear waste radioactivity. 242Pu's gamma ray emissions are also weaker than those of the other isotopes. It is not fissile (but it is fissionable by fast neutrons) and its neutron capture cross section is also low. In the nuclear fuel cycle Plutonium-242 is produced by successive neutron capture on 239Pu, 240Pu, and 241Pu. The odd-mass isotopes 239Pu and 241Pu have about a 3/4 chance of undergoing fission on capture of a thermal neutron and about a 1/4 chance of retaining the neutron and becoming the following isotope. The proportion of 242Pu is low at low burnup but increases nonlinearly. Plutonium-242 has a particularly low cross section for thermal neutron capture; and it takes three neutron absorptions to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Plutonium
Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940. Twenty plutonium radioisotopes have been characterized. The most stable are plutonium-244 with a half-life of 80.8 million years, plutonium-242 with a half-life of 373,300 years, and plutonium-239 with a half-life of 24,110 years. All of the remaining radioactive isotopes have half-lives that are less than 7,000 years. This element also has eight meta states; all have half-lives of less than one second. The isotopes of plutonium range in atomic weight from 228.0387 u (228Pu) to 247.074 u (247Pu). The primary decay modes before the most stable isotope, 244Pu, are spontaneous fission and alpha emission; the primary mode after is beta emission. The p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, it is fissionable by fast neutrons, and is ''fertile'', meaning it can be transmuted to fissile plutonium-239. 238U cannot support a chain reaction because inelastic scattering reduces neutron energy below the range where fast fission of one or more next-generation nuclei is probable. Doppler broadening of 238U's neutron absorption resonances, increasing absorption as fuel temperature increases, is also an essential negative feedback mechanism for reactor control. Around 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41 seconds (4.468 years, or 4.468 billion years). Due to its natural abundance and half-life relative to other radioactive elements, 238U produces ~40% of the radioactive heat pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pu-239
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years. Nuclear properties The nuclear properties of plutonium-239, as well as the ability to produce large amounts of nearly pure 239Pu more cheaply than highly enriched weapons-grade uranium-235, led to its use in nuclear weapons and nuclear power plants. The fissioning of an atom of uranium-235 in the reactor of a nuclear power plant produces two to three neutrons, and these neutrons can be absorbed by uranium-238 to produce plutonium-239 and other isotopes. Plutonium-239 can also absorb neutrons and fission along with the uranium-235 in a reactor. Of all the common nuclear fuels ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pu-241
Plutonium-241 (241Pu or Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes (especially 239Pu), 241Pu is fissile, with a neutron absorption cross section about one-third greater than that of 239Pu, and a similar probability of fissioning on neutron absorption, around 73%. In the non-fission case, neutron capture produces plutonium-242. In general, isotopes with an odd number of neutrons are both more likely to absorb a neutron, and more likely to undergo fission on neutron absorption, than isotopes with an even number of neutrons. Decay to americium 241Pu has a half-life of 14 years, corresponding to a decay of about 5% of 241Pu nuclei over a one-year period. The longer spent nuclear fuel waits before reprocessing, the more 241Pu decays to americium-241, which is nonfissile (although fissionable by fast neutrons) and an alpha emitter with a halflife of 432 years; 241Am is a major contributor to the radioactivity o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Burnup
In nuclear power technology, burnup (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per initial metal atom) or %FIFA (fissions per initial fissile atom) as well as, preferably, the actual energy released per mass of initial fuel in gigawatt-days/metric ton of heavy metal (GWd/tHM), or similar units. Measures of burnup Expressed as a percentage: if 5% of the initial heavy metal atoms have undergone fission, the burnup is 5%FIMA. If these 5% were the total of 235U that were in the fuel at the beginning, the burnup is 100%FIFA (as 235U is fissile and the other 95% heavy metals like 238U not). In reactor operations, this percentage is difficult to measure, so the alternative definition is preferred. This can be computed by multiplying the thermal power of the plant by the time of operation and dividing by the mass of the initial f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Actinides
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. The 1985 IUPAC ''Red Book'' recommends that ''actinoid'' be used rather than ''actinide'', since the suffix ''-ide'' normally indicates a negative ion. However, owing to widespread current use, ''actinide'' is still allowed. Since ''actinoid'' literally means ''actinium-like'' (cf. ''humanoid'' or ''android''), it has been argued for semantic reasons that actinium cannot logically be an actinoid, but IUPAC acknowledges its inclusion based on common usage. All the actinides are f-block elements, except the final one (lawrencium) which is a d-block element. Actinium has sometimes been considered d-block instead of lawrencium, but the cla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spontaneous Fission
Spontaneous fission (SF) is a form of radioactive decay that is found only in very heavy chemical elements. The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 56 (e.g., iron-56); spontaneous breakdown into smaller nuclei and a few isolated nuclear particles becomes possible at greater atomic mass numbers. History By 1908, physicists understood that alpha decay involved ejection of helium nuclei from a decaying atom. Like cluster decay, alpha decay is not typically categorized as a process of fission. The first nuclear fission process discovered was fission induced by neutrons. Because cosmic rays produce some neutrons, it was difficult to distinguish between induced and spontaneous events. Cosmic rays can be reliably shielded by a thick layer of rock or water. Spontaneous fission was identified in 1940 by Soviet physicists Georgy Flyorov and Konstantin Petrzhak by their observations of uranium in the Moscow Metro Dinamo stati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium Series
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached. Decay stages are referred to by their relationship to previous or subsequent stages. A ''parent isotope'' is one that undergoes decay to form a ''daughter isotope''. One example of this is uranium (atomic number 92) decaying into thorium (atomic number 90). The daughter isotope may be stable or it may decay to form a daughter isotope of its own. The daughter of a daughter isotope is sometimes called a ''granddaughter isotope''. The time it takes for a single parent atom to decay to an atom of its daughter isotope can vary widely, not only between different parent-daughter pairs, but also randomly between identical pairings of parent ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alpha Decay
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucleus of a helium-4 atom, which consists of two protons and two neutrons. It has a charge of and a mass of . For example, uranium-238 decays to form thorium-234. While alpha particles have a charge , this is not usually shown because a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms. Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum and the nuclides are therefore unstable toward spont ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fast Reactor
A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons (carrying energies above 1 MeV or greater, on average), as opposed to slow thermal neutrons used in thermal-neutron reactors. Such a fast reactor needs no neutron moderator, but requires fuel that is relatively rich in fissile material when compared to that required for a thermal-neutron reactor. Around 20 land based fast reactors have been built, accumulating over 400 reactor years of operation globally. The largest of this was the Superphénix Sodium cooled fast reactor in France that was designed to deliver 1,242 MWe. Fast reactors have been intensely studied since the 1950s, as they provide certain decisive advantages over the existing fleet of water cooled and water moderated reactors. These are: * More neutrons are produced when a fission occurs, resulting from the absorption of a fast neutron, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Reactor
A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons. ("Thermal" does not mean hot in an absolute sense, but means in thermal equilibrium with the medium it is interacting with, the reactor's fuel, moderator and structure, which is much lower energy than the fast neutrons initially produced by fission.) Most nuclear power plant reactors are thermal reactors and use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons to low-velocity, thermal neutrons. Neutrons are uncharged, this allows them to penetrate deep in the target and close to the nuclei,Squires, G.L. (2012, March 29). Introduction of the Theory of Thermal Neutron Scattering. https://books.google.com/books?hl=en&lr=&id=KUVD8KJt7_0C&oi=fnd&pg=PR9&dq=thermal-neutron+reactor&ots=1tn_4dppSF&sig=QDWkMU5-iW8_4GCXjItypUchKBQ#v=onepage&q=thermal-neutron%20reactor&f=false thus scattering neutrons by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Californium
Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding curium with alpha particles ( helium-4 ions). It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all elements that have been produced in amounts large enough to see with the naked eye (after einsteinium). The element was named after the university and the U.S. state of California. Two crystalline forms exist for californium at normal pressure: one above and one below . A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Californium compounds are dominated by the +3 oxidation state. The most stable of californium's twenty known isotopes is californium-251, with a half-life of 898 years. This short half-life means the element is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
_Halflife_of_Radionulides_depending_on_Z²_to_A_ratio.png "Click for more on -> Spontaneous Fission")
