Nuclear reactions radioactive isotopes, producing

The study of electron transfer reactions began in earnest when radioactive isotopes, produced for nuclear research and the atom bomb program during World War II, became accessible. Glen Seaborg, in a 1940 review of artificial radioactivity, noted the first attempt to measure the self-exchange reaction between aqueous iron(III) and iron(II), equation (1.9).1"... 

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... 

Its terrestrial abundance has been estimated as 2x10" ppm, which corresponds to a total of only 15g in the top 1km of the earth s crust. Other isotopes have since been produced by nuclear reactions but all have shorter half-lives than Fr, which decays by energetic emission, t j2 21.8 min. Because of this intense radioactivity it is only possible to work with tracer amounts of the element. 

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. 

The discoveries of Becquerel, Curie, and Rutherford and Rutherford s later development of the nuclear model of the atom (Section B) showed that radioactivity is produced by nuclear decay, the partial breakup of a nucleus. The change in the composition of a nucleus is called a nuclear reaction. Recall from Section B that nuclei are composed of protons and neutrons that are collectively called nucleons a specific nucleus with a given atomic number and mass number is called a nuclide. Thus, H, 2H, and lhO are three different nuclides the first two being isotopes of the same element. Nuclei that change their structure spontaneously and emit radiation are called radioactive. Often the result is a different nuclide. 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

Finally, P also differs from other elements in that it is overwhelmingly dominated by a single, stable isotopic form containing 15 protons and 16 neutrons. There are only two naturally occurring radioactive forms of P P and P, which are produced in the atmosphere by nuclear reactions with argon. A small amount of P is... 

Cerium, an element in the lanthanide series, has a number of radioactive isotopes. Several of these are produced in abundance in nuclear fission reactions associated with nuclear industry operations or detonation of nuclear devices. This report summarizes our present knowledge of the relevant physical, chemical, and biological properties of radiocerium as a basis for establishing radiation protection guidelines. 

As a result of slow (thermal) neutron irradiation, a sample composed of stable atoms of a variety of elements will produce several radioactive isotopes of these activated elements. For a nuclear reaction to be useful analytically in the delayed NAA mode the element of interest must be capable of undergoing a nuclear reaction of some sort, the product of which must be radioactively unstable. The daughter nucleus must have a half-life of the order of days or months (so that it can be conveniently measured), and it should emit a particle which has a characteristic energy and is free from interference from other particles which may be produced by other elements within the sample. The induced radioactivity is complex as it comprises a summation of all the active species present. Individual species are identified by computer-aided de-convolution of the data. Parry (1991 42-9) and Glascock (1998) summarize the relevant decay schemes, and Alfassi (1990 3) and Glascock (1991 Table 3) list y ray energy spectra and percentage abundances for a number of isotopes useful in NAA. 

In 1937 the element of the atomic number 43 was discovered by Perrier and Segre who showed that radioactivity obtained by irradiation of molybdenum with deuterons was due to isotopes of the missing element ekamanganese. The metastable isomers Tc and " Tc had been produced by the nuclear reactions... 

ISOTOPES There are 50 Isotopes of Yttrium. Only one Is stable (Y-89), and It constitutes 100% of the element s natural existence on Earth. The other Isotopes range from Y-77 to Y-108 and are all produced artificially In nuclear reactions. The radioactive Isotopes have half-lives ranging from 105 nanoseconds to 106.65 days. 

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. 

Neither californium nor its compounds are found in nature. All of its isotopes are produced artificially in extremely small amounts, and all of them are extremely radioactive. All of its isotopes are produced by the transmutation from other elements such as berkelium and americium. Following is the nuclear reaction that transmutates californium-250 into cahfornium-252 Cf + (neutron and A, gamma rays) — Cf + (neutron and A, gamma rays) —> Cf. 

Indeed, this happens every moment in the Earth s atmosphere. The upper atmosphere is bombarded with cosmic rays fast-moving subatomic particles produced by extremely energetic astrophysical processes such as nuclear fusion in the sun. When cosmic rays hit molecules in the atmosphere, they induce nuclear reactions that spit out neutrons. Some of these neutrons react with nitrogen atoms in air, converting them into a radioactive isotope of carbon carbon-14 or radiocarbon , with eight neutrons in each nucleus. This carbon reacts with oxygen to form carbon dioxide. About one in every million million carbon atoms in atmospheric carbon dioxide is C. 

During the late 1960s and early 1970s, neutron activation analysis provided a new way to measure bulk chemical composition. Neutron activation analysis utilizes (n,y) reactions to identify elements. A sample is placed in a nuclear reactor where thermal neutrons are captured by atoms in the sample and become radioactive. When they decay, the radioactive isotopes emit characteristic y-rays that are measured to determine abundances. Approximately 35 elements are routinely measured by neutron activation analysis. A number of others produce radioactive isotopes that emit y-rays, but their half-lives are too short to be useful. Unfortunately, silicon is one of these elements. Other elements do not produce y-ray-emitting isotopes when irradiated with neutrons. There are two methods of using neutron activation to determine bulk compositions, instrumental neutron activation analysis (INAA) and radiochemical neutron activation analysis (RNAA). 

In the activation method an element undergoes nuclear reactions by means of some source producing sufficiently high thermal neutron flux( preferably by a nuclear reactor) to yield radioactive isotopes. These isotopes are usually unstable and return to their ground state by releasing energy in the form of emitted radiations. By measuring these radiations it is possible to identify, in most cases, one or several components in a mixt. Such nuclear transitions are not affected by the state... 

Activation analysis is based on the production of radioactive nuclides by means of induced nuclear reactions on naturally occurring isotopes of the element to be determined in the sample. Although irradiations with charged particles and photons have been used in special cases, irradiation with reactor thermal neutrons or 14 MeV neutrons produced by Cockcroft-Walton type accelerators are most commonly used because of their availability and their high probability of nuclear reaction (cross section). The fundamental equation of activation analysis is given below ... 

The neutral isotope of iodine is an essential element in the human body most of the iodine-127 is located in the thyroid gland. Iodine s radioactive isotope, iodine-131, is readily absorbed in the body, where it becomes concentrated in the thyroid gland and may produce cancers. Exposure to radioactive iodine is an increasing concern since it is produced by fission reactions in nuclear reactors and by nuclear weapons tests. 

Boron is one of the three light elements (Li, Be, B) that are not effectively synthesized by nuclear reactions in stable stars. Its origin in nature must be sought in other astrophysical processes. These involve cosmic-ray collisions with interstellar atoms and neutrino-burst nucleosynthesis in supernova matter. Transient production at the solar center of one of its radioactive isotopes, however, produces energetic neutrinos that have been the easiest of the solar neutrinos to detect. 

Major concern about rapidly increasing levels of radioactive fallout in the environment and in foods developed as a result of the extensive testing of nuclear weapons by the United States and the Soviet Union in the 1950s. Nuclear fission generates more than 200 radioisotopes of some 60 different elements. Many of these radioisotopes are harmful to humans because they may be incorporated into body tissues. Several of these radioactive isotopes are absorbed efficiently by the organism because they are related chemically to important nutrients for example, strontium-90 is related to calcium and cesium-137 to potassium. These radioactive elements are produced by the following nuclear reactions, in which the half-life is given in parentheses ... 

Scientists have learned how to make some isotopes undergo nuclear reactions. Artificial radioactivity is induced by bombardment of certain nuclei with subatomic particles (or atoms), which are produced either by other nuclear reactions or in machines called particle accelerators. For example, the first artificially induced nuclear reaction was produced by Ernest Rutherford (1871-1937) in 1919 ... 

Radioactive xenon (radioxenon) is produced by the fissioning of nuclear material, either via neutron-induced or spontaneous fission, and also via neutron activation or other nuclear reactions involving xenon gas. The most abundant radioactive xenon isotopes in... 

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