Man-made isotopes

Sulfur-35 does not occur in nature it is an artificial or man-made isotope. 

Note that for U and Th measurements, the use of man-made isotopes that are no longer existing in natural samples ( h and U) can minimize the magnification factor. In the above cases, only 0.08% and 0.03% increase in the relative uncertainties for U and Th concentrations. 

There are two additional modes of decay that are important. These, however, are exhibited only by man-made isotopes, in particular by those having low neutron/proton ratios (for example, eC10,8015, and i2Mg 3). The net effect of both types of decay is opposite to that in decay. A proton is converted to a neutron, the atomic number drops by a single unit, but there is no change in mass number. 

There are four naturally occurring isotopes of iron. Their abundances and atomic masses are fisted in Table 2 together with data for other man-made isotopes of iron whose atomic masses have been determined with precision. The most abundant of the natural isotopes is Fe, and this is also the most stable nuclear configuration of all the elements in terms of nuclear binding energy per nucleon. Its stability, viewed in terms of nuclear equihbria established in the last moments of supemovae, perhaps explains its widespread occurrence in the cosmos. The isotope Fe has several applications, most notably in Mossbauer spectroscopy, and it has proved to be... 

Many of the naturally occurring and man-made isotopes are unstable. The nuclei of these isotopes decay to more stable forms by one or more of the processes shown in Table 6-1. Such isotopes are called "radioactive... 

This equation represents a nuclear transmutation, the conversion of one element into another. Nuclear transmutation is a process human beings control. S-35 is an isotope of sulfur that doesn t exist in nature. It s a man-made isotope. Alchemists, those ancient predecessors of chemists, dreamed... 

Uranium, element 92, is a member of the actinide family of the periodic table, which includes elements 89-104. It has 3 primordial and 12 artificial or man-made isotopes, all of which are radioactive. The naturally occurring uranium series is headed by which subsequently decays... 

Some man-made isotopes and naturally-occurring materials emit ionising radiation, all of which can be harmful in excessive doses. 

In addition, there are ten, short-lived man-made isotopes of which Se, Se, and Se are the most used in neutron activation, radiology, etc. The isotope used in medical and biological tracer studies, is Se usually in the form of Se selenomethionine [33]. 

Tritium [15086-10-9] the name given to the hydrogen isotope of mass 3, has symbol or more commonly T. Its isotopic mass is 3.0160497 (1). Moletecular tritium [10028-17-8], is analogous to the other hydrogen isotopes. The tritium nucleus is energetically unstable and decays radioactively by the emission of a low-energy P particle. The half-life is relatively short (- 12 yr), and therefore tritium occurs in nature only in equiUbrium with amounts produced by cosmic rays or man-made nuclear devices. 

Americium (pronounced,, am-8- ris(h)-e-8m) is a man-made, radioactive, actinide element with an atomic number of 95. It was discovered in 1945. Actinides are the 15 elements, all of whose isotopes are radioactive starting with actinium (atomic number 89), and extending to lawrencium (atomic number 103). When not combined with other elements, americium is a silvery metal. Americium has no naturally occurring or stable isotopes. There are two important isotopes of... 

Chromium in the crystalline form is a steel-gray, lustrous, hard metal characterized by an atomic weight of 51.996, an atomic number of 24, a density of 7.14 g/cm3, a melting point of 1857°C, and a boiling point of 2672 C. Four chromium isotopes occur naturally Cr-50 (4.3%), -52 (83.8%), -53 (9.6%), and -54 (2.4%), and seven are man-made. Elemental chromium is very stable but is not usually found pure in nature. Chromium can exist in oxidation states ranging from -2 to +6, but is most frequently found in the environment in the trivalent (+3) and hexavalent (+6) oxidation states. The +3 and +6 forms are the most important because the +2, +4, and +5 forms are unstable and are rapidly converted to +3, which in turn is oxidized to +6 (Towill et al. 1978 Langard and Norseth 1979 Ecological Analysts 1981 USPHS 1993). 

Ellis et al. (2003) reduced Se(Vl) with anaerobic sediment slurries in order to approximate conditions in natural wetlands. Sediments and waters from the northern reach of the San Francisco estuary, the San Luis Drain, and a man-made wetland, all in California, were used. Reduction was apparently carried out by microbes, as autoclaved control experiments exhibited little reduction. Despite differences between the sediments and concentrations of Se(Vl) used in the various experiments, ese(vi)-se(iv) varied little, from 2.6%o to 3.1%o. The starting Se(Vl) concentrations of three experiments ranged from 230 nmol/L to 430 nmol/L that of a fourth experiment was much greater, at 100 pmol/L. Thus, it appears based on these few data that signihcant Se isotope fractionations persist to very low concentrations, though extrapolation to seawater concentrations (e.g., 1 nmol/L) would be risky. 

ISOTOPES There are 36 isotopes of tungsten. Five are naturally stable and therefore contribute proportionally to tungsten s existence on Earth, as follows W-180 = 0.12%, W-182 = 26.50%, W-183 = 14.31%, W-184 = 30.64%, and W-186 = 28.43%. The other 31 isotopes are man-made in nuclear reactors and particle accelerators and have half-lives ranging from fractions of a second to many days. 

ISOTOPES There are 19 isotopes of nitrogen, two of which are stable. The stable ones and their proportion to the natural abundance of nitrogen on Earth follow N-14 = 99.634% and N-15 = 0.366%. The other 17 isotopes are radioactive and man-made in nuclear reactors and have half-lives ranging from a few nanoseconds to 9.965 minutes. 

Astatine is located just below iodine, which suggests that it should have some of the same chemical properties as iodine, even though it also acts more hke a metal or semimetal than does iodine. It is a fairly heavy element with an odd atomic number, which assisted chemists in learning more about this extremely rare element. The 41 isotopes are man-made in atomic reactors, and most exist for fractions of a second. The elements melting point is about 302°C, its boiling point is approximately 337°C, and its density is about 7g/cm. ... 

ISOTOPES There are a total of 37 isotopes of krypton. Six of these are stable Kr-78, Kr-80, Kr-82, Kr-83, Kr-84, and Kr-86. The isotope Kr-78 has such a long half-life (0.9x1 years) that it is considered stable even though it contributes only 0.35% to the natural krypton in the Earth s atmosphere. All the others are radioactive, man-made by-products of nuclear power plants and radioactive isotopes with half-lives ranging from 107 nanoseconds to 2.29x 10+ years. 

Americium does not exist in nature. All of its isotopes are man-made and radioactive. Americium-241 is produced by bombarding plutonium-239 with high-energy neutrons, resulting in the isotope plutonium-240 that again is bombarded with neutrons and results in the formation of plutonium-241, which in turn finally decays into americium-241 by the process of beta decay. Both americium-241 and americium-243 are produced within nuclear reactors. The reaction is as follows Pu + (neutron and X gamma rays) —> " Pu + (neutron and X gamma rays) —> Pu—> Am + beta minus ([ -) followed by " Am—> jNp-237 + Hej (helium nuclei). 

ISOTOPES There are 23 isotopes of curium. All of them are man-made and radioactive. The most stable is curium-247, with a half-life of 1.56xl0+ years (156,600,000 years), which through alpha decay transmutates into plutonium-243. 

There is no natural curium on Earth. All of its isotopes are man-made and artificially produced through nuclear reactions with other elements. The curium isotope Cm-242 was first produced by bombarding plutonium-239 with helium nuclei (alpha particles), which contributed neutrons that changed Pu to g Cm. 

Italian scientists Emilio Segre and Carlo Perrier Discovered when molybdenum was bombarded with the nuclei of a hydrogen isotope the first man-made element, hence its name, which means artificial in Greek. 

Berkelium does not occur in nature. The element was synthesized in 1949 at the Lawrence Berkeley Laboratory in Berkeley, California hy Thompson, Ghiorso and Seahorg (Thompson, S.G., Ghiorso, A. and G. T. Seahorg. 1950. Phys. Rev., 77, 838). It has 12 isotopes. It is the fifth man-made transuranium element. Presently, the element has no commercial apphcation. 

Symbol Fm atomic number 100 atomic weight 257 a man-made transuranium radioactive element of the actinide series electron configuration [Rn]5/i27s2 oxidation state -1-3 sixteen isotopes are known most stable isotope Fm-257, ti/2 100.5 days. 

Symbol Md atomic number 101 atomic weight (most stable isotope) 257 a man-made radioactive transuranium element an inner-transition element of actinide series electron configuration [Rn]5/i37s2 valence +2, -i-3. Isotopes, half-lives and their decay modes are ... 

Symbol Np atomic number 93 atomic weight 237 (most stable isotope) a man-made transuranium radioactive element actinide series electron configuration [Rn]5/" 6di7s2 oxidation states +3, +4, -i-5 and +6 most stable valence... 

Symbol Pu atomic number 94 atomic weight 244 an actinide series transuranium element a man-made radioactive element electron configuration [Rn]5/ 7s2 partially filled f suhsheU valence states +3, +4, -i-5, +6 eighteen isotopes in the mass range 228-230, 232-246 aU isotopes radioactive the longest lived isotope Pu-244, ti/2 8.2x10 year the shortest hved isotope Pu-233, ti/2 20.9 minute. 

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