Uranium longest lived isotope

The element exists as an intermediate in uranium and thorium minerals through their decay. There is no stable isotope. The longest-living isotope has a half-life of 8.3 hours. In the crust of the Earth, the total steady-state mass is estimated at a few tens of grams. Thus astatine is the rarest element (record ). A few atoms of this relative of iodine can be found in all uranium ore. It exhibits certain metallic properties. 

Li, Rb and Cs are of lower abundance and are obtained from silicate minerals. Francium (Fr) is a radioactive element and occurs in very small quantities in uranium minerals. The longest-lived isotope of francium is 223Fr (ty2 = 22 min). 

Promethium occurs in tiny amounts in uranium ores, thus a sample of Congolese pitchblende was found to contain (4 1) x 10 g of " Pm per kg of ore it was formed mainly by spontaneous fission of It is also one of the fission products of uranium-235 and can be obtained from a mixture of lanthanides by ion exchange. The longest-lived isotope is... 

The discovery of Pu has been described in detail by Seaborg in his Plutonium Story (chapter 1 of the book The Transuranium Elements 1958). First, the separation of Pu from Th caused some difficulties, because both elements were in the oxidation state 4-4. After oxidation of Pu(IV) by persulfate to Pu(VI), separation became possible. Pu is produced in appreciable amounts in nuclear reactors (section 14.1), but it has not immediately been detected, due to its low specific activity caused by its long half-life. After the discovery of Pu, plutonium gained great practical importance, because of the high fission cross section of Pu by thermal neutrons. Very small amounts of Pu are present in uranium ores, due to (n, y) reaction of neutrons from cosmic radiation with The ratio Pu/ U is of the order of 10 In 1971, the longest-lived isotope of plutonium, Pu (ri/2 = 8.00 lO y) was found by Hoffman in the Ce-rich rare-earth mineral bastnaesite, in concentrations of the order of 10 gAg-... 

The half-lives of the longest-lived isotopes of transuranium elements (Fig. 14.8) show a continuous exponential decrease with increasing atomic number Z. Whereas up to element 103 the half-life is mainly determined by a decay, the influence of spontaneous fission seems to become predominant for elements with Z > 106. The drop model of nuclei predicts a continuous decrease of the fission barrier from about 6 MeV for uranium to about zero for element 110. That means that according to the drop model, elements with Z > 110 are not expected to exist, because normal vibrations of the nuclei should lead to fission. 

Only sodium and potassium are moderately abundant on Earth, and are major elements of life (see Topic J3 ). They occur in many silicates, but weathering reactions at the Earth s surface lead to the dissolution of the very soluble cations, which are common in sea water and are eventually deposited in halide minerals such as NaCl and KC1 (see Topic J2). Li, Rb and Cs are of lower abundance, and obtained from silicate minerals. Francium is radioactive. Its longest-lived isotope Fr has a half-life of only 22 min and occurs in exceedingly small amounts in uranium minerals (see Topics AT,... 

Radium is element number 88, in which all of its isotopes are radioactive hence, what little radium is found on Earth is mostly as a trace element in uranium ores. The most common isotope has a mass number of 226 with a half-life of 1,604 years. The second longest-lived isotope is radium 228, with a half-life of 5.77 years. The other isotopes have much shorter half-lives ranging from microseconds to days. Radium is constantly being formed as part of the radioactive decay series of uranium and thorium. Because it decays so quickly, however, only minute quantities of radium ever exist at any one time. 

Astatine is the heaviest member of group 17 and is known only in the form of radioactive isotopes, all of which have short half-lives. The longest lived isotope is At (fi = 8.1 h). Several isotopes are present naturally as transient products of the decay of uranium and thorium minerals At is formed from the 3-decay of Po, but the path competes with decay to Pb (the dominant decay, see Figure 2.3). Other isotopes are artificially prepared, e.g. "At (an a-... 

Mg and Ca are the eighth and sixth most abundant elements in Earth s crust at 2.5 and 3.6 percent, respectively. Be, Sr, and Ba comprise 0.001, 0.025, and 0.05 percent, respectively. Ra is radioactive, and since its longest-lived isotope Ra has a half-life of 1,600 years, there is very little Ra in Earth s crust. It is nonetheless present because Ra is continuously formed by the decay of uranium ( U). Alkali earth elements are... 

CaS04 2 H2O) in plasters to decorate their tombs. These two alkaline earths are among the most abundant elements in the Earth s crust (calcium is fifth and magnesium sixth, by mass), and they occur in a wide variety of minerals. Strontium and barium are less abundant but like magnesium and calcium, they commonly occur as sulfates and carbonates in their mineral deposits. Beryllium is fifth in abundance of the alkaline earths and is obtained primarily from the mineral beryl, 863 2(8103)6. All radium isotopes are radioactive (the longest lived isotope is Ra, with a half-life of 1600 years). Pierre and Marie Curie first isolated radium from the uranium ore pitchblende in 1898. Physical properties of the alkaline earths are given in Table 8.4. 

This reaction is the lission of uranium nucleus by protons accelerated to very high energies. When such a fast proton hits uranium nucleus it produces something like an explosion with ejection of a multitude of particles, namely, six protons and 21 neutrons. Of course, the reaction is not due to a blind chance but is based on careful theoretical predictions. Uranium may be replaced with thorium. The reaction product, francium-212, for some time was considered to be the longest-lived isotope (a half-life of 23 min) but later the half-life was found to be only 19 min. 

The 4 + 3 chain is the only one that (barely) includes every element from uranium to thallium. Although included, francium and especially astatine are very minor components. The parent, 704 X 10 year has a half-life considerably smaller than the 4,500 x 10 year age of the Earth. It is long enough for significant amounts (0.720% of the atoms in natural uranium) to remain. The chain includes by far the longest-lived isotopes of protactinium (32.8 x 10 year Pa) and actinium (21.77 year Ac). 

On the earth, the most likely source of macroscopic amounts for technetium and promethium is the reprocessing of irradiated uranium and plutonium from fission reactors. This mechanism produces only a few, and not the longest-lived, isotopes. 

The longest-lived isotope of americium is Am with a half-life of about 7370 years. Other relatively long-lived isotopes are Am and Am. Americium can also form four oxidation states in aqueous solution trivalent, tetravalent, pentavalent and hexavalent. No data are available for the tetravalent and hex-avalent oxidation states and only a relatively small amount for both the trivalent and pentavalent states. The behaviour of all oxidation states should be reasonably similar to those of uranium, neptunium and plutonium. 

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