Isotopes of cerium

The masses of the naturally occurring isotopes for lanthanum and cerium are shown. For lanthanum, the isotope at 138 is only present in 0.09% natural abundance and is isobaric with Ce. For this reason the isotope La is used to measure the amount of lanthanum. Similarly, Ce and Ce are present in low abundance "Ce is present in greatest abundance and is used to measure the amount of cerium. Another isotope of cerium, C, although quite abundant, is isobaric with Nd and is therefore not used for measurement. 

Most of the radioactive isotopes of cerium have very short physical half-lives and do not normally represent a radiological hazard to humans. Only the three longer-lived isotopes, 141Ce, l3Ce, and H4Ce,... 

ISOTOPES There are 44 Isotopes of cerium, four of which are considered stable. Ce-140 accounts for most of the cerium (88.450%) found In the Earth s crust, and Ce-138 makes up just 0.251% of the element In the crust. There are two Isotopes with half-lives long enough to be considered stable Ce-136 (0.185%), with a half-life of 0.7x10+ years, and Ce-142 (11.14%), with a half-life of 5x10+ years. All the other Isotopes are radioactive with half-lives ranging from 150 nanoseconds to 137.641 days. All are made artificially. 

There is one radioactive isotope of cerium that is used in medicine. It is Ce-l4l, with a half-life of 32,641 days. 

Four naturally occurring isotopes of cerium have been discovered cerium-136, cerium-138, cerium-140, and cerium-142. The last of these isotopes is radioactive. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element s name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. A radioactive isotope is one that breaks apart and gives off some form of radiation. 

Thirty-three radioactive isotopes of cerium have also been made. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. None of the radioactive isotopes of cerium has any commercial use. 

Fig. 17. Biological model recommended for describing the uptake and retention of cerium by humans after inhalation or ingestion. Numbers in parentheses give the fractions of the material in the originating compartments which are cleared to the indicated sites of deposition. Clearance from the pulmonary region results from competition between mechanical clearances to the lymph nodes and gastrointestinal tract and absorption of soluble material into the systemic circulation. The fractions included in parentheses by the pulmonary compartment indicate the distribution of material subject to the two clearance rates however, these amounts will not be cleared in this manner if the material is previously absorbed into blood. Transfer rate constants or functions, S(t), are given in fractions per unit time. Dashed lines indicate clearance pathways which exist but occur at such slow rates as to be considered insignificant compared to radioactive decay of the cerium isotopes.

Moskalev, Yu.I. (1961a). Effect of pH of initial solution on distribution of cerium-144, page 191 in Distribution, Biological Effects and Migration of Radioactive Isotopes, Report No. AEC-tr-7512, Lebedinskii, A. V. and Moskalev, Yu.I., Eds. (National Technical Information Service, Springfield, Virginia). 

Three groups had roles in the discovery of nobelium. First, scientists at the Nobel Institute of Physics in Stockholm, Sweden, used a cyclotron to bombard Cu-244 with heavy carbon gC-13 (which is natural carbon-12 with one extra neutron). They reported that they produced an isotope of element 102 that had a half-life of 10 minutes. In 1958 the team at Lawrence Laboratory at Berkeley, which included Albert Ghiorso, Glenn Seaborg, John Walton, and Torbjorn Sikkeland, tried to duplicate this experiment and verify the results of the Nobel Institute but with no success. Instead, they used the Berkeley cyclotron to bombard cerium-... 

Symbol Nd atomic number 60 atomic weight 144.24 a rare earth lanthanide element a hght rare earth metal of cerium group an inner transition metal characterized by partially filled 4/ subshell electron configuration [Xe]4/35di6s2 most common valence state -i-3 other oxidation state +2 standard electrode potential, Nd + -i- 3e -2.323 V atomic radius 1.821 A (for CN 12) ionic radius, Nd + 0.995A atomic volume 20.60 cc/mol ionization potential 6.31 eV seven stable isotopes Nd-142 (27.13%), Nd-143 (12.20%), Nd-144 (23.87%), Nd-145 (8.29%), Nd-146 (17.18%), Nd-148 (5.72%), Nd-150 (5.60%) twenty-three radioisotopes are known in the mass range 127-141, 147, 149, 151-156. 

The berkelium (IV) extraction coefficients have been determined by stripping solvents previously loaded with tetravalent cerium and berkelium in the presence of sodium bismuthate. Sodium bismuthate has been found to be an efficient oxidizing agent for trivalent cerium. Because of its small solubility it does not affect the distribution coefficients of tetravalent cerium. These two properties have been demonstrated by comparing the distribution coefficients of cerium (IV) measured by spectrophotometry with those of cerium oxidized by sodium bismuthate and measured by beta counting of the cerium isotope tracer. The data are summarized in Table I and indicate no real difference in the distribution coefficients of cerium obtained by these two methods when using trilaurylmethylammonium salts-carbon tetrachloride as solvent. 

Fission yields of the stable and long-lived isotopes of xenon, cesium, barium, cerium, neodymium, samarium, krypton, rubidium, strontium, zirconium, molybdenum, ruthenium, have been measured mass spectro-metrically for the thermal neutron fission of U23B (40, 61, 90), U233 (4, SI, 61, 82, 100), and Pu239 (32, 61, 66, 124). In addition, the relative yields of the xenon and krypton isotopes produced in the fast neutron fission (fission spectrum neutrons) of U238 and Th232 (64, US) have been determined. 

Challenger and Masters (7) presented excellent evidence to support their viewpoint that the increase in G(Cem) induced by nitrate ion was because of the oxidation of nitrate ion by OH radical nitrate ion simultaneously reduced the G-value for isotopic exchange between radioactive cerium (III) and inactive cerium (IV) induced by oxidation of cerium-(III) by OH radical. Although we previously presented (15, 23) excellent evidence that any reaction of OH with nitrate ion could not be the cause of the increase in G(Cem), no alternative mechanism was previously proposed for the isotopic exchange results of Challenger and Masters (7). We now propose that the lower G-value for cerium (III)-cerium(IV) exchange observed in 1.0M nitric acid is caused by the reaction of a significant fraction of the OH and N03 radicals with nitrous acid. 

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