Cerium isotope

Radiocerium absorbed into the systemic circulation will be transported by blood proteins and be deposited predominantly in liver and bone. Deposition fractions will be about 0.45 for liver, 0.35 for bone, and 0.1 for other soft tissues with the remainder excreted in urine and feces. The retention times in liver and bone are long compared to the radioactive half-lives of the cerium isotopes. Therefore, their effective biological half-times in these organs will be approximately equal to their physical half-lives. Experimental data on internal organ distri-... 

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.

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. 

The appearance of non-volatile fission products or actinide isotopes in the coolant can indicate the presence of fuel rod defects with a direct contact between the fuel and liquid water. This can occur with large-sized defects, in particular in comparatively cold regions of the fuel rod at the vertical or horizontal periphery of the reactor core. However, any statement in this regard can only be based on radionuclides that are not present in the coolant as a remnant from preceding transients this means that in a PWR Cs or Cs are not appropriate indicators for such fuel rod failures. The requirements are in principle fulfilled by Np, which is a reliable indicator for defects with fuel-to-water contact, as are ruthenium and cerium isotopes, as well. However, because of the complex behavior of these radionuclides in the coolant (adsorption on suspended corrosion products and deposition on primary circuit surfaces), only qualitative assessments can be made, which means that a quantitative evaluation of the number of fuel rods showing... 

In general, release of actinide isotopes from failed fuel rods and their subsequent behavior in the primary circuit is very similar to that of certain fission products, e. g. of cerium isotopes. For this reason, the y-emitting cerium isotopes which can easily be measured in the coolant by y spectrometry, can serve as a suitable indicator for early recognition of higher releases of actinides to the coolant. The release behavior of the actinides from failed mixed-oxide fuel rods to the coolant is almost identical to that from uranium fuel rods. This means that in both cases the U Pu... 

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. 

Accurate atomic weight values do not automatically follow from precise measurements of relative atomic masses, however, since the relative abundance of the various isotopes must also be determined. That this can be a limiting factor is readily seen from Table 1.3 the value for praseodymium (which has only 1 stable naturally occurring isotope) has two more significant figures than the value for the neighbouring element cerium which has 4 such isotopes. In the twelve years since the first edition of this book was published the atomic weight values of no fewer than 55 elements have been improved, sometimes spectacularly, e.g. Ni from 58.69( 1) to 58.6934(2). 

Cerium is the most abundant rare earth metal. Pure cerium ignites when scratched by even a soft object. It has four known isotopes l36Ce (atomic mass = 135.907 amu), 138Ce (atomic mass = 137.905 amu), 140Ce (atomic mass = 139.905 amu), and 142Ce (atomic mass = 141.909 amu). Ce-140 and Ce-142 are fairly abundant. Which is the more abundant isotope ... 

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,... 

Lebedeva, G. A. (1966). Some findings on the development of cirrhosis of the liver under the influence of radioactive cerium, page 463 in Distribution and Biological Effects of Radioactive Isotopes, Report No. AEC-tr-6944 (National Technical Information Service, Springfield, Virginia). 

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. 

Radiation activity levels for a dirty bomb made with spent fuel depend on the age of the fuel. A simple rule to consider is that any radionuclide will decay to 1% of the original concentration after seven half-lives or will decay to insignificant concentrations after ten half-lives. Therefore, if a fuel rod is removed from a reactor several days before detonation in a dirty bomb, all the isotopes listed in Table 2.1 will likely be present. If a fuel rod was last used in a reactor 5 years before detonating a bomb, ruthenium-106 and cerium-144 will have decayed to insignificant concentrations. 

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. 

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-... 

Fig. 5.5. Decomposition of Solar System abundances into r and s processes. Once an isotopic abundance table has been established for the Solar System, the nuclei are then very carefully separated into two groups those produced by the r process and those produced by the s process. Isotope by isotope, the nuclei are sorted into their respective categories. In order to determine the relative contributions of the two processes to solar abundances, the s component is first extracted, being the more easily identified. Indeed, the product of the neutron capture cross-section with the abundance is approximately constant for aU the elements in this class. The figure shows that europium, iridium and thorium come essentially from the r process, unlike strontium, zirconium, lanthanum and cerium, which originate mainly from the s process. Other elements have more mixed origins. (From Sneden 2001.)... 

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. 

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