Calcium nuclides

What nuclide is produced when (a) calcium-41 undergoes electron capture (b) oxygen-15 undergoes positron emission ... 

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Isotope Methods. The isotopes of calcium have relatively short half-lives and are readily counted using liquid scintillation or gamma counters as appropriate to the nuclide. Calcium isotopes may be quantitated in the excreta, blood, tissues or in the whole body. This has made them useful for many nutritional metabolic studies. However, because of safety concerns, radioactive isotopes are cumbersome to work with and many researchers are unwilling to administer them to human beings. This has limited the use of isotopes to those studies in which alternate methods are not available or are imprecise. Methodologies for stable isotopes of calcium, which may be safely used in human being, are becoming available for use in metabolism studies. These will be practical alternatives to radioactive isotopes in the future. 

Using nuclide-stability rules, form a hypothesis that explains why calcium-40 should be a more stable nuclide than potassium-40. 

As evidenced by the tremendous power of nuclear bombs, nuclear reactions involve quite a lot of energy. In the laboratory, researchers fabricate nuclides with the aid of special, high-energy equipment such as reactors in which nuclear reactions can take place, or particle accelerators in which particles such as protons are accelerated to high speed and crash into one another, or some other target. For example, in 2006, researchers at the Joint Institute for Nuclear Research in the Russian Federation and the Lawrence Livermore National Laboratory in California synthesized isotopes of element 118 for the first time. To make the new isotope, researchers smashed calcium atoms into a target made of californium (which has an atomic number of 98). These new isotopes decayed quickly. (Element 118 and other recently discovered elements have not yet been named.)... 

The chemical properties of the radiation source. When a radioactive nuclide is ingested into the body, its effectiveness in causing damage depends on its residence time. For example, f Kr and gSr are both /3-particle producers. However, since krypton is chemically inert, it passes through the body quickly and does not have much time to do damage. Strontium, being chemically similar to calcium, can collect in bones, where it may cause leukemia and bone cancer. 

The extraction of transuranic elements has been made by co-precipi-tation in several ways (5,6). We use either one of two methods, depending on what other nuclides are also sought in the sample. The first method is co-precipitation with 0.5-1.0 g iron as hydroxide at pH 9-10 using ammonium hydroxide while the second method is co-precipitation with calcium and strontium oxalate at pH 5-6 using oxalic acid. There are about 22 g calcium and 0.44 g strontium in 55 1. of open-ocean seawater. Because Sr is usually measured in the same seawater sample, we normally add 2 g strontium to that which is naturally present. 

One of the requirements of any nuclear facility is to monitor the effluent uxiste water to show compliance with existing standards. This paper describes a sequential procedure for the separation of the transuranic elements from water samples up to 60 1. The elements of interest are coprecipitated with calcium fluoride and then individually separated using a combination of ion exchange and solvent extraction, with a final sample preparation by electrodeposition. Alpha spectrometry of these samples allows the measurement of neptunium, plutonium, and transplutonium nuclides at sub-fCi/l, levels. 

The procedure involves the coprecipitation of the transuranic nuclides on calcium fluoride from acid solution after reduction of the plutonium and neptunium with bisulfite. The calcium fluoride precipitate is dissolved in aluminum nitrate-nitric acid solution and the plutonium and neptunium separated on an ion-exchange resin column. The column... 

Procedure. The procedure is outlined in Figure 1. The first step is the separation of the desired nuclides by coprecipitation with calcium fluoride. The optimum nitric acid concentration for effective carrying on calcium fluoride is between O.IN and 0.2N. Reduction of the plutonium to Pu(III) was necessary to obtain quantitative carrying on calcium fluoride. Plutonium (IV) is known to form colloidal or non-ionic species in neutral solution, and in this form may be incompletely carried by calcium fluoride. Bisulfite was effective and gave complete reduction in 3.5 hr at 50° C or overnight at room temperature. The concentration of calcium must be at least 0.1 mg/ml for quantitative carrying. 

Dissolution of the calcium fluoride in aluminum nitrate-nitric acid oxidizes the plutonium to the tetravalent hexanitrate complex (3), while the transplutonium nuclides remain in the trivalent state. The only actinides retained by a nitrate-form anion-exchange column are thorium, neptunium, and plutonium. The uranium distribution coeflBcient under these conditions is about ten, but uranium should not be present at this point since hexavalent uranium does not carry on calcium fluoride (4). 

The column effluent solution containing the transplutonium nuclides is evaporated, adjusted to pH 2, and extracted with 30% Aliquat-336. The organic phase is scrubbed with lOM NH4NO3 to remove the residual calcium and aluminum, and the transplutonium nuclides are stripped into dilute acid. Water samples up to 60 1. have been analyzed by this procedure. 

The investigation of isotopic separations in systems with cyclic polyethers has been carried out up to now for the elements lithium, calcium and sodium, in particular. Among these elements, the enrichment of Li is of essential importance for the production of tritium and that of the heavy calcium isotopes for medical labeling experiments. An enrichment aspect does not exist for the monoisotopic element sodium. Investigations with the radioactive nuclides Na and Na are obviously of interest for fundamental investigations because these isotopes can be easily and precisely measured by their y-activity. Except for uranium, most of the investigations on other chemical exchange systems with metal ions are also based on measurements with lithium and calcium, respectively. 

Some radioactive nuclides are especially damaging because they tend to concentrate in particular parts of the body. For example, because both strontium and calcium are alkaline earth metals in group 2 on the periodic table, they combine with other elements in similar ways. Therefore, if radioactive strontium-90 is ingested, it concentrates in the bones in substances that would normally contain calcium. This can lead to bone cancer or leukemia. For similar reasons, radioactive cesium-137 can enter the cells of the body in place of its fellow alkali metal potassium, leading to tissue damage. Non-radioactive iodine and radioactive iodine-131 are both absorbed by thyroid glands. Because iodine-131 is one of the radioactive nuclides produced in nuclear power plants, the... 

In stars with very heavy average masses, helium burning may last for only a few million years before it is replaced by carbon fusion. In time this leads to the production of elements such as calcium, titanium, chromium, iron, and nickel fusion partly by helium capture, partly by the direct fusion of heavy nuclides. For example, two Si can combine to form Ni that can decay to Co which then decays to stable Fe. These last steps of production may occur rather rapidly in a few thousand years. When the nuclear fuel for fusion is exhausted, the star collapses and a supernova results. 

Which of the following nuclides have magic numbers of both protons and neutrons (a) helium-4, (b) oxygen-18, (c) calcium-40, (d) zinc-66, (e) lead-208 ... 

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