Aluminum nuclides

Aluminum-26 is produced by stellar nucleosynthesis in a wide variety of stellar sites. Its abundance relative to other short-lived nuclides provides information about the stellar source(s) for short-lived nuclides and the environment in which the Sun formed. Aluminum-26 is also produced by interactions between heavier nuclei such as silicon atoms and cosmic rays. Aluminum-26 is one of several nuclides used to estimate the cosmic-ray exposure ages of meteorites as they traveled from their parent asteroids to the solar system. 

Aluminum-26 is an important nuclide for investigating the cosmic-ray exposure history of meteorites on their way to Earth from the asteroid belt. It can also be used to estimate the terrestrial age of a meteorite. In both of these applications, the 26 A1 is alive in the samples, having been produced by cosmic-ray interactions with elements heavier than aluminum, primarily silicon. Cosmic-ray-exposure dating will be discussed in Chapter 9. 

The first of these equations shows that the result of the nuclear reaction in which aluminum is bombarded with or-partides is the emission of a neutron and the production of a radioactive isotope of phosphorus. The second equation shows the radioactive disintegrations of the latter to yield a stable silicon atom and a positron. Continuation of this line of investigation by several research groups confirmed that radioactive nuclides are formed m many nuclear reactions. 

Radionuclidic Purity Radionuclidic purity is defined as the fraction of the total radioactivity in the form of the desired radionuclide present in a radiopharmaceutical. Radionuclide impurities may arise from impurities in the target material or from fission of heavy elements in the reactor [2], In radionuclide generator systems, the appearance of the parent nuclide in the daughter nuclide product is a radionuclidic impurity. In a "Mo/"mTc generator, "Mo may be found in the "mTc eluate due to breakthrough of "Mo on the aluminum column. The presence of these extraneous radionuclides increases the radiation dose to the patient and may also obscure the scintigraphic image. 

The inter-comparison analysis adopted consists of the sample dividing method and the reference standard sample method . The former method is to divide various environmental samples collected by monitoring laboratories or the hygiene institutes of local government into two parts. One of them is then analysed by such laboratories and the other by JCAC for comparison. The latter method uses reference standard samples which are prepared by JCAC and Japan Isotope Association Corp., by adding appropriate radioactive nuclides to the materials such as aluminum oxide powder or agar. These mock-up samples are analysed by both JCAC and the monitoring laboratories. 

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... 

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 development of more sensitive ways to measure levels of radioactive substances has allowed scientists to take advantage of the decay of nuclides other than carbon-14. For example, chlorine-36 can be used to date ground water, marine sediments can be dated by measuring levels of beryllium-11 and aluminum-26, and krypton-81 has been used to estimate the age of glacial ice. 

A radionuclide generator consists of a glass coluiim filled with an adsorbent material such as aluminum oxide or an ion-exchange resin to which the parent nuclide is bound (Richards 1966). The column is fitted with a filter at the outlet to retain particulate matter. On top is the elution platform, where an evacuated sterile vial is connected with the outlet of the column through which saline or another suitable eluent is drawn from the eluent reservoir. 

Tc is available through the /l -decay of Mo (Fig. 2.1.B), which can be obtained by irradiation of natural molybdenum or enriched Mo with thermal neutrons in a nuclear reactor. The cross section of the reaction Mo(nih,v) Mo is 0.13 barn [1.5], Molybdenum trioxide, ammonium molybdate or molybdenum metal are used as targets. This so-called (n,7)-molybdenum-99 is obtained in high nuclidic purity. However, its specific activity amounts to only a few Ci per gram. In contrast, Mo with a specific activity of more than in Ci (3.7 10 MBq) per gram is obtainable by fission of with thermal neutrons in a fission yield of 6.1 atom % [16]. Natural or -enriched uranium, in the form of metal, uranium-aluminum alloys or uranium dioxide, is used for the fission. The isolation of Mo requires many separation steps, particularly for the separation of other fission products and transuranium elements that arc also produced. 

To understand the varied chemistry of the aluminas, techniques need to be developed for studying the surface independent of the bulk. Structural and dynamical aspects of the surface do have their origins in the bulk, but the specific details delineating the surface will be different. Clearly it would be advantageous to apply the same surface selective CP methodology developed for the silicas [12-16] to the surface of the aluminas. Before addressing this particular point, however, we need to consider the feasibility of the experiment. Are the aluminum atoms at the surface indeed observable by NMR methods If surface aluminum atoms are observable, we must then recognize that the spin of interest, Al, is not a spin-1/2 nuclide (/ for Al is 5/2) hence Al has a nonzero nuclear electric quadrupole moment. Cross-polarization from protons to a quadrupolar nucleus presents the experimenter with another layer of complication in compari-... 

To avoid recoil nuclides from the Tmonitor foil in the sample (or the standard) a recoil foil is inserted between the I-monitor foil and the sample (or the standard). As the range of the recoil nuclides is much lower than the range of the charged particles commonly used in CPAA, a few micrometers of aluminum foil is sufficient to stop the recoil nuclides completely, while the energy of the charged particles is reduced by a minor (but not negligible) fraction. 

Powders to be measured are usually spread out with uniform thickness between thin foils of Mylar or aluminum. Sometimes, in order to avoid vibrational effects, the powder is embedded in a matrix with low atomic absorption (e.g., paraffin, granulated organic, and polymer). It is important that neither the matrix nor the foil should contain any traces of the resonant nuclide (which can happen with aluminum in the case of Fe measurements). 

Sample solutions measuring 50 pi were mixed with 350 pi 5 M HNO3 and 2.4 ml 0.1 M A1 (NOaja. The aluminum nitrate was used to complex fluoride ions. and disturbing nuclides (mainly lanthanides) were extracted into 1.0 M HDEHP (bis-2-ethylhexyl orthophosphoric acid) in Solvent 70 (an aliphatic kerosene) 2.0 ml of the aqueous phase was taken out, and... 

Because nuclides of iron are especially stable with the highest binding energy per nucleon (e.g., -8.79 MeV/nucleon for Fe), its cosmic abundance is particularly high, and it is thought to be the main constituent of the Earth s inner core as an iron-nickel alloy (see Section 13.2), named for its chemical composition NiPe by the Austrian geophysicist Suess. The relative Earth s crust abundance is about 5.63 wt.% Fe hence it is the fourth most abundant element after oxygen, silicon, and aluminum and the second most abundant metal after aluminum. 

Boron, aluminum, nitrogen, and oxygen are of analytical interest, but no nuclides are available with half-lifes longer than 10 min... 

With this nomenclature, the notation 13-A1-27 represents stable aluminum as found in nature. If you look at a Chart of the Nuclides, you will find there are 11 different aluminum isotopes (all are aluminum because they have 13 protons, but they have masses from 23-33 They are all isotopes of aluminum, and all but 13-A1-27 are radioactive isotopes --radioisotopes). Since only aluminum has 13 protons in the nucleus, we often leave the Z value off the notation, such as Al-27. Some of our information sheets have the entries arranged in order of increasing Z, so it is helpful to remember about what the atomic numbers of different elements are to make it easier to find entries in tables. 

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