Neptunium tests

Self-Test 17.5B The decay constant for the nuclide neptunium-237 is 3.3 X... 

Radioactivity (continued) compounds in atmosphere, 3 287-288 einsteinium, 31 34 neptunium, 31 21 plutonium, 31 23-24 thorium, 31 17 uranium, 31 19 Radiocarbon, 3 301-317 artificial, 3 327 atmospheric, 3 328 nuclear testing and, 3 312-314 constancy in atmosphere, 3 309 dating, fundamental assumptions of, 3 308-309... 

Self-Test 17.6B The decay constant for the nuclide neptunium-237 is 3.3 X 10 7 y-1. What mass of the isotope will be present if a sample of mass 5.0 pg survives for 1.0 X 106 y ... 

These compounds, tested in NPHE at Cadarache, were used as reference compounds for the extraction of actinides by functionalized calixarenes (see below). The distribution ratios for neptunium mainly at the oxidation state (V), plutonium at the oxidation state (IV), and americium (III) are shown in Table 4.21 for OOCMPO. They were also used as references for the americium over europium selectivity (Table 4.22). 

Extraction of neptunium, plutonium, and americium from simulated radioactive liquid waste was carried out in particular with tert-butyl and dealkylated tetramers, hexamers, and octamers of calixarene [ethoxy(diphenylphosphine oxide)]. Among these six calixarenes, the highest distribution ratios were obtained with the dealkylated calix[8]arene. Using a different sample of the dealkylated hexamer, the Strasbourg group concluded that this compound is the most efficient. This discrepancy can be explained by the presence of impurities, detected by NMR, which were probably responsible for the poor performances of the dealkylated hexamer tested at Cadarache. 

Neptunium and plutonium sorption behaviors were remarkably similar, implying that they had similar sorption reactions and solution species. Both NaOH and NaA102 decreased neptunium and plutonium sorption. Several explanations can be offered to rationalize this behavior. First, NaOH and NaAlO, may have reacted with the sediment minerals to yield solids of lower sorptive capacity. Aluminate ion, as an anionic species, also may have competed with the similar neptunate and plutonate anions for sorption sites. Finally, sodium hydroxide may have stabilized the hydrolyzed Np02(0H) and Pu02(0H)2" species in solution, as was shown in the solubility tests, and prevented sorption. Explanation of the effect of NaOH and NaA102 on neptunium and plutonium sorption will require further investigation. 

Actinides in the environment can be classified into two groups (i) the uranium and thorium series of radionuclides in the natural environment and (ii) neptunium, plutonium, americium and curium which are formed in a nuclear reactor during the neutron bombardment of uranium through a series of neutron capture and radioactive decay reactions. Transuranics thus produced have been spread widely in the atmosphere, geosphere and aquatic environment on the earth, as a result of nuclear bomb tests in the atmosphere, and accidental release from nuclear facilities (Sakanoue, 1987). Most of these radionuclide inventories have deposited in the northern hemisphere following the tests conducted by the United States and the Soviet Union. 

Only five transuranic elements exist or are anticipated to be produced in amounts which could lead to significant environmental concentrations. These are neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), and californium (Cf). Of these five, only two, plutonium and americium, have been detected and measured already in the marine environment as a result of global fallout of nuclear testing debris. The procedures described below were developed specifically to measure plutonium and americium. However, as will be expanded later, the techniques for measuring americium are also able to detect curium and californium should they be present in significant amounts in the future. 

In the frame of the PACT project, irradiation of several kilograms of Np-237 to produce Pu-238 was planned for the years after 1973. A test irradiation of ca. 180 g Np-237 was initiated by the Alkem company in 1970. The neptunium was fabricated by Alkem into target rods containing pellets of a 10 % NpO -iron-cermet. The targets were irradiated in the BR-2 reactor at Mol, Belgium, for about 2 months, and were then cooled for 9 months before processing in the Milli. 

Iodine (including 131I when short-cooled targets are processed) can be removed in head end by in situ precipitation with Mn02 (10). Mn02 oxidizes both neptunium and plutonium to M(VI). Therefore initial tests were made with Np(VI) and Pu(VI) produced by in situ precipitation of Mn02. 

In 1940, element 93 was discovered, or created, depending on how experimental research is described. The Berkeley team of Edwin McMillan (1907-1991) and Philip Abelson (1913-2004) bombarded uranium foil with neutrons and found that one of the fission products lasted for 2.3 days before naturally decaying. This did not match with known elements, and they suspected it was a new element. With 2.3 days to conduct tests, they were able to test oxidation states and positively identify that it was unique. The name neptunium was suggested because the planet Neptune was beyond Uranus. 

The situation for actinide ions is ambiguous due to a lack of experimental data. Because of the larger crystal-field parameters of the actinides, one would anticipate that the ion-lattice coupling is stronger. This assumption was not obviously shown to be true in the recent line width measurements of neptunium (47). Experimental measurements of the temperature dependence of the fluorescence lifetimes and quantum efficiencies will provide a direct test for the multiphonon coupling and the universality of the energy gap dependence of the multiphonon spontaneous transition rate. 

The first method was employed with both neptunium and plutonium when these metals were tested for superconductivity down to temperatures of about 0.75°K [1]. Brass capsules of 1 mm wall thickness were used which had at one end platinum—glass seals through which the platinum wires for the current-potential measurement were passed. The active specimens were inserted into the capsules inside a glove box in which the electrical contacts were also made and in which the capsule was filled with helium gas and then sealed off. Prior to its introduction into the glove box, the capsule had been covered with a layer of shellac. After sealing off, the capsule was immersed in acetone which dissolved the shellac and in this manner the contamination sticking to the outside of the capsule was removed. 

For experimentalists, measurements of the transport properties of metals are also of great practical interest, since they are very sensitive to the purity of the studied materials. It is known that the residual resistivity ratio p(300 K)/p(4.2 K) is commonly used as a global purity test. Values as high as 1000 have been obtained for ultra-pure thorium refined by electro-transport (Peterson et al. 1967). Even in the purest lanthanides this ratio is below 300. A value of 50 has been reached for electro-refined plutonium (Arko et al. 1972) and one of 65 for electro-refined neptunium (Fournier and Amanowicz 1992). 

Neptunium. Np is in a class with Pa no efforts have been made to use it as a fuel solute, but consideration has been given to its formation in and removal from blanket solutions of [30a]. The chemistry of neptunium has been reviewed by Hindman et al. [30b], and the hydrolytic behavior has been reviewed by Kraus [30c]. Continuous separation of Np239 would provide a Pu product of high purity by radioactive decay, whereas plutonium recovered from long-term irradiation of usually contains appreciable amounts of Pu °. Spectrophotometric cells for use at elevated temperatures and pre.ssures in the study of the chemistry of neptunium (and other materials) have recently been developed by Wag-gener [30d] and have been used to measure the absorption spectra of dilute neptunium perchlorate in its six-, five-, four-, and three-valence states, using heavy w ater as the solvent. Dilute solutions of neptunyl nitrate in nitric acid have been so studied at temperatures up to 250°C the pentavalent state was found to be stable under the test conditions [30e]. 

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