Neptunium radioactivity

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

ISOTOPES There are a total of 23 isotopes of neptunium. None are stable. All are radioactive with half-lives ranging from two microseconds to 2.144xl0+ years for the isotope Np-237, which spontaneously fissions through alpha decay. 

Neptunium is a silvery-white radioactive, heavy metal. Its melting point is 644°C, its boiling point is 3,902°C, and its density is 20.25g/cm. ... 

Neptunium is the first of the subseries of the actinide series known as the traiisuratiic elements—those heavy, synthetic (man-made) radioactive elements that have an atomic number greater than uranium in the actinide series of the periodic table. An interesting fact is that neptunium was artificially synthesized before small traces of it were discovered in nature. More is produced by scientists every year than exists in nature. 

The most important radioactive isotope of neptunium is Neptunium-237, with a half-life of 2.l44xl0+ years, or about 2.1 million years, and decays into protactinium-233 through alpha decay. Neptunium s most important use is in nuclear research and for instruments designed to detect neutrons. 

All isotopes of neptunium are highly radioactive and are hazardous and thus need to be carefully used in controlled laboratory settings. These isotopes as well as neptuniums compounds are radioactive poisons. 

All isotopes of plutonium are radioactive. The two isotopes that have found the most uses are Pu-238 and Pu-239. Pu-238 is produced by bombarding U-238 with deuterons in a cyclotron, creating neptunium-238 and two free neutrons. Np-238 has a half-life of about two days, and through beta decay it transmutates into plutonium-238. There are six allotropic metallic crystal forms of plutonium. They all have differing chemical and physical properties. The alpha (a) aUotrope is the only one that exists at normal room temperatures and pressures. The alpha allotrope of metallic plutonium is a silvery color that becomes yellowish as it oxidizes in air. AH the other allotropic forms exist at high temperatures. 

Synthesis of plutonium in significant quantities requires a sufficiently long reactor fuel irradiation period. Uranium, plutonium, and the fission products obtained after neutron irradiation are removed from the reactor and stored under water for several weeks. During such cooling periods most neptunium-239 initially formed from uranium and present in the mixture transforms to plutonium-239. Also, the highly radioactive fission products, such as xenon-133 and iodine-131 continue to decay during this period. 

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... 

A radioactive element is an element that disintegrates spontaneously with the emission of various rays and particles. Most commonly, the term denotes radioactive elements such as radium, radon (emanation), thorium, promethium, uranium, which occupy a definite place in the periodic table because of their atomic number. The term radioactive element is also applied to the various other nuclear species, (which arc produced by the disintegration of radium, uranium, etc.) including (he members of the uranium, actinium, thorium, and neptunium families of radioactive elements, which differ markedly in their stability, and are isotopes of elements from thallium (atomic number 81) to uranium (atomic number... 

NEPTUNIUM. [CAS 7439-99-8]. Chemical element, symbol Np, at. no, 93, at. wt, 237,0482 (predominant isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. Neptunium was the first of [he Transuranium elements [o be discovered and was first produced by McMillan and Abelson (1940) at the University of California at Berkeley. This was accomplished by bombarding uranium with neutrons. Neptunium is produced as a by-pruduct from nuclear reactors. 237Np is the most stable isotope, with a half-life of 2.20 x 106 years, The only other very long-lived isotope is that of mass number 236. with a half-life of 5 x 10- years. 

Neptunium-237 undergoes an a, p, a, a, p, a, a, a, p, a, p sequence of radioactive decays. Determine the daughter nuclide after each decay and write a balanced nuclear equation for each step. 

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. 

After a few years of storage, the main radioactive heat emitters in HLW are 90Sr and 137Cs. In addition, extremely long-lived actinides—neptunium, plutonium, americium, and curium—should be collected for transmutation in the future. Therefore, different flowsheets can be proposed for waste processing. It is possible to extract each radionuclide in the special extraction (sorption) cycle, for example, uranium and plutonium in the PUREX process, and after that, minor actinides (MAs) by the TRUEX process,4 strontium by the SREX process,5,6 and cesium by sorption7 or extraction.8... 

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