Neptunium Neutrons

The new elements neptunium and plutonium have been produced in quantity by neutron bombardment of uranium. Subsequently many isotopes have been obtained by transmutation and synthetic isotopes of elements such as Ac and Pa are more easily obtained than the naturally occurring species. Synthetic species of lighter elements, e.g. Tc and Pm are also prepared. 

Planet pluto) Plutonium was the second transuranium element of the actinide series to be discovered. The isotope 238pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley, California. Plutonium also exists in trace quantities in naturally occurring uranium ores. It is formed in much the same manner as neptunium, by irradiation of natural uranium with the neutrons which are present. 

Its importance depends on the nuclear property of being readily fissionable with neutrons and its availability in quantity. The world s nuclear-power reactors are now producing about 20,000 kg of plutonium/yr. By 1982 it was estimated that about 300,000 kg had accumulated. The various nuclear applications of plutonium are well known. 238Pu has been used in the Apollo lunar missions to power seismic and other equipment on the lunar surface. As with neptunium and uranium, plutonium metal can be prepared by reduction of the trifluoride with alkaline-earth metals. 

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. 

C02-0053. Predict whether each of the following nuclei is stable or unstable and give the reason for each prediction (a) carbon-10 (b) neptunium-239 and (c) cadmium with 60 neutrons. 

It should be noted that the ytterbium listed above was a mixture discovered in the mineral erbia by de Marignac in 1878 and not the neoytterbium/aldebaranium element renamed ytterbium that was foimd in the mineral ytterbia. The columbium was a mixture found in the mineral samarskite and was not the present day columbium/niobium. The ionium listed above was a mixture of terbium and gadolinium that was found in the mineral yttria and does not refer to °Th. Finally, the neptunium refers to material fovmd in niobium/tantalum minerals and does not refer to the 1940 discovery of the trans-uranium element produced via a neutron capture reaction on a uranium sample. 

At one time, neptunium s entire existence was synthesized by man. Sometime later, in the mid-twentieth century, it was discovered that a very small amount is naturally produced in uranium ore through the actions of neutrons produced by the decay of uranium in the ore pitchblende. Even so, a great deal more neptunium is artificially produced every year than ever did or does exist in nature. Neptunium is recovered as a by-product of the commercial production of plutonium in nuclear reactors. It can also be synthesized by bombarding uranium-238 with neutrons, resulting in the production of neptunium-239, an isotope of neptunium with a half-life of 2.3565 days. 

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 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. 

Heavier isotopes Es-253, Es-254 and Es-255 can be produced in a nuclear reactor by multiple neutron capture reactions that may occur when uranium, neptunium and plutonium isotopes are irradiated under intense neutron flux. These and other isotopes also are produced during thermonuclear explosions. 

Neptunium, the first transuranium element, was discovered hy E. M. McMdlan and P. H. Ahelson in 1940 in Berkeley, California. It was produced in the cyclotron in a nuclear reaction by bombarding uranium-238 with neutrons. An isotope of mass 239 and atomic number 93 and ti/2 of 2.4 days was produced in this reaction. Neptunium-237, the longest-lived alpha-emitter with half-life 2.14x10 years, was discovered two years later in 1942 by Wahl and Seaborg. The new element was named after the planet Neptune, the planet next to Uranus in the solar system. 

Neptunium is not found in nature in any extractable quantities. However, it occurs in uranium ores in exceedingly small concentrations resulting from neutron capture of uranium isotopes. No major application is known for this element. Its isotope, Np-237, is used in neutron detection instruments. 

Neptunium-237 may be synthesized by bombarding uranium-235 or uranium-238 with neutrons ... 

Neptunium-239 may be obtained from uranium-238 by neutron bombardment as it was first produced ... 

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. 

This element has not been found in any naturally occurring mineral but Seaborg believes it may exist in minute amounts as the result of neutron bombardment in uranium ores (63). Neptunium is not absorbed from the digestive tract of animals, but when it is injected it tends to accumulate in the bones. Subsequent loss from this site is very slow (64, 65). 

Edwin McMillan and Philip Abelson obtain the first transuranium element, neptunium (element 93), by bombardment of uranium with neutrons. 

Uranium. Perricos and Belkas (25) have determined uranium in six coals by neutron activation followed by separation of the uranium daughter neptunium-239 by carrier-free extraction chromatography. The coals, from mines in northern Greece, had very high uranium concentrations (0.012-0.037%). However, uranium at the few parts per million level found in most coals could no doubt be determined by a modification of this method. 

One of the fascinating features of fission power is the breeding of fission fuel from nonfissionable uranium-238. Breeding occurs when small amounts of fissionable isotopes are mixed with uranium-238 in a reactor. Fission liberates neutrons that convert the relatively abundant nonfissionable uranium-238 to uranium-239, which beta-decays to neptunium-239, which in turn beta-decays to fissionable plutonium-239. So in addition to the abundant energy produced, fission fuel is bred from relatively abundant uranium-238 in the process. 

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. 

Industrial utilization of neptunium has been very limited. The isotope 1 Np has been used as a component in neutron detection instruments. Neptunium is present in significant quantities in spent nuclear reactor fuel and poses a threat to the environment. A group of scientists at the U.S. Geological Survey (Denver, Colorado) has studied the chemical speciation of neptunium (and americium) in ground waters associated with rock types that have been proposed as possible hosts for nuclear waste repositories. See Cleveland reference. 

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