Neutron irradiation reactions products from

Evaporation residues arising in complete-fusion reactions between actinide targets and radioactive-beam particles are controlled by the same < r /Ff > and dynamical hindrance effects as are the reaction products from stable-ion beam irradiations. It has been observed that fusion cross sections for reactions with neutron-rich radioactive beam particles can be enhanced over those with stable-isotope beams at the same Z, possibly due to an effective lowering of the fusion barrier with the increasing neutron number of the projectile facilitated by neutron flow in the dinuclear reaction intermediate [226, 454, 458]. It is unclear how dynamical hindrance effects and a reduced resistance to deexcitation by fission at high excitation energies in heavier systems will influence the formation of evaporation residues. It has been suggested that the formation of products at the... 

Production-Scale Processing. The tritium produced by neutron irradiation of Li must be recovered and purified after target elements are discharged from nuclear reactors. The targets contain tritium and He as direct products of the nuclear reaction, a small amount of He from decay of the tritium and a small amount of other hydrogen isotopes present as surface or metal contaminants. 

Maddock and Sutin (56) observed the formation of numerous oxygenated products in neutron-irradiated AsPhj which, they argued, must have come from reaction of AsPh radicals with oxygen or water during the separation. The annealing effect of heating at 45° led to increased yields of AsPhj, while AsPhj products first increased and then decreased. This was interpreted as showing the involvement of phenyl radicals in a series of consecutive reactions ... 

As a result of slow (thermal) neutron irradiation, a sample composed of stable atoms of a variety of elements will produce several radioactive isotopes of these activated elements. For a nuclear reaction to be useful analytically in the delayed NAA mode the element of interest must be capable of undergoing a nuclear reaction of some sort, the product of which must be radioactively unstable. The daughter nucleus must have a half-life of the order of days or months (so that it can be conveniently measured), and it should emit a particle which has a characteristic energy and is free from interference from other particles which may be produced by other elements within the sample. The induced radioactivity is complex as it comprises a summation of all the active species present. Individual species are identified by computer-aided de-convolution of the data. Parry (1991 42-9) and Glascock (1998) summarize the relevant decay schemes, and Alfassi (1990 3) and Glascock (1991 Table 3) list y ray energy spectra and percentage abundances for a number of isotopes useful in NAA. 

The uranium-graphite nuclear reactor (or nuclear pile ) was important not merely because it proved the feasibility of a self-sustaining fission chain. It could be used, with minor modification, for neutron irradiation of a sample by placing the sample in the interior of the reactor. Also, the system could be used as a source for the easily fissionable Pu239. This isotope (half-life 24,100 years) is a product in the decay chain from U239, which in turn results from the (n,y) reaction on U238 ... 

The isotope used to prepare labelled compounds is obtained by irradiation in a nuclear reactor, of solid targets containing atoms of nitrogen (aluminium or beryllium nitride), by neutrons of low energy, known as thermal neutrons, themselves the product of the controlled atomic fission of The radiocarbon formed is next isolated from the target sample by oxidation to Ba " 003, the variety in which it is delivered to chemists. From C02, it is possible to use a plethora of organic chemical reactions to synthesize different compounds in which the radio-isotope can be introduced to a specific position. 

The lithium is in the form of an alloy with magnesium or aluminium which retains much of the tritium until it is released by treatment with acid. Alternatively the tritium can be produced by neutron irradiation of enriched LiF at 450° in a vacuum and then recovered from the gaseous products by diffusion through a palladium barrier. As a result of the massive production of tritium for thermonuclear devices and research into energy production by fusion reactions, tritium is available cheaply on the megacurie scale for peaceful purposes. The most convenient way of storing the gas is to react it with finely divided uranium... 

For irradiation in a constant neutron flux, the activity of any fission-product nuclide can be evaluated from the equations in Chap. 2. When fissions occur at a constant rate and when neutron-absorption reactions in the fission product and its precursors can be neglected, the activity of a nuclide with relatively short-lived precursors can be evaluated by applying Eq. 

Since the isotope Am can be prepared in relatively pure form by extraction as a decay product over a pmod of years from strongly neutron-bombarded plutonium, Pu, this isotope is used for much of the chemical investigation of this element. Better suited is the isotope Am due to its longer half-life (7.37 x 10 years as compared to 432.2 years for Am). A mixture of the isotopes Am, Am, and Am can be prepared by intense neutron irradiation of Am according to the reactions Am (n, y) —> Am (n, y) —> Am. Nearly isotr ically pure Am can be prepared by a sequence of neutron bombardments and chemical separations as follows neutron bombardment of Am yields Pu by the reactions Am (n, y) Am after chemical separation the Pu can be transformed to Am via the reactions Pu (n, y) Pu Am, and the Am can... 

A French radioisotope production group provided radionuclides such as Cr, Fe, Cu, Zn, and As by the Szilard-Chalmers processes (Henry 1957). At the Japan Atomic Energy Research Institute, this process was applied to obtain pure from neutron-irradiated potassium phosphate. Ordinary products using (n,p) reaction in a nuclear reactor contain an impurity isotope P in P, but P produced by (n,y) reaction in neutron-irradiated phosphate does not contain P. Hot atom chemically obtained P by (n,y) reaction was therefore appropriate for some special experiments in which contamination of P with different half-life and P-particle energy had to be excluded (Shibata et al. 1963). 

Besides the work of Caspar and coworkers described above and the work by Cetini and coworkers " mentioned earlier, there are several other studies employing the Si(n,y) Si transformation. Studies of the chemical effects subsequent to the above nuclear transformation in tetramethylsilane have been carried out by Snediker and Miller in 1968 in both gas and liquid phases with or without nitric oxide as a scavenger, and by Kawamoto in 1975 on the effect of irradiation conditions. The formation of Si-labeled products from neutron irradiation of tetra-, tri-, and diphenylsilane in the condensed phase have been studied by Wheeler and Trabal. Most of the results obtained in these studies are likely to be complicated by various kinds of radical reactions. 

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