Ejection of atoms from uranium by fission fragments

Rogers, M.D.; Adam, J.

doi:10.1016/0022-3115(62)90268-4

Cited by 36 publications

(5 citation statements)

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“…As we noted already, it was shown in ]6] that purifying the emitter surface from oxide film increases the ejection capability, raising K from 24 to thousands of atoms. Rogers and Adam [17] confirmed this result and also showed the dependence between the sputtering ratio and the emitter integral irradiation dose by neutrons. Peterson and Thorpe ]18] studied the effect of the oxide film at the sample surface on sputtering.…”

supporting

confidence: 74%

“…Therefore, as the integral irradiation dose increases, the value of the ejection ratio decreases. According to data in [17], the reejection factor begins to play a noticeable role with integral fluxes with respect to thermal neutrons equal to 10 I~ neutrons/era 2. Its effect may be decreased by changing the ratio of emitter to collector surfaces.…”

Section: K Gorshkov and L N L'vovmentioning

confidence: 96%

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Sputtering of matter by fission fragments

Bessonov¹

1974

At Energy

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Metal-surface-sputtering regularities under the influence of charged particles are of interest for various branches of science and technology; they were considered in [1][2][3]. However, little research has been done on sputtering of uranium and other fissionable-material surfaces during nuclear fission and fragment yield into the surroundings. Knowing the laws of this phenomenon can be important, for example, in radiation chemistry when realizing radiation-chemical processes using fission-fragment kinetic energy [4,5] and in some other branches, where thin layers of uranium-containing materials are used or where nuclear fuel is not enclosed in a special envelope.There is still no perfected and rigorous theory concerning surface sputtering under the influence of fission fragments, but it has been established that the sputtering or ejection ratio K, which is defined as the number of fissionahle-material atoms carried away by one fission fragment leaving the surface, is related to several experimental parameters. The present paper briefly considers the sputtering ratio's dependence on the emitter (fission fragment source) surface state. It is also shown how crystal structure and emitter-material properties influence the ratio K and how the sputtering ratio and integral neutronirradiation dose are interrelated. An~attempt is made to analyze the state of sputtered-material nuclei gathered at the collector and to delimit the probable ejection mechanism from these data.F. S. Lapteva and B. V. Ershler [6] were the first to confirm experimentally the fissionable-material ejection phenomenon. They showed that on the order of a thousand uranium atoms may leave a pure polished 233U or 239pu surface with one fission fragment. If the simple surface is covered with an oxide film, this value is on the average 24 atoms per fragment. B. Lastman [7], referring to [8], names a similar figure -45 molecules of uranium dioxide per fission event in a surface layer with thickness equal to the recoil-atom mean free path.The concepts of radiation-damage theory [9,10] are used to explain surface-sputtering effects under the influence of fission fragments. Fissionable-material surface-layer sputtering can be explained by using the .thermal-peak. hypothesis [9][10][11][12] or the .displacement-peak" theory proposed b~ Brinkman [13][14][15]. Another explanation for ejection (sputtering) is based on the theory of atomic expulsion at the expense of recoil-atom energy; these atoms produce displacement cascades [9,10]. Whaphan and Makin [16] believe damage may occur to a surface from which high-energy charged ions emerge at the expense of expelling larger particles. If we accept the proposition that there exists a high-temperature region along the fission-fragment motion trajectory, then in the .peak. region there arises instantaneously an explosive pressure. This may give rise to motion in the solid-state layers surrounding the track and lead to particle expulsion from the material surface layer. When the temperature in the .thermal-peak. regio...

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supporting

confidence: 74%

Section: K Gorshkov and L N L'vovmentioning

confidence: 96%

Sputtering of matter by fission fragments

Bessonov¹

1974

At Energy

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“…While the early Russian results gave dramatically different results for the sputtering yields of oxidized foils (about 30 fissile atoms per escaped fission fragment) and polished foils, the oxide layers were presumably rather thick. In contrast, Rogers and Adam [5] did not detect any difference in sputtering yields from oxide free or oxidized samples. The oxide film in their specimens were presumably much thinner.…”

Section: B) Surface Conditionsmentioning

confidence: 65%

“…Foils with substantial oxide films were reported to have sputtering yields lower by a factor of 100. [5]. In these experiments, particular attention was paid to the time dependence of the sputter-deposited material.…”

Section: Introductionmentioning

confidence: 99%

FY04&05 LDRD Final Report Fission Fragment Sputtering

Ebbinghaus¹,

Trelenberg²,

Meier³

et al. 2006

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“…The sputtering coefficient was approximately 2·10 3 atoms per fragment. According to data obtained in other works [4,5], the self-sputtering coefficient of uranium films (metallic uranium or uranium dioxide) reaches (1-5)·10 4 atoms per fragment.…”

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confidence: 90%

Absorption of optical radiation by nanoclusters of sputtered metallic uranium and its oxides

Meshakin

Budnik

2007

At Energy

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Thin films of uranium-containing materials are used as energy-releasing elements in nuclear-pumped lasers. They serve as a source of fission products which ionize and excite the gaseous medium. In this pumping method, a uranium layer is sputtered by its own fission products. This is one of the factors that limit the service life of energy-releasing elements. The products of sputtering can enter the gas and affect the optical and kinetic properties of laser media. In the present work, calculations are performed of the electrodynamic cross-sections for photoabsorption of optical radiation by nanoparticles of metallic uranium and its oxides. The main space-time relaxation parameters are determined. The effect of sputtered uranium-containing nanoparticles on the absorption of optical radiation in a laser element is evaluated.Thin layers of uranium-containing materials are used as energy-releasing elements in the nuclear-pumped lasers. They serve as a source of fission products which ionize and excite the gaseous medium. As a rule, thin-film uranium-containing coatings are characterized by a finely dispersed structure and high porosity, which are due to the method used to obtain the films (magnetron spraying, deposition from the vapor phase, and others). Such coatings have anomalously high sputtering coefficients, reaching 10 3 -10 5 atoms per fission fragment [1]. If it is assumed that 10 4 uranium atoms enter the gas together with a fission fragment, which at the exit from the uranium layer possesses characteristic energy 40 MeV, then the typical energy input 1 J/cm 3 during nuclear pumping will correspond to the average density of sputtered atoms 1.5·10 15 cm −3 . This quantity of contaminants, for example, water vapor, is sufficient not only to weaken but also make it completely impossible to obtain lasing. In reality, the picture is more complicated. Atomization of the coating material into individual atoms does not occur. Most of the sputtered material is contained in clusters ranging in size from several to tens of nanometers [2].The objective of the present work is to study the optical properties of sputtered nanoparticles containing uranium and to develop recommendations for eliminating the harmful effect of the products of sputtering and for extending the service life of laser elements.The coefficient of sputtering of thin-film coatings by fission fragments depends on many factors, the most important ones being the microstructure of the film and the structure of the boundary between crystallites. The physical reason for the anomalous sputtering of coatings is evaporation of surface grains as result of their being heated by decelerating fission fragments [1]. The probability of sputtering of a grain as a whole is determined by the ratio of the energy absorbed inside a grain, the flux of energy on neighboring crystallites through the complicated intergrain boundary, and the energy required to detach a grain from the substrate. The model of a completely isolated grain gives a qualitative description of the sput...

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Ejection of atoms from uranium by fission fragments

Cited by 36 publications

References 1 publication

Sputtering of matter by fission fragments

Sputtering of matter by fission fragments

FY04&05 LDRD Final Report Fission Fragment Sputtering

Absorption of optical radiation by nanoclusters of sputtered metallic uranium and its oxides

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