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Natural zircons can contain up to several thousand parts per million rare earths, including up to ppm of Gd, and zircon exhibits nearly complete solid solution with hafnon, HfSiO 4.
Thus, neutron absorbing nuclides may be incorporated into the zircon structure; however, farmers only dating app neutron absorber must remain within atomic scale proximity of the fissile radionuclide Pu or U.
This is why fine-scale chemical zoning and isotopic signatures are preserved in the inherited cores of zircon crystals that have experienced protracted thermal events in their past history. In contrast, the rare-earth elements REE diffuse at rates 4в5 orders of magnitude faster than the tetravalent cations Other phases that have been suggested as waste form phases, e.
Studies of natural zircons under extreme laboratory conditions have confirmed the loss of U, Th, and Pb 3031The lead loss can be the result of grain boundary or volume diffusion in which there is no dissolution of the zirconor the bulk dissolution of zircon. There are much less leach data in the literature than necessary for a full evaluation of zircon as a waste form.
The cumulative effect of dose will be time- and temperature-dependent because of annealing and recrystallization of damaged areas. Studies of radiation effects in zircon have a long history 86 в All three types of damage experiments include detailed studies of annealing kinetics. The natural zircon studies e. In situ ion beam irradiation combined with high resolution transmission electron microscopy have demonstrated that the damage microstructures and the ingrowth of damage with increasing dose can be simulated by using heavy ion irradiation Fig.
Thus, there is a firm basis for predicting the microstructure of the radiation-damaged zircon as a function of dose, temperature, and type of radiation 9193Systematic studies have been completed for monazite- and zircon-structure orthophosphates of a wide variety of A-site end-member compositions 9596 and orthosilicates 97 в The temperature above which amorphization does not occur i.
When irradiated with heavy ions, all four orthosilicates may decompose into crystalline oxides: Ion beam irradiation studies of synthetic and natural zircons and monazites with impurities revealed that impurities lower the dose required for amorphization and correspondingly increase the temperature above which a material cannot be amorphized.
This farmers only dating app that impurities increase susceptibility to amorphization and inhibit annealing, particularly when coupled charge balance substitutions are required 96Details of structural rearrangements during damage accumulation and annealing have been obtained by extended x-ray absorption fine structure spectroscopy EXAFS studies of metamict zircons 89Metamictization is accompanied by major atomic reorganization: Finally, transmutation effects Pu decays to U are important in crystalline materials because they may lead to phase instability.
Comparison of radiation damage in natural A в C and 1. Complete amorphization in both was observed after 0.
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