Radiation damage effects

As previously noted, monazite usually contains significant amounts of thorium as well as uranium, and xenotime also contains uranium. Naturally radioactive minerals are, therefore, exposed to displacive radiation damage events over geological time scales. Accordingly, such minerals are frequently found in the metamict state, i.e. they can 

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Lumpkin, G. R Colella, M., Smith, K. L., Mitchell, R. H. Larsen, A. O. 1998a. Chemical composition, geochemical alteration, and radiation damage effects in natural perovskite. Materials Research Society Symposium Proceedings, 506, 207-214. 

Lumpkin, G. R., Ewing, R. C., Williams, C. T. Mariano, A. N. 2001. An overview of the crystal chemistry, durability, and radiation damage effects of natural pyrochlore. Materials... 

In an important study of accelerated radiation damage effects in polyphase Synroc samples doped with 244Cm, Mitamura et al. (1992, 1994) studied the behaviour of Mo, Sr, Ca, Cs, Ba, and Cm for up to 56 days in distilled water at 90 C. These ceramics were doped with either Na-free simulated Purex waste (PW-4b) or simulated waste containing 1.65 wt% Na20 (e.g., JW-A type). We should note here that the... 

In selecting the materials ( W), major emphasis is given to neutron activation and radiation damage effects in materials close to the plasma and further considerations are given to other factors such as corrosion, long-term creep strength, fabrication technology, and cost. 

Ewing RC, Chakoumakos BC, Lumpkin GR, Murakami T, Greegor RB, Lytle FW (1988) Metamict minerals natural analogues for radiation damage effects in ceramic nuclear waste forms. Nucl Instr Meth B32 487-497... 

Sickafus KE, Larson AG, Yu N, Nastasi M, Hollenburg GW, Gamer FA, Bradt RC (1995) Cation disordering in high-dose neutron-irradiated spinel. J Nucl Mater 219 128-134 Sickafus KE, Matzke Hj, Hartmaim Th, Yasuda K, Valdez JA, Chodak P III, Nastasi M, Verrall RA (1999) Radiation damage effects in zirconia. J Nucl Mater 274 66-77. 

Lattice disorder and radiation-damage effects are produced in the substrate by the incident ion. As an implanted ion slows down and comes to rest, it has many violent collisions with lattice atoms, displacing them from their lattice sites. These displaced atoms can in turn displace others, and the net result is the production of a highly disordered region around the path of the ion, as shown schematically in Fig. 1.3 for the case of a heavy implanted atom at typically 10-100 keV. At sufficiently high doses, these individual disordered regions may overlap, and an amorphous or metastable crystalline layer may form. 

Bordas (1982) suggests that from experience of biological samples in small angle experiments on DORIS there is a limitation to the intensity one can use for a typical specimen due to radiation damage effects, i.e. 

Radiation effects. As with apatite, the increased release rates of radionuclides as a function of radiation damage has lead to rather detailed studies of the behavior of monazite under a variety of irradiation conditions. Karioris et al. (1981) and Cartz et al. (1981) established that natural monazite can be readily transformed to an amorphous state by irradiation with 3 MeV Ar ions at moderate doses. Robinson (1983) simulated the cascades that formed in monazite and found them to be similar in size and shape to simulated cascades in metals. The lack of observed radiation damage effects in monazite is related to the dominance of annealing processes. These early studies lead to detailed studies of damage accumulation as a function of temperature. 

The main advantages of phosphate phases as nuclear waste forms are the high capacity for actinides (up to 20 wt %), a relatively high chemical durability (Donald et al. 1997, Trocellier 2001), and the ability to anneal radiation damage effects at relatively low temperatures (300 to 400°C). Of particular importance for monazite and apatite is the fact that they occur naturally thus, models that are used to extrapolate the physical and chemical behavior of the waste form over long periods can be confirmed by comparison to natural occurrences. 

Sickafus, K., Matzke, H., Hartmann, T. et al. 1999. Radiation damage effect in zirconia. J. Nucl. Mater. 

Radiation damage effects are likely to be of prime importance in organic matrix composites. Screening measurements to assess the severity of the problem are needed. For most of these materials, there is no low-temperature data base. Specifications for industrial laminates (NEMA/ASTM) are generally electrical in nature, and mechanical specifications may be necessary additions for low-temperature applications. Very few 4 K data exist for the advanced (high-modulus) composites and specialty fiberglass composites, which may be needed for low-temperature structural applications near pulsed coils. 

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