Irradiation of InP with MeV Se ions directed a few degrees off the surface normal leads to a lateral displacement of the implanted material. Adjacent surface regions that are not irradiated remain unaffected. The dependence of the displacement on ion energy and its directionality strongly suggest that the effect is caused by momentum transfer from the ion to the solid. The amount of displaced material as a function of ion beam energy or angle of incidence can be described with a simple model incorporating a shear stress, applied to the target as the ion slows down, and radiation enhanced viscosity.PACS numbers: 61.80.Jh, 68.55.Ln, 79.20.Nc When an energetic ion penetrates a solid it is decelerated via two different processes: elastic collisions with target nuclei and electronic excitation of target atoms. Both processes are regarded normally as energy loss processes, and for an evaluation of macroscopic consequences of ion irradiation the momentum of the incident ion is not considered. For example, a method for estimating the number of displaced atoms generated by the ion is to evaluate the rate of energy loss into elastic collisions [1]. Some results have been reported which indicate that energy loss may not be the full story, and that the ion momentum has to be considered as well. In the case of a high fluence, high Aux, and high temperature keV As implantation into Si, the material became porous near the surface, whereas deeper layers contained dislocation loops [2]. This defect structure suggested that microscopic momentum transfer from the ion to target atoms during elastic collisions resulted in a spatial separation of vacancies and interstitials, with the vacancies remaining near the surface and the interstitials kicked into deeper regions. An observation of a different nature is that during ion irradiation of amorphous metal alloys, at several hundred MeV, thin films become larger but thinner, as if the films were between a hammer and anvil [3]. It has been explained in terms of Coulomb explosions in the wake of the ions. This explanation has met with some controversy, since Coulomb explosions are more likely to occur in insulators than in conductors.In this Letter we present experimental observations that are strongly suggestive of macroscopic momentum transfer effects. Patches of InP were found to be displaced laterally following off-normal, MeV ion implantation.The displacement is orders of magnitude larger than the vacancy-interstitial separation observed as a result of microscopic momentum transfer. The energy dependence of the process shows that the momentum transfer occurs along the entire ion track, i.e. , not only in the elastic collision but also in the electronic excitation regime. 2.5 2.0-BEAM CL tt1

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Purpose: To estimate the misclassification rate of self-reported visual disabilities in a hospital-based population with known visual impairment. Methods: Subjects (N=570) were recruited among patients aged 50 years and more and classified to three categories of visual impairment level. The questionnaire was administered to consenting patients through a telephone interview. Data collected from questionnaires and medical records were compared regarding severity of visual impairment. Sensitivity and specificity were determined for each question. Predictive ability and misclassification rates were computed for various prevalences. Results: Questions related to near and far distance visual acuity with glasses have both a good sensitivity (82.6% and 81.8%) and a good specificity (85.6% and 88.9%) for the presence of severe visual impairment. Conclusion: The findings allow the determination of the misclassification rate and predictive ability. This could be useful to estimate the prevalence of visual impairment from health surveys. La traduction du résumé se trouve à la fin de l'article.

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