The physical and chemical properties of plutonium are related to its environmental transfer and uptake by man. Once incorporated, plutonium is avidly retained in the lungs, liver and skeleton, the relevant amounts being determined by its solubility in body fluids. A knowledge of the toxicity of plutonium is largely dependent upon animal studies where exposure to relatively large amounts, compared with those associated with known human exposure, can cause tumours in those tissues where it is retained. With one exception, epidemiological studies have not been able to demonstrate adverse health effects in humans.Precautions taken in the processing of plutonium have ensured that average intakes by workers have been consistently low. When it has been released to the environment, it has been of little ecological importance and has caused only small doses to man with no observable adverse effects.The long half-life of plutonium causes anxiety about its storage and disposal, but plutonium is not unique. It is often forgotten that very much larger amounts of permanently toxic elements such as arsenic, cadmium and lead are stored and disposed of with much less concern. Plutonium is a valuable resource and for that reason should not be treated as a waste for disposal into the environment.
The transfer of an electron from a carbon nanotube (CNT) tip into vacuum under a high electric field is considered beyond the usual one-dimensional semi-classical approach. A model of the potential energy outside the CNT cap is proposed in order to show the importance of the intrinsic CNT parameters such as radius, length and vacuum barrier height. This model also takes into account set-up parameters such as the shape of the anode and the anode-to-cathode distance, which are generically portable to any modelling study of electron emission from a tip emitter. Results obtained within our model compare well to experimental data. Moreover, in contrast to the usual one-dimensional Wentzel-Kramers-Brillouin description, our model retains the ability to explain non-standard features of the process of electron field emission from CNTs that arise as a result of the quantum behaviour of electrons on the surface of the CNT.
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