MadSci Network: Chemistry |
Hello – I didn’t get your name, but hope the answer below helps you. Firstly, you are right to wonder about such a heavy gas as radon – it’s about 7.5 times as heavy (dense) as air and so it will certainly not want to disperse upwards in air! Being a gas, though, it does behave in all other respects just like gasses do. That is, the thing that makes it a gas, as opposed to a liquid or solid, is that its smallest individual parts (molecules we call them) don’t really want to stick together. They are all very independent and move around randomly this way and that without any sense of direction. So, for any gas, and radon is no exception, a volume of the gas will expand outwards as the molecules on the outside get further away from the centre of the original volume, thanks to their “random walking”. To stop this happening, there needs to be something in the way – a constraint. Well, a less dense gas around it will prevent it dispersing away from a source of gravitational attraction, acting on both gasses. So the Earth pulls down more on the radon than it does on the air, and of course, below is the surface of the ground – which as far as it is impervious to the gas will prevent the gas going further downwards. The only way left is sideways – until another obstruction gets in the way. Of course, removing the obstruction and providing a shove – say with a blast of air, will disperse the gas. An example would be opening a door and an opposite window at the same time on a windy day! Some facts about radon for you: Radon-220 (thoron; 51.5-second half-life) was first observed (1899) by the British scientists R.B. Owens and Ernest Rutherford, who noticed that some of the radioactivity of thorium compounds could be blown away! Radon- 219 (actinon; 3.92-second half-life) was found (1904), associated with actinium, independently by Friedrich O. Giesel and André-Louis Debierne. More than a dozen artificial radioactive isotopes of radon are known. Air contains tiny traces of radon near the ground as a result of seepage from soil and rocks, all of which contain minute quantities of radium. (Radium is a natural decay product of uranium, itself present in various types of rocks.) By the late 1980s, naturally occurring radon gas had come to be recognised as a potentially serious health hazard. The gas, arising from soil and rocks, seeps through the foundations, basements, or piping of buildings and can accumulate in the air of houses that are poorly ventilated. Exposure to high concentrations of radon over the course of many years can greatly increase the risk of developing lung cancer. In fact, radon is now thought to be the second most important cause of lung cancer after smoking. Your risk, depending on where you live, is much, much lower than the risk from smoking. Radon levels are highest in homes built over geological formations that contain uranium mineral deposits. The good news is its short lifetime – the half-lives above are how long it takes for half of the stuff to disappear by itself, and they are measured in seconds. So long as ventilation is good, and you don’t crawl around sniffing the air at your feet all day long, there’s not much to worry about…
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