Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Mr Andrew on 22/10/2007 00:06:18
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Do ions emit different spectra of light when stimulated than their neutral counterparts? Is that difference noticable enough to differentiate between the two?
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Yes and yes. I think if you ionise an atom the emision spectra will look like the element with one less electron, but with everything moved up in energy slightly because the nucleus has a higher charge. but I am not a chemist, so there are probably more subtleties which I don't know about.
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Ions behave differently, chemically, from their neutral neighbours.
this suggests that the energy situation is very different - hence you would expect the spectra to be different.
Yes, Daveshorts, it seems reasonable to expect a similar pattern of spectral lines, though - just shifted, because of the overall energy difference.
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I am trying to develop a way to detect static charge at a distance. Using something like RADAR to stimulate atoms to emit radiation I hope to find static charge in say...a clean room or laboratory near sensitive equipment.
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So you need to spot charge imbalance on the surface of a solid. That is harder than detecting ionised gas atoms because the energy differences are very small when you remove an electron - you don't really get ionisation - you get a redistribution / polarisation of the charges around the nearby atoms. The effect is diluted - particularly in metals., where the effect is spread throughout the whole piece.
Unless the charge is large enough and the potential is high enough to ionise the surrounding air, I should say you have no chance.
I might suggest introducing some airborne powder which would fluoresc in UV light. It would congregate around the offending objects and highlight them - but that would be no good in a CLEAN ROOM DURRR.
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I am trying to develop a way to detect static charge at a distance. Using something like RADAR to stimulate atoms to emit radiation I hope to find static charge in say...a clean room or laboratory near sensitive equipment.
Well... typical ways to remove static include radioactive sources which ionise the air (make it weakly conducting). Air-ionisers which do the same thing (I'm not sure how you ensure you don't charge up something from the ions though).
You can also use UV light to free excess electrons from a metal surface (there was an A-level physics demo with a gold-leaf electroscope to show this). Not sure of that would work for +ve charged surfaces. For negatively-charged bodies at least, would the freed electrons then ionise the air and enable detection in any (optical) way???
Somewhat handwaving - doubt if practical in reality... [::)]
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I am trying to develop a way to detect static charge at a distance. Using something like RADAR to stimulate atoms to emit radiation I hope to find static charge in say...a clean room or laboratory near sensitive equipment.
You could have a handheld widget with a very high-impedance input plate which you wave around and would detect static charges at a range of 10-30cm. Just use a MOSFET input op-amp wired as a unity-gain non-inverting amplifier ... and something like a reed switch to short the input to ground when the thing is not in use, to prevent static damage to the input. You'd probably need to "zero" the input every few seconds during use too, to prevent the input from saturating. Quite effective, but it isn't going to be as convenient as a "photograph" with superimposed static hotspots! Would likely go haywaire when the operator shifts their shoes on the floor too [;)]
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You could always have detectors attached to sensitive items and monitor them, constantly,
OR, just earth everything in sight and boil a kettle in the corner.
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You could always have detectors attached to sensitive items and monitor them, constantly,
OR, just earth everything in sight and boil a kettle in the corner.
Static problems very sensitive to the weather. Few probs on damp or "muggy" (humid) days. Cold, dry winter days however, and the sparks begin to fly (the internal humidity gets very low).
Some years ago I slid across my office in a wheeled office chair and then touched the metal frame at the front of the desk ... and yelped. The chap from the office next door came in to see what had happened as he'd heard the spark as well as my yelp!
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It seems like the only ways to detect charge (static electric fields) at any great distance is to somehow use radiation (traveling electric fields) to convey information about the electric field to a sensor. I need some way to 'see' an electric field on a large scale. This is difficult.
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This is a really difficult problem.
Firstly, there's no point in looking at the spectra of the atoms of the solid - they don't exhibit lines, but bands, and you couldn't detect any tiny shifts.
You can also use UV light to free excess electrons from a metal surface (there was an A-level physics demo with a gold-leaf electroscope to show this).
This is the photo electric effect and, with UV light, produces very slow electrons (a very few electron-volts) even from Group 1 (or group 2?) metals, in their pure metalic state - not as compounds. I can't imagine these photoelectrons producing ionisation under these circumstances because they couldn't build up any energy in the field around the object. (The effect is used in photomultipliers and image intensifiers but they are accelerated with a high voltage through a vacuum - not air)
If you were in a vacuum, you could observe the paths of charged particles to reveal a static field - but you aren't. You could, possibly, use a Cathode Ray tube, operating at relatively low voltage and observe the beam deflection - either optically or with electrodes on the target area of the tube. I don't know how many locations in your lab you need to cover but this could be a bit invasive if you needed a lot of these tubes.
Prevention is better than cure, in any case. Just monitor the humidity and control it with the old boiling kettle, when necessary.
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I analysed my first long range static electrical field detector nearly forty years ago. Someone was trying to sell the device to an intruder alarm company owned by my employers. It performance was truly amazing it would detect and alarm on people moving around at several metres it would also detect you standing still a couple of meteres away and tensing and relasing the muscles in your arm. The problem was it would also alarm on other slowish field changes in the environment not associated with people and could easily suffer from false alarms. Needless to say I could not reccommend that they used the device in their alarm systems. At that time the infra red and microwave movement detection devices that are commonplace nowadays were very large, complex, and expensive. The electric field detector offered a simpler and cheaper solution to the infra red and microwave ones at the time. Simple analogue filters cannot solve the problem of isolating human movements from other sources of interference however multiple static detectors and the complex computer analysis that is so cheap these days might just possibly solve this problem.
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Well, SS, did it work and how? I seems to me that, as you describe it, it would be incredibly prone to LF interference. And it wouldn't / couldn't(?) do very well with 'static', static fields.
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It was basically a mosfet electrometer with an antenna on its gate that detected extremely tiny changes in charge at low frequencies. It was incredibly snsitive and when set up with a meter would detect the tiny movements and even the charge change associated with tensing an relaxing muscles without movement. but as you say it was also subject to interference from things like flourescent tubes starting
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The problem is that you would need to detect steady fields. It could be easier if a number of probes could be used. The PDs involved would be much higher than with the motor nerves but DC drift would be a major factor. If amplifier passband were something like 0 to .001Hz it would eliminate a lot of common sources of interference. Of course, it would only indicate the presence, not the location, of charges.