High Frequency, High Energy Ultra Violet - Page 1
Forum section: electronics / general

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: December 21, 2014, 04:12:30 pm
content: I have a question for all you particle physicists out there, (If there are any). Can high frequency, high energy UV knock electrons out of their orbit? I know other ionizing radiations such as X-Rays, Gamma, etc. can easily do this but I need to know if it was possible with HF UV.Thanks in advance...

author: SeanB
author_rank: Super Contributor
timestamp: December 21, 2014, 04:37:04 pm
content: Yes, that is why things fluoresce under UV light. However it will be absorbed by the outer layer of your skin, so you will just have the same sunburn that you get outdoors, and the same risk of melanoma. It can also cause your eyes to develop cataracts for the same reason.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: December 21, 2014, 05:12:50 pm
content: Quote from: SeanB on December 21, 2014, 04:37:04 pmThanks SeanB, I understand the effects of UV, electrons which are knocked from a lower orbit to a higher orbit emit a photon when falling back. I just need to figure out the energy/wavelength needed for my application. I think I found some formulas to assist me with that. I also presumed that it took a higher energy (higher frequency) UV to effectively do this in a relatively short period of time. UV, such as 395nm may not contain enough energy to make this happen.Again, thanks for the quick reply!

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2014, 06:01:52 pm
content: Disclaimer: this isn't my area of expertise.It depends on what you're trying to do.Generally UV is still classified as non-ionising radiation, (especially the longer UVA wavelengths which boarder the visible spectrum) although it does have enough energy to catalyse certain chemical reactions, including those which cause cancer.According to the formula on Wikipedia, the energy of a photon at 390nm is 3.18eVhttp://en.wikipedia.org/wiki/Electronvolt#PropertiesThe element with the smallest ionisation energy and is stable is caesium at 3.894eV which corresponds to a UV wavelength of 318.4nm.http://environmentalchemistry.com/yogi/periodic/1stionization.html

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: December 21, 2014, 06:19:00 pm
content: Thanks Hero999, I am starting my experiment with a 100W UVC at 230nm them moving to FUV then EUV. Thanks again for the links!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2014, 07:41:10 pm
content: Quote from: SeanB on December 21, 2014, 04:37:04 pmSometimes, but never always. Those are usually electronic transitions within a crystal -- complete ionization does not occur.The analogy with semiconductors: light with energy greater than the bandgap is able to produce free conduction electrons (and holes), making it conductive. The electrons remain bound within the material, but are free to move about until recombined or conducted away. Whereas, light with energy greater than the work potential of the material, is able to free electrons entirely -- blasting them off the surface as photoelectrons. (Vacuum tubes, which operate on free electrons rather than solid-state conduction electrons, can be seen, quite appropriately, as the next energy level up from semiconductors.)You might imagine a phosphor as a semiconductor where recombination (usually mediated by a low-concentration dopant) occurs at a slightly lower energy level than the energy gap, thus, it takes light of Eg or greater to induce fluorescence, while light of Er < Eg (or thereabouts) is emitted.QuoteYes, UV causes damage to biological matter for similar reasons: freed electrons, disrupting chemical bonds. There are also, you might say, parasitic resonances, where molecules are rearranged or cleaved altogether, forming undesirable products (like damaged DNA or oxidative stress), which though mostly repairable, can accumulate at high concentrations, causing... bad stuff.Quote from: Terabyte2007 on December 21, 2014, 04:12:30 pmAs for electrons in 'orbit', the answer depends entirely on the material or atom, and the energy of light. The atomic quantity you are looking for is called ionization energy. Tables are available. These will be monatomic or diatomic values.Ionization energy is not representative of compound molecules or crystalline solids. For solids, you want the work potential (the same thing occurs -- an electron evaporates, leaving the substrate at least partially ionized in a sense; but usually, it is also conductive, so that the charge lost causes a current flow through an outside circuit, as in a photocell). For compounds, the resonant frequencies (spectra) which cause absorption, ionization or dissociation may be available, but you'll need a UV-vis spectrophotometric database to determine an unknown sample ($$?).For high UV (up into soft x-rays), sufficient energy can be delivered to displace electrons other than valence electrons bound in the atom, molecule or crystal; namely, inner shell electrons which are otherwise stuck firmly in place, crowded by the others in lower energy potentials outside. If you had a EUV-to-X-ray spectrophotometer, you would observe not-quite-periodic absorbance lines up to a limiting value, the K lines -- characteristic to the atom. K lines are characteristic of knocking out the tightest, smallest, highest energy electrons, closest to the nucleus, which causes a cascade of falling energy levels (so in addition to the absorbance, you get, in essence, x-ray fluorescence for a whole range of lines, potentially all the way down to the ground state valence electrons). Additional ionization may also occur (in which case the beta radiation is called an Auger electron -- for an analogy, think of the physics demo where a small ball rests on top of a bigger ball, and the two-ball system is dropped on the floor: the small ball gets launched the fuck out of there, because it absorbs the kinetic energy of both balls in the rebound).Reference: I'm a physicist too, so thereTim

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: December 21, 2014, 07:50:22 pm
content: Quote from: T3sl4co1l on December 21, 2014, 07:41:10 pmVery nice indeed!Thanks much!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2014, 07:50:42 pm
content: Oh, and;Quote from: Hero999 on December 21, 2014, 06:01:52 pmFascinatingly, there are crystalline compounds with even lower ionization energy. Cesium coatings are frequently used in phototubes, because -- indeed, the work potential (ionization from a crystal) is small (maybe not proportional to the atomic ionization energy, but of similar order, anyway), but in fact, certain compounds, and in combination with weak gasses and vapors (such as vaporized cesium), have work potentials down in the < 1eV range! This not only allows phototubes to respond to visible and infrared light, but allows thermionic generators with non-negligible efficiency (a few percent, I think?).Even more fascinating, apparently Rydberg matter is involved -- that is, clusters of atoms, where the valence electrons are in a very large-n state (10-20 or more, versus 1-6 for ground state atoms). When n is large, the electron is at a high potential from the ground state, and a low potential away from being bound at all. Therefore, these clusters have even lower potentials for excitation and dissociation, but they are frustratingly hard to study -- because, of course, you need to put in big wads of energy to vaporize and ionize atoms from a crystal, but then take out *just* enough energy to allow these clusters to form, in this tenuous envelope near "unbound", just barely sticking together.Tim

author: Zero999
author_rank: Super Contributor
timestamp: December 27, 2014, 06:09:31 pm
content: Any EM radiation can cause ionisation, if the intensity is high enough. We normally think of visible, IR and RF to be non-ionising but if the power density is very high, the E field can be strong enough to cause ionisation. A very powerful IR laser can ionise the air into a plasma as the electric field exceeds breakdown voltage of air.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2014, 06:32:08 pm
content: A couple of ways you can think of that:- Any EM wavelength can be used for accelerating particles! Normally RF (100s of MHz) is used in LINACs and such because it's easier to construct a beamline that way. Particles striking a surface cause radiation in various wavelengths (x-rays).Or vice versa, where traveling wave tubes have been used for many years to achieve radio frequency gain, or free electron lasers, which have been constructed up into the x-ray range (particle energy --> E&M).Recent research in extremely high power lasers have shown a combination of plasma, laser and relativistic particles can achieve acceleration well in excess of traditional methods. (We're talking 100s GeV from UV-vis range lasers, over a distance of fractions of a meter.)- Nonlinear media (usually certain crystals, but pretty much anything will do if pushed hard enough..) have been used as optical frequency mixers for some time now; the active part of a green laser pointer is an IR laser diode, focused on a doubler crystal. Often, a substantial quantity of IR remains in the output...- A combination of these processes can occur at a surface or focus, where the sheer intensity causes intense heating (broad UV, x-ray emission?) or acceleration (electric field tearing things up?), resulting in broad spectrum radiation, harmonics (maybe?) or characteristic lines (ionization, absorption) from the material.Really, many of these are equivalent on some level, or active in combination, hence you often get kind of a mess of things.Tim

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: December 27, 2014, 06:41:32 pm
content: Awesome info! Thanks guys!

author: vindoline
author_rank: Unknown
timestamp: December 27, 2014, 10:45:49 pm
content: Well, we no longer think of electrons having an "orbit" to be knocked out of. Energy in the UV range can promote electrons in a lower energy molecular orbital into a higher energy orbital. Depending on a number of issues, the decay of the electron back into the "ground state" (where it started) may be accompanied by release of a photon which can be fluorescence or phosphorescence. UV energy will not generally "ionize" molecules. It's all very dependent on the materials you are working with though.

author: Psi
author_rank: Super Contributor
timestamp: December 27, 2014, 11:08:52 pm
content: Quote from: Terabyte2007 on December 21, 2014, 06:19:00 pm"It's only 100W of UVC, what could go wrong..."

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2014, 11:40:21 pm
content: Quote from: vindoline on December 27, 2014, 10:45:49 pmAnd, ionize means different things: the most fundamental is atomic ionization, but this is rare outside of, well, atomic plasmas! Semiconductors exhibiting free charge carriers (typical of photocells and bipolar transistors) might be said to exhibit a lower grade kind of ionization, where electrons (and holes) are free to move about, but only within the solid; the photoelectric and thermionic effects concern the freedom of electrons outside the material entirely, which can be considered, in turn, a low grade of molecular or atomic ionization (the crystal is left an electron short after an emission event, but the electric potential of the crystal is essentially untouched due to its sheer bulk). Likewise, ions float around in ionic solvents (such as NaCl in H2O) without causing problems, in fact many crystals dissolve exothermically in solvents (they "want" to be solvated), NaOH being one example.Tim

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2014, 03:05:33 pm
content: Quote from: Psi on December 27, 2014, 11:08:52 pmI missed that. Is it 100W of UVC out or is that the input power? Assuming 20% efficiency for low pressure mercury vapour lamps, you'd need 500W in to get 100W out. No need to mention the obvious safety issues about eye damage, skin cancer and risk of death if the exposure is prolonged and intense.