Wikipedia:Reference desk/Archives/Science/2012 June 14

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June 14

Mir Mine vs. Grand Canyon

I read the recent article on the Mir Mine in Russia. In the article, it is noted that helicopters are not permitted to fly over the mine due to the hazards associated with the strong downdraft. I assume the same rule is in place for other large open pit mines. Does the same problem of downdraft dangers exist for other, naturally occuring locals such as the Grand Canyon? 99.250.103.117 (talk) 03:00, 14 June 2012 (UTC)

They do fly choppers over the Grand Canyon (and only occasionally crash them), so it must not be too bad. The ambient wind conditions certainly would play a factor. StuRat (talk) 04:36, 14 June 2012 (UTC)

The Mir Mine is 1200 feet wide, according to the article, getting narrower and narrower as it goes down, and it looks circular from what I see in the photo. The Grand Canyon is up to 18 miles wide. Wnt (talk) 11:14, 14 June 2012 (UTC)

In Barringer Crater in Arizona, a Cessna 150 attempting to fly low over the crater lost lift, got trapped in the crater and ended up crashing when the plane stalled trying to climb over the rim - not sure if this was the same type of problem. Mikenorton (talk) 21:29, 14 June 2012 (UTC)

And there are a few canyons that are narrower than the Mir mine and also deeper, for example the Black Canyon of the Gunnison in Colorado. Looie496 (talk) 21:57, 14 June 2012 (UTC)

Origin of atomic orbital codes

The orbitals / standing wave functions of electrons in an atom are known by the codes s, p, d, f, ... Why these particular code letters? Do they stand for something? Wickwack120.145.193.223 (talk) 03:13, 14 June 2012 (UTC)

From atomic orbital, "These names indicate the orbital shape and are used to describe the electron configurations. They are derived from the characteristics of their spectroscopic lines: sharp, principal, diffuse, and fundamental, the rest being named in alphabetical order (omitting j).". Someguy1221 (talk) 03:17, 14 June 2012 (UTC)

While Someguy1221 is utterly correct, one could suggest that orbitals are named in sequence after the letters in the name of the rockband Spdfgh. It certainly makes remembering orbital shape names easier if you were into 1990s Australian rock. Fifelfoo (talk) 03:34, 14 June 2012 (UTC)

I'm pretty sure it worked the other way around, causatively speaking... --Jayron32 03:36, 14 June 2012 (UTC)

I remember them as "SPuD Farts". StuRat (talk) 04:32, 14 June 2012 (UTC)

Thank you, Someguy. Sorry, Fifelfoo, I had never heard of the rockband. Wickwack120.145.193.223 (talk) 04:08, 14 June 2012 (UTC)

They had the dumbest name in Australian rock and you can still hear their Wikky(pedia) ode. (video). DriveByWire (talk) 16:19, 14 June 2012 (UTC)

Sputum

Is sputum phlegm or mucus? The phlegm article says it's phlegm that's been expectorated, but the sputum says it's mucus. See the last section in Talk:Sputum. Rojomoke (talk) 09:52, 14 June 2012 (UTC)

I don't see a contradiction in what's written in the three articles, but the "distinction between mucus and phlegm" looks a bit rough and perhaps misleading. Mucus is a general term for the secretions, whether normal or in response to disease. Phlegm refers to the non-nasal mucus of the respiratory tract. And sputum is only the phlegm that has actually exited the premises. That sounds OK to me. The problem is that the writer of the one section says "phlegm is more related to disease than mucus", though acknowledging it's a kind of mucus. So there might be an other or a per se missing there. (There's also the issue that phlegm/sputum isn't pure mucus, as other things can be mixed in) Wnt (talk) 11:21, 14 June 2012 (UTC)

Phlegm is lower respiratory excreta, mucus and its contaminants. Once it has been coughed up it is sputum. See spit and humorism]. μηδείς (talk) 21:52, 14 June 2012 (UTC)

Resolved

X-ray lenses, will camera optics do?

Is it possible to use a camera to picture a low intensity X-ray source?, or is the material in the camera lenses unsuitable? ie the photons pass right through it? and how to determine what material that is suitable? (app solder photo) Electron9 (talk) 19:20, 14 June 2012 (UTC)

No, neither the camera lenses nor the sensor are suited for x-rays. Refraction indexes for glass lenses are very different (much higher) for lower wavelengths and therefore will not focus x-rays correctly if at all. The camera's sensor can only measures levels of red green and blue, maybe some ultraviolet or infrared may be measured, but x-rays are so far off the scale that they will not be detected. See also X-ray optics. - Lindert (talk) 19:43, 14 June 2012 (UTC)

I have read that the x-ray photo causes the sensor device to be charged, and thus readable. Maybe the x-ray nature isn't sharp one, such that one can accomplish a compromise by using specific wavelengths that will still penetrate ceramic and plastic materials? Electron9 (talk) 20:23, 14 June 2012 (UTC)

I don't know, I guess it is possible that the sensor will pick up some signal, but the problem remains how to focus the x-rays correctly. X-ray optics suggests using a pinhole camera may work. May I ask what application you are thinking of? - Lindert (talk) 20:53, 14 June 2012 (UTC)

I remember my lecturer for x-ray crystallography saying that no material has a high enough refractive index to focus x-rays.203.27.72.5 (talk) 21:03, 14 June 2012 (UTC)

That's true, but you can get around it by focusing the X-rays with mirrors instead of lenses. At extremely high angles of incidence, X-rays will reflect off of some materials, making an x-ray telescope possible. See x-ray optics for more information. Someguy1221 (talk) 22:54, 14 June 2012 (UTC)

X-ray of BGA

I guess that depend on what is defined as "x-rays". If one simple see it as a photon of a specific wavelength. Then the transition between being lensable and not should be gradual. And a optimum be possible. If the photons pass through ceramic and plastic with a resolution near 0.1 mm it's fine for the objective. Though I can think of uses at 9 nm and below ;) The application is Ball grid array#Difficulty of inspection. One method would be radio tube diode with CMOS imager. Electron9 (talk) 21:19, 14 June 2012 (UTC)

I wonder if you could take a point source of X-rays, and use a digital videocamera CCD to scan around for transmitted rays, using image software to assemble the moving frames and compensate for any variations due to absorption in the camera. Of course, this would be a foolhardiness akin to old fashioned fluoroscopy, dangerous to camera and patient alike, but technically ... well, I'm not sure. ;) Wnt (talk) 01:26, 15 June 2012 (UTC)

Indeed; traditional medical x-ray imaging is based on the concept of having the xray source approximate a point source, thus no attempt at focusing x-rays is required. Definately not a good idea health wise unless you take very thorough precautions, but home-made x-ray apparatus is quite easy, using high voltage vacuum tubes intended for 1950's colour TV sets. Try "homemade x-ray" on Google. Ratbone58.164.224.145 (talk) 03:16, 15 June 2012 (UTC)

Precaution will be a robot .. :-) (x-y servo), I guess the photo is accomplished by a point source then? Electron9 (talk) 09:30, 15 June 2012 (UTC)

Your english is unclear. I assume you meant "I guess the ball grid array photo was accomplished using an x-ray point source then? I guess so - but the image quality is so poor there is no evidence that it even is a BGA. Incidentally, when I was an university, I used an ordinary medical grade x-ray machine to examine the internal construction of electronic components. The resolution was surprisingly good - good enough to determine the wire gauge of coils - good enough to measure approximately the diameter of a pin head. Ratbone120.145.14.192 (talk) 15:30, 15 June 2012 (UTC)

How was this medical grade machine designed? (point source?) Electron9 (talk) 17:06, 15 June 2012 (UTC)

There's no way I can remember the specific x-ray machine now, but as I posted earlier, medical x-ray machines have emission tubes that are designed to approximate a point source. An ordinary traditional sort of machine you'd commonly find has emission confined to a spot less than 1 mm². Modern specialist machines can have emission spots down to 10 μm diameter or even smaller. Ratbone60.230.213.11 (talk) 00:46, 16 June 2012 (UTC)

Electron9: You seem to have several misunderstandings. The problem is not that the x-ray photons won't pass through the material of the lens, but rather that they pass through the lens and are not focused by it. The x-ray photons just go straight through (almost) as if the lens were not there at all. You seem to be thinking of absorption, but the problem is index of refraction. The refractive index of materials varies with wavelength. At x-ray wavelengths the index is essentially the same as that of vacuum. The transition with wavelength is gradual, but x-rays are very far beyond the wavelength region where that transition occurs. --Srleffler (talk) 17:27, 15 June 2012 (UTC)

I do understand that the lens will be transparent when wavelength is shorter and that the lens will be unable to bend photons at that wavelength. But I was unsure on the the properties of pro-consumer camera lens material because it's unlikely any ordinary window glass. What is the mathematical relation between refraction index (n) and wavelength (λ) and the proportion quote bent vs not bent?, I did look at the refractive article without finding any really clear mathematical relationship. Electron9 (talk) 18:24, 15 June 2012 (UTC)

The general rule is that refractive index falls with wavelength. There is a "knee point" wavelength at which the fall in RII becomes hopeless rapid. The Sellmeier equation describes the relationship for "simple" materials where the RI is usuable, but for x-rays, like other posters have said, forget about lens focusing. You can use aperture beam limiting (ie using a thick x-ray opaque material with a hole in it to block out x-rays going in unwanted directions. Ratbone60.230.213.11 (talk) 00:57, 16 June 2012 (UTC)

At which wavelength does this "knee" occur at approximately ? Electron9 (talk) 04:04, 16 June 2012 (UTC)

All light is bent by a lens, but the index of refraction determines the angle by which the rays are bent. The closer the index is to that of the surrounding medium, the smaller the angle by which the rays will be bent. If the index of refraction is close to that of the surrounding medium, the angle by which the rays are bent becomes proportional to the difference between the two. For x-rays, the index of refraction of almost all media is very close to 1, so bending of x-rays through refraction is negligible. You may also be interested in the thin lens equation and Snell's law--Srleffler (talk) 03:04, 16 June 2012 (UTC)

Guess the most rational approach would be a small "peek" hole for emission of x-rays and a below the circuit board, and below that a picture scanner with the lid on that has a wide (CCD) sensor and uses stepper motor for the other axis. Image sensor chips will be too small. Electron9 (talk) 04:04, 16 June 2012 (UTC)