03/16/2005
More Hot Bubbles
Where else but here in Southwest Florida would the subject of traffic on a particular local road (not the infamous I-75) warrant almost four full pages in the Sunday paper? As Brian Trumbore mentioned in his Week in Review column after a recent visit, this area is overdeveloped and traffic can be horrendous. The same March 13 Sunday edition of the Naples Daily News included an AP report by David Royse that highlighted another issue that could well warrant future multi-page coverage – toilet paper! A Florida state legislator has proposed a bill that would levy a tax of 2 cents a roll on that crucial item, with the money raised by the tax to be spent on wastewater treatment and upgrading of sewer systems.
The handling of wastewater and sewage is an environmental issue of considerable importance anywhere, especially in Florida. However, the toilet paper bill is given little chance of passage and apparently would require Governor Jeb Bush’s approval to become law. Bush doesn’t seem too sure about the bill, opining that the tax might lead to people using less toilet paper and he wasn’t sure that would be a good thing. Needless to say, Florida is flush with bathroom humor concerning the bill but we certainly don’t want to stoop that low. Besides, there are other newsworthy subjects that are more universal in nature.
For example, a cover story by Dan Vergano in the March 8 edition of USA Today reminds us that this month marks the centennial anniversary of the first of Einstein’s seminal contributions in 1905, his “miracle year”. In March 1905 Einstein answered the question, “How could light, a mere wave, hit a metal or other surface and knock electrons out of the material, the so-called photoelectric effect?” Einstein’s answer was that light travels in “quanta”, little packets of light we now know as photons. These photons carry enough energy to knock out the electrons. This won Einstein his only Nobel Prize and jump-started quantum mechanics, with its weird conclusion that light behaves as both a particle and a wave.
Later in 1905, Einstein concluded that matter and energy are related by the simple equation E = mc^2. Destroy matter, as happens in nuclear fusion (as in the hydrogen bomb) and you get energy. The Star Ledger of March 8 (both clippings from the Ledger and USA Today kindly supplied by Brian Trumbore) contained a lengthy obituary of Hans Bethe, who died last week at the age of 98. Born in Strasbourg in 1906, his life just missed overlapping Einstein’s miracle year. However, Bethe was a giant in the field of physics who understood Einstein’s equation quite well. Bethe won his Nobel Prize by showing that hydrogen and carbon are involved in a nuclear fusion reaction that supplies most of the power in our Sun and other brilliant stars.
Both Einstein and Bethe fled Nazi Germany in 1933, Einstein ending up at Princeton and Bethe at Cornell. Einstein’s letter to FDR prompted the Manhattan Project and Bethe became the head of the theoretical physics division at Los Alamos. He and his colleagues turned Einstein’s equation into the atom bomb (nuclear fission), later followed by the hydrogen bomb. Bethe was the last survivor of that group of superstars of the physics world that worked on the Manhattan Project. He continued to work at Cornell into his 90s, reputedly never learned to program the simplest computers and brought out his trusty 70-year-old slide rule when needed.
This morning, as every morning, I whip up a mix of a banana and orange juice in a blender. I rinse the blender by whizzing it with hot water, watching those many bubbles doing their job. Invariably, I think of the work we’ve discussed in previous columns by Taleyarkhan and coworkers at Oak Ridge National Lab. For those who missed those columns, these Oak Ridge researchers claimed to have found evidence of nuclear fusion in bubbles. When bubbles expand and contract, there can be a large amount of energy released and local bubble temperatures can be quite high. Essentially, the Oak Ridge workers were saying that the temperature in their bubbles was high enough to fuse deuterium, a heavy form of hydrogen. After the cold fusion hullabaloo some years ago, scientists tend to be skeptical of any reports of fusion in a beaker, so to speak.
However, the March 7 Chemical and Engineering News had an article by Ron Dagani on work related to the possibility that this “bubble fusion” might be real. At Oak Ridge, they used “acoustic cavitation” to expand and collapse the bubbles. In acoustic cavitation, the liquid is blasted with ultrasound; the ultrasound waves cause the pressure to rise and fall rapidly, leading to the desired expansion and contraction of the bubbles. Dagani’s article refers to recent acoustic cavitation work by Kenneth Suslick and graduate student David Flannigan at the University of Illinois. The work, published in a recent issue of Nature, does not confirm bubble fusion but holds out hope that fusion in bubbles might be possible.
It has long been known that under certain conditions cavitating bubbles give off light, so-called “sonoluminescence”. This light is typically pretty weak in intensity. However, most studies were done is water or some sort of water solution. A bubble in water contains water vapor. We all know water is H2O and must have bonds between hydrogen and oxygen. In a collapsing bubble, most of the energy released is taken up by the water vapor molecules. This energy goes into vibration and bending of bonds, leaving little energy to be released in the form of light.
What Suslick and Flannigan have done is to study the sonoluminescence in cavitating single bubbles in sulfuric acid. The bubbles were filled with either argon or xenon. Sulfuric acid has a low vapor pressure and the argon or xenon gas in the bubbles is in the form of atoms, not molecules. There aren’t any bonds to bend or vibrate. As a result, more energy is emitted as light thousands of times more intense than the light from bubbles in water. The Illinois researchers also found that, with more intense light, they can detect and measure intensities of spectral lines, something they couldn’t do with bubbles in water.
Suslick and Flannigan used these spectra and the intensities to deduce two important results. First, the temperature inside the bubble was found to be more than 15,000 degrees Kelvin. This is 3 or 4 times the temperature on the surface of the sun! It’s truly hot in those bubbles. Second, they found spectra corresponding to an oxygen molecule with a positive charge, O2+. This means an electron has been knocked out of the molecule.
The finding of the charged oxygen molecules has an important consequence. The high temperatures in the bubble would not cause an electron to fly off; the heat would break the bond between the two oxygen atoms in the molecule. The workers conclude that the electron is knocked off in collisions with other ions or electrons in the bubble. The existence of the charged molecule indicates that the cavitation of the bubble creates a plasma, a mix of charged ions and other charged particles. Creation of a high energy plasma in a bubble is just the sort of thing that you would hope for if you’re shooting for fusion.
Suslick is careful to point out that no nuclear fusion has been detected. Their system differs from that employed by the Oak Ridge workers, who used acetone in which the hydrogen was replaced with deuterium, which fuses at a lower temperature than ordinary hydrogen. The Illinois workers are now working on sulfuric acid in which the hydrogen is replaced with deuterium.
Meanwhile, I’ll keep a sharp eye out for any nuclear fusion in my banana-orange juice blend.
Allen F. Bortrum
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