Slashdot Mirror
NC State Creates Most Powerful Positron Beam Ever
eldavojohn writes "A fairly large breakthrough took place earlier this month with the most powerful man-made antimatter electron beam ever being created at North Carolina State University. Professor Hawari who worked on the project explains its benefits: 'The idea here is that if we create this intense beam of antimatter electrons — the complete opposite of the electron, basically — we can then use them in investigating and understanding the new types of materials being used in many applications.'"
Electron microscopes can already image at the atomic level, but a positron microscope has advantages because it can give complimentary information (e.g. about the positions of atomic vacancies). You can also use positron beams for PALS (Positron Annihilation Lifetime Spectroscopy), which is a powerful tool for determining the distribution of sizes in (nano-scale) voids in materials (difficult to measure by any other technique). It's also worth remembering that PET scans used in medicine involves a positron-emitting chemical injected into the patient.
There are probably a whole bunch of other experiments that positrons would be great for performing, but intense positron sources are not readily available. The development of more intense positron sources will certainly be welcomed by the scientific community, as it may allow previously unimagined types of measurements.
Tarheel? Thems fightin' words, son! It's WOLFPACK...
You know, when you've read as many science fiction books as I have, this shit is a liiiitle creepy.
Why? These are usually research reactors, from what I understand. They're not meant to power cities; they're not meant to run at a profit. They're meant to generate some types of isotopes for nuclear medicine students, and to give the nuclear engineers something to do.
I've read a lot of science facts, and that's why this shit doesn't feel that creepy at all. I don't mean to single you out, of course, and there are plenty of valid security and OSHA-like concerns at pretty much any nuclear facility; the public's allergy to anything remotely involving the word "radiation," however, is something that could stand a lot of improvment. The dangers of nuclear science are more to do with mismanagement and a lazy operating culture--which are thankfully not fundamental physical issues but rather human ones that can potentially be fixed.
And, frankly, I'd rather the public learn about nuclear science from scientists rather than science fiction authors.
The Stanford Linear Accelerator Center, or SLAC, generates and accelerates electron and positron beams (and when needed, polarized or spin oriented beams) for colliding beam and fixed target experiments. SLAC has literally hundreds of dipole, quadrapole, and sextupole electromagnets placed along their accelerator, beam lines, and storage rings, all for focusing and directing their charged particle beams. If the center of mass of colliding electron and positron beams is high enough (at a collision energy called a "resonance") new particles will be created from the combined beam energies. During the 1990's, SLAC accelerated electrons and positrons to approximately 49 Giga Electron Volts (or GeV) each with their accelerator. After the two beams drifted in evacuated beam lines away from the accelerator, they were directed such that the electron beam and the positron beam approached an interaction point in the center of a large particle detector called SLD, from opposite sides. In the detector, the two beams would collide, creating new chargeless particles called Z-Zero or Z-Naught particles, with a collision energy of about 95.5 GeV. The Z-Zero, before it decays, is about one half as heavy as a silver atom, but quickly decays into a lot of smaller fragments, some charged and others not charged. The mass of that Z-Zero particle represents the direct conversion of the accelerator's energy into matter.
http://www2.slac.stanford.edu/vvc/detectors/sld.html
In the diagram shown in the link above, look for the e- and e+ labels. Those represent the electron (e-) and positron (e+) beams entering the SLD detector from opposite sides. In the center of the SLD detector is a small cylindrical piece called a Vertex Detector. The center of the vertex detector (a silicon CCD device about the size of a soft drink can with several million pixels in three concentric layers) is where SLAC's electrons actually collided with positrons. The parts of the detector around the Vertex detector are like the layers of an onion. Each layer gathers a different kind of data about the collisions that took place inside the vertex detector at the interaction point. There are a lot of very sophisticated electronics in the layers of all particle detectors, but all of the electronics have one purpose, to gather information about the decay fragments coming from the electron/positron collisions so the events that took place during and immediately after the collision can be reconstructed and analyzed with very sophisticated computers.
Beginning in 1998, SLAC began an experiment called the asymmetric B-meson factory, or "B Factory" for short. In the B Factory, the electron beams run at a little over 9 GeV beam energy, while the positron beams run at only about 3 GeV. Both colliding beams run at very high currents, on the order of two amperes in the electron storage ring, and three amperes in the positron storage ring. The collision of these two high current beams produces millions of B mesons, each with a residual momentum (due to the asymmetric beam energies) that makes it possible for the particle physicists to study more effectively how those B mesons decayed.
Here is a link to more information about "Storage Rings" and their electromagnets:
http://en.wikipedia.org/wiki/Storage_ring
And here are links to three of SLAC's web pages, where you can learn more about colliding beam physics. BaBar is name of the particle detector used to study their decaying B Mesons, and PEP-II is the storage ring collider used to make those B Mesons.
The PEP-II storage ring collider is at: http://www.slac.stanford.edu/grp/ad/ADPEPII/ADPEPII.html
The BaBar detector is at: http://www-public.slac.stanford.edu/babar/
And SLAC's main web page (the first web page in t
An analog gray hair frantically clinging to the trailing edge of technology.