Sudoku and Velocity Fields...

Image Source: Link below

Topics: Materials Science, Probability, Radiation, X-rays

To see what happens inside a pile of sand or another volume of granular material, researchers rely either on deformation observations at the surface, which don’t always reflect any internal flows, or on simulations. Several existing techniques can image interior flows, but they each have one or more disadvantages, such as limited spatial and temporal resolutions, high costs, and invasiveness. A new technique, developed by James Baker, Itai Einav, and their colleagues at the University of Sydney, overcame those hurdles by using sets of two-dimensional x-ray radiographs to uncover the three-dimensional velocity field inside a volume of opaque grains.

X rays were fired from three orthogonal locations through a container of opaque grains that were being sheared from below by a conveyor belt, as shown in the diagram above. By spatially correlating successive radiographs, the researchers extracted the probability density functions (PDFs) of the two displacement components orthogonal to the x-ray direction for each grid cell. Each PDF was then sampled evenly to generate an unsorted array of the different displacements through the beam direction.

By combining the PDF results orthogonal to each other and solving a Sudoku-style puzzle, the researchers were able to reconstruct the 3D velocity field shown from 2D projections. As in Sudoku, the displacement values that should be placed in each row and column are known from the two sets of PDFs, but how to arrange those displacements in space defines the puzzle. Unlike in Sudoku, though, there is no unique solution.

X-ray correlations assemble a complete velocity field, Alex Lopatka, Physics Today

Compact Radiocarbon Detector...

Physics Today: Optical detection of radiocarbon dioxide (partial view)

Topics: Modern Physics, Radiation, Spectrograph

A compact spectroscopic system can measure radioactive carbon dioxide concentrations as low as five parts per quadrillion.

Carbon’s only naturally occurring radioactive isotope, ¹⁴C, is exceedingly rare. Produced when neutrons from cosmic rays interact with nitrogen, the radioisotope makes up just one part per trillion of the carbon in Earth’s atmosphere. Yet because of its continual production, its diffusion through the planet’s carbon cycle, and its long half-life of 5700 years, ¹⁴C is routinely used to date organic matter as old as 50 000 years. Archaeologists, forensic scientists, and environmental researchers, among others, essentially measure the concentration of radiocarbon in a sample to determine its age.

Since the late 1970s, accelerator mass spectrometry (AMS) has served as the benchmark method for the job. In that approach, samples are burned, chemically converted to graphite, and bombarded with cesium ions. The negative carbon ions ejected from the solid samples are then accelerated to a few percent of the speed of light and their mass-to-charge ratios deduced from their trajectories through electric and magnetic fields. Fortuitously, the most common isotope of nitrogen in the atmosphere, ¹⁴N, forms no stable negative ion; and its absence eliminates its otherwise large interference with the ¹⁴C signal. Likewise, ¹²CH₂ and ¹³CH molecules are broken apart during a later, electron-stripping stage and don’t survive to interfere with the signal.

Both effects help free ¹⁴C signals from background noise. But although the technique is powerful—and applicable to other trace elements—the spectrometers can cost millions of dollars and often require a dedicated facility to maintain their electrodes at hundreds of thousands to millions of volts in a vacuum.

A technically simpler approach also begins with burning a sample, but only to transform its carbon atoms into carbon dioxide molecules. With their strong vibrational absorptions in the mid-IR, the many isotopic combinations of CO₂ can be distinguished optically. The challenge is to measure the intensities of their spectral lines to determine the concentration ratios. The task is not easy if the goal is to count trace isotopes in a sea of abundant ones. The CO₂ molecule has hundreds of vibrational and rotational lines, many of them closely spaced in frequency. And even the most stable lasers suffer from intensity fluctuations.

Physics Today: Smaller, faster, cheaper detection of radiocarbon, R Mark Wilson

Fifth Force...

Credit: Avariel Falcon/Flickr, CC BY 2.0

Topics: Experimental Physics, Particle Physics, Radiation, Theoretical Physics

The Four (currently well-known) Forces: The Strong Force, the Electromagnetic Force, the Weak Force and Gravity. See: this link, which includes a brief primer on each and Feynman Diagrams on the strong and weak forces. Debate is going on now whether the new Force is evidence of Dark Energy, Dark Matter; a "Dark Photon" at 17 MeV, or what they refer to in the article as a "protophobic X (Greek letter Chi) boson." As with all reporting of scientific investigations, this is in its preliminary stages.

A laboratory experiment in Hungary has spotted an anomaly in radioactive decay that could be the signature of a previously unknown fifth fundamental force of nature, physicists say—if the finding holds up.

Attila Krasznahorkay at the Hungarian Academy of Sciences’s Institute for Nuclear Research in Debrecen, Hungary, and his colleagues reported their surprising result in 2015 on the arXiv preprint server, and this January in the journal Physical Review Letters. But the report – which posited the existence of a new, light boson only 34 times heavier than the electron—was largely overlooked.

Then, on April 25, a group of US theoretical physicists brought the finding to wider attention by publishing its own analysis of the result on arXiv. The theorists showed that the data didn’t conflict with any previous experiments—and concluded that it could be evidence for a fifth fundamental force. “We brought it out from relative obscurity,” says Jonathan Feng, at the University of California, Irvine, the lead author of the arXiv report.

Four days later, two of Feng's colleagues discussed the finding at a workshop at the SLAC National Accelerator Laboratory in Menlo Park, California. Researchers there were sceptical but excited about the idea, says Bogdan Wojtsekhowski, a physicist at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. “Many participants in the workshop are thinking about different ways to check it,” he says. Groups in Europe and the United States say that they should be able to confirm or rebut the Hungarian experimental results within about a year.

Scientific American:
Some theorists say a radioactive decay anomaly could imply a fundamental new force
Edwin Cartlidge

Radio Electron...

An electron in a magnetic field will turn circles and emit radiation. Adrian Cho - Science Mag

Topics: Cyclotron, Electromagnetism, Neutrinos, Particle Physics, Radiation

Physicists have long known that charged particles like electrons will spiral in a magnetic field and give off radiation. But nobody had ever detected the radio waves emanating from a single whirling electron—until now. The striking new technique researchers used to do it might someday help particle physicists answer a question that has vexed them for decades: How much does a ghostly particle called the neutrino weigh?

"This is a great achievement on its own, and we're really looking forward to seeing this technology develop over time," says Guido Drexlin, an astroparticle physicist at the Karlsruhe Institute of Technology in Germany who was not involved in the work.

To understand the experiment, suppose an electron flies horizontally through a vertical magnetic field. It will experience a sideways force that is proportional to both its velocity and the strength of the field. That constant sideways shove will cause the electron to run in circles (see diagram). But that turning will also cause the electron to radiate electromagnetic waves, much as a wet dishcloth will fling off drops of water if you whirl it above your head. Of course, the radiation will sap the electron's energy, so that it will gradually spiral inward.

This effect has been understood for a century. It's used to generate x-ray beams by sending electrons racing around circular particle accelerators known as synchrotrons. Such radiation also emanates from swirling particles in interstellar space. Now, 27 physicists with Project 8, an experiment based at the University of Washington, Seattle, have detected radiation from a single electron. "I thought surely somebody must have done this," says Brent VanDevender, a nuclear physicist and team member from Pacific Northwest National Laboratory in Richland, Washington. "I looked and looked and looked in the literature and couldn't find anything."

Science Mag: Physicists detect radio waves from a single electron, Adrian Cho