Physics

Livermore researchers have moved one step closer to being able to turn on and off the decay of a nuclear isomer.

The protons and neutrons in a nucleus can be arranged in many ways. The arrangement with the lowest energy is called the ground state and all others are called excited states. (This is analogous to the ground and excited states of electrons in an atom except that nuclear excited states are typically thousands of times higher in energy.) Excited nuclear states eventually decay to the ground state via gamma emission or to another nucleus via particle emission. Most excited states are short-lived (e.g., billionth of a second). However, a few are long-lived (e.g., hours) and are called isomers.

The last quadripolar magnet was brought down into the tunnel of the world’s largest particle accelerator; the CERN’s1 LHC, or Large Hadron Collidor. This magnet is part of a series of 392 units which will ensure that the beams are kept on track all along their trajectory through the tunnel. Its installation marks the completion of a long and fruitful collaboration between the CERN, the CNRS/IN2P32 and the CEA/DSM3 in the field of superconductivity and advanced cryogenics. This collaboration has lasted over ten years and was part of the special contribution made by France, as the host country, to the construction of the LHC.

Using measurements of the four ESA's Cluster satellites, a study published this week in Nature Physics shows pioneering experimental evidence of magnetic reconnection also in turbulent 'plasma' around Earth.


This image provides a model of magnetic fields at the Sun's surface using SOHO data, showing irregular magnetic fields (the ‘magnetic carpet’) in the solar corona (top layer of the Sun's atmosphere). Small-scale current sheets are likely to form in such turbulent environment and reconnection may occur in similar fashion as in Earth's magnetosheath. Credits: Stanford-Lockheed Inst. for Space Research/NASA GSFC

Nanomechanical oscillators -- tiny strips of vibrating silicon only a few hundred atoms thick -- are the subject of extensive study by nanotechnology researchers. They could someday replace bulky quartz crystals in electronic circuits or be used to detect and identify bacteria and viruses.

The catch is that measuring their vibrations isn't easy. It is usually done by bouncing laser beams off them -- which won't work when the nanodevices become smaller than the wavelength of the light -- or with piezoelectric devices -- those bulky quartz crystals we're trying to get rid of.


Schematic of the experimental setup.

Researchers in Japan have developed a pair of molecular-scale scissors that open and close in response to light. The tiny scissors are the first example of a molecular machine capable of mechanically manipulating molecules by using light, the scientists say.

The scissors measure just three nanometers in length, small enough to deliver drugs into cells or manipulate genes and other biological molecules, says principal investigator Takuzo Aida, Ph.D., professor of chemistry and biotechnology at the University of Tokyo.


The scissors-like molecular machine extends or folds in response to different wavelengths of light. Credit: University of Tokyo.

As an electromagnetics guy I stay in touch with a lot of what is happening in that segment of physics by subscribing to plain, ol' email lists. People who need info just fire off a question to the group and someone helps.

Occasionally recruiters spam the place because, you know, all of their recruiting emails are terribly important to the whole planet. When I got my email this morning, I saw this:

University of Chicago scientists will demonstrate how to incinerate a white dwarf star in unprecedented detail at the “Paths to Exploding Stars” conference on Thursday, March 22, in Santa Barbara, Calif.

White dwarf stars pack one and a half times the mass of the sun into an object the size of Earth. When they burn out, the ensuing explosion produces a type of supernova that astrophysicists believe manufactures most of the iron in the universe.

A new nanoscale apparatus developed at JILA—a tiny gold beam whose 40 million vibrations per second are measured by hopping electrons—offers the potential for a 500-fold increase in the speed of scanning tunneling microscopes (STM), perhaps paving the way for scientists to watch atoms vibrate in high definition in real time.


This slow-motion simulation of the JILA nanoscale motion detector shows the wiggling of a floppy metal beam, just 100 nanometers thick, as it is struck by an electric current at the dot. Red indicates the greatest change in position from the rest state. Credit: Credit: K. Lehnert/JILA

Despite advances in experimental nuclear physics, the most detailed probing of atomic nuclei still requires heavy doses of advanced nuclear theory. The problem is that using theory to make meaningful predictions requires massive datasets that tax even high-powered supercomputers.

In a March 16 Physical Review Letters article, researchers from Michigan State and Central Michigan universities report dramatic success in stripping away much of this stubborn complexity. The advance, which slashes computational time from days or weeks to minutes or hours, may help address one of the most important questions in nuclear physics today: what is the structure of heavy atomic nuclei?

For the first time, scientists of the BaBar experiment at the Department of Energy's Stanford Linear Accelerator Center (SLAC) have observed the transition of one type of particle, the neutral D-meson, into its antimatter particle. This observation will now be used as a test of the Standard Model, the current theory that best describes all the universe's luminous matter and its associated forces.


Silicon Vertex Tracker. The SVT is the heart of the BABAR experiment at SLAC—in the photo, physicists are putting the finishing touches on improvements to the detector. (Photo Courtesy of Peter Ginter)