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Archive for the ‘ATOMIC PHYSICS’ Category

The First Measurements Of The Antihydrogen Spectrum

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A New Result From ALPHA

Once you’ve trapped antihydrogen what do you do? You measure it! That’s just what we’ve done. Published in Nature, we report the first resonant quantum transitions in antihydrogen atoms. We’ve used microwave radiation to change the internal state of the atom, from one which can be kept in our trap, to one that is kicked out. This process depends on the frequency of the microwave radiation and the magnetic field in the trap, so by changing both of these, we demonstrated that we had enough control and sensitivity to sucessfully carry out the experiment. This is by no means easy, as antihydrogen is not found in nature, but must be prepared in our apparatus from antiprotons made in the Antiproton Decelerator, and positrons from a radioactive source, Even more, it must have low enough energy to remain trapped in the magnetic fields making up our trap. Here’s an animation describing how we do our measurement.


http://youtu.be/dY5Zdqxoc8U

Eventually, we will use this technique to compare the structure of antihydrogen and hydrogen atoms, to search for difference between matter and antimatter, but In this first experiment, we do not yet have enough precision to test these fundamental symmetries. This is important, as the Universe has shown a preference for matter over antimatter as it has evolved, but so far, no measurements can explain why this came about. If matter and antimatter were truely identical, the Universe as we know it could not have come about. The next step at ALPHA is to construct an apparatus that will allow us to make these more precise measurements, using both microwave radiation, and laser light.
We’ve been waiting a long time for this result, so we’re really happy — the CERN People documentary has been following us through the process — check out the first video here.

Read more: alpha-new.web.cern.ch/

Written by physicsgg

March 8, 2012 at 4:27 pm

Posted in ATOMIC PHYSICS

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Scientists image the charge distribution within a single molecule for the first time

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For their experiments the IBM scientists used their home-built combined scanning tunneling microscope (STM) and atomic force microscope (AFM). In this focused ion beam micrograph, the tip attached to a tuning fork can be seen. The tuning fork measures a few millimeters in length. The tiny tip measures only a single atom or molecule at its apex

IBM scientists were able to measure for the first time how charge is distributed within a single molecule. This achievement will enable fundamental scientific insights into single-molecule switching and bond formation between atoms and molecules. Furthermore, it introduces the possibility of imaging the charge distribution within functional molecular structures, which hold great promise for future applications such as solar photoconversion, energy storage, or molecular scale computing devices.
As reported in in the journal Nature Nanotechnology, scientists Fabian Mohn, Leo Gross, Nikolaj Moll and Gerhard Meyer of IBM Research – Zurich directly imaged the charge distribution within a single naphthalocyanine molecule using a special kind of atomic force microscopy called Kelvin probe force microscopy at low temperatures and in ultrahigh vacuum.
Whereas scanning tunneling microscopy (STM) can be used for imaging electron orbitals of a molecule, and atomic force microscopy (AFM) can be used for resolving its molecular structure, until now it has not been possible to image the charge distribution within a single molecule.
“This work demonstrates an important new capability of being able to directly measure how charge arranges itself within an individual molecule”, states Michael Crommie, Professor for Condensed Matter Physics at the University of Berkeley. “Understanding this kind of charge distribution is critical for understanding how molecules work in different environments. I expect this technique to have an especially important future impact on the many areas where physics, chemistry, and biology intersect.”
In fact, the new technique together with STM and AFM provides complementary information about the molecule, showing different properties of interest. This is reminiscent of medical imaging techniques such as X-ray, MRI, or ultrasonography, which yield complementary information about a person’s anatomy and health condition.

Schematic of the measurement principle. At each tip position, the frequency shift is recorded as a function of the sample bias voltage (inset, red circles). The maximum of the fitted parabola (inset, solid black line) yields the KPFM signal V* for that position. Image courtesy of IBM Research - Zurich

“The technique provides another channel of information that will further our understanding of nanoscale physics. It will now be possible to investigate at the single-molecule level how charge is redistributed when individual chemical bonds are formed between atoms and molecules on surfaces. This is essential as we seek to build atomic and molecular scale devices,” explains Fabian Mohn of the Physics of Nanoscale Systems group at IBM Research – Zurich…..
Read more: physorg.com

Written by physicsgg

February 27, 2012 at 11:50 am

Posted in ATOMIC PHYSICS, TECHNOLOGY

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Single atom transistor gets precise position on chip

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A voltage applied across the electrodes induces a current in the perpendicular electrodes, with the phosphorus atom making it all possible

In a remarkable feat of micro-engineering, UNSW physicists have created a working transistor consisting of a single atom placed precisely in a silicon crystal.


http://youtu.be/ue4z9lB5ZHg

Read more here

Written by physicsgg

February 19, 2012 at 8:01 pm

Posted in ATOMIC PHYSICS, TECHNOLOGY

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Rutherford, Radioactivity, and the Atomic Nucleus

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Young Ernest Rutherford, at the time he was a professor at McGill University

Helge Kragh
Modern atomic and nuclear physics took its start in the early part of the twentieth century, to a large extent based upon experimental investigations of radioactive phenomena. Foremost among the pioneers of the new kind of physics was Ernest Rutherford, who made fundamental contributions to the structure of matter for more than three decades and, in addition, founded important research schools in Manchester and Cambridge.
This paper reviews the most important aspects of Rutherford’s scientific work in the period from about 1900 to 1920, and it also refers to some of his last experiments of the 1930s.
The emphasis is on his theory of radioactive disintegration (1902), the discovery of the atomic nucleus (1911), and the first artificially produced element transformation (1919).
Following the transmutation experiments, Rutherford developed elaborate models of the atomic nucleus, but these turned out to be unsuccessful.
Other subjects could be included, but the three mentioned are undoubtedly those of the greatest importance, the nuclear atom perhaps the greatest and the one with the most far-reaching consequences…..
Read more: http://arxiv.org/pdf

Written by physicsgg

February 7, 2012 at 5:29 pm

Posted in ATOMIC PHYSICS, NUCLEAR PHYSICS

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Anti-matter atoms to address anti-gravity question

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Anti-matter can be made in the lab - but keeping it apart from matter in order to study it has been difficult

The question of whether normal matter’s shadowy counterpart anti-matter exerts a kind of “anti-gravity” is set to be answered, according to a new report.

Normal matter attracts all other matter in the Universe, but it remains unclear if anti-matter attracts or repels it.

A team reporting in Physics Review Letters says it has prepared stable pairs of electrons and their anti-matter particles, positrons.

A beam of these pairs can be used to finally solve the anti-gravity puzzle.

Falling up

For every particle in physics, there is an associated anti-particle, identical in every respect that scientists have yet measured, except that it holds an opposite electric charge.

Current theory holds that, at the birth of the Universe, matter and anti-matter were created in equal amounts. When they meet, however, they destroy each other in energetic flashes of light.

The question has remained, then, why did any Universe come into being at all, and why is the one we see overwhelmingly made of normal matter?

One of the characteristics that may differentiate anti-matter is its gravitational behaviour. Most scientists believe that anti-matter will be attracted to normal matter.

Others are not so sure; anti-matter may repel – it may “fall up”.

That has implications for the question of why the Universe didn’t disappear into a grand flash of light just as soon as it formed. It also might help explain why the Universe is expanding ever more quickly.

It has simply been impossible to test the idea, but researchers at the University of California Riverside are getting closer to addressing the question once and for all.

They have created electron-positron pairs that are in stable orbits around one another – the result is called positronium.

The pairs are kept from bumping into and destroying each other by carefully dumping energy into them to create what are known as “Rydberg states”.

Like the lanes of an automotive test track, particles can move into different orbits around one another if they reach higher energies, and these Rydberg positronium atoms are spun up to high energies, lasting for a comparatively long three billionths of a second.

The team hopes to extend the method, up to a few thousandths of a second, preparing a beam of the artificial atoms and seeing just which way they fall.

Read more: www.bbc.co.uk

Written by physicsgg

January 27, 2012 at 7:16 pm

Rice lab mimics Jupiter’s Trojan asteroids inside a single atom

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Rice University physicists have built an accurate model of part of the solar system inside a single atom. In a new paper in Physical Review Letters, Rice’s team and collaborators from Oak Ridge National Laboratory and the Vienna University of Technology showed they could make an electron orbit the atomic nucleus in the same way that Jupiter’s Trojan asteroids orbit the sun. The findings uphold a 1920 prediction by physicist Niels Bohr.


http://youtu.be/t9sJ-H2hM88

Creating and Transporting Trojan Wave Packets

B. Wyker, S. Ye1, F. B. Dunning, S. Yoshida, C. O. Reinhold, and J. Burgdörfer
Nondispersive localized Trojan wave packets with ni∼305 moving in near-circular Bohr-like orbits are created and transported to localized near-circular Trojan states of higher n, nf∼600, by driving with a linearly polarized sinusoidal electric field whose period is slowly increased. The protocol is remarkably efficient with over 80% of the initial atoms being transferred to the higher n states, a result confirmed by classical trajectory Monte Carlo simulations
prl.aps.org

Written by physicsgg

January 24, 2012 at 9:59 pm

Posted in ATOMIC PHYSICS, QUANTUM PHYSICS

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Landmarks–Millikan Measures the Electron’s Charge

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The Millikan oil drop experiment, published in final form in 1913, demonstrated that charge comes in discrete chunks and was a bridge between classical electromagnetism and modern quantum physics.

Oil can. Millikan’s apparatus included an atomizer to create a mist of oil droplets and a telescope to observe them

Researchers now routinely isolate single electrons in quantum dots, but a century ago the state-of-the-art charge-trapping device was a droplet of clock oil. Robert Millikan’s oil drop experiment provided the first clear measurement of the fundamental electric charge and thus helped cement the notion that nature is “grainy” at the smallest level. The first results came out in 1910, but the seminal work was a 1913 paper in the Physical Review. Millikan reported a value for the fundamental electric charge that was within half a percent of today’s accepted value. The experiment helped earn Millikan a Nobel prize in 1923 but has been a source of some controversy over the years…
Read more: physics.aps.org

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January 23, 2012 at 9:28 pm

Posted in ATOMIC PHYSICS, QUANTUM PHYSICS

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Carbon Dating with Lasers

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I. Galli et al., Phys. Rev. Lett. (2011) For a date, give me a ring. To determine the age of a sample, the SCAR technique uses a highly stable infrared laser to excite carbon dioxide molecules in a mirrored cavity. When the laser is turned off, trapped light dies away in the cavity (or “rings-down”) at a rate that depends on the amount of carbon-14 in the sample.

Phys. Rev. Lett. 107, 270802 (2011) [4 pages]
Molecular Gas Sensing Below Parts Per Trillion: Radiocarbon-Dioxide Optical Detection
I. GalliS. BartaliniS. BorriP. Cancio*D. MazzottiP. De Natale, and G. Giusfredi
Istituto Nazionale di Ottica-CNR (INO-CNR) and European Laboratory for Non-Linear Spectroscopy (LENS) Via N. Carrara 1, I-50019 Sesto Fiorentino, Italy

Radiocarbon (14C) concentrations at a 43 parts-per-quadrillion level are measured by using saturated-absorption cavity ringdown spectroscopy by exciting radiocarbon-dioxide (14C16O2) molecules at the 4.5  μm wavelength.
The ultimate sensitivity limits of molecular trace gas sensing are pushed down to attobar pressures using a comb-assisted absorption spectroscopy setup. Such a result represents the lowest pressure ever detected for a gas of simple molecules.
The unique sensitivity, the wide dynamic range, the compactness, and the relatively low cost of this table-top setup open new perspectives for 14C-tracing applications, such as radiocarbon dating, biomedicine, or environmental and earth sciences.
The detection of other very rare molecules can be pursued as well thanks to the wide and continuous mid-IR spectral coverage of the described setup.

Read more: physics.aps.org

Written by physicsgg

January 3, 2012 at 8:38 am