Archive for the ‘Sparks ‘n’ thunderbolts’ Category

How antineutrino monitoring could prevent nuclear proliferation

Friday, May 2nd, 2008

Antineutrino monitoring

The Nuclear Non-Proliferation Treaty has been ratified by more countries than any other arms limitation or disarmament treaty (187 at the last count). Its goal is to prevent the spread of nuclear weapons and weapons technology.

The task of monitoring compliance of the treaty is the job of the International Atomic Energy Authority and one area of particular concern is the spread of fissile material, particularly of weapons grade. But how to monitor this?

Ideally, the IAEA would like a non-invasive device that can be placed in the vicinity of a nuclear reactor that monitors its power output and its fissile isotopic content.

Now Adam Bernstein from the Lawrence Livermore National Laboratory in California and colleagues have developed and tested just such a device which works by measuring the reactor’s rate of antineutrino production, which in turn depends on the reactor’s fissile isotopic content and its power output.

The detector is about a cubic metre in volume and consists essentially of a liquid core doped with 0.1% gadolinium. This core is surrounded by various shields to screen out unwanted signals and various detectors to pick up the interesting ones. The detectors are looking for two pulses of energy (from a positron-electron annihilation followed by a neutron capture by a gadolinium nucleus) which are the characteristic signature of an antineutrino reaction.

Bernstein says he and his team have been testing the device for the last two years at unit 2 of San Onofre Nuclear Generating Station in Southern California and all the evidence is that it works well. They say the prototype can determine whether a reactor is on or off with a time resolution of 5 hours with greater than 99% confidence, which is handy because down times are when fuel is removed. It also directly measures power levels over month long periods. The isotopic content is a little more tricky to measure because it changes as fuel is used up within the reactor but should be within reach of the design.

Obviously such a device would also need to be able to operate remotely and record information securely but that’s for development further down the line

The detector’s biggest advantage, however, is its simplicity, says the group: “Our experience is that the simplicity of the detector design will play a key, even decisive role in determining whether this technology is adopted by the IAEA or other safeguards regimes.”

Interesting stuff.

Ref: arxiv.org/abs/0804.4723: Monitoring the Thermal Power of Nuclear Reactors with a Prototype Cubic Meter Antineutrino Detector

First observation of antibonding in artificial molecules

Wednesday, April 23rd, 2008

Antibonding

When electrons are confined in a flat space, they interact in much the same way as electrons in ordinary atoms by forming into pairs of various energy levels. They can even be made to emit light when they jump from one level to the next, just like electrons in the orbitals in real atoms.

These flat spaces are easily created in a thin semiconductor layer. Because of their similarity with the real thing, these electronic patterns are called “artifical atoms” and they form a kind of periodic table depending on the number of electrons they contain. And get this: put two artificial atoms next two each other and the electrons can tunnel across the gap to form a kind of covalent bond. That makes an artificial molecule.

The chemistry of artificial molecules has received widespread interest in recent years because it is possible to use them to make materials with properties that are otherwise not found in nature. And today, Matt Doty from the Naval Research Labraotry in DC and a few pals announce the first experimental observation of one of these strange properties in artificial diatomic molecules: antibonding.

Doty says that as the distance between two atoms increases, the bond linking them together suddenly switches to an antibond that pushes them apart. Antibonds are never seen in nature. They arise because artificial atoms contain “holes”, the absence of an electron in the structure which can be thought of as positively charged. Doty spotted their effect by looking for the characteristic light signature that an antibond can be made to emit in a magnetic field.

Antibonds could turn out to have useful properties. Doty and pals say molecules containing anitbonds could one day be used to manipulate the spin of passing electrons, a property that could be useful for the emerging field of spintronics.

Let’s wait and see.

Ref: arxiv.org/abs/0804.3097: Antibonding Ground States in Semiconductor Artificial Molecules

The hunt for superheavy elements

Monday, April 7th, 2008

Superheavy elements

The heaviest elements are a shy, retiring bunch. No sooner are they created than they disappear in a puff of smoke. The heaviest, ununoctium, has an atomic number of 118 and an atomic weight of 294. The Russians made a single atom of the stuff back in 2002 only to discover that it hung around for all of a millisecond.

But it has long been thought that islands of stability exist higher up in the periodic table, where much heavier elements might exist for much longer. Today Chhanda Samanta from the University of Richmond in Virginia, gives the low down on what to expect.

One important factor turns out to be the number of neutrons an element posseses, with islands of stability thought to exist at N=162 and 184.

Around N=162, Samanta says keep an eye out for seaborgium-268 with a half life of 3.2 hours. And at N=184 he points to  darmstadtium-294, which looks as if it’ll hang around for at least 311 years and seaborgium-290 which has a half life of a whopping 10^8 years.

The race is on to find these elements and the main players are the Russians at Flerov Laboratory of Nuclear Reactions in Dubna and the Americans at the Lawrence Livermore National Laboratory in California. (Although in the true spirit of post cold war co-operation they’ve together formed a collaboration called the Joint Institute for Nuclear Research.)

What’s the betting we’ll see one of these superheavies within the year?

Ref:  arxiv.org/abs/0803.4151: Superheavy Elements in the Magic Islands

Read it and beep

Tuesday, February 19th, 2008

Reading text is a simple enough task for humans. But unless it’s cleaned up and served on a plate computers just can’t do it.

At least they couldn’t until Mireille Boutin and pals from Purdue University took a shot at the problem.

These guys have built an impressive algorithm that looks for and finds text in real-life cluttered images.

And it works well. In their, albeit limited, tests on  65 real-life images, the algorithm correctly identified the text 97 per cent of the time.

Cars that can read signposts, anyone?

Ref: arxiv.org/abs/0801.4807: Automatic Text Area Segmentation in Natural Images

Why silos burst

Thursday, January 31st, 2008

Force chain

Believe it or not, grain silos are interesting structures. They’ve been known to explode without warning, which is hard to explain since they are filled with, well, grain.

But grain turns out to be kinda interesting too. In recent years, researchers have begun to get a handle on some of the strange and counterintuitive ways in which grain behaves as it flows and as it is placed under pressure.

One of the most interesting developments has been the discovery of “force chains”, networks of particles that form as the force is passed from one grain to the next (see picture). In this way, forces of many orders of magnitude greater than expected can be transmitted through the medium.

John Wambaugh and colleagues at Duke University in Durham have been studying the force networks that are set up within a two-dimensional silo and how these can make the forces behave in an extraordinary, non-linear way.

When grain is added to the top of the silo, the pressure in the medium increases but goes on increasing in a non-linear way even after the addition of material has stopped before decaying, a so-called “giant overshoot” effect.

How to explain this? Usually, force chains break and reform as the pressure changes in a granular medium and this helps to spread the forces evenly within it.

But Wambaugh thinks the non-linear behaviour suggests that something else is going on. He says that in certain circumstances, the force chains become locked in place and so that the additional pressure spreads much further and deeper than usual, creating the giant overshoot.

It might also explain why silos sometimes burst unexpectedly.

Ref: arxiv.org/abs/0801.3387: Force Networks and Elasticity in Granular Silos

Mapping the radioactive heat beneath our feet

Thursday, January 17th, 2008

Heat

Geochemical bods tell us that the Earth is heated from within by the decay of various isotopes, mainly uranium, thorium and potassium. Knowing the distribution of these elements is crucial for understanding the Earth’s inner dynamics.

Geochemists have penty of ideas about how the Earth’s interior may work but no way of taking measurements to prove their ideas. For example, they think there are far more of these hot elements in the Earth’s crust than its mantle but without data, they can’t prove it.

But the geobods ain’t givin’ up and are a-hopin’ and a-prayin’ that the humble neutrino is gonna come to their rescue. The process of radioactive decay gives off neutrinos that would alert geobods to exactly what’s going on and where, if only they could measure ’em.

Truble is that neutrinos are hard to catch at the best of times. Physicists have recently spotted terrestrial neutrinos for the first time, although only by their energy spectrum, not by their direction which is what will be needed if geochems are to work out the distribution of radioactive stuff down there.

Now Stephen “Live and Let” Dye at the University of Hawaii and a pal have worked out exactly what will be needed to map the radioactive brew within the planet. They reckon a large ocean-based detector plus a smaller land based one should do the trick (both will have to be well away from nuclear power stations which produce unwanted neutrinos that would swamp the signal).

The technology to do this is available now but whether they can drum up the support (and the money) needed to make it happen is another question.

Ref: arxiv.org/abs/0801.2366: Estimating Terrestrial Uranium and Thorium by Antineutrino Flux Measurements

Black holes may convert dark matter into cosmic rays

Friday, December 21st, 2007

M87 Active Galactic Nucleus

Active galactic nuclei are the brightest objects in the universe and among the most puzzlin’. Astrobods think they are supermassive black holes that spew out huge amounts light over some or all of the electromagnetic spectrum.

Now a coupla Ruskies are saying that active galactic nuclei are capable of converting dark matter into high energy protons. Here’s how. Yurii Pavlov at The Herzen University in St Petersburg and his tovarich Grib, hypothesise that dark matter particles are big critturs, about 15 times heavier than protons, and that they can decay into pairs of other particles.

Near an active galactic nucleus, one of these particles can get sucked into the black hole, and accelerated to huge energies in the process, while the other escapes. But some of those that escape will collide with incoming particles creating collisisons of mind boggling energy.

It is in these collisions, says Pavlov, that ordinary visible protons can form, accept they’d have huge energies beyond anything that can be created on Earth.

Interesting idea but ah know what you’re thinkin’: this is all too neat ‘n’ theoretical. What ya need is good hard evidence, right?

Pavlov says he’s got it in the form of ultra high-energy cosmic rays, particles such as protons that smash into the Earth having been accelerated to such extreme energies that astrobods have yet to figure out how it’s done.

Now get this: data from the Auger telescope and other places have recently determined that ultra high-energy cosmic rays come from active galactic nuclei.

Could active galactic nuclei be converting dark matter into ultra high-energy cosmic rays?

I know ya’ll will want a lil bit more evidence than this. Fair enough but a lotta crazier ideas have gained a popular followin’ on less.

Ref: arxiv.org/abs/0712.2667: Do Active Galactic Nuclei Convert Dark Matter into Visible Particles?

A wishlist of experiments to do in space

Monday, November 5th, 2007

What should we do in space? NASA has bet the farm on the International Space Station, a giant orbiting Lego set where astronauts can play Mommies and Daddies, practice sharing and become zero-g toilet trained. Almost everyone else wants to do something useful.

So a bunch of chief eggheads from the world of physics have drawn up a wishlist of space missions to look for new physics and test the old stuff to breaking point. Here’s a few of the gems:

SpaceTime: a mission to fly atomic clocks in a highly elliptical orbit around the Sun to see if the fine structure (or other fundamental) constant varies. Could also test the Equivalence principle

Inverse Square Law Experiment in Space (ISLES) does what it say on the tin by bouncing laser beams off the Moon and Mars to test whether gravity really follows an inverse square law at large distances

The Laser Astrometric Test of Relativity (LATOR) would use laser interferometry to measure the non-Euclidean geometry of giant light triangle around the Sun. The mission would test whether the infamous evidence in favour of dark matter could be explained instead by a modified theory of gravity

LISA (the Laser Interferometer Space Antenna) measures gravity waves using a constellation of laser interferometers

The Extreme Universe Space Observatory (EUSO) watches how a segment of the Earth’s atmopshere lights up when struck by ultra-high energy cosmic rays and neutrinos. Might also spot dark matter particles

Cold atom sensors in space could test the inverse square law at the scale of a few micrometers.

And so on…

If these sound like a physicist’s wet dream, yer probably right. But don’t write it off, there are some big cheeses behind this list, including Francis “Probe” Everitt (although the last spacecraft he built took 40 years to get into space ). They got the clout to get at least one of these things off the ground.

Ref: arxiv.org/abs/0711.0150: Space-based Research in Fundamental Physics and Quantum Technologies

When gamma rays strike

Sunday, August 26th, 2007

On 6 January earlier this year, one of the strongest thunderstorms in livin’ memory a-crashed and a-roared its way across the Sea of Japan, rattlin the daylights outta the Kashiwazaki-Kariwa nuclear power plant on the coast.

This power plant is fitted with one of the most advanced radiation detectors on the planet and durin’ the storm it collected some extraordinary data. After a lil number crunchin, a team of physicists led Kazuo “Tiger” Makishima at the Cosmic Radiation Lab RIKEN, are publishing details of what they saw.

That night the nuclear power station was bombarded with gamma rays with energies of at least 10 MeV (that was the limit of the detectors).

Now gamma rays bursts ain’t commonly detected on the ground cos they ain’t easy to make (if you spot any it’s a good sign your local nuclear power station ain’t workin properly. It’s also why n-plants have the kit to detect ’em) .

The RIKEN team says the gamma rays were probably caused by the sudden deceleration of high energy electrons as they smashed into atoms in the thunderclouds above, forcing the electrons to given up their energy in the form of gamma ray photons. But how did the electrons get accelerated to energies of 10 MeV or higher?

That’s a bit of mystery cos our ground-based accelerators require a near perfect vacuum to get particles a-movin and a-groovin at any kinda decent energy. Without a vacuum, particles start a-crashin and a-bangin into atoms and molecules in the air before they can get going.

Thunderclouds are known to have hugely powerful electric fields of more than 400 kiloVolts per meter so getting to 10 MeV from scratch requires quite a few metres of acceleration.

Unless the electrons start off with a fairly high energy, that is. The RIKEN team speculates that the gamma ray bursts in the thunderstorm were triggered by cosmic rays– high energy particles from outta space that come a-smashin and a-bargin their way through the atmosphere, creatin a shower of energetic electrons in their wake, a well known phenomenon.

So it’s quite possible that high energy electrons were created by a cosmic ray shower in the thundercloud and then accelerated to even higher energies by the electric field.

That seems to be backed up, at least in part, by the fact that the gamma ray bursts did not occur at the same time as visible lightning strikes so the mechanism behind that kinda discharge don’t seem to be responsible.

Fascinatin’ stuff, huh?

Ref: arxiv.org/abs/0708.2947:Detection of High-Energy Gamma Rays from Winter Thunderclouds

Invasion of the jivin’ nano-shrooms

Friday, August 24th, 2007

Convertin’ a constant force into an oscillatin’ one is a useful trick. Ya’ll seen em: gravity-powered pendulums and wind-powered turbines for example, them both set machines a-spinin and a-swingin by exploitin’ a constant force.

Them machines might work sweetly at macroscopic scales but ain’t nobody cracked it on the nanoscale even though nanobods are a-chompin at the bit to reproduce this trick. The trouble is that gravity ain’t strong enough at this level and as for wind, who you kiddin?

That leaves only tricky-dicky forces from the dizzy world of electrostatics and magnetics and these are so poorly understood on tiny scales that them nanobods are still a-wondrin and a-ponderin over how to harness them.

But Hyun “Mighty” Kim and his crew at the University of Wisconsin-Madison say they cracked it.

Their device is a kinda nano-mushroom that stands between the plates of a capacitor, in a constant DC field.

Give the mushroom a push and it leans towards the source electrode where electrons tunnel across into the mushroom head. The DC field exerts a force on this extra charge on the ‘shroom, pushing it towards the drain electrode where the electrons jump ship. The force disappears and the mushroom’s stiffness sends it swinging back to the source again like metronome, and the process starts again.

Voila! A nanomechanical oscillator that converts a a constant force into an oscillation.

Them nanobods are gonna be cockahoop over this one, betcha!

Ref: arxiv.org/abs/0708.1646: Self Excitation of Nano-Mechanical Pillars