Archive for the 'UCL Science Picture of the Week' Category

Positron beam

By Oli Usher, on 7 July 2015

UCL's Positronium Beam

UCL’s Positronium Beam

Positronium is an exotic atom made up of an electron and a positron in orbit around each other. Positrons are the antimatter equivalent of electrons, so these particles are highly unstable composite particles made up of both matter and antimatter.

Because of this, positronium atoms only last a few nanoseconds before the matter and antimatter annihilate each other.

Despite their short lives, these peculiar particles have interesting features – including being able to form compounds despite not actually being an element.

UCL is home to the only positronium beam in the world. In this device, positrons created by a radioactive source pass through a chamber of hydrogen gas, where they pick up electrons, before being guided towards a target.

Standing by the Positronium Beam in this photo are UCL PhD students Andrea Loretti (left) and Sam Fayer (right), both from the Department of Physics & Astronomy.

High resolution images



All set for Saturn

By Oli Usher, on 19 June 2015

Cassini shortly before launch. Photo credit: NASA

Cassini shortly before launch. Photo credit: NASA

The Cassini probe launched in October 1997 and arrived in the Saturn system in July 2004. Its Huygens lander touched down on Titan, Saturn’s largest moon, in December 2004. The photo above shows the spacecraft shortly before launch.

CAPS instrument

More than a decade on, the probe is still sending back data, teaching us about Saturn and its moons.

One of the instruments on board, the Cassini Plasma Spectrometer (CAPS) was designed in part by Prof Andrew Coates at UCL’s Mullard Space Science Laboratory. This week, he has published new research based on data from his instrument.

He has found that the interaction between the Sun, magnetic field lines and the atmosphere of Titan – Saturn’s oddly Earth-like moon – behaves similarly to what we observe here on Earth.

The LHC is back in operation at record energy

By Oli Usher, on 3 June 2015

After two years of repairs and upgrades, the Large Hadron Collider (LHC) is back in operation – and UCL scientists are at the heart of the action. Engineers at CERN confirmed today that the beams of protons that circle in the 27km tunnel near Geneva are stable, and scientific data is once again being collected.

The ATLAS experiment is made of concentric rings of detectors (the particle beam passes through the centre), as seen here during shutdown in 2008. Credit: CERN (CERN licence)

The ATLAS experiment is made of concentric rings of detectors (the particle beam passes through the centre), as seen here during shutdown in 2008. Credit: CERN/Claudia Marcelloni De Oliveria (CERN licence)

UCL scientists have been closely involved in the design, construction and operation of ATLAS, one of the giant detectors that track the high-energy particle collisions in the LHC, so this is an important milestone for the university’s High Energy Physics group.

Until now, the LHC has not been operating at full power. The faults that led to its shutdown shortly after it was inaugurated in 2008 meant that it could only be used to accelerate particles to around half the energy it was designed for.

* * *

Einstein’s equation E=mc2 states that energy and matter are interchangeable.

Atom bombs, famously, create vast amounts of energy by destroying small amounts of matter.

Particle accelerators like the LHC do the opposite, pumping vast amounts of energy into tiny particles, making them move at close to the speed of light. When they collide together, some of that energy is converted into extra matter, in the form of new particles flung out from the site of the collision. The greater that energy, the heavier the particles that can be generated.

Physicists describe the world around us using the ‘standard model’ of particle physics, a set of a handful of particles which can explain the properties and makeup of all the matter and energy we see around us.

The last of those particles to be detected in the lab was the Higgs boson, discovered at CERN in 2012 shortly before the upgrade began.

This doesn’t mean there is nothing left to discover, though. Scientists, including CERN’s director, have begun speaking of a tantalising ‘new physics’ – whole new uncharted areas of science that are currently totally unknown, but which might be explored with higher-energy collisions and heavier particles generated.

One of these areas could be a solution to the riddle of dark matter.

Dark matter can be detected by astronomers (as seen in this Hubble image of a galaxy cluster), but it has not been spotted on Earth, and is known to not be made out of any of the particles in the standard model. Credit: NASA/ESA (CC-BY)

Dark matter can be detected by astronomers (as seen in this Hubble image of a galaxy cluster), but it has not been spotted on Earth, and is known to not be made out of any of the particles in the standard model. Credit: NASA/ESA (CC-BY)

Dark matter has been detected in distant galaxies, thanks to its gravitational effects, but astronomers have determined that it cannot be made of any of the particles described in the standard model.

ATLAS, the building-sized instrument that UCL participates in, played a key role in the Higgs boson discovery, and will play a starring role in the future work of the LHC, and could help explain how dark matter relates to the standard model of particle physics.

* * *

The LHC consists of two 27km-long pipes that use powerful magnets to accelerate beams of protons in opposite directions.

Inside ATLAS, the two beams are brought together on a collision course. The beams are not continuous: the protons come in pulses (“bunches”) about 10cm long and the width of a human hair, each containing around a hundred billion particles. When these bunches cross each other, protons collide and new particles cascade out through the concentric rings of detectors that make up the ATLAS experiment.

One of the detections made by ATLAS today. This picture is a cross-section of the instrument, with each concentric ring detecting particles' location or energy, and the particles' tracks (shown as multi-coloured curved lines) inferred from this data. Credit: CERN

One of the detections made by ATLAS today. This picture is a cross-section of the instrument, with each concentric ring detecting particles’ location or energy, and the particles’ tracks (shown as multi-coloured curved lines) inferred from this data. Credit: CERN (CC BY SA)

Scientists can then trace the path that the particles took – and determine their energy, mass and electrical charges. And from those, they can infer the process that take places in each proton-proton collision.

During the two-year LHC shutdown, the ATLAS scientists also made several improvements to their detector, most notably with the installation of an extra ring of detectors close to the beam pipe, making it more precise than ever before, and part of the team’s work now that the LHC is running again is to ensure that this is all properly calibrated and working as expected.

When it runs at full capacity, ATLAS detects 40 million particle collisions every second, far more than could ever be studied.

Part of the challenge is to discard the unimportant data so that scientists can focus on what’s important. One of the major contributions UCL scientists have made to ATLAS is to the design and operation of the hardware and software algorithms used to discard trivial events in real time and select only the interesting ones – reducing 40 million collisions per second down to a far more manageable 1,000 that are recorded offline.

Another challenge is the simple matter of timing and synchronisation.

With millions of events per second, and everything moving at close to the speed of light, untangling the data from different collisions is challenging. ATLAS is still detecting particles ejected by one collision while another is already taking place.

Particles from multiple events cascade through the detectors at one time, and synchronising them is not straightforward. Credit: CERN (CC-BY-SA)

Particles from multiple events cascade through the detectors at one time, and synchronising them is not straightforward. Credit: CERN (CC-BY-SA)

UCL scientists played key roles in developing the electronics that ensure that the data is accurately recorded and readouts from the different components of ATLAS are all kept properly synchronised.

* * *

So what’s next for the LHC?

It’s very hard to say – and that’s what is so exciting about particle physics today.

The standard model is complete. There could be a radical departure, revealing areas of physics never explained before.

Equally, there might just be further confirmation of the dramatic discoveries of the past few decades, giving more precision and certainty to the standard model.

In either case, there is now a chance to explore physics without the constraint of theoretical preconceptions – an unusual and liberating place for a physicist to be.

With thanks to Prof Nikos Konstantinidis for help with this article





The coolest place in London

By Oli Usher, on 18 May 2015

Quantum refrigerator. Photo: O. Usher (UCL MAPS)

Quantum refrigerator. Photo: O. Usher (UCL MAPS)

This photo shows a specialised refrigerator, used for cooling objects to within a fraction of absolute zero, located in the Physics building on UCL’s main campus.

When in operation, the refrigerator is entirely enclosed in a sealed and insulated housing, which has been removed here for maintenance.

As with a household fridge, the temperature drops as you go down – with the highest of the four shelves being at a temperature of about 50 Kelvins (-223 Celsius) and the bottom one at just 0.03 K (-273 C).

The refrigerator is used to cool small objects, such as transistors, down to levels where thermal effects (such as the vibration of the atoms in them) are eliminated, allowing quantum effects to be observed.

Samples can be raised or lowered through each shelf via a circular hole in the centre of the refrigerator.

The refrigerator is cooled by a mixture of liquid Helium-3 and Helium-4. The lowest shelf of this refrigerator has a strong claim to being the coldest place in London (alongside a handful of similar facilities at other London universities).

High resolution images

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X-Ray observations probe Sagittarius A*

By Oli Usher, on 14 May 2015

Sagittarius A*

Sagittarius A* region, as observed by NASA’s Chandra X-Ray Observatory. Credit: NASA/CXO

This image shows the centre of the Milky Way galaxy, as seen in X-rays by the Chandra X-Ray Observatory. X-rays are produced by high-temperature, high-energy phenomena.

Within this region lies Sagittarius A*, the Milky Way’s central black hole.

An international team of astronomers, including UCL’s Silvia Zane, has just published new research on a magnetar (a type of super-magnetic neutron star) that is orbiting Sagittarius A*, explaining why it is cooling far slower than theories suggest.

New space photos from UCL’s observatory

By Oli Usher, on 29 April 2015

Messier 51, from the University of London Observatory. Credit: UCL/ULO/Ian Howarth

Messier 51, from the University of London Observatory. Credit: UCL/ULO/Ian Howarth

The University of London Observatory – UCL’s astronomical observatory in Mill Hill, North London – has to deal with England’s murky skies and London’s bright lights, but it can still make some impressive images. Messier 51, seen in the picture above, is actually not one galaxy but two – a large spiral galaxy (Messier 51a) interacting with a smaller dwarf galaxy (NGC 5195). Over the next few hundred million years, they will merge together into one larger galaxy.

Such mergers are quite common. Large spiral galaxies can absorb dwarf galaxies without major disruption to their shapes, though the (rarer) mergers between similarly-sized galaxies tend to destroy all structure, leaving a largely featureless elliptical galaxy. This will be the fate of the Milky Way when it merges with the Andromeda Galaxy in a few billion years time.

The Messier 51 pair are a popular target for amateur astronomers – on a dark night, even relatively basic telescopes can pick out the very faint comma-shape of the galaxy pair, visible near one end of the Plough (Ursa Major).

The picture is one of several newly processed images just published by UCL’s observatory, based on data gathered by astronomy students. The observatory now routinely archives all the digital data gathered with its Celestron telescopes, which are used intensively for undergraduate teaching. This growing archive of data means that multiple observations can be easily combined into a single image, improving contrast and revealing faint details that would otherwise be invisible.

A selection of several dozen of these images from the observatory, with multiple observations processed and combined to form colour composites, is available online to the public. They are free to reuse and reproduce.

Darkness falls across the land

By Dewi W Lewis, on 24 March 2015



These two photographs were taken in the quad during the eclipse. The first at 9:25 the second at 9:31am.

During this time the light dropped by a factor of 16: dropping from an Exposure Value (EV) value of 11 to 7, or 4 stops, to the photographers amongst you.

My eyes told me it got “a bit darker”, the reality was far more!

Hydrophobic art

By Oli Usher, on 5 March 2015


Yau Lu (UCL Chemistry) is the lead author of some research which hit the headlines last week. His team has succeeded in making a water-resistant and self-cleaning coating which is both highly effective and very strong. Previous coatings have been weak, and easily scratched or flaked off.

Here, he shows how the hydrophobic  paint can be used to create a water-repellent design on glass. The hydrophobic coating, water and dye all come together to create an ephemeral artwork:

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Where noble gases won UCL a Nobel Prize

By Oli Usher, on 2 March 2015


Readers familiar with UCL will immediately recognise the Slade School of Fine Art – the North Wing on UCL’s historic (and grade I listed) quadrangle. What they may not know is that the building, which dates back to the 1870s, was originally also home to UCL’s Department of Chemistry.

It was in this building that some of UCL’s most famous contributions to chemistry were made: William Ramsay and his successor J Norman Collie both worked here.

In fact, as far as we can work out, it is the building in the world which has seen the discovery of the greatest number of chemical elements. Ramsay discovered argon, neon, krypton and xenon while working here, as well as isolating helium (which had been seen in the spectrum of the Sun, but not observed here on Earth) and radon. These elements are together known as the noble gases, and Ramsay’s discoveries secured for him the 1904 Nobel Prize in Chemistry – UCL’s first.

In 1913, the year of Ramsay’s retirement, UCL’s Chemistry department moved to a new purpose-built lab immediately behind its old home. The building – which still houses some of the department’s laboratories and offices – is now named after another towering figure in chemistry: Kathleen Lonsdale.

After a century of heavy use and piecemeal remodelling, the building is looking a little tired . A multi-million pound complete refurbishment of the building is planned to begin later this year.


High resolution image


Twinkle: a new mission to study distant planets

By Oli Usher, on 9 February 2015

Twinkle. Credit: SSTL/Twinkle/DSS

A new satellite for observing extrasolar planets could be in orbit within four years, under plans drawn up by UCL and Surrey Satellite Technology Limited (SSTL). The Twinkle satellite, pictured above, will observe the light of distant stars with planets orbiting them.

As a planet passes between the star and Twinkle’s telescope, a small amount of the light passes through its atmosphere, imprinting on it the chemical signature of its atmosphere. This technique has been used by Hubble to analyse the atmospheres of a handful of exoplanets, but the Twinkle team hopes to probe at least 100 during the spacecraft’s mission.

UCL leads a consortium of UK institutes who will construct Twinkle’s scientific instrumentation, a highly precise infrared spectrometer which can tease out the faint signature of the planetary atmospheres from the starlight.


High resolution image