S207 Weekend Update | Planetary Exploration at MK | Quanta and Continuum | Binding Energy Clarified | Fusion at Open Day | Competition Winners | Spitzer - A Cool View of the Cosmos | Babar the PENGUIN? | When does particle physics need MICE?

Fusion at Open Day


Christine Seaman and Jim Grozier sporting their new Einstein T-shirts on the Fusion stand at Open Day. Our stand featured the Fusion competition "How Many Neutrons in a Cup of Tea?". There were three winners and below our very own Neutron Wrangler explains how to calculate the answer!


Neutron Competition Winners

Dave Etchell, from Doncaster, made the closest estimate of the number of neutrons in our cup of tea. His answer, 4.8 × 1025, was only slightly too big (by a factor of 1.5, which is perhaps understandable when you consider that Dave's interests include metallurgy, so that the levels of mercury, lead etc., and hence the number of neutrons, in his tea are possibly greater than those of the average OU student!).

Dave is a true OU veteran, having been in at the start of the University in 1971, and subsequently gained a science degree (mainly chemistry) which came in useful in his career with the National Coal Board. In more recent years he has moved over to the arts side, and helped to found the University's Shakespeare Society. The runners-up were Felicity Drouet, a doctor, of Milton Keynes, who had just popped in to see what all the fuss was about, and S207 student Pam Fineberg of Leeds. Felicity told us: "the quiz re-activated bits of my brain that had lain dormant for ages and I really enjoyed it". All three win copies of Bill Bryson's book "A Short History of Nearly Everything".

How Many Neutrons in a Cup of Tea?

There are 120 ml or 1.2 × 10-4 m3 of tea in the cup. Tea is mostly water, and so we can assume that its physical properties are the same as those of water; in the following the terms "tea" and "water" are therefore held to be equivalent everywhere, and not just in the vicinity of a Sirius Cybernetics Corporation tea machine.

At normal temperature and pressure, the density of water is 997.02 kgm-3 and so the mass of the tea is approximately 1.2 × 10-4 × 997.02 kg. The molecular weight of water is 18.016, and so a mole of tea has a mass of approximately 0.018016 kg. The number of moles of tea in our cup is therefore

(1.2 × 10-4 × 997.02 / 0.018016) ≅ 6.6

A mole contains NA molecules, where NA is Avogadro's Number and equals 6.022 × 1023. Furthermore, each molecule of tea contains one oxygen atom, and therefore 8 neutrons (168O being the dominant isotope); so the number of neutrons in our cup of tea is

(1.2 × 10-4 × 997.02 / 0.018016) × 6.022 × 1023 × 8 = 3.2 × 1025

(Although there are several simplifying assumptions made in this calculation, they do not affect the result, since the first three answers are approximately an order of magnitude apart. As with all Fusion competitions, the judges' decision is final, unless you buy them enough drinks).


Spitzer - A Cool View of the Cosmos

NASA's latest Great Observatory

by Dr Mark H. Jones, Open University

If you ask people to name a space telescope, the most likely response would be "Hubble" - the optical telescope that was launched in 1990 and which has captured the public imagination with its stunning astronomical pictures. Yet Hubble is not the only space telescope in operation: there are currently space-based observatories that operate across the electromagnetic spectrum from gamma-rays to the infrared, and it is in the infrared that observations are currently being made with NASA's latest "Great Observatory" - the Spitzer Space Telescope. This telescope, which before launch went under the less-than-pronounceable name of SIRTF (the Space Infrared Telescope Facility), was launched on 25 August 2003. After launch it was named in honour of the late Lyman Spitzer, Jr, an outstanding astrophysicist who pioneered the idea of space-based observatories.

Space telescopes are phenomenally expensive to build and operate, but are necessary when observations are required at wavelengths at which electromagnetic radiation is heavily absorbed by the Earth's atmosphere. While near-infrared radiation, up to a few microns in wavelength, does pass through the atmosphere and can be detected using ground- based telescopes, infrared radiation from about ten microns to several hundreds of microns in wavelength is completely absorbed and space- based measurements are necessary.

So why is the infrared region of the spectrum so important to astronomers? The simple answer is that it provides a way of studying cool material in the Universe. In this context cool means at lower temperatures than the typical surface temperatures of stars: infrared emission provides a direct way to trace material at temperatures of a few tens to a few hundred Kelvin. At such temperatures, molecules and solid particles (dust) can exist and can be detected by their spectral signatures in the infrared. As a bonus, unlike visible light, infrared radiation is not heavily absorbed by the dust in the interstellar medium. So it is possible to use infrared observations to study objects which can't even be detected at visible wavelengths.


Spitzer under construction at Lockheed Martin. Photo: Russ Underwood, Lockheed Martin Space Systems.

The types of astrophysical environment that can be studied at infrared wavelengths are some of the most exciting areas of astronomy. For instance, Spitzer will provide vital information about the process of star- formation - a topic with wide-ranging importance to astronomy, cosmology and even astrobiology. Stars are born from enormous cool clouds of gas and dust. Such clouds absorb light at visible wavelengths, but high sensitivity observations at infrared wavelengths can be used to look into these star-forming regions. From a cosmological perspective, star-formation is important because stars are the building blocks out of which galaxies and larger structures form. Astronomers need to understand in detail how stars form so that they can piece together the history of the Universe from the big bang to the present day. Although it is possible to model star formation for idealised situations, we have a far from complete understanding how the process works in real life. Studies with Spitzer will help to fill gaps in our knowledge of this fundamental process.

The conditions that allowed life to arise are also linked ultimately to the process of star formation. For instance, the only place where we have detected life in the Universe - the Earth - has its material origins in the solid dust grains that existed in the interstellar cloud from which the Sun formed. Thermal emission from dust grains around young stars can be mapped at far-infrared wavelengths and such studies will develop our understanding of how planetary systems form. But that is not all; some of the molecules that are necessary for the development of life also have a cosmic origin. Spectroscopic studies in the infrared can identify the signatures of some of these pre-biotic molecules in interstellar clouds. Infrared observations with Spitzer will play a key role in helping us to understand the astronomical origins of places in the Universe where life might develop.

Some novel features have been developed to make the Spitzer Space Telescope a highly-sensitive and effective infrared observatory. The basic design of the telescope is similar to a familiar optical telescope - it has primary and secondary mirrors which collect and focus infrared radiation onto scientific instruments at the focal plane. The diameter of the primary mirror is 85 cm - larger than any previous space infrared telescope. A minor difference is that the mirrors on Spitzer are fashioned from beryllium rather than the traditional glass and aluminium construction that is used for optical telescopes. More substantially different is the fact that the entire telescope must be operated at cryogenic temperatures to minimise the infrared emission from the instrument itself. Space-infrared telescopes prior to Spitzer, such as IRAS (the Infrared Astronomical Satellite, launched in 1983) and ISO (the Infrared Space Observatory, launched 1995) were built such that the entire telescopes were contained within Dewars - think of a 'telescope in a thermos flask'! While this was effective in producing high sensitivity telescopes, this design required a large mass of consumable liquid helium coolant: these earlier missions had limited lifetimes (of 11 and 28 months respectively) before their coolant ran out.

Spitzer takes a new approach: the mirrors are housed, not in a Dewar, but in a structure whose outer temperature of 35 K is maintained by passive cooling - the body of the telescope simply radiates heat away to space. Several factors allow such a low temperature to be achieved without the use of cryogen. Firstly, the telescope shell is always shielded from direct sunlight. Furthermore those parts of the shell which face the observatory's sunshield are coated in highly reflective aluminium, whereas the rest of the structure is coated with high-emissivity black paint. Finally, the telescope is not in orbit around the Earth - a significant source of heat - but rather is in a sun-centred orbit. At present (summer 2005) Spitzer is about 30 million km from the Earth and will drift slowly away from us as the mission progresses.

Even though 35 K is a low temperature, it is still not low enough for effective infrared observations. Consequently, Spitzer has a reservoir of liquid helium which is used to provide additional cooling to the mirror assembly. When observations at the longest infrared wavelengths are planned, the mirror assembly can be cooled to 5.6K.


An artist's conception of the Spitzer Space Telescope against a background of the far-infrared sky (100 microns). Photo: NASA/JPL-Caltech.

The instruments that are available to astronomers are: an imaging camera (IRAC) which provides 256 × 256 pixel resolution in wavelengths from 3 to 9 μm; an infrared spectrograph (IRS) which provides moderate spectral resolution (λ / Δ λ ∼ 600) at wavelengths from 5 to 37 μm; and a photometer (MIPS) to measure flux densities in bands across a wide range of wavelengths (20 to 160 μm). While the spatial and spectral resolution of these instruments is modest in comparison to instruments used at visible wavelengths, they are a significant advance for infrared detectors. At the heart of all of these instruments are semiconductor devices whose electrical properties are sensitive to the infrared radiation that is incident on them. Not surprisingly, the instruments have to be maintained at even lower temperatures than the mirrors, and the focal plane assembly sits within a cryostat vacuum shell. So, despite its use of radiative cooling, Spitzer will stop operating when its coolant is exhausted. The spacecraft was launched carrying 337 litres of liquid helium, and the lifetime of the mission is currently projected to be 5.3 years.

As well as the cooling systems, the design of Spitzer also highlights other interesting problems in spacecraft engineering. For instance, because Spitzer lies outside of the Earth's magnetic field, it is not possible to use the usual technology of magnetic torques to control the angular momentum of the spacecraft, and a gas-reaction system has to be employed instead (under normal conditions, the supply of nitrogen for this system should last 15 years - far longer than the cryogenic coolant). Another consequence of being outside of the magnetosphere is that the radiation environment (in this case 'radiation' refers to charged particles, electrons, protons and heavier nuclei) is quite different to that experienced by earlier infrared observatories. Rather surprisingly, being outside of the magnetosphere has an advantage as it avoids the problem of repetitive passes through radiation belts - regions in which particles are trapped in the Earth's magnetic field. However it carries a risk because it also exposes Spitzer to the full force of solar proton storms - unpredictable events which could, in principle, damage the observatory's instruments and electronic systems. In fact, just after launch, Spitzer encountered an extremely strong solar proton storm, but fortunately it seems to have caused no lasting damage to the observatory.

The technical innovations that have been made in developing the Spitzer Space Telescope seem to be paying off. The mission is unfolding according to plan and observational programmes are underway. The telescope will generate a wealth of data which will keep researchers busy for many years after the mission itself is over, and ultimately we can expect that Spitzer will help us to come to a better understanding about our cosmic origins.

Further reading: Werner et al, 2004, The Spitzer Space Telescope Mission, Astrophysical Journal Supplement Series, Vol 154, 1-9.
Spitzer Space Telescope web site www.spitzer.caltech.edu.
More photos from the Spitzer media pages at www.spitzer.caltech.edu/Media/mediaimages/hardware.shtml.

Latest NASA Spitzer News

The Spitzer Space Telescope has for the first time captured the light from two planets orbiting stars other than our Sun. The findings mark the beginning of a new age of planetary science, in which "extrasolar" planets can be directly measured and compared (www.spitzer.caltech.edu/Media/releases/ssc2005-09/release.shtml).

Mark Jones is a Staff Tutor in the Department of Physics and Astronomy. He is course team chair of S282 - Astronomy, and has a particular interest in the infrared properties of evolved stars.

Babar the PENGUIN?

News from the Particle Physics Community

by Jim Grozier

The Institute of Physics' High Energy Particle Physics group held its annual conference at University College, Dublin, in March. This conference, attended by nearly 200 researchers, academics and students, is an opportunity for particle physicists to update one another on their experiments and swap ideas; however, given the dominance of CERN in UK particle physics, holding such an event while CERN is closed for upgrading to the Large Hadron Collider is a bit like holding a gathering of cricket commentators during the football season (and a 5 year football season at that!); all that can be discussed is "work in progress" - there will be no new data until at least 2007.

Luckily, UK institutions are also involved in other facilities which are not being upgraded, such as DESY in Hamburg, and Fermilab and Stanford in the USA, and so we were able to see data from projects such as BABAR, a long running experiment to compare the decay rates of B mesons and their antiparticles (B-bars). One of the talks in this section of the conference had the intriguing title "Radiative Penguin Decays at BABAR". I missed the talk, but animal lovers need not be alarmed, since I believe the avian epithet is meant to refer to the shape of the Feynman diagram for a particular type of decay, rather than to any real live penguins.

There is also, of course, the small number of us who do not spend our time smashing ever-more-energetic particles together and sifting through the resulting debris. One of the talks in this section had a special interest for me, as it was given by my colleague, Phil Symes. As Sussex, where we are both studying for PhDs, is not known for its prominence in UK particle physics, I was immensely proud to hear Phil reporting on just about the only "hot news" of the whole conference - the first home-grown neutrino detection by the MINOS project (see my article in the Spring 2002 Newsletter, "Jekyll and Hyde" Particles May Hold a Clue to the Fate of the Universe). Phil had arrived in Dublin hotfoot from Soudan, Minnesota, USA, where the MINOS detector is (so hotfoot, in fact, that his luggage was still in London where he had changed planes!) and the neutrino had been seen only two days earlier - so it really was hot news!


Phil Symes' plot showing the first ever beam neutrino event seen at the MINOS far detector, 20 March 2005.

Speaking in the same session as Phil, Dr Lara Howlett of Sheffield University gave a talk on just about the most exciting particle physics development in this country for many years. Her project is known as MICE (Muon Ionisation Cooling Experiment) and the talk so impressed me that I decided to write an article about it - then I thought "well, why not get it from the horse's mouth?" (apologies to Lara) - and you can read the result below.

When does particle physics need MICE?

by Dr Lara Howlett, University of Sheffield

When does particle physics need MICE? The answer to this question lies with an elusive particle called the neutrino. The neutrino is so light that it is only recently that it has been found to have any mass at all. In addition to its low mass the particle is electrically neutral and very weakly interacting making it extremely difficult to detect. Of the millions of neutrinos that pass through you every day only one will interact. So how do physicists study a particle which is so hard to see? The answer is somewhat obvious, when you think about it. They play the numbers game: they make their detectors as large as possible to give them the largest probability of seeing the neutrinos, and they use as many neutrinos in their experiments as they can.

This is one of the reasons that the neutrino physics community believe that the ultimate tool for studying the neutrino will be the neutrino factory - a proposed facility that particle physicists hope will be being built in around 10 years time. The neutrino factory would be capable of producing a much higher intensity neutrino beam than any other existing or proposed facility. In addition the method by which the neutrinos are produced gives the beam a well known composition.

The concept of the neutrino factory is relatively simple. You smash high energy protons into a target made of a heavy material such as tantalum. This produces a spray of particles including pions. The pions are collected and decay to produce muons, and the muons in turn decay to produce the beam of neutrinos that you want. In order to produce an intense beam of neutrinos at high energy the muons are collected and accelerated in a recirculating linac (linear accelerator) before being fed into a decay ring. To maximise the number of neutrinos going in the desired direction, the decay ring is designed to have long straight sections with minimal distance being taken up by turns, because once the neutrinos have been emitted, they cannot be deflected by magnetic fields. Typical designs are the "racing track" or the "figure of eight", with the straight sections pointing to the detectors a few thousand km away through the earth.

Unfortunately the engineering for such a task is far from simple. To get the high number of neutrinos you want, you need as many of the muons produced to end up in the decay ring as possible. So you need to decrease the phase space of the muons to get them into the acceptance of the recirculating linacs. The lifetime of the muon incidentally is a few millionths of a second so you don't have very long to do it in! All the normal cooling methods (electron cooling stochastic cooling, laser cooling) are too slow. It turns out the only method there is time for is ionisation cooling.

So what exactly is ionisation cooling? The technique consists of passing the muons first through an energy absorbing material where they lose momentum in all directions due to their interactions with matter. The muons are then passed through a radio frequency (rf) cavity where they are accelerated by the electric field, replacing the momentum lost in the longitudinal direction. This means that overall the muons have been cooled transversely. In accelerator physics speak we have reduced the emittance of the beam, a technique that gives us a factor of between 4 and 10 in performance of the neutrino factory depending on the exact design. Ionisation cooling was first proposed 20 years ago and is believed to be theoretically sound, but in fact the technique has never been demonstrated in practice.

This is where MICE comes in. MICE is the international Muon Ionisation Cooling Experiment. It aims to give the first demonstration of a working cooling channel. MICE brings together 150 particle and accelerator physicists from around the world spanning 3 continents and 17 time zones! An exciting aspect of the project is that MICE will be based in the UK (at the Rutherford Appleton Laboratory in Didcot, in fact) - the first large particle physics experiment to be based there in many years.

The objectives of the MICE experiment are:

  • To show that it is possible to design, engineer and build a section of cooling channel capable of giving the desired performance for a Neutrino Factory;
  • To place it in a muon beam and measure its performance in various modes of operation and beam conditions, thereby investigating the limits and practicality of cooling.
So the experiment represents an important milestone towards the building of a neutrino factory.

Lets take a look at the beamline first. This is clearly a crucial element - after all if we don't have any muons we don't have anything to cool! MICE will run parasitically on ISIS, which is a pulsed neutron source. The muons are created by the ISIS protons hitting a titanium target. This produces pions which decay to give us the muons we require. However we can't just stick a target in the beam and leave it there. The ISIS machine runs in cycles, protons are injected at low energy and accelerated round the ring until they reach their nominal energy of 800MeV. If we leave the target in there we'll be intercepting lots of lower energy protons, heating the target unnecessarily and removing protons from the beam before they are accelerated to the correct energy! So in fact the target needs to be dipped in only for the last few ms of the cycle, by which point the beam has shrunk within the beam pipe. The short time and required travel mean that the target is required to accelerate at around 100g! The design of this target mechanism is the project that the group that I belong to at Sheffield is involved in. After the particles have been produced by the target they are guided down the beamline by a series of dipole and quadrupole magnets.


Engineering drawing of the MICE cooling channel and particle detectors. The beam enters from the left passing through a time of flight detector and the scintillating fibre tracker inside a solenoid magnet. It then enters the cooling channel consisting of alternate hydrogen absorbers and RF cavities before passing through another tracker and set of particle identification detectors.

So what exactly will this experiment at RAL consist of? There will basically be 3 components: the beamline, the cooling channel and the particle detectors.

The cooling channel consists of two sets of four radio frequency cavities sandwiched between three liquid hydrogen absorbers. Each hydrogen absorber is surrounded by a focus coil bringing the beam to a focus at the centre of the absorber. The building of such a channel poses significant technical challenges, not least of which is building beryllium windows for the hydrogen absorbers as thin as possible to reduce multiple scattering whilst still complying with the safety considerations for such a highly flammable liquid.

Last but not least we need some particle detectors. It's no good cooling the muons if we can't see that we've done it! Tracking is provided by scintillating fibre detectors. These allow us to determine the trajectories of particles before and after the cooling channel, allowing us to determine both position and momentum. We also need to be able to discard any pions which have not yet decayed, and to check that the muons haven't decayed in the cooling channel, so we also need particle identification detectors. For this we have a Time Of Flight (TOF) System, two Cherenkov detectors and a Calorimeter.

MICE expects to take first data in 2007. Its results will be crucial to the design of a neutrino factory and thus to the ushering in of a new era of high precision neutrino measurements.

For more information on MICE visit www.mice.iit.edu. For more information on the work of the Sheffield group visit www.shef.ac.uk/physics/research/pppa/research/mice.htm.





Pictures by Norrette Moore


First Preparation Weekend for S207 - The Physical World confirmed for January 2006

Booking has now started for the first S207 Preparation Weekend which is being held at the Open University, Milton Keynes from 11:00 on 28th January until 16:00 on 29th; Over 30 students have already registered their interest. The weekend is organised by Fusion with the support of the OU's Department of Physics & Astronomy. The cost inclusive of Saturday and Sunday lunch is £50 (plus £6 if not already a Fusion member). Accommodation at the special rate of £55 per single occupancy room (including full English breakfast) has been arranged at the Hilton adjacent to the OU campus.

The aim of the weekend is to ease the transition from level 1 science to level 2 physics by ensuring that students are well prepared for the course by consolidating and building on material learned on earlier courses and revisiting material that might not have been clear the first time around. This should lead to an improvement in course results and reduce the drop-out rate.

Tutors and Fusion members Dr Ian Saunders and Dr David Keen will lead the weekend focussing on mathematics on Saturday and physics on Sunday. Tuition will be based on S151 - Maths for Science, S103 - Discovering Science and the early units of S207.

On Saturday evening S103 tutor Paul Ruffle of the University of Manchester will be discussing his research into molecular clouds that lie at the edge of the Milky Way. Paul will explain what astronomers mean when they talk about spectra, metallicity, stellar processing and the like. He will also show how they use radio telescopes to detect molecules like carbon monoxide and ammonia. There will be audience participation in the form of various calculations using the physics and mathematics encountered in S103.

To guarantee your place on this weekend book now. Email This e-mail address is being protected from spambots. You need JavaScript enabled to view it for full details and an application form or write to: Fusion S207, 142 Kingsley Road, Northampton, NN2 7BY.


Planetary Exploration at MK

Fusion warmly invites its members to attend an evening of Planetary Exploration at the Open University in Milton Keynes on Friday 18th November 2005 from 5.30-8.30pm. We have two lectures planned: the first from Professor Colin Pillinger explaining the fascinating complexities behind the idea of landing the Beagle probe, the size of a bicycle wheel, on the surface of Mars and then remotely controlling its 'paw' in order to pick up rock samples; and the second from Dr. Andrew Ball explaining how the Huygens probe, a sophisticated robotic laboratory equipped with six scientific instruments, was able to land on Titan and monitor its winds, atmosphere, cloud physics and gas distribution.

If any of you would like to join us for the evening, then please contact Lorraine our Events Coordinator to reserve your seat. There is no charge for this, but you will need to make a booking in order to attend the lectures. If there are any members with special needs, then please also contact Lorraine.

For those attending these lectures, who want to experience the work of the Beagle2 team first hand, it is recommended that you visit the National Space Centre in Leicester where they have re-created the Beagle2 Operation Control Centre.


Nexus Update

by Shavinder Kalcut

Nexus is the student wing of the Institute of Physics (IoP). We were founded about 12 years ago by one of our student members and our aim is to provide Institute of Physics membership benefits tailored specifically to students of physics. The IoP has 37,000 members of which approx 7,000 are student members, of these we have about 160 Open University members.

So what do we do? The IoP acts to promote and support physics in academia, industry and society. More precisely by encouraging more young people to study physics, creating a network for people working in physics related industries and raising the profile of physics and physicists in the general public. Nexus, however, concentrates on social events, visits to places of scientific interest and student conferences, we have an enthusiastic committee of students who help to organize and plan these events and these are all advertised on our new web site nexus.iop.org.

The IoP has many resources available to its members whatever stage in their career they are at and to reflect this we have different stages of membership that you can apply for. You can find these on the institute web site www.iop.org. Here you can also get access to physics journals and get access to a physics search engine 'physics.org' where you can also have your physics related questions answered.

It's Einstein Year, and the Institute of Physics has been busy organizing a year long program of events to enthuse young people about physics, these include 'lab in a lorry' a project where four articulated lorries will tour the UK bringing physics experiments to school children. Talks, lectures and dinners all over the UK to celebrate the centennial of Einstein publishing his three famous papers have also been planned. See the Einstein year web site for details of events in your area and how to get involved. During this year Nexus will be putting on a set of regional Einstein Year dinners for students, bidding to host the International Conference of Physics Students (ICPS) in 2007 and organising the annual Young Physicists Conference. Details of these events can be found on our web site or by request.

For more information about any of our events or about the IoP in general email me, the Student Liaison Officer at This e-mail address is being protected from spambots. You need JavaScript enabled to view it or by post to the Institute of Physics, 76 Portland Place, London W1B 1NT.

Institute of Physics Online

Log on to the members area at members.iop.org and receive your own portable email address, or whatson.iop.org/events/index.cfm for details of other seminars and lectures organised by the Institute of Physics. To change your contact details log on to members.iop.org or email This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Fusion Web Site Update

We now have a Google powered search facility on the Fusion web site. The Google Public Service Search is free to educational organisations and does not put any ads on the search results. The results are also displayed in the layout style of our site. Try it out - it works a treat! Around 150 Fusion pages have been indexed by Google.

Web Links

The Albert Einstein Experience includes Einstein jokes.

Eric Weisstein's World of Science is a useful site for looking up physics stuff.

Binding Energy Clarified

Fusion member James Swallow was confused by the statement in Professor Brian Fulton's article on "Nuclear Astrophysics" (Fusion Newsletter Spring 2005) that the energy generated in the nuclear fusion process "comes from the binding energy released when light nuclei fuse together to form heavier ones".

He has a point. A logical interpretation of the term "binding energy released" implies that before the process began the binding energy was stored somewhere, and the process causes it to be released. This is clearly absurd when you consider one of the simplest fusion reactions - the pp chain, which occurs in stars like the Sun, and in which four protons combine together to form a helium nucleus. As the constituent particles are not bound to anything, where is the binding energy?

One explanation, of course, is that it is stored, but in the form of mass: the combined mass of the original particles is greater than the combined mass of the products (the helium nucleus, two positrons and two neutrinos) and it is this excess mass which is converted to energy. The reason that fusion happens at all is that the helium nucleus is in a lower energy state than the original protons, so the system "finds its own level" in energy terms, like water running down a mountain. The height of the mountain is called the binding energy, but it is negative; to make the energy balance overall, there must be an accompanying release of kinetic energy, like the velocity of the water when it gets to the bottom. This is the energy output of the fusion process.

We contacted Prof Fulton, who commented: "The term "binding energy released" in this context of nuclear "burning" when two nuclei fuse together could just as well be used in the context of chemical reactions. For example, when two atoms join together to form a molecule (e.g. in burning of a fossil fuel where free carbon and oxygen atoms join together) we often talk about "chemical energy being released". This is in fact a form of words which reflects the same thing, the two atoms are now bound together and this binding energy appears as heat release. It is often easier to think of it the other way around. Take the carbon dioxide molecule formed and think about pulling it apart to the constituent atoms again. As you pull the atoms apart there will be a force (electric) trying to keep them together and as you pull against this you do work (energy). The amount of work (energy) you need to expend is directly related to the binding energy of the molecule. Now think of the nuclear case. If we want to pull the heavier (fused) nucleus apart into the two component nuclei, the attractive nuclear force opposes this and again it costs energy. This is the energy released when the two nuclei fuse (or "bind" together). Hence the use of the term "binding energy".

It is true that an alternative way of putting this is that the fused nucleus is lighter than the original, so this mass difference must be released as energy, according to E=mc2 but I don't think it really explains things - it is just a statement of fact. From a physics viewpoint it is more important to understand that the energy release is related to the binding of the nuclei through the attractive nuclear force, and that this is therefore analogous to the energy release which arises in a chemical case (where it is the electric force rather than the nuclear force which provides the energy source)".

Ageism Revisited (Again)

by Jim Grozier

Veteran Fusion members may remember an early Newsletter article about the CERN Summer Student Programme, and its unfortunate exclusion of applicants over the age of 27 because it was apparently "designed to attract young people to the field of particle physics". I am delighted to announce that, on visiting the CERN web site recently, I discovered that the age restrictions have now been lifted. Whether or not this had anything to do with my badgering my MP, and then, via him, Lord Sainsbury, Parliamentary Under Secretary of State for Science and Innovation, on the subject is by no means clear, but it is nice to think that it did, and that ordinary people can influence "the system" if they shout loudly enough and often enough. So, if you are nearing the end of your degree, fancy going into Particle Physics, and have between 8 and 13 weeks available next summer (you will be given a subsistence allowance and help with accommodation), have a look at the Summer Student Programme's web site or This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Career Links Project

Anne Milne asks if we can bring the Career Links web site www.open.ac.uk/careers/links to your attention. They have a large number of OU students who have registered as Career Seekers - wanting to talk to specialists in their careers areas. They need to recruit more volunteer Career Helpers. Career Helpers volunteer time to talk to students about their work and career. They also want to promote the site to students who are considering a career change.

IAPS Journal Online

Latest JIAPS (Journal of the International Association of Physics Students) is now on the IAPS web site in PDF form at www.iaps.info.

OU Departmental News

It's Einstein Year! (OK, not really Departmental News but hang on.) To celebrate, Rambert Dance Company have created a dance entitled Constant Speed. Your local IoP branch may be holding a talk when the production is in a town near you (physicsweb.org).

Sean Ryan has recently become Head of Department here but is soon to be leaving us for the University of Hertfordshire. Another new addition to the astronomy department is a new RCUK fellow, Simon Clark who has recently joined us from UCL and, house moves and burst water pipes aside, will soon be a familiar name to some of you.

Barrie Jones was made a Professor of Astronomy in 2001 and gave his inaugural lecture Planets and Life Beyond the Solar System to an excited audience on 22 June 2005! Professor Jones has had a very wide ranging career from gamma-ray astronomy to architecture and most things in between.

Revision Weekends

Science Revision Weekend, University of York

30 Sept - 2 Oct 2005

This year's programme will comprise a combination of seminars, tutorials, workshops and problem-solving sessions for most 'S' courses. The costs of the weekend, including all meals from Friday evening to afternoon tea on Sunday, and all teaching, are: £190 for en-suite, £175 for standard, £120 for non-resident (includes a £5 discount for Fusion members). Full details and booking form available at www.sciencerevision.org.uk.

M500 Revision Weekend,
Aston University, Birmingham

9 - 11 September 2005

The weekend is designed to help with exam revision for most 'M' courses. Full board or non-resident tariffs available. Full details at www.m500.org.uk/sept.htm

Newsletter published by Fusion - The Open University Physics Society, 92a Springfield Road, Brighton, East Sussex BN1 6DE, UK.
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ISSN 1746-9015 (Print), ISSN 1746-9023 (Online).

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Last Updated (Wednesday, 13 March 2013 19:41)