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An Insight Into Nature's Strongest Force

Introduction:

My name is Lloyd and I am in the third year of my PhD studying Theoretical Nuclear Physics. I am attempting to provide a better theory to describe the phenomenon of neutral pion (a relatively light, short-lived particle that is found in nuclear and particle reactions) production from a photon (light) incident on a proton (a nuclear particle that is found in the nucleus of every atom).  Before starting my research I studied theoretical physics at the University of Manchester.


Strong Nuclear forces remain to be one of the least understood processes in nature. Yet it is the source of immense energy that can power our cities, from harnessing the emitted radiation in power-plants; or level countries by concentrating radioactive materials in a bomb. The manner in which the fundamental matter particles (or quarks) exchange the strong force carrying particle (or the gluon boson) is far more complex than any of the other forces (weak nuclear, electromagnetic or gravity). Unlike the other forces, gluons themselves can carry a strong nuclear charge, known as colour charge; this allows them to interact with themselves in-between quark interactions, allowing for infinite scenarios to describe the simplest of processes. 

In Depth:

The study of the strong nuclear force is known as quantum chromodynamics (QCD), this theory helped scientists understand important properties of particle physics, mainly why we only see composite quark states in nature. In other words why you will never find a sole quark by itself, instead you will see it in bound states (hadrons) which form protons and neutrons (baryons) and lighter states such as pions (mesons). But trying to make any practical calculations with QCD is very difficult, so difficult in fact that if anyone were to solve the QCD equation into a usable form then they would win 1 million dollars from the Clay Mathematics Institute!

I do away with these complexities of QCD by only working in energy regimes where the protons and other hadrons won't break down into their constituent quarks. So we can describe proton or neutron scattering through pion exchange instead of using gluons. Furthermore, I take advantage of some symmetries present in QCD, related to the quark masses, to simplify aspects of the calculations. This is a very vague picture of the theory I work in called Chiral Perturbation Theory (ChPT).


My work has been motivated by a recent experiment in Germany at the Mainz Microtron by the A2 and CB-TAPS collaborations where they have obtained the most accurate data to date on this interaction. I am in the process of taking theories that have already been made to describe parts of this process and sticking them together to get a more complete picture of the reaction. The most important part I have included is an intermediate resonance state prior to pion emission.

This research isn't going to be part of the new fastest computer in 20 years time, nor is it going to cure diseases. But it will give us an insight in to what happens in nature at the sub-atomic level. Then maybe who knows what this might lead to in the future, 100 years from now it is impossible to predict how important this process will be in understanding nuclear fusion both in power plants or in stars. When Paul Dirac, one of the pioneers of quantum mechanics, predicted the existence of massless Dirac fermions in the 1920s he had no idea that a century later people would be trying to use these states within graphene to dramatically improve technology.

Going Further:

To follow exactly what it is I do I am afraid you will need a degree in theoretical physics, which you can start looking into at the University of Manchester. (http://www.physics.manchester.ac.uk/study/undergraduate/undergraduate-courses/physics-with-theoretical-physics-mphys/)

The European Centre for Nuclear Research (CERN) have lots of information available on particle and nuclear physics (http://home.web.cern.ch/students-educators)

The Jefferson Lab in the USA also has useful information for students and teachers (https://www.jlab.org/education-students)

MAMI, the experimental group that analyse this interaction (http://www.kph.uni-mainz.de/eng/108.php)


 

Researching safe ways to dispose of nuclear waste

Introduction

My name is Robert Worth and I am currently part way through a PhD in Nuclear Engineering with the Nuclear Graphite Research Group at the University of Manchester – how did I get here? Almost by accident. It was during my A Level study in Physics that I first came across the phenomenon of radioactivity, which I thought was a bizarre and exciting process that I had not encountered before, and I needed to know more! This eventually led me to my degree in Mechanical (Nuclear) Engineering at the University of Manchester, which was very enlightening and encompassed many aspects of both mechanical and nuclear engineering. It was during my degree that I stumbled across an email containing upcoming PhD research projects – did I know what a PhD involved? Nope, not really. Did I want to do one? I wasn’t sure. I’m glad I applied, however, as it turned out that this is the sort of work I’d wanted to do all along, I just hadn’t realised it. You are no longer just absorbing information from others – I am also now doing the finding out, and helping answer questions that nobody in the world yet has answers to!

I’ve been very lucky with this PhD project, and have been encouraged to attend many prominent events and conferences around the country, talking with and working alongside some of the most inspiring people and minds in the country. I’ve been fortunate enough to travel further afield too, as far as Lithuania, where we stood on the top of a nuclear reactor core of the same basic design as the famed Chernobyl, and even over to the United States, to visit a research group at Idaho State University and to help on an experiment at a synchrotron particle accelerator in California.

My specific research project is on thermal treatment of irradiated graphite waste. It turns out that there is an awful lot of it (around 96,000 tonnes) in our small country, the UK. So far, there are good ideas about how we might deal with this large volume of radioactive waste, and the Nuclear Decommissioning Authority (NDA) have plans to bury most of it in a future geological disposal facility, a large controlled facility far underground that could house and contain all of our radioactive waste for thousands of years to come. Since a location for this facility is yet to be found, and it is yet to be built, you could argue that a disposal route is not set in stone. Which is where treatment comes in – can we do something else with the graphite waste to reduce the hazard, instead of burying it, which could potentially save money and may leave valuable space in the repository open for other more hazardous wastes? This is a point of controversy amongst the nuclear waste research community! 

In Depth

What is graphite and how is it used?

Graphite is a very stable hexagonal formation of carbon atoms, that can be found naturally but is also artificially manufactured to very high purities, at great expense! This involves many different processes to reach the final product including heating to around 3000oC for a number of days. It is essentially many planes of the material ‘graphene’ all layered up on top of each other, and is found in pencils; the ‘lead’ in your pencil is actually graphite, and it is these layers of carbon atoms sliding relatively easily over each other that allows you to write and draw quite easily.

Graphite is used in many nuclear reactors in the UK in the shape of enormous blocks, which can be over a metre in height, all stacked on top of each other and arranged into a large reactor core. Its purpose is to slow the neutrons in the core down, by acting as a physical barrier for the neutrons to bounce off, a little like billiard balls, so that they will react more easily with the nuclear fuel, producing energy for us to power our homes. 

Why is it radioactive?

Carbon has been selected as a fairly ‘neutron transparent’ material so that neutrons will bounce off and scatter away from the carbon atoms instead of being absorbed. This does not happen every time, however, and on occasion a neutron will be absorbed into the carbon atom, making the nucleus of the atom heavier and larger than it was previously. This can make the atom become unstable, as it can no longer physically sustain itself in a stable state, and so the atom will ‘decay’ by releasing some energy – in this instance, a radioactive carbon-14 atom will spit out an electron from the atom and transmute into nitrogen-14, which is a stable atom. Voila! This is the process of radioactive decay.

What do I actually do?

I spend a lot of time working in a laboratory with radioactive samples, taken from a nuclear reactor, wearing a white lab coat, goggles, layers of gloves, and working with tongs behind special shielding or in a glove box, like Homer Simpson. I also wear a dosimeter to record the amount of radiation I have received from the samples, so that I know I am well below safe levels for working. I then take these samples and place them in a specially designed tube furnace, and very carefully oxidise them using a gas flow of 1% oxygen to try and remove a good fraction of the surface radioactivity as a gas. The radioactive portion of this gas is then trapped and collected in a ‘bubbler system’, where the gas is forced to bubble up through a clever fluid, before it is taken away for analysis to determine how much radioactivity has been successfully removed. I can then use this data to make a reasoned judgment of how I might improve the process, by adjusting the temperature, for instance.

Going Further

More information about the array of Nuclear Engineering research in the School of MACE at the University of Manchester can be found at: http://www.mace.manchester.ac.uk/our-research/research-themes/nuclear-engineering/

A fairly detailed overview of ‘radioactive waste management’ around the world has been produced by the World Nuclear Association, and can be found at: http://world-nuclear.org/info/Nuclear-Fuel-Cycle/Nuclear-Wastes/Radioactive-Waste-Management/

A further insight into the role of the Nuclear Decommissioning Authority in the UK, working on behalf of the government and responsible for overseeing the clean-up of many UK nuclear power sites, can be gleaned from the following website: http://www.nda.gov.uk/what-we-do/