Nuclear physics and technology – inside the atom

Contents346810121415ForewordIntroductionThe complex heart of matterScienceExploring the nucleusApplications – HealthNuclear medicineApplications – EnergyHarnessing the nucleus for powerApplications – Industry, environment and societyA powerful analytical toolTechnology transfer and trainingNew technologiesEducation in nuclear science2

Nuclear physics and technology – inside the atomForewordThe uncovering of the structure of atoms – the basic units of matter – as composed of clouds of electrons surroundinga central nucleus is one of the landmark 20th-century discoveries, underpinning modern healthcare, advanced materialsand information technology. However, while the chemical and physical characteristics of atomic electrons have beenstudied thoroughly, and have been successfully exploited to make pharmaceuticals, plastics and electronic devices, forexample, the nucleus is less well understood.The forces binding together the components of the nucleus are extremely strong, and so require the input of highenergies, using large accelerator facilities, to probe and manipulate their structure and behaviour. Furthermore, thestrong interactions involved are extremely complex and difficult to unravel both theoretically and experimentally.The importance of nuclear physics and technologyOver the past decades, studies of the nucleus have led to many major developments that have transformed our lives. Oneof the most significant has been in medicine: in developing nuclear methods to treat cancer safely, to analyse biologicalprocesses and diagnose disease using medical isotopes, and to image the body non-invasively. The application of nuclearbasedanalytical techniques continues to revolutionise the chemical and life sciences, and plays an increasing role inmonitoring environmental change, as well as providing new portable devices used to aid national security.A prominent application of nuclear research is in developing the long-term means of securing our energy needs within alow-carbon economy. Tapping into the powerful forces within the nucleus to generate power is a major goal of nuclear scientistsand engineers. Revolutionary designs of fission reactors, some using novel fuel sources, are already being tested, while variousapproaches to nuclear fusion – the ideal environmentally-friendly solution to our energy needs – are being developed on aninternational scale. Nuclear transmutation is also being investigated as a means of destroying nuclear waste safely.Studies of the nucleus are also extending our understanding of the basic laws of nature and how the universe evolved.Much of nuclear physics research involves exploring the forces and particles characterising everyday matter, as well as moreexotic phenomena found in stars and the early universe. One of the most exciting areas of research is the investigation ofstellar processes by which all the elements are created, which involve unusual, unstable nuclear species. It is this kind ofresearch that attracts students into physics.This report describes the research carried out in nuclear physics and technology, and shows how the discoveries madeare leading to a growing range of applications in medicine, power generation, as well as environmental and security monitoring.Dr Robert Kirby-HarrisChief ExecutiveThe Institute of PhysicsThe UK roleThe atomic nucleus was discoveredat the University of Manchester, andmuch of the early, seminal researchinto nuclear structure was carriedout in the UK. Today, vibrant nuclearphysics research programmes continueacross Europe, including at expandinginternational facilities in Germany andFrance. The EU recognises the economicimportance of these centres through itssupport of the European Roadmap forResearch Infrastructures (ESFRI).Nuclear research in the UK is fundedprimarily by two members of the UKresearch councils family. The Engineeringand Physical Sciences Research Council(EPSRC) funds nuclear engineeringand also leads the UK Energy ResearchProgramme. The Science and TechnologyFacilities Council (STFC) funds nuclearphysics and also manages facilities whichare used for a broad range of research,including some for nuclear physics andengineering challenges.3

Nuclear physics and technology – inside the atomThe seminal work that led to thediscovery of the atomic nucleus wascarried out a century ago by the fatherof nuclear physics, Ernest Rutherford,at the University of Manchester.http://schools.medphys.ucl.ac.ukLung function can be assessed by breathing in agas containing radioisotopes of xenon or kryptonAn essential tool for societyNuclear research continues to lead tothe development of new isotopes andmethods that have become essentialanalytical tools in medicine, industryand environmental studies.The technical challengesNuclear physics requires largescalesophisticated equipment –accelerators, large complex detectorsand computer systems. Europeannuclear physicists, including the UKcommunity, have developed astrategy to provide transnationalaccess to a network of new nuclearresearch facilities.Future benefitsThe research carried out will providedeeper insights into the everydayworld, as well as the universe,while potentially furnishing theunderpinning knowledge for future,economically invaluable and worldsavingtechnologies.A guide tothe mighty atom•yAtoms consist of a positivelycharged nucleus with aconcentrated mass, surrounded bylightweight negative electrons.•yThe electrons are responsible forthe chemical binding of atoms intomolecules, and for conducting electricity.•yNuclei consist of positively charged protonsand neutral neutrons.•yTogether, they are responsible for the mass of the element.•yThe number of protons gives the element’s atomic number.•yThe lightest element, hydrogen, has one proton in its nucleus; helium has twoprotons and usually two neutrons.•yThe heaviest naturally-occurring element, uranium, has 92 protons.•yElements can have varying numbers of neutrons, which are essential for stability,giving rise to isotopes with different masses.•ySome isotopes are unstable, spitting out alpha particles (helium nuclei),electrons (beta-radiation) or positrons (the positive, antimatter version ofelectrons), together with high-energy electromagnetic radiation (gamma-rays).They are then transmuted into other elements.•yMany radioactive isotopes exist naturally on Earth and in stars, but they are alsomade in the laboratory.Even smaller• Protons and neutrons each consist of three fundamental particles called quarks.• They are combinations of the two lightest quarks; there are also four, heavierquarks that form unstable nuclear particles.• Quarks can also bind in nuclear pairs calledmesons, some of which played a significantrole in the universe’s evolution.• Particles such as quarks andelectrons also exist in antimatterforms with opposite charge.5

Nuclear physics and technology – inside the atomExperimentsExperiments to understand nucleirequire large-scale equipment thatcan accelerate to high energiesbeams of subatomic particles andcharged ions (atoms stripped of mostof their electrons). These projectilenuclei are then directed onto atarget. The principle is to make newnuclear species, either by fusion ofthe projectile nuclei with those in thetarget, or by fragmenting the nuclei.The masses, lifetimes and energiesof the particles and the radiation(gamma-rays) emitted are measured.One aim is to make new magic nucleiand study their structure. Often, thenuclei are generated in high-energystates with unusual shapes, and maybe set spinning fast. The gamma-raysemitted, as the nuclei lose energy,provide information about nuclearstructure and behaviour. To understandthe binding forces better, nuclei mayalso be prepared where the proportionsof protons and neutrons have beeninterchanged – to create ‘mirror’ nuclei.Additional experimental approachesinclude smashing together beams ofheavy nuclei at high energies, withthe aim of breaking them up into theconstituent quarks; high-energy lasersand electron beams are used to probethe structure of target nuclei; and veryhigh-energy lasers can induce nuclearreactions such as fission and fusion.Experiments have shown that the lead-186nucleus can adopt three different shapes at quitesimilar low energies. Physicists at the University ofLiverpool contributed to this seminal studyThe NuSTAR experiment at FAIR in GermanyNuclear physics in the UKThe existence of the atomic nucleuswas uncovered in experiments at theUniversity of Manchester a centuryago. Today, UK nuclear physicistscontinue their studies at facilitiesaround the world: in Europe, theUS, Canada, Japan, South Africaand Australia. The core communityincludes groups from the Universitiesof Birmingham, Brighton, Edinburgh,Glasgow, Liverpool, Manchester,Surrey, the West of Scotland andYork, as well as the STFC DaresburyLaboratory in Cheshire. Theycollaborate in international teams todevelop new experimental set-ups, inparticular, dedicated devices such asdetectors (p14). Increasingly, nuclearphysics and its applications arebecoming multidisciplinary, involvingastrophysicists, and atomic, laser,The Exogam detector at the GANIL facilityin France where UK nuclear physicistsoften carry out experimentsmedical and particle physicists, as wellas materials scientists and engineers.The UK is contributing to anexperiment called NuSTAR (NuclearStructure, Astrophysics and Reactions)at a major new European facility basedin Darmstadt, Germany – the Facilityfor Antiproton and Ion Research (FAIR).It will comprise a large acceleratorcomplex for generating intense beamsof a wide range of nuclei, of whichmany are unstable and very rare.They will be used in experimentsto investigate all of the questionson p6. Beams of antiprotons (theantimatter version of protons) willalso be generated to investigate quarkinteractions. At CERN in Geneva,Switzerland, the UK is already involvedin ALICE, an experiment using theLarge Hadron Collider (LHC) to studyhow quarks first interacted in the earlyuniverse. European physicists are alsoconsidering a future facility, EURISOL,to produce even more intense beamsof exotic nuclei.The new FAIR facilityLow-energy experimentsNuclear studies include experimentsinvestigating very rare radioactivedecays of certain nuclei in highlycontrolled environments. Themeasurements aim to shed light onthe behaviour of matter and energyat the most fundamental level.Experiments involving the binding ofantimatter particles into, for example,antihydrogen, offer another avenueof investigation.7

Applications – HealthNuclear medicineNuclear physics research has contributed significantly to improving the health of the nationhttp://schools.medphys.ucl.ac.ukThe behaviour of particular nuclei, both stable and unstable, can be manipulatedand monitored to diagnose and cure disease.Medical isotopesScientists and clinicians have longrealised that the radiation emitted byshort-lived isotopes offers a highlysensitive tool for diagnosing illnessesand studying disease. The mostcommonly employed radioisotope,technetium-99, is used in at least30 million hospital diagnoses ayear, worldwide. It emits readilydetectable, low-energy gamma-raysand has a half-life of a few hours.Aligning a patient for radiotherapyThe isotope is obtained from thedecay of molybdenum-99, which ismade in dedicated nuclear reactorsin which a target is irradiated withneutrons. Specific isotopes such asiodine-131 are often bound to bioactivecompounds, which, when taken in bythe body, concentrate in specific organsand so can be used as tracers to followmetabolic processes linked to disease.Magnetic resonance imaging (MRI),a routine hospital procedure inwhich the UK has led the field,has its basis in fundamentalnuclear physics research carriedout a few decades ago.Basic research into nuclearstructure and reactions is essentialin characterising and evaluating newisotopes for medical use, as wellas developing improved methodsof making and detecting them. Thismay mean designing more efficientaccelerators, targets and detectors.A more sensitive detector enables thedose of radioactive tracer to be lowered.University groups such as those atBirmingham, Glasgow, Liverpool,Manchester and Surrey have appliedmedical physics research programmes.Because most isotopes used donot survive for long, they need tobe made close to the clinic. Whilesome large hospitals have their ownaccelerator facilities for isotopeproduction, physicists are investigatingsmaller, cheaper accelerators andalternative methods of production, inresponse to the growing demand. TheUniversities of Strathclyde and theWest of Scotland recently achieveda first in using high-power lasers togenerate medical isotopes.Radiation therapiesAs well as providing sensitive imagingtechniques, carefully directed doses ofnuclear radiation can be targeted to killcancer cells, which are more sensitiveto radiation than normal tissue. Aroundone in six of the UK population willreceive radiotherapy at some pointin their lives. The simplest approachis to insert an implant containing asmall amount of a radioisotope closeto the tumour – a technique calledbrachytherapy. This is used to treatthyroid and prostate cancer. A moreexperimental therapy, boron neutroncapture therapy (BCNT), being tested atthe University of Birmingham, exploits8

Technology transfer and trainingNew technologiesMuch of the new technology developed for nuclear physics finds use in other fieldsNuclear physics experiments are demanding. They require highenergyparticle accelerators and advanced detectors, combinedwith fast data-acquisition and processing software.Accelerator technologyNew methods of acceleratingnuclear particles, including compactmachines and laser acceleration, arealready being developed, which canthen be applied in other fields. TheSCAPA project set up by the ScottishUniversities Physics Alliance (SUPA) isdeveloping a laser facility to accelerateion beams for cancer treatment (p9).Germaniumdetectorssuch as AGATA(right) are usedextensively innuclear physicsresearchDetectorsExperiments involve detecting rare,highly unstable isotopes (p7) via thegamma-rays, protons and neutronsthey emit when they lose energy ordecay. Most UK nuclear physics groupsare involved in developing new, moresensitive detectors, which are thentailored for other applications (p13).Segmented arrays of semiconductingmaterials such as silicon are usedto register charged particles andhigh-energy radiation. Researchersat the University of Edinburgh andRAL have developed advanced siliconstrip devices, originally for nuclearastrophysics experiments (p6), thatalso incorporate the necessarymicroelectronics. They work closely withindustry; silicon-strip technology isfound in medical X-ray machines usedfor mammography.Gamma-ray trackingUltra-pure germanium is the materialof choice for detecting gamma-rays.A germanium-based detector, AGATA,involves novel detection methodsdeveloped in the UK that candisentangle how a gamma-ray interactsin the detector. The trajectory can thenbe tracked, the total energy measuredaccurately and the event producing itdetermined. The technology is alreadybeing applied in medical (p9) andsecurity detectors (p13).Digital pulse-shape processingAn important ingredient in extractingthe gamma-ray data is to characterisethe intensity of the signal recorded overtime – the pulse shape. This helps todetermine the precise location of eachinteraction within the detector volume.The COBRA CZT detectorRoom-temperature detectorsGermanium detectors must be cooledto liquid-nitrogen temperatures, butalternative detector materials basedon cadmium, zinc and tellurium(CZT) work at room temperature. AUK university collaboration, HEXITEC,is applying the technology in mobileX-ray and gamma-ray cameras foranalytical, medical and spacescienceapplications. In addition, theUniversities of Surrey and York areworking with the company, DiamondDetectors Ltd, on radiation-harddevices using synthetic diamond formonitoring environmental radiation.Neutron detectorsNeutrons emitted from nuclearreactions are more difficult to detect,because they do not respond toelectric fields. A new neutron detectorbeing developed at the University ofYork for astrophysics experimentscombines a liquid scintillator withdigital pulse-shape technology, andcould be used for radiation monitoringin nuclear power stations.14

Nuclear physics and technology – inside the atomEducation in nuclear scienceA strong nuclear skills base is a national assetAs well as driving advances in a broad range of sectors, nuclear physics andtechnology train people who work in associated industries such as nuclear medicine.Nuclear physics plays a role in inspiring students to take up science, supplying sciencegraduates with technical skills that are vital to a modern economy.Jim Al-Khalili, nuclear theorist andEPSRC Senior Media FellowActive targetsMany nuclei, created in reactions ina target, exist transiently in minutequantities that are difficult to detect.Physicists at the Daresbury Laboratory,and the Universities of Liverpool andYork are working on a new detectionsystem in which the target – a gas ofhydrogen or helium nuclei – also actsas the detector. The gas is ionised bynuclear particles, releasing electronsthat then produce a signal.Universities and industryConcerns about climate change andthe potential of the nuclear poweroption, together with a growingrecognition of the value of nuclearmethods in providing good healthcareand vital national security, has led thegovernment to evaluate how to improvecore competencies in the nuclearsectors. All the main UK academicnuclear physics groups now havestrong, interdisciplinary collaborativeprogrammes to ensure that there is atransfer of knowledge and skills frombasic research into fields such as powergeneration and radiological science.David Jenkins, nuclear physicist and a formerSTFC Science in Society FellowThe helium gas active target used by UKresearchers working at MAXLab in Lund, SwedenMany institutions offer postgraduatecourses, partially supported by industry,covering a wide range of applications,from reactor physics and wastemanagement to radiation measurementand medical physics.To address nuclear power issuesspecifically, the research councils,with support from stakeholders inthe energy industry, have set up auniversity consortium called ‘Keepingthe Nuclear Option Open’ (KNOO)to carry out research in key areas offission research.Schools and outreachSurveys have shown that nuclearphysics, along with particle physics andastronomy, attracts school studentsinto science. The STFC, which fundsnuclear physics research, encouragesresearchers to engage in activities thatenable children and the general publicto appreciate and understand whatnuclear physics is about. David Jenkins,a nuclear physicist at the Universityof York, was for two years an STFCScience in Society Fellow, providingmaterial for teachers’ continuingdevelopment programmes and eventsfor schoolchildren. Jim Al-Khalili, anuclear theorist at the Universityof Surrey and EPSRC Senior MediaFellow, is well-known for his books andbroadcasts on the subatomic world.Details on all UK nuclear courses canbe found at www.nuclearliaison.comand www.world-nuclear-university.org15

AcknowledgmentsThis report was prepared with the help of the Institute of Physics’ NuclearPhysics Group, and its Nuclear and Particle Physics Division.The Institute of Physics appreciates the financial support provided by theScience and Technology Facilities Council in the preparation of this report.Further information on UK support for nuclear physics and technology canbe found on the STFC and EPSRC websites:www.stfc.ac.ukwww.epsrc.ac.ukEditor and writer:Nina HallDesigner:h2o CreativeFor further information, contact:Tajinder Panesor76 Portland PlaceLondon W1B 1NTTel +44 (0)20 7470 4800Fax +44 (0)20 7470 4848Email: tajinder.panesor@iop.orgwww.iop.orgRegistered charity no. 293851© The Institute of Physics 2010The Institute of Physics is a scientific charity devoted to increasing thepractice, understanding and application of physics. It has a worldwidemembership of over 36 000 and is a leading communicator of physicsrelatedscience to all audiences, from specialists through to governmentand the general public. Its publishing company, IOP Publishing, is a worldleader in scientific publishing and the electronic dissemination of physics.This document is also available to download as a PDF from our website.The RNIB clear print guidelines have been considered in the production ofthis document. Clear print is a design approach that considers the needsof people with sight problems. For more information, visit www.rnib.org.uk.