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nuclear science and radioactive beams

In order to explore ever-more exotic regions of the nuclear chart, towards the limits of stability of nuclei, European nuclear physicists have built several large-scale facilities in various countries of the European Union. Today they are collaborating in planning a new radioactive ion beam (RIB) facility which will permit them to investigate hitherto unreachable parts of the nuclear chart. This European ISOL (isotope-separation-on-line) facility is called EURISOL.

Radioactive nuclides are produced by spallation, fission or fragmentation reactions of a projectile with a thick target.The products of these reactions diffuse out of the target, are ionized, separated on-line, and reaccelerated. The secondary beams are very intense.

The RIBs are produced by fragmentation of a projectile on a thin target. The radioactive nuclei created are separated in flight. The secondary beam has high energy and high selectivity, but low intensity.

The EURISOL project is aimed at the design – and subsequent construction – of the “next-generation” European ISOL radioactive ion beam (RIB) facility. The ion yields delivered by the current ISOL facilities, or those under construction (HIE-ISOLDE, SPES, SPIRAL2) will be exceeded by at least a factor 100. This will open a wide field of research for physicists.

The EURISOLProject

A view of the SPIRAL2 facility (Caen, France) currently under construction, a precursor to EURISOL.

Fragmentation ISOL: Isotope Separation On-Line

The European Expert Committee NuPECC has recommended the construction of EURISOL as one of two “next-generation” RIB infrastructures in the EU. The other project, FAIR (GSI, Germany), will use the fragmentation technique.

Heavy ionaccelerator

Thinproduction target

Radioactiveion beam

Fragmentseparator

Experiment

Experiment

Driveraccelerator

Thick,hot target

Isotope/isobarseparator

Radoactiveion beam

Productionbeam

Transfertube

Ion source

Post-Accelerator

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The most neutron-rich among the light nuclei, such as 11Li, 14Be, 22C, present a halo structure, one or more of their neutrons orbiting around a core. They have a very large spatial extension, 11Li with only 11 nucleons being as big as 208Pb. Only interactions in the continuum make these nuclei bound. To fully understand the structure of halo nuclei, researchers will need better detection techniques, more intense beams, and also access to heavier nuclear systems. In this field, EURISOL will provide many new opportunities.

Nuclei are characterized by magic numbers of neutrons and protons for which their binding energy is enhanced. The changes of the nuclear structure near the drip-lines are one of the key issues for nuclear physicists today. Experimental evidence of vanishing shell effects at N=20 and N=28 for nuclei with large neutron excess has already been found by many experimenters. To study the structure of more exotic nuclei and answer the questions raised by these observations, a facility like EURISOL is necessary to produce such nuclei in large amounts.

Shell structure

Exotic radioactivity

Neutron halos

The targets at the EURISOL facility will allow a number of hitherto unknown exotic nuclei to be produced. One interesting possibility is to continue a systematic investigation of their radioactive decay. Recently a new type of radioactivity has been discovered in very neutron-deficient nuclei, where two protons are emitted simultaneously by the nucleus.

Superheavy elementsNuclear chemists and physicists strive to complete the Mendeleiev

table of the elements by discovering ever heavier elements and studying their chemical and physical properties. The high intensity radioactive beams from EURISOL will lead to the production and study of new isotopes of these elements, and possibly to the

discovery of the elusive long lived «magic» superheavy nuclei, predicted since the seventies but never found.

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3

2

1

012 16 20 24 N

E* (MeV)

20Ca

16S12Mg

11Li

halos

Illustration of the mechanism for 2p radioactivity.

Excerpt of the Medeleiev table focusing on the heaviest elements.

76Os

107Bh

106Sg

105Db

104Rf

108Hs

77Ir

78Pt

79Au

80Hg

81Ti

82Pb

83Bi

108Hs

107Bh

106Sg

105Db

104Rf

108Hs

109Mt

110Ds

111Rg

112?

113?

114?

115?

61Pm

60Nd

59Pr

58Ce

57La

62Sm

63Eu

64Gd

65Tb

66Dy

67Ho

68Er

93Np

92U

91Pa

90Th

89Ac

94Pu

95Am

96Cm

97Bk

98Cf

99Es

100Fm

The 3-body “borromean” system 11Li composed of 2 neutrons and a 9Li core.

When one bond is broken the system falls apart, just like

the rings of the Borromean family crest.

Energies of the first excited states of nuclei. A high energy indicates a magic number, here N=20, which vanishes for 32Mg located far from stability.

Theoretical predictions for nuclear shell structure far from stability.

3p

2f

1h

3s

2d

1g

h9/2f5/2p1/2p3/2h9/2f7/2h11/2

p1/2f5/2i11/2p3/2h9/2f7/2

d3/2h11/2s1/2g7/2d5/2

g9/2

g7/2d3/2

s1/2

d5/2

g9/2

N=5

N=4

82

50

126

very diffusesurface

neutron drip lineharmonicoscillator

no spin orbitexotic nuclei/hypernuclei

around thevalley of

β - stability

nuclear structureNUCLEAR STRUCTURE

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The r-process

Neutron starsNeutron stars are the remnants of core collapse supernovae. They are the most compact stellar object after black holes. Indeed, pulsars (space lighthouses), and magnetars, generating the most intense magnetic field of the Universe, are neutron stars. The modelling of their inner crust is essential in order to understand the cooling process of the star, and also observational irregularities (glitches).

The crust is composed of neutron-rich nuclei immersed in a neutron gas. Vortices (quantum tornadoes) at work in the nuclear matter of the neutron star could be the explanation for glitches. The investigation of exotic nuclei is essential to understand the crucial role of superfluidity in these systems. EURISOL will open a new field of experiments on neutron-rich nuclei, aimed at a better understanding of neutron stars.

The energy generated by nuclear processes on the surface of accreting neutron stars is observed as short X-ray bursts if the nuclear burning is unstable. In such scenarios, matter is accreted for hours or days until a thermonuclear explosion is triggered by the ignition of the triple-alpha reaction and the break-out reactions from the hot CNO cycles into the rapid proton-capture process (rp-process) – a sequence of (α,p), (p,γ) and β+ reactions. There are many open questions concerning X-ray bursts. In many cases, the motivation is to obtain information on neutron stars and on the properties of matter under extreme conditions. To answer these questions, experimental masses and electron-capture rates on neutron-rich nuclei are now needed and can be provided by a facility like EURISOL.

Approximately half of the nuclear species in nature beyond iron are produced via neutron capture processes on very short time scales in neutron-rich astrophysical environments, i.e. the so-called r-process. Only under such conditions is it possible that highly unstable nuclei near the neutron drip-line are produced, also leading – after decay back to stability – to the formation of the heaviest elements in nature like Th, U and Pu. Despite its importance, the exact stellar site where the r-process occurs is still a mystery. The key to its understanding will probably only be obtained from a close interaction between astronomy, cosmochemistry, nuclear physics and astrophysical modelling of explosive scenarios. The questions of neutron capture, β-decay and mass measurement in the regions of closed neutron shells will be carefully investigated with the high intensity RIBs of EURISOL.

X-ray bursts

Comparison of nuclear abundances with predictions of astrophysical models.

ISOLTRAP at CERN: A precision instrument to measure nuclear masses

Copyright - Hubble site

nuclear astroPHYsicsNUCLEAR ASTROPHYSICS

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The study of nuclear decay modes has played a crucial and undeniable role in determining the basic structure of fundamental interactions. In particular, β-decay has contributed to establishing such aspects of particle physics as parity violation, the nature of the neutrino or lepton number conservation, and has thus provided the experimental foundations for a large part of the Standard Model (SM) of electroweak interactions. Precision measurements in nuclear β-decay and in atomic transitions constitute simple means to search for signatures of new interactions or small violations of the fundamental symmetries. At low energies the search for new physics beyond the SM is a very exciting activity presently carried out at several ISOL facilities, as well as at cold and ultra-cold neutron sources around the world. The importance of this field, where the atomic nucleus is used as a laboratory for the tests of fundamental conservation laws, has been recognized in the description of the EURISOL proposal and is considered to be one of the four key areas of modern science on which RIB facilities will have a major impact.

Neutrinos come in three varieties. One of the major discoveries of the last decade is spontaneous oscillations between these neutrino families, which imply that neutrinos are not massless as previously assumed. In order to learn more about these elusive particles and perform stringent tests of quantum symmetries, neutrino physicists need a new type of neutrino beam called beta-beam. The neutrinos would be produced by the radioactive beta decay of massive amounts of unstable nuclei, for example 6He and 18Ne, accelerated close to the speed of light. The seed nuclei would be produced by EURISOL and the beta-beam facility, elaborated within the Design Study, would be a natural extension of EURISOL.

Sketch of a beta beam facility

Beyond the standard model

Beta beam

Neutrino detection through the Cerenkov effect(from the Super-Kamiokande Collaboration)

Results of precision beta decay measurements to test the standard model.

FUNDAMENTAL INTERACTIONSFundamental interactions

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The Design Study includes fabrication and tests of fully-equipped superconductivity cavity prototypes and design, fabrication and test of a multipurpose cryomodule for the low-energy section of the proton driver linear accelerator.

A 4-year Design Study began in 2005 in order to work on the technologically challenging aspects of the project, the instrumentation and the radiation safety issue. Synergy with other projects is being examined, including a feasibility study for the new ‘beta-beam’ neutrino proposal, forming an integral part of the Design Study. After this, possible sites will be evaluated, and the community will be ready for a full Engineering Design, to be followed by construction of the facility.

Researchers and engineers of several European laboratories are collaborating in twelve tasks to further the EURISOL design.

The EURISOL layout consists of a superconducting linear accelerator providing protons of energy 1 GeV and an impressive power of 5 MW, but also capable of accelerating deuterons, 3He and ions up to mass 40. The beams will impinge simultaneously on two types of targets, either directly or after conversion of the protons into neutrons through a loop containing 1 ton of mercury surrounded by kilograms of fissile material. The unstable nuclei produced diffuse out of the target, are ionized and selected, and can be used directly at low energy or reaccelerated by another linear accelerator to energies up to 150 MeV per nucleon in order to induce nuclear reactions.

Prototypes of some of the most critical parts of the facility are being built within the Design Study, in particular:

Technical preparatory work and demonstration of principle for a high-power target station for production of beams of fission fragments using the mercury proton-to-neutron converter-target and cooling technology is carried out in collaboration with the communities working on spallation neutron sources, accelerator-driven systems and neutrino factories. The converter will be surrounded by large amounts of fissile material.

Multi-MW target station

Superconducting cavity development

Furthering target and accelerator technology

tHe eurisol concePtTHE EURISOL CONCEPT

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12 tasks to further the Science and Technology

20 participants from 14 European countries

21 contributors from around the world

Management•Multi-MW Target Station•Direct Target•Fission Target•Safety & Radioprotection•Heavy Ion Accelerator Design•Proton Accelerator Design•SC Cavity Development•Beam Preparation•Physics and Instrumentation•Beam Intensity Calculations•Beta-Beam Aspects •

GANIL Grand Accélérateur National d’Ions Lourds, Caen, France

CNRS/IN2P3 Centre National de la Recherche Scientifique/ Institut National de Physique Nucléaire et de

Physique des Particules

Paris, France

INFN Istituto Nazionale di Fisica Nucleare Frascati (Roma), Italia

CERN European Organization for Nuclear Research Geneva, Switzerland

UCL Université Catholique de Louvain, Centre de Recherches du Cyclotron

Louvain-la-Neuve, Belgium

CEA Commissariat a l’Energie Atomique (Direction des Sciences de la Matiere)

Paris, France

NIPNE ‘’Horia Hulubei’’ National Institute for Physics and Nuclear Engineering

Bucharest-Magurele, Romania

JYU University of Jyväskylä Jyväskylä, Finland

LMU Ludwig Maximilians Universitaet Muenchen Muenchen (Munich), Germany

FZJ Forschungszentrum Juelich GmbH Jülich, Germany

FI Institute of Physics Vilnius, Lithuania

UW Warsaw University Warsaw, Poland

SAV Institute of Physics - Slovak Academy of Sciences Bratislava, Slovakia

U-LIVERPOOL The University of Liverpool Liverpool, U.K.

GSI Gesellschaft fuer Schwerionenforschung m.b.H Darmstadt, Germany

USDC Universidade de Santiago de Compostela Santiago de Compostela, Spain

STFC Science and Technology Facilities Council Swindon, U.K.

PSI Paul Scherrer Institute Villigen, Switzerland

IPUL Institute of Physics, University of Latvia Salaspils, Latvia

SU-MSL Stockholm University - Manne Siegbahn Laboratory

Stockholm, Sweden

U-FRANKFURT Johann Wolfgang Goethe-Universität Frankfurt, Germany

BINP Budker Institute of Nuclear Physics of Novosibirsk

Novosibirsk, Russia

VNIITF Russian Federal Nuclear Center - Zababakhin Institute of Technical Physics

Snezhinsk, Russia

PNPI Petersburg Nuclear Physics Institute Gatchina, Russia

ORNL Oak Ridge National Laboratory Oak Ridge, TN, USA

ANL Argonne National Laboratory Argonne, IL, USA

KAERI Korea Atomic Energy Research Institute Daejeon, Korea

JAERI Japan Atomic Energy Research Institute Kashiwa, Japan

TRIUMF Tri-University Meson Facility Vancouver, Canada

SOREQ Soreq Nuclear Research Centre Yavne, Israel

U-MAINZ Johannes Gutenberg Universität Mainz Mainz, Germany

KVI Kernfysisch Versneller Institut Groningen Groningen, Netherlands

U-SURREY The University of Surrey Guildford, UK

U-YORK The University of York Heslington, UK

U-PAISLEY University of Paisley Paisley, UK

VINCA VINCA Institute of Nuclear Sciences, Laboratory of Physics

Belgrade, Serbia

U-UPPSALA Uppsala University Uppsala, Sweden

NSCL National Superconducting Cyclotron Laboratory, Michigan State University

East Lansing, MI, USA

FNAL Fermi National Accelerator Laboratory Batavia, IL, USA

HUG Hospital University of Geneva Geneva, Switzerland

ITN Instituto Technologico e Nucleare Scavém, Portugal

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The EURISOL Design Study is financially supported

by the European Community under the FP6

“Research Infrastructure Action - Structuring the

European Research Areas” EURISOL DS project

contract n°515768 RIDS. The EC is not liable

for any use that can be made of the information

contained herein.

www.eurisol.orgMore information can be found at:

tHe eurisol desiGn studYTHE EURISOL DESIGN STUDY