Nuclear structure in extremely exotic systems explored by laser spectroscopy of pure ion beams.

Lead Research Organisation: University of Liverpool
Department Name: Physics

Abstract

Atomic nuclei form the fundamental building blocks for most of what we see around us. Understanding the quantum arrangement of protons and neutrons within the nucleus, their stability, the nature of the forces which hold them together and even how the elements were formed in the universe are the subject of nuclear structure research. Surrounding the nucleus, orbiting electrons occupy quantum 'shelves' at discrete energies, with an arrangement largely dependent upon the proton number (ie. element) under study. However, on a hyperfine level, these energy levels move and split as a result of changing nuclear properties such as size, shape, magnetization and quantum spin as neutrons are added to create different isotopes. Precision lasers can be used to excite electrons between these levels to reveal such properties. To more fully understand the nature of the nuclear forces we need to know how nuclear properties change for exotic nuclei with unnatural combinations of proton and neutron numbers (Z and N). Such nuclei may live for less than a millisecond. Produced with a distribution in N and Z from nuclear reactions at 'isotope factories', they are electrostatically transported as a beam of ions to a station for spectroscopy. A specific mass (N+Z) is selected using in-flight magnetic deflection, but how can we choose a single element? The isotope (N,Z) we wish to study may be a part per million of the total beam selected by mass only. A few sheep would be hard to see in a field of a million goats. New international facilities aim to produce more, but will not fulfill their potential if they produce more of both. This is a long standing problem in nuclear physics research. To a laser beam, quantum electron levels provide a fingerprint for each element. At a characteristic frequency of light, the electrons are excited between levels in one element alone. Moreover, a combination of laser beams and excitation steps will remove an additional electron altogether. A bunch of ions (released from a trap, with ample time to interact with the laser) with two electrons removed from their neutral atomic state rather than one, and therefore twice the charge, will travel to the spectroscopy station faster under electrostatic acceleration. Arriving earlier, only nuclei of a single N and Z will be present, and other combinations (all arriving later) kicked away. Using a laser to study (as well as purify) the beam of nuclei reveals all the properties above by detecting photons emitted by electrons relaxing back after excitation as a function of frequency. Purification will allow lasers to study nuclei which are produced at a rate of less than one per second (compared with 1000/s required today), and irrespective of what other elements with isotopes of the same mass are present. Within the nucleus, neutrons and protons each occupy their own quantum shelves, lying at discrete energies. These are filled sequentially, and the interaction between nucleons raises or lowers their energy as the levels are filled. Level migrations, the consequent changes to the energy gaps between them or even a reordering, fundamentally affect the nuclear properties. These measurements will provide a sensitive probe of species far from stability in order to understand nuclear interactions. Lying at the corner stone of the natural (and unnatural) world nuclear science finds applications beyond its chapter. It has long been suspected that thorium-229 contains an isomer - that is, a nuclear state excited in energy which lives at least momentarily. If observed, this would have the lowest energy of any seen in nature and could be the first demonstration of nuclear excitation with a laser. Considerable interest has been gathered to use the isomer as an accurate clock (from an oscillating nuclear transition), testing Einstein's theory of relativity and how constant the fundamental physical constants really are - one of the greatest unanswered problems in physics.

Publications

10 25 50
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Yordanov DT (2016) Simple Nuclear Structure in (111-129)Cd from Atomic Isomer Shifts. in Physical review letters

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Neugart R (2017) Collinear laser spectroscopy at ISOLDE: new methods and highlights in Journal of Physics G: Nuclear and Particle Physics

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Lautenschläger F (2016) Developments for resonance ionization laser spectroscopy of the heaviest elements at SHIP in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

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Cheal B (2015) Recent Advances in On-Line Laser Spectroscopy in Nuclear Physics News

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Bissell M (2016) Cu charge radii reveal a weak sub-shell effect at N = 40 in Physical Review C

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/I004726/1 01/10/2011 30/06/2013 £420,742
ST/I004726/2 Transfer ST/I004726/1 01/07/2013 30/09/2016 £279,136
 
Description Established a method of moving atomic electrons into different energy levels in an ion trap, so that high resolution laser spectroscopy can be performed more efficiently, and with greater sensitivity to properties of nuclei. This has been used at the radioactive nuclear facility at ISOLDE, CERN, initially in the study of deformation in neutron-rich manganese isotopes.

Additionally, at a complementary accelerator facility at JYFL, Finland, the experimental layout has been optimised to allow this to happen, and been applied to the studies of scandium and yttrium isotopes.
Exploitation Route Used for efficient and effective laser spectroscopy, which is an invaluable tool in the determination of properties of nuclear ground and isomeric states.
Sectors Other

 
Description COLLAPS, ISOLDE Laser Spectroscopy 
Organisation Catholic University of Louvain
Country Belgium 
Sector Academic/University 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables costs.
Collaborator Contribution Provision of laboratory apparatus and expertise.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available. Several publications have been published or are in preparation.
Start Year 2013
 
Description COLLAPS, ISOLDE Laser Spectroscopy 
Organisation European Organization for Nuclear Research (CERN)
Department CERN - ISOLDE
Country Switzerland 
Sector Academic/University 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables costs.
Collaborator Contribution Provision of laboratory apparatus and expertise.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available. Several publications have been published or are in preparation.
Start Year 2013
 
Description COLLAPS, ISOLDE Laser Spectroscopy 
Organisation Heidelberg University
Country Germany 
Sector Academic/University 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables costs.
Collaborator Contribution Provision of laboratory apparatus and expertise.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available. Several publications have been published or are in preparation.
Start Year 2013
 
Description COLLAPS, ISOLDE Laser Spectroscopy 
Organisation Technical University of Darmstadt
Country Germany 
Sector Academic/University 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables costs.
Collaborator Contribution Provision of laboratory apparatus and expertise.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available. Several publications have been published or are in preparation.
Start Year 2013
 
Description GSI Laser Spectroscopy 
Organisation Helmholtz Association of German Research Centres
Department GSI Helmholtz Centre for Heavy Ion Research
Country Germany 
Sector Public 
PI Contribution Assist in set-up and running of experiments. Co-spokesperson of proposal (ENSAR coordinator).
Collaborator Contribution Equipment, facility and expertise.
Impact At least two publications currently in press. First measurement of an optical resonance in nobelium.
Start Year 2014
 
Description GSI Laser Spectroscopy 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz Institute Mainz
Country Germany 
Sector Public 
PI Contribution Assist in set-up and running of experiments. Co-spokesperson of proposal (ENSAR coordinator).
Collaborator Contribution Equipment, facility and expertise.
Impact At least two publications currently in press. First measurement of an optical resonance in nobelium.
Start Year 2014
 
Description GSI Laser Spectroscopy 
Organisation Johannes Gutenberg University of Mainz
Country Germany 
Sector Academic/University 
PI Contribution Assist in set-up and running of experiments. Co-spokesperson of proposal (ENSAR coordinator).
Collaborator Contribution Equipment, facility and expertise.
Impact At least two publications currently in press. First measurement of an optical resonance in nobelium.
Start Year 2014
 
Description GSI Laser Spectroscopy 
Organisation Technical University of Darmstadt
Country Germany 
Sector Academic/University 
PI Contribution Assist in set-up and running of experiments. Co-spokesperson of proposal (ENSAR coordinator).
Collaborator Contribution Equipment, facility and expertise.
Impact At least two publications currently in press. First measurement of an optical resonance in nobelium.
Start Year 2014
 
Description GSI Laser Spectroscopy 
Organisation University of Leuven
Country Belgium 
Sector Academic/University 
PI Contribution Assist in set-up and running of experiments. Co-spokesperson of proposal (ENSAR coordinator).
Collaborator Contribution Equipment, facility and expertise.
Impact At least two publications currently in press. First measurement of an optical resonance in nobelium.
Start Year 2014
 
Description JYFL Laser Spectroscopy 
Organisation University of Jyvaskyla
Country Finland 
Sector Academic/University 
PI Contribution Running of the laser spectroscopy set-up, contribution to equipment/consumable funding, spokesperson of several experiments.
Collaborator Contribution Provision of laboratory space, equipment and accelerator use.
Impact Active experimental proposals have been awarded accelerator beam time by the local Programme Advisory Committee. The experimental apparatus required to carry out the research has now been commissioned. Many publications in progress.
Start Year 2013
 
Description JYFL Laser Spectroscopy 
Organisation University of Manchester
Country United Kingdom 
Sector Academic/University 
PI Contribution Running of the laser spectroscopy set-up, contribution to equipment/consumable funding, spokesperson of several experiments.
Collaborator Contribution Provision of laboratory space, equipment and accelerator use.
Impact Active experimental proposals have been awarded accelerator beam time by the local Programme Advisory Committee. The experimental apparatus required to carry out the research has now been commissioned. Many publications in progress.
Start Year 2013
 
Description TRIUMF Laser Spectroscopy 
Organisation McGill University
Country Canada 
Sector Academic/University 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables.
Collaborator Contribution Provision of laboratory space, apparatus and experience.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available.
Start Year 2013
 
Description TRIUMF Laser Spectroscopy 
Organisation TRIUMF
Country Canada 
Sector Public 
PI Contribution Proposal and running of experiments. Contribution to equipment and consumables.
Collaborator Contribution Provision of laboratory space, apparatus and experience.
Impact Active experiments directly related to the research proposal have been approved by the local Programme Advisory Committee. The experimental apparatus required and accelerator beam time have been made available.
Start Year 2013