Single-particle structure in neutron-rich isotopes

Lead Research Organisation: University of Manchester
Department Name: Physics and Astronomy

Abstract

A fundamental way of understanding the structure of the atomic nucleus is to consider the motion of its constituent particles, protons and neutrons, under the influence of the individual interactions between them. These so-called ab-initio calculations are difficult in all but the lightest nuclei due to increasing complexity as the number of constituents gets larger. Approaches that consider the motion of individual particles in the average field generated by all the other particles have enjoyed some success in near stable nuclei, when corrections or residual interactions are included. Such success is actually rather limited as the number of stable systems is very small in comparison with the total number of bound isotopes, but despite this such methods appear frequently even in student textbooks, giving an air of permanence and solidity to the theories. However, with increasing experimental sophistication, new effects have been found that only become apparent when studying single-particle structures over a wide range of neutron excess. Such changes in single-particle structures are surprising within the context of these models; for example, in some cases they disturb even the 'well-known' sequence of magic numbers dervived for stable systems. But they also have deeper consequences since the underlying single-particle nature of a nucleus dramatically effects other properties such as the nuclear shape and the existence and type of other excitation modes like collective vibrations and rotations of the whole nucleus. This grant proposal aims to study two aspects of single-particle structure. Firstly to investigate the mechanisms which may be responsible for the changes that are being uncovered. These can be related directly back to the force between two nucleons. It has been suggested that some of these changes are due to the tensor component of this force; this is particularly interesting if substantiated as there are only a few direct manifestations of this component in nuclear structure. Secondly the proposal aims probe a region of exotic nuclei where calculations based on the single-particle structure extrapolated rather crudely from stable systems predict some interesting new phenomena. Such calculations are based on single-particle levels extrapolated from stability, which need to be questioned given the dramatic changes in shell structure which are being uncovered recently. The plan is to measure single-particle orbitals using transfer in the A~100 region to tie down calculations in that region and to make extrapolations to the more exotic systems more reliable. The experiments will use reactions involving the transfer of single particles in collisions initiated with radioactive beams. These will be supplied by the CARIBU facility at Argonne National Laboratory which performs isotopic selection of fission fragments using a method largely independent of chemical effects and accelerates them to the required energies. The chemical independency is important as it allows beams of refractory elements to be produced. This is a unique feature which is essential for studying the A~100, Sr-Zr-Mo region. The experiments will also employ another unique device, the novel HELIOS spectrometer. This is a new concept in spectrometer design which uses a superconducting solenoid to analyse ejectile ions from transfer reactions initiated with heavy beams on light targets. It has considerable advantages over traditional methods in terms of acceptance, energy resolution and ease of particle identification. The proposal requests funds to build an essential part of this spectrometer, a device to detect the heavy recoiling ions.

Publications

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Back BB (2010) First experiment with HELIOS: the structure of 13B. in Physical review letters

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Lighthall J (2010) Commissioning of the HELIOS spectrometer in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

 
Description Development of gas detectors for the HELIOS project.
Exploitation Route Design of gas detectors for heavy ion detection.
Sectors Aerospace, Defence and Marine,Energy,Security and Diplomacy

 
Description Findings used to advance fundamental research in nuclear physics. Also fed into public understanding of science through engagement activities.
First Year Of Impact 2007
Sector Education,Culture, Heritage, Museums and Collections,Other
Impact Types Cultural

 
Description STFC Nuclear Physics Grants
Amount £1,579,024 (GBP)
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 08/2008 
End 07/2011
 
Description Argonne National Laboratory 
Organisation Argonne National Laboratory
Department Physics Division
Country United States 
Sector Public 
PI Contribution Intellectual input, performing experiments, data analysis, writing publications
Collaborator Contribution Facility provision and intellectual input
Impact Publications.
 
Description HELIOS 
Organisation Argonne National Laboratory
Department Physics Division
Country United States 
Sector Public 
PI Contribution Gas detector system and electronics, intellectual input
Collaborator Contribution Intellectual input, silicon detector arrays, electronics
Impact Publications
 
Description HELIOS 
Organisation Western Michigan University
Department Department of Physics
Country United States 
Sector Academic/University 
PI Contribution Gas detector system and electronics, intellectual input
Collaborator Contribution Intellectual input, silicon detector arrays, electronics
Impact Publications
 
Description Rutherford Exhibition at Museum of Science and Industry 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation Workshop Facilitator
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Three month exhibition Aug to Oct 2011 of nuclear physics past and present to celebrate the Rutherford Centennial. Estimated visitors 200,000.

Manchester played advisory and facilitator role.

Media coverage.
Year(s) Of Engagement Activity 2011
 
Description Variety of activities as Schools Liaison Officer 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Primary Audience Schools
Results and Impact The PI of the grant was the Schools and Colleges Liaison Officer for Physics and Astronomy. The research outputs of the grant have contributed to talks given as part of the responsibilities this post, to local schools and colleges, at University Open Days held three times a year, and at many one-off events.

Many.
Year(s) Of Engagement Activity 2006,2007,2008,2009,2010