University of the West of Scotland Nuclear Physics Group Consolidated Grant

Lead Research Organisation: University of the West of Scotland
Department Name: School of Science

Abstract

It is almost exactly 100 years since Ernest Rutherford's pioneering experiments which demonstrated the existence of the atomic nucleus. In the century that has followed, landmark developments, such as the inception of the nuclear shell model in the 1940s, the construction of heavy-ion accelerators in the 1960s, and major advances in nuclear-detector techniques, have firmly established nuclear physics as an international activity at the forefront of scientific research. In the past few decades, the quest to understand the properties of exotic nuclei ever further from the valley of stability has led to considerable experimental progress. The programme of research described in this Consolidated Grant application covers research into the structure and properties of atomic nuclei that lie far from stability. One of the main aims of our research programme is to achieve a better understanding of the structure and behaviour of exotic nuclei on both the neutron-rich and proton-rich sides of the valley of stability. Recent experimental observations, supported by theoretical calculations, have begun to suggest that the structure of neutron-rich nuclei may be different from those near stability. For example, the well known sequence of magic numbers, corresponding to energy gaps in nuclear shell structure, is now thought to change in nuclei with an extreme excess of neutrons. The evidence for such a change is already convincing around neutron number N=20, and similar effects are expected for the other shell gaps at N=28, 50, and 82. We will study the evolution of shell gaps in neutron-rich nuclei using both gamma-ray and charged-particle spectroscopy techniques. Above mass number A~100, electrostatic repulsion causes stable nuclei to have more neutrons than protons. Proton-rich nuclei just above the doubly-magic Sn100 nucleus are those with near equal numbers of neutrons and protons. These nuclei are known to decay by exotic decay modes such as proton emission. Spectroscopic study of the properties of these decays can give invaluable information about the properties of the nucleus in its ground state and in the first few excited states. Our research programme will include studies of proton-rich nuclei around A~110 by investigating their particle decays and by gamma-ray spectroscopy. Another aspect of our research programme will be devoted to studying fission of the nucleus. Fission is a collective mode of decay most commonly associated with heavy nuclei in the uranium region, but in our research we will study the beta-delayed fission of exotic nuclei in the lead region that lie very far from stability (by ~20-25 neutrons) and which have only recently become experimentally accessible with the development of radioactive beams. A study of the properties of beta-delayed fission, such as the mass distributions of the fission fragments, will give important information about nuclear structure and shell effects at low excitation energy. In a related part of our research programme, we will use radioactive At beams to study other nuclear-structure effects such as shape coexistence. Our research programme has several themes which will use different methodologies. Primarily, our experiments will be carried out using state-of-the-art apparatus at large international facilities. Gamma-ray spectroscopy offers one of the best methods of studying the structure of exotic nuclei, and here we will exploit the new AGATA gamma-ray tracking spectrometer at Legnaro National Laboratory, GSI and GANIL. Another part of our research will make use of the Jurogam gamma-ray spectrometer with the RITU recoil separator at Jyväskylä in Finland. Our programme to study beta-delayed fission will make use of beams of radioactive isotopes from the ISOLDE facility at CERN and at the JAEA laboratory in Japan. Furthermore, we will exploit the development of new radioactive beams of astatine at ISOLDE.

Publications

10 25 50

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Andreyev A (2013) ß -delayed fission of 192 , 194 At in Physical Review C

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Andreyev A (2014) a decay of Au 176 in Physical Review C

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Andreyev A (2013) Signatures of the Z = 82 Shell Closure in a -Decay Process in Physical Review Letters

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Andreyev A (2013) Colloquium : Beta-delayed fission of atomic nuclei in Reviews of Modern Physics

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Cocolios T (2012) Early onset of deformation in the neutron-deficient polonium isotopes in Journal of Physics: Conference Series

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De Witte H (2013) ß - decay of the neutron-rich isotope 215 Pb in Physical Review C

Related Projects

Project Reference Relationship Related To Start End Award Value
ST/J000183/1 23/11/2011 31/08/2012 £225,526
ST/J000183/2 Transfer ST/J000183/1 01/09/2012 31/05/2016 £101,673
 
Description Thanks to this award, I was able to initiate a new (to the UK's nuclear physics community) branch of research - the studies of a very exotic process of beta-delayed fission. This is a unique research strand not paralleled by anybody in the world.
Exploitation Route Traditional models of nuclear fission predict that heavy nuclei break into unequally sized (asymmetric) parts, which is consistent with the findings of most experiments in low-energy fission. This is naturally explained by the fact that one of the fragments tends to be in the vicinity of doubly magic tin-132132, which is highly stable.

The vast majority of fission experiments, however, have focused on heavy nuclides ranging from thorium to fermium. Now, new experiments performed at the ISOLDE facility in CERN and presented in Physical Review Letters (Andrei Andreyev et al.), probe a different corner of the nuclear chart. The team studies mercury-180180 (with 8080 protons and 100100 neutrons) and finds that the fission products are also asymmetric. However, in this particular case, the outcome is counterintuitive, since a symmetric decay of the nucleus into two copies of zirconium-9090 (with 4040 protons and 5050 neutrons) would have produced exceptionally stable nuclei.

The ISOLDE team's puzzling result hints that a very subtle interplay between macroscopic and microscopic interactions plays a deeper role in the fission process than expected and is likely to inspire detailed theoretical studies and further experiment. - Abhishek Agarwal
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.105.252502
Sectors Energy

URL http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.252502
 
Description Collaboration with the Japanese Atomic Energy Agency (JAEA) 
Organisation Japan Atomic Energy Agency (JAEA)
Country Japan 
Sector Public 
PI Contribution I have performed a very successful experiment at JAEA in Feb.2010. The JAEA partners provided their detection setup.
Collaborator Contribution JAEA provides their detectors to my experiments JAEA pays for the beam time provided to my experiments
Impact data analysis from '2010 experiment is underway, a paper will be prepared soon
Start Year 2010
 
Description ISOLDE(CERN) 
Organisation European Organization for Nuclear Research (CERN)
Department ISOLDE Radioactive Ion Beam Facility
Country Switzerland 
Sector Public 
PI Contribution ISOLDE pays for beam time
Collaborator Contribution ISOLDE pays for the beam time provided to my experiments
Impact a paper in under preparation
Start Year 2010