ISOL-SRS: ISOL Beam Storage Ring Spectrometer

Lead Research Organisation: University of Liverpool
Department Name: Physics

Abstract

The elements we see around us, and that constituent our bodies, are predominantly stable, yet we know these were forged in violent astrophysical scenarios. The traces from this violent history can be found in sensational new detailed astronomical observations of element abundances from exploding stars, meteoritic inclusions attributed to condensation of material following single explosive events, and observations of gamma-ray emission indicating these process are still ongoing in our universe. The synthesis of the elements in these explosive scenarios involves nuclear reactions involving unstable nuclei. The unknown structure and reactions of these unstable nuclei critically affects our understanding of the origin of elements we now see in a relatively quiescent state around us, and the nature and dynamics of the stellar environments in which they formed. As we have begun to explore the properties of these nuclei, surprising results have been found on the evolution of shell structure, indicating what we find to be the case in stable nuclei, cannot be simply extrapolated to unstable systems. Nature is far more rich and diverse then we anticipated, leading to new shell structures driven by the underlying nature of the nuclear interaction. The locations of these shell structures are subtley and intimately associated with the shapes of nuclei. One such example are Pear-shaped nuclei exhibiting permanent static octupole deformations.These provide a very promising laboratory to search for finite atomic electric dipole moments, indicative of CP violation beyond the Standard Model of Particle Physics. Precision measurements of the evolution of atomic levels of unstable nuclei using lasers, can in turn provide measurements of the underlying charge radius of the nucleus. This is particularly important for the study of halo nuclei, which exhibit an almost pure mantle of neutron matter.

The science described above requires precision measurements of the structure and reactions of unstable nuclei. Furthermore, the studies need to be performed in the appropriate energy regime where these properties can be best probed. The new TSR heavy ion storage ring will be located at the ISOLDE facility CERN. This will be a unique facility worldwide. ISOLDE is the world's leading facility for the production of radioactive beams. Following new upgrades, these radioactive beams will be accelerated to the energy range perfect for precision reaction studies. These beams will be injected into the storage ring where they can be rapidly cooled to give very high quality radioactive beams enabling ultra high resolution measurements of nuclear reactions to be performed using very thin, pure gas targets or measurements of the ground-state properties using lasers. In each case the storage ring allows a repeated probing of the radioactive beam as it circulates with a frequency ~1 MHz in the ring, ensuring high luminosity is combined with high precision. For heavier radioactive species, the lifetime of the beam in the ring is significantly reduced by atomic collisions with the gas target. In this case, the high quality beam can be extracted from the ring and injected into a novel solenoidal magnet and detector system. The overall ISOL-SRS spectrometer systems proposed by the UK community for use in conjunction with the TSR storage ring will therefore enable a major breakthrough in precision studies of the reactions and properties of unstable nuclei across the vast range of masses and isotopes produced by the ISOLDE radioactive beams facility, CERN.

Planned Impact

Knowledge transfer: We foresee a number of areas where knowledge transfer could occur. All detectors used with the external solenoid must operate successfully in high magnetic field. In particular, we have highly pixellated silicon detectors. The challenges making these highly-integrated detectors function in this environment are extremely close to the demands of combined PET/MRI or SPECT/MRI, seen as a high priority for medical imaging in the future. Highly integrated electronics and ASICs may also be transferred over to the medical or other relevant sectors. The detectors to be used inside the storage ring must survive baking out to high temperatures and be compatible with very high vacuum. This may have applications to other areas of science. In the exploitation phase, the ISOL-SRS system could be used to gather
nuclear data relevant to fission reactors, decommissioning or future fusion reactors. A specific example is the ability to measure beta-delayed neutron branches of ions stored in the ring. All the groups have a strong background in knowledge transfer. The Liverpool and Daresbury groups have experience in transferring nuclear physics detector technology towards the medical sector in areas such as SPECT imaging. York established an industry-facing detector development laboratory working on coupling scintillators to novel photosensors. Manchester has the Dalton Institute in-house who provide a natural linkage to the nuclear energy sector, while Surrey have a diverse group working in applications. Manchester, York and Surrey working on nuclear data relevant to present and future fission reactors, supported by an EPSRC grant. Knowledge transfer may be facilitated between groups and companies concerned with applications in nuclear measurement techniques and instrumentation, including GE Healthcare, BAE Systems, AWE, Canberra, Centronic, Kromek, Canberra Harwell UK, Ametek (Ortec), John Caunt Scientific, National Nuclear Laboratory (NNL) and Rapiscan. Liverpool has a 4 year STFC IPS Fellowship to maximize the impact of the STFC science portfolio. The Fellow will work closely with Liverpool, STFC Daresbury Laboratory and the Cockcroft Institute for Accelerator Science. The role will deliver increased numbers of industrial studentships, enable "pump priming" of collaborative ideas through appropriate routes such as mini-IPS or mini-KTP projects and will facilitate potential staff exchanges with industrial collaborators. The Edinburgh Nuclear Physics Group has been at the forefront of nuclear physics applications of silicon strip detectors since this technology became commercially available. They have a long-standing relationship with the UK company Micron Semiconductor Ltd (MSL). With MSL, they have developed silicon strip detector designs with very thin (~20 micron) and thick wafers (~mm) for our research applications. MSL now has a range and depth of technical capability unmatched by any commercial company worldwide and this technology is now applied to X-ray and space-based applications. Public engagement: There is considerable scope to engage with a variety of general audiences from schoolchildren to the wider public. Big science like nuclear/particle physics and astronomy is acknowledged as one of the key motivators for young people to decide to study Physics at university level and for a career. This project has an inspirational story attached relating to our fundamental understanding of nuclear structure and our understanding of the origin of the chemical elements. We are developing new instrumentation for the world's most famous scientific laboratory. The test bed solenoid magnet has featured in an article in New Scientist. Ongoing educational initiatives include Nuclear Physics Masterclasses for schoolchildren held at Surrey, Liverpool and York, supported by outreach officers co-funded by the Ogden Institute. Public engagement work will be facilitated by the STFC outreach officer, Elizabeth Cunningham.

Publications

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Butler P (2016) TSR: A storage and cooling ring for HIE-ISOLDE in Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

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Butler P (2016) TSR: A Storage Ring for HIE-ISOLDE in Acta Physica Polonica B