Nuclear Structure Physics at KTH

Nuclear structure physics research aims at furthering our understanding of the wide range of physical phenomena exhibited by atomic nuclei. Measurements of nuclear properties at extreme values of a specific degree of freedom can provide important simplifications that may yield new insights into the complex structure of nuclei and facilitate the development of more advanced theoretical model descriptions. The KTH nuclear physics group pursues research programmes in both experimental and theoretical nuclear structure physics (often in close collaboration) as well as applications of nuclear physics in medicine and industry.

The experimental nuclear physics programme at KTH is focused on spectroscopic studies of nuclei at the extremes of neutron/proton ratio, angular momentum and deformation. The worldwide developments of new radioactive ion beam facilities and novel, more sensitive, detector systems open new opportunities to study a large number of exotic nuclei. In Europe, the FAIR (Facility for Antiproton and Ion Research) international accelerator facility is being constructed in Darmstadt, ND is expected to start operations around 2018. Sweden is via the Swedish Research Council one of the founding members of FAIR. FAIR has a broad scientific base in nuclear, hadron, atomic, astro- and biophysics, as well as plasma and material research. Many intriguing questions connected to the structure of nuclear (hadronic) matter and the strong interaction will be attacked at FAIR. The KTH group is strongly involved in the preparations for experiments using relativistic radioactive ion beams from the FAIR accelerators, in particular the HISPEC/DESPEC experiment , but also R3B and the antiproton beam for the PANDA experiment. Funding of these activities comes from the Swedish Research Council and the Knut and Alice Wallenberg foundation. The second main future nuclear physics facility in Europe is SPIRAL2 at GANIL, France, (expected to be operational around 2017) which utilises the isotope separation on-line technique to produce radioactive ion beams. Such beams are complementary to those produced by fragmentation at the SuperFRS at FAIR.

In parallel with the development of new accelerator facilities a major European breakthrough has been made in instrumentation for γ-ray spectroscopy, one of the main tools to investigate the complex structure of nuclei. The European AGATA (Advanced GAmma Tracking Array) detector is presently in its first construction phase operating at the GSI accelerator facility, Darmstadt, in preparation for experiments at FAIR. AGATA is solely built from germanium detectors and is based on the new concept of γ-ray tracking, a technique developed with important contributions from the KTH group. AGATA will have an unparalleled sensitivity to nuclear electromagnetic radiation. At SPIRAL2, the KTH involvement in EXOGAM will continue within the upgraded EXOGAM2 project utilizing the AGATA technology. The AGATA detector will be moved from GSI to GANIL for its next experimental campaign 2014-2016.
The KTH group is also investigating the performance of AGATA type detectors at the DESPEC experiment at FAIR, where both their high efficiency and the inherent Compton imaging capabilities are needed for selecting rare γ-ray from an intense background. Compton polarimetry is another area where the KTH group investigates the use of highly segmented solid state detectors in new directions.
By working in the technological frontier in basic science a bridge to applications in society can be created. The development of segmented Ge detectors and novel scintillators are two highly promising future applied research directions at KTH. Both represent interesting potential applications for X-ray and γ-ray imaging in medicine and industry. Compton imaging may become a widely used tool in medical imaging etc. The patented wide-range optical sensor concept developed at KTH based on SiPM technology is uniquely designed for multimodality medical imaging systems such as CT/PET and in the future CT/PET/MRI systems.

The interpretation of experimental data as well as predictions for future experimental research directions requires adequate theories. Theoretical descriptions of nuclei and nucleonic forces are progressing rapidly, strongly benefitting from access to new and faster supercomputers. In theoretical nuclear physics, one may differentiate between three frontlines: i) The connection of nuclear structure to ab initio models, including the derivation of effective interactions from QCD; ii) The development of the nuclear shell model with respect to large scale, unified description of nuclear states, and; iii) The development of universal density functional like theories for the nucleus. The KTH nuclear theory group has a main focus on ii) and iii) as well as a deeper understanding of clustering effects and radioactive decay mechanisms. The group will continue to develop the shell model including aspects of the continuum.. The aim is to develop codes for super-scale shell model calculations. A basic understanding of nuclei far from stability is a key task for the next ten years, enabling society to fully understand the origin of the elements and nuclear processes in stars. We also plan to develop a new generation of configuration interaction theories with fundamental nucleon pairs as building blocks including a proper treatment of the continuum. With these tools we aim to explore the properties of highly unstable nuclei around the driplines and to provide new insight into phenomena that are beyond the description of present models Nuclear physics also forms the base of nuclear engineering; developing new knowledge and more accurate calculations of nuclear reactions will contribute to the development of nuclear engineering in a longer perspective.

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