My primary research interest is centered on the production of rare isotope beams with fragment separators and the study of the structure of nuclei at the limits of existence. At NSCL, rare isotope beams are produced by projectile fragmentation. The coupled cyclotrons accelerate stable ions to a velocity up to half the speed of light. The fast ions then impinge on a production target where they break up into fragments of different mass and charges. Most of the fragments are unstable and many of them have an unusual ratio of protons and neutrons. To study their properties, the fragments of interest need to be separated from all other produced particles. The A1900 fragment separator at NSCL filters rare isotopes by their magnetic properties and their energy loss in thin metal foils. Detector systems installed in the path of the beam allow the unambiguous identification of every single isotope transmitted through the device. The large acceptance of the separator together with intense primary beams from the cyclotrons allow access to the most exotic nuclei that exist, some of which were observed for the first time at NSCL. The investigation of the limits of nuclear stability provides a key benchmark for nuclear models and is fundamental to the understanding of the nuclear forces and structure.
Another research area is the development of particle detectors made from diamond produced by chemical vapor. Radioactive beam facilities of the newest generation can produce rare isotope beams with very high intensities. The special properties of diamond allow the development of radiation-hard timing and tracking detectors that can be used at incident particle rates up to 108 particles per second. Detectors based on poly-crystalline diamond were built and tested at NSCL and excellent timing properties were achieved. Those detectors have been successfully used as timing detectors in several NSCL experiments. First, detectors based on single-crystal diamond showed superior efficiency and energy resolution. Further development will continue with the investigation of properties of single-crystal diamond detectors and the production of position-sensitive detectors with larger active areas.
Evidence for a Change in the Nuclear Mass Surface with the Discovery of the Most Neutron-Rich Nuclei with 17 ≤ Z ≤ 25, O. B. Tarasov et al., Phys. Rev. Lett. 102, 142501 (2009)
First observation of two-proton radioactivity in 48Ni, M. Pomorski et al., Phys. Rev. C 83, 061303 (2011).
Discovery of 40Mg and 42Al suggests neutron drip-line slant towards heavier isotopes, T. Baumann et al., Nature 449, 1022 (2007)
Heteroepitaxial diamond detectors for heavy ion beam tracking, A. Stolz et al., Diamond and Related Materials 15, 807 (2006)
First observation of 60Ge and 64Se, A. Stolz et al., Phys. Lett. B 627, 32 (2005)