My research interests are related to nuclear and atomic physics with focus on the study of basic properties of atomic nuclei very far away from the valley of stability. A major activity in my group is the determination of the mass of such rare isotopes, which is their most fundamental property. An accurate knowledge of atomic masses is important for revealing the inner structure of exotic nuclei and to provide crucial tests for nuclear model predictions. Atomic masses are one of the key information required for the description of the synthesis of the elements in the universe.
Certain special nuclei are important for testing our understanding of symmetries and the fundamental forces in nature; their masses need to be determined with an accuracy of 10 parts per billion or better. Such high-precision mass measurements have become possible at NSCL with the Low Energy Beam and Ion Trap facility, or LEBIT. This device makes use of very low-energy ions that are obtained by slowing down fast beams from the A1900 through gas-stopping technologies. This technique slows the ions enough that they can be kept floating in a vacuum in a device called an ion trap. Here their mass can be determined with very high precision via the observation of their cyclotron motion in a strong 9.4 Tesla magnetic field. LEBIT, in operation since 2005, has started its mass measurement program very successfully; rare isotopes with half-lives of less than 100 ms have been captured and studied and mass accuracies below 10-8 have been reached. In addition to determining their mass I am interested in atomic spectroscopy of rare isotopes using lasers. This, for example, can provide information on the size and shape of the atomic nucleus. My group is involved in the on-going realization of such a laser spectroscopy facility at NSCL.
Another research area is the development of advanced manipulation techniques for rare isotope beams. Developments of that kind are critical for maximizing the performance of experiments and for creating new experimental opportunities for the study of rare isotopes. My group is working on techniques that allow fast rare isotope beams to be slowed down and converted into low-energy beams efficiently and fast, on beam-cooling and bunching techniques, and on the development of a device that increases the charge state of ions. Such a charge breeder is a key component of the re-accelerator project presently underway at NSCL, which will provide rare isotope beams that are world-unique and add a new and exciting component to the strong research program of NSCL.
The LEBIT ion trap: shown are the gold-plated high-precision electrodes that provide the electric fields needed for capturing and storing rare isotope ions in the 9.4 T field of the LEBIT Penning trap mass spectrometer.
First Direct Double-Beta Decay Q-Value Measurement of 82Se in Support of Understanding the Nature of the Neutrino, D. Lincoln et al., Phys. Rev. Lett. 110 012501 (2013)
“Ion Surfing" with Radiofrequency Carpets. G. Bollen, Int.J. Mass Spectrom. 299 (2011) 131. doi: 10.1016/j.ijms.2010.09.032
Precision test of the isobaric multiplet mass equation for the A=32, T=2 quintet, A.A. Kwiatkowski, et al., Phys. Rev. C80 051302 (2009)
rp Process and Masses of N~Z~34 Nuclides, J. Savory, P. Schury, C. Bachelet et al. Phys. Rev. Lett. 102132501 (2009)
The LEBIT 9.4T Penning trap mass spectrometer, R. Ringle,et al., Nucl. Instr, Meth. A 604 536 (2009)
Discovery of a nuclear isomer in Fe-65 with Penning trap mass spectrometry, M. Block, C. Bachelet, G. Bollen et al., Phys. Rev. Lett. 100 132501 (2008)
An electron beam ion trap for the NSCL reaccelerator, S. Schwarz, et al., Nucl. Instr, Meth. B266 4466 (2008)
Manipulation of rare isotope beams - from high to low energies, G. Bollen, et al., Nucl. Instr, Meth. B266 4442 (2008)