Selected Publications: Beta decay of Co-71,73: probing single-particle states approaching doubly-magic Ni-78, M.M. Rajabali, et al., Phys. Rev. C 85, 034326 (2012).
Tests of atomic charge-exchange cells for collinear laser spectroscopy, A. Klose, K. Minamisono, Ch. Geppert, N. Froemmgen, M. Hammen, J. Kraemer, A. Krieger, C.D.P. Levy, P.F. Mantica, W. Noertershaeuser, and S. Vinnikova, Nucl. Instrum. Methods Phys. Res. A 678, 114 (2012).
Beta decay of nuclei around Se-90: search for signatures of a N=56 subshell closure relevant to the r process, M. Quinn, et al., Phys. Rev. C 85, 035807 (2012).
High-spin microsecond isomeric states in Ag-96, A.D. Becerril, et al., Phys. Rev. C 84, 041303(R) (2012).
"Half-lives of ground and isomeric states in Cd-97 and the astrophysical origin of Ru-96,"
G. Lorusso, A. Becerril, A. Amthor, T. Baumann, D. Bazin, J.S. Berryman, B.A. Brown, R.H. Cyburt, H.L. Crawford, A. Estrade, A. Gade, T. Ginter, C.J. Guess, M. Hausmann, G.W. Hitt, P.F. Mantica, M. Matos, R. Meharchand, K. Minamisono, F. Montes, G. Perdikakis, J. Pereira, M. Portillo, H. Schatz, K. Smith, J.B. Stoker, A. Stolz, and R.G.T. Zegers, Phys. Lett. B 699, 141 (2011).
The low-energy properties of atomic nuclei are predicted to show dramatic changes when the ratio of neutrons-to-protons in the nucleus becomes extremely unbalanced. My research group is working to deduce the electromagnetic properties of nuclei that have extreme neutron-to-proton ratios. The desired nuclei, which exist for only fractions of a second, are produced in very small quantities using intermediate-energy reactions at NSCL.
Two electromagnetic properties of primary interest are the nuclear magnetic dipole moment and nuclear electric quadrupole moment. The dipole moment is sensitive to the orbital component of the angular momentum of any unpaired protons and/or neutrons in the nucleus. The dipole moment provides information on the nuclear quantum structure and the occupied single-particle states. The quadrupole moment is a measure of the deviation of the average charge distribution of the nucleus away from spherical symmetry. The shape of the collection of protons and neutrons in the nucleus, e.g. the nuclear collectivity or deformation, can be inferred from the quadrupole moment.
One way to deduce the electromagnetic moments of nuclei is via Collinear Laser Spectroscopy (CLS). The CLS method involves the co-propagation of a low-energy beam (~ 60 keV) of atoms/ions with laser light. Fixed-frequency laser light is Doppler tuned into resonance by varying the energy of the beam, with the subsequent fluorescence detected by a photomultiplier tube. The resulting hyperfine spectrum, a product of the interaction of atomic electrons with the nucleus, is analyzed to extract the nuclear magnetic dipole and electric quadrupole moments.
We have installed a CLS beam line in the low-energy beam experimental area at NSCL as part of the Beam Cooling and Laser Spectroscopy (BECOLA) facility. The BECOLA facility also includes a cooler/buncher, which will accept the direct current (DC) rare isotope beams from the NSCL gas stopping area and convert them into a low-emittance, pulsed beam to improve the sensitivity for laser hyperfine measurements via the CLS technique. Commissioning of the CLS beam line is underway, using DC beams from a commercial off-line ion source. Hyperfine spectra for Ca, K, and Mn atoms, as well as Ca singly-charged ions, have been collected and analyzed. An example spectrum for stable K-39 is given here, where the four peaks correspond to transitions between hyperfine states that arise from the interaction between the atomic electrons and the K-39 nucleus, which has spin 3/2. These off-line laser studies are important for optimizing the performance of BECOLA and the CLS in advance of on-line measurements with short-lived radioisotopes, where sample sizes are of order 10,000 per second.