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Paul Mantica University Distinguished Professor of Chemistry and Associate Di Nuclear Chemistry   PhD, Nuclear Chemistry, University of Maryland 1990 Joined NSCL in August 1995 Phone (517) 908-7456 Fax (517) 353-5967 Office W200   mantica at nsclmsuedu

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 which 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. Nuclear moments of short-lived radioisotopes are measured at NSCL using the beta assisted Nuclear Magnetic Resonance technique. The beta-NMR technique makes use of a high power, continuous-wave radiofrequency source to deliver oscillating magnetic fields in excess of a few gauss averaged over a broad (hundreds of kilohertz) frequency modulation range at the sample position. The technique requires the nuclear ensemble to be spin-polarized, and past moment measurements at NSCL have used the intermediate energy production reactions to ahieve the necessary spin polarization. The typical magnitude of the reaction-based polarization is only of order a few percent, but still sufficient to realize successful nuclear moment measurements. A recent example is the magnetic dipole moment of Ni-55, which has a half-life of only 204 milliseconds and a single neutron hole outside of the double closed-shell nucleus Ni-56 (Z = N = 28). The magnetic moment value deduced for Ni-55 agreed with shell model calculations that presumed a softness of the Ni-56 double-magic core.

A new laser beam line has been installed at NSCL to spin polarize, via laser optical pumping, slow-moving (< 60 keV) beams of radioactive atoms and/or ions. The spin polarized species will be studied with the beta-NMR technique to again determine dipole and/or quadrupole moments with high precision. The advantage of the laser optical pumping is that spin polarization of order tens of percent are expected, increasing the sensitivity of the beta-NMR measurements and providing a means to extend nuclear moment measurements to the far reaches of the nuclear chart. Off-line laser hyperfine structure studies of alkali, alkali-earth, and transition metal species will be pursued first with the new laser beam line, followed by on-line moment measurements of short-lived radioisotopes utilizing the beta-NMR technique.