M. Reese

Progress on M1 Research

Magnetic dipole transitions in nuclei can offer crucial information on nuclear structure, e.g., on spin-flip processes or on nuclear charge currents. Driven by the need for more comprehensive or more precise data on M1 transitions in nuclei, we have recently tried to advance pre-existing experimental methods to meet the present needs. This contribution reports on the current status of our efforts on three aspects: (i) access of spin-flip M1 strength in radioactive nuclei, (ii) quadrupole-collectivity of the M1 scissors mode, and (iii) highest- precision measurements for strong ground-state M1 excitations.

Evolution of Collectivity in the Vicinity of 208Pb: Preliminary Results

Knowledge on the spectroscopic data of nuclei in the region of Pb provides key information to probe parameter sets of nuclear models, both shell-model and meanfield based. It also serves as a basis for the extrapolation of any nuclear model into the area of actinides and superheavy nuclei. SincePb is the heaviest doubly-magic nucleus known to date, it is also the last firm anchor point for extrapolations. Within the PreSPEC-AGATA campaign at GSI [1], fragmentation of aPb beam at 1GeV/u on a 2.5 g/cm Be target was performed to study Pb, Hg and Pt isotopes. Charge and mass-to-charge ratio of the incoming particles were obtained in an event-by-event basis using the standard FRS detectors [2]. Figure 1 shows the identification plot obtained for the reference isotope Pb. The reducedZ resolution observed is due to the creation of

Search for one-phonon mixed-symmetry states in the radioactive nucleus 140Nd

Low-spin excited states of 140Nd have been studied via the 140Ce(3He,3n)140Nd reaction. The results from the data analysis show that one of the candidates for the one-phonon mixed symmetry state of 140Nd, namely the 2+3 state at 2140 keV with an effective lifetime of 220(90) fs, decay with a fast M1 transition to the 2+1 state. Therefore consequently this state can be treated as, at least a fragment of the one-phonon MSS of 140Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A ? 140 region based on the data on absolute M1 transition rates.