A significant reduction of absorption for single gamma photons has been experimentally observed by studying Mössbauer spectra of 57 Fe in a FeCO 3 crystal. The experimental results have been explained in terms of a quantum interference effect involving nuclear level anticrossing due to the presence of a combined magnetic dipole and electric quadrupole interaction. [16] in Mössbauer spectra, gamma-microwave double resonance [13,17,18], or gamma-optical double resonance [19]. Recently, interesting proposals have been discussed to obtain lasing for gamma rays by utilizing coherent effects [20][21][22][23]. In this Letter, we report on experiments demonstrating the EIT effect at the singlephoton level via the level (anti)crossing technique. A theory of the one-photon interaction with a nucleus has been developed to describe the experimental results. The obtained results open an interesting perspective to extend coherent effects to nuclear transitions. Figure 1 represents the main results of the paper. It shows the observed Mössbauer spectrum of a single crystal of FeCO 3 at a temperature of 30.5(5) K which corresponds to a magnetic hyperfine field of B 15:1 3 T. At this field the hyperfine levels jm 1=2i and jm ÿ3=2i anticross. For the transitions connected to the anticrossing levels, a deficit of absorption of 25% is observed at the peak velocity. It means that some transparency is induced by interference, similar to EIT observed in optics.The experiments were performed by using a conventional Mössbauer setup. It includes a source of gamma radiation ( 57 CoRh), an absorber of FeCO 3 cleaved on the f1014g faces (optical thickness is of the order 10), and a detector. The absorber was mounted on a target holder which allows for a precise temperature control at the target position in the interval 4-600 K. Besides the magnetic hyperfine field, the Fe 2 nucleus in the FeCO 3 crystal [24,25] is subjected to a large axially symmetric electric field gradient (EFG) which results in a well-resolved quadrupole doublet. The level structures of the source and the absorber are shown in Fig. 2. In a magnetic field, the levels might shift to the position where their energies coincide; this situation is referred to as level crossing. But due to the presence of additional fields, the energies of levels might never be equal, and it is the case of level anticrossing.If the magnetic field is collinear with the EFG axis, the axial symmetry is preserved and the m states are eigenfunctions of the total nuclear Hamiltonian if the z axis is chosen along the symmetry axis. However, in such a mineral containing impurities and defects, one can expect a small distribution of fields which are responsible for the

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The nuclear magnetic moment of 9 Li and the quadrupole moments of 8 Li and 9 Li have been measured by use of the β-asymmetry detection of nuclear magnetic resonance on optically polarized beams at ISOLDE/CERN. The radioactive beams were implanted in Si for g-factor measurements and in Zn, LiNbO 3 , and LiTaO 3 crystals for quadrupole moment measurements. The electric-field gradient V zz = 4.26(4) × 10 15 V/cm 2 is deduced for Li in Zn. Using a recently adopted reference value, Q( 7 Li) = −40.0(3) mb, we reevaluated all earlier reported nuclear quadrupole moments of 8 Li and 9 Li. Based on all available previous and present data, the adopted quadrupole moments for these isotopes are Q( 8 Li) = +31.4(2) mb and Q( 9 Li) = −30.6(2) mb. The magnetic moment of 9 Li is deduced as µ( 9 Li) = 3.43678(6)µ N . The values are compared with predictions from shell-model and cluster-model calculations.

We have obtained information on the atomic hyperfine splitting and, hence, on magnetic moments in neutron-rich 68,70 Cu isotopes by scanning the frequency of the narrow-band laser of the first excitation step in the resonance ionization laser ion source. The method of in-source atomic spectroscopy, as well as the analysis of the obtained data, is described. The results are discussed in terms of single-particle configurations coupled to the 68 Ni core.

The rate at which nuclei are produced in a multistep laser ionization process is calculated as a function of the resonant laser excitation frequency. The model enables the fitting of the hyperfine spectra obtained by resonantly exciting and ionizing beams of (short-lived) nuclei. The fit parameters are the nuclear dipole and quadrupole moments, an isotope/isomer shift and the laser powers. The dressed-states approach for the interaction of laser light with an ensemble of atoms and the influence of the ionizing step as an irreversible process in a two-level system allow a very clear understanding of the physical process. In addition, it is seen that the yield of the on-resonance produced ions is sensitive to the angular momenta of the electron levels and to the nuclear spin.