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We present a fully quantum mechanical treatment of resonant scattering of gamma radiation in a nuclear Λ-scheme. Simulations of the closed-form solution for the radiation intensity for N effective scatterers contributions are compared with Mössbauer spectra of FeCO3. It is shown that, although the nuclear level mixing scheme does not fulfill EIT conditions, the observable effects are similar. The change in polarization of the scattered radiation, due to level mixing, gives rise to the development of a strong complementary polarization state which is delayed with respect to the incident photon and to a reduction in absorption because this state does not interfere with the incident photon. [ABSTRACT FROM AUTHOR]

This work was performed to understand the structure of neutron-rich fission fragments around the 130 mass region. A thin 235U target was bombarded by a 14N beam with 10 MeV/ A from the Separated Sector Cyclotron at the iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. The main goal was to detect and identify fission fragments and to obtain their mass distribution by using solar cell detectors in the AFRODITE (African Omnipurpose Detector for Innovative Techniques and Experiments) spectrometer. The X-rays emitted from fission fragments were detected by LEP (Low Energy Photon) detectors and γ-rays emitted from excited states of the fission fragments were detected by CLOVER detectors in the spectrometer. [ABSTRACT FROM AUTHOR]

The measured spectroscopic quadrupole moments and deduced deformations of the 194,196Pb(11-) intruder isomers are reevaluated, making use of the recently measured magnetic moments of these states. This adjustment is necessary since the quadrupole moments were obtained from Level Mixing Spectroscopy measurements, being sensitive to the ratio of the quadrupole interaction frequency and the magnetic moment. The results confirm the moderate deformation of the states. A systematic comparison between the updated experimental and the available theoretical values is presented. [ABSTRACT FROM AUTHOR]

We have observed the effect of electromagnetically induced transparency (EIT) in a nuclear system. A series of Mössbauer measurements was performed on a single crystal of natural FeCO3. When the condition of nuclear level crossing is fulfilled, a clear reduction in absorption or transparency is seen at the point of level crossing. This reduced absorption cannot be ascribed to saturation effects because of the specific geometry of the experiment. We present an explanation in terms of level mixing by a small non-axial component of the electric field gradient. It can be shown that such a scheme is equivalent, at least in principle, with the schemes considered for EIT in quantum optics. [ABSTRACT FROM AUTHOR]

The recently measured spectroscopic quadrupole moments of the 11− intruder isomers in 194,196Pb are being discussed in the particle-core coupling model. The essential physics behind the nature of these isomers is revealed by a simple two-level-mixing calculation, showing that the coupling of the valence proton particles with vibrations of the underlying Hg core induces a factor of two increase of the quadrupole moments. [Copyright &y& Elsevier]

The quadrupole interaction of high-spin isomers in 193Pb implanted into solid Hg cooled at a temperature T = 170 K has been investigated by the time-differential perturbed γ-ray angular-distribution method. Spectroscopic quadrupole moment values of |Qs| = 0.22(2) eb and 0.45(4) eb have been deduced for the 21/2- and 33/2+ three-neutron states, respectively. A much higher value |Qs| = 2.84(26) eb has been determined for the 29/2- isomer, the band head of a magnetic rotational band. [ABSTRACT FROM AUTHOR]

The method of the level mixing spectroscopy (LEMS) was applied for the first time for the study of the static quadrupole moments of high-K isomers in the A ≈ 180 mass region. Results from a preliminary experiment for the static quadrupole moment of the [InlineMediaObject not available: see fulltext.] (750 ns) isomer in W give a limit for its upper value Q < 7 b, corresponding to a quadrupole deformation of β2< 0.343. [ABSTRACT FROM AUTHOR]

The spectroscopic quadrupole moment of the T1/2=9.4(5) ns isomer in 193Pb at an excitation energy Eex=(2585+x) keV is measured by the time-differential perturbed angular distribution method as ∣Qx∣=2.6(3) e b. Spin and parity Iπ=27/2¯ are assigned to it based on angular distribution measurements. This state is the band head of a magnetic-rotational band, described by the 1i13/2 subshell with the (3s1/2-21h9/21i13/2)11- proton excitation. The pairing-plus-quadrupole tilted-axis cranking calculations reproduce the measured quadrupole moment with a moderate oblate deformation ϵ2=-0.11, similar to that of the 11¯proton intruder states, which nuclei in the region. This is the first direct measurement of a quadrupole moment and thus of the deformation of a magnetic-rotational band head. [ABSTRACT FROM AUTHOR]

The g-factor of the ground state of 31Al (T1/2=640 ms) has been measured by the β-NMR technique on a polarized secondary fragment beam at GANIL, Caen, France. The measured value of |g|=1.517(20) is compared with sd-shell model calculations, which allows the assignment of spin and parity Iπ=5/2+ to this state. The spectroscopy of neutron-rich Al isotopes on the border of the “island of inversion” is discussed in terms of the persistence of the N=20 shell closure for Z=13 nuclei. [Copyright &y& Elsevier]

A significant reduction of absorption for single gamma photons has been experimentally observed by studying Mössbauer spectra of 57Fe in a FeCO3 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.

The quadrupole moment of the 11(-) isomer in 196Pb has been measured by the level mixing spectroscopy method. This state has a pi(3s(-2)(1/2)1h(9/2)1i(13/2))11(-) configuration which is involved in most of the shears band heads in the Pb region. The first directly measured value of Q(s)(11(-)) = (-)3.41(66) b, coupled to the previously known quadrupole moment of the nu(1i(-2)(13/2))12(+) isomer allows us to estimate the quadrupole moment of the 16(-) shears band head as Q(s)(16(-)) = -0.32(10) b. The experimental values are compared to tilted axis cranking calculations, giving insight into the validity of the additivity approach to couple quadrupole moments and on the amount of deformation in the shears bands.

The spectroscopic quadrupole moment of the high-spin, high- K five-quasiparticle isomer (K(pi) = 35/2(-), T(1/2) = 750(80) ns, E(i) = 3349 keV) in (179)W has been determined using the level mixing spectroscopy method. A value Q(s) = 4.00(+0.83-1.06)e b was derived, which corresponds to an intrinsic quadrupole moment Q0 = 4.73(+0.98-1.25)e b and to a quadrupole deformation beta(2) = 0.185(+0.038-0.049). These values differ significantly from the deduced ground-state quadrupole moments and are in disagreement with the current theoretical predictions in this mass region.

The fusion-fission cross sections of the 4He+238U and 6He+238U systems have been measured, at Louvain-la-Neuve, for energies around and below the Coulomb barrier, using an array of Si detectors surrounding a UF4 target. The data taken with 4He are in good agreement with previous data and with the coupled channel fusion calculation performed with ECIS. The 6He data show a regular trend with a large enhancement below the barrier which is attributed to the halo structure of the 6He nucleus.