A new avenue in the search for <i>CP</i> violation:Mössbauer spectroscopy of ²²⁷ Ac

This work proposes a new avenue in the search for CP-violating odd-electric and even-magnetic nuclear moments. A promising candidate to find such moments in the ground state is the quadrupole-deformed and octupole-correlated nucleus 227-actinium. In this nucleus, the 27.4-keV $E1$~transition that connects the $3/2^+$ parity-doublet partner and the $3/2^-$ ground state is perfectly suited to apply the sensitive technique of recoil-free selfabsorption, commonly known as M\"ossbauer spectroscopy. In this experimental approach, the lifetime of the $3/2^+$ upper parity-doublet partner allows an estimate of the lower limit of $\Delta E = 2\cdot \Gamma_{\gamma}$= $23.7(1) \times 10^{-9}$ eV for the achievable energy resolution to be made. This resolution must be exceeded by the interaction of a CP-violating moment and the corresponding multipole moment of the field distribution in the lattice. This work presents the first ideas for patterns caused by CP-violating moments on the expected quadrupole splitting and nuclear Zeeman effect.Comment: 9 pages, 4 figure

Collective Quadrupole Behavior in \u3csup\u3e106\u3c/sup\u3ePd

Excited states in 106Pd were studied with the (n,n′γ) reaction, and comprehensive information for excitations with spin ≤6ℏ was obtained. The data include level lifetimes in the femtosecond regime, spins and parities, transition multipolarities, and multipole mixing ratios, which allow the determination of reduced transition probabilities. The E2 decay strength to the low-lying states is mapped up to ≈2.4 MeV in excitation energy. The structures associated with quadrupole collectivity are elucidated and organized into bands

E0 transitions in 106Pd:Implications for shape coexistence

Level lifetimes in 106Pd were measured with the Doppler-shift attenuation method following inelastic neutron scattering, and electric monopole transition strengths between low-lying 2+ states were deduced. The large $\rho^{2}$(E0) values obtained provide evidence for shape coexistence, extending observation of such structures in the N = 60 isotones. Included in these results is the first determination of the E0 transition strength in the Pd nuclei between levels with K = 2

The decay pattern of the Pygmy Dipole Resonance of ¹⁴⁰Ce

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus ¹⁴⁰Ce using a novel combination of nuclear resonance fluorescence and γ–γcoincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [2+1×PDR]is extracted

Fragmentation of low-lying dipole modes in odd-mass nuclei at the N=82 shell closure

Die ungeraden Kerne 135Ba, 139La und 141Pr am N=82 Schalenabschluß wurden am Bremsstrahlungsmessplatz des Stuttgarter 4.3 MV DYNAMITRON Beschleunigers mit Kernresonanzfluoreszenzexperimenten vermessen. Bis zu einer Anregungsenergie von 4.1 MeV konnten umfangreiche spektroskopische Datensätze (Anregungsenergien, Anregungsstärken, Verzeigungsverhältnisse) der Dipolanregungen gewonnen werden. Der Vergleich der Dipolstärkeverteilungen der ungeraden Kerne mit denen ihrer gg-Rumpfkerne ermöglicht eine systematische Untersuchung der Wechselwirkung des ungepaarten Teilchens mit den kollektiven Dipolanregungen der Rumpfkerne. In gg-Kerne nahe abgeschlossener Schalen ist der 1- Zustand der [2+ x 3-]-Zwei-Phononen-Kopplung die dominierende niedrigliegende Dipolanregung. Im neutronenungeraden Kern ergab der Vergleich der aufsummierten E1-Stärke mit der E1-Stärke der 1- Zustände der beiden Rumpfkerne 134Ba und 136Ba identische Werte. Die beiden protonenungeraden Kerne 139La und 141Pr auf dem N=82 Schalenabschluß zeigten in Bezug auf die 1- Zustände ihrer Rumpfkerne nur ca. 60% der E1-Stärke. Im Rahmen dieser Arbeit wird gezeigt, daß es sich hierbei um einen bisher nichtverstandenen Kernstruktureffekt handelt.The odd-mass nuclei 135Ba, 139La und 141Pr at the N=82 shell closure were investigated with nuclear resonance fluorescence experiments at the bremsstrahlungfacility of the 4.3 MV Stuttgart DYNAMITRON accelerator. Until an excitation energy of 4.1 MeV detailed spectroscopic information (excitation energies, excitation strengths, branching ratios) of dipole excitations were obtained. The comparision of the resulting dipole strength distributions to the ones of the even-even core nuclei enables a systematic study of the interaction of the unpaired particle and the collective dipole excitations of the core nuclei. The dominating low-lying dipole excitation in even-even nuclei near closed shells is the 1- state of the [2+ x 3-]-two-phonon-coupling. The neutronodd nucleus 135Ba shows an identical strength as observed for the 1- states of its core nuclei 134Ba and 136Ba. The semimagic, protonodd nuclei 139La and 141Pr show only 60% of the E1-strength observed for the 1- states in their core nuclei. It is shown that this is a nuclear structure effect which is not understood yet