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## A Mononuclear Fe(III) Single Molecule Magnet with a 3/2↔5/2 Spin Crossover

Mossin, Susanne; Tran, Ba L.; Adhikari, Debashis; Pink, Maren; Heinemann, Frank W.; Sutter, Jörg; Szilagyi, Robert K.; Meyer, Karsten; Mindiola, Daniel J.
Tipo: Artigo de Revista Científica
Português
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The air stable complex [(PNP)FeCl2] (1) (PNP = N[2-P(CHMe2)2-4-methylphenyl]2−), prepared from one-electron oxidation of [(PNP)FeCl] with ClCPh3, displays an unusual S = 3/2 to S = 5/2 transition above 80 K as inferred by the dc SQUID magnetic susceptibility measurement. The ac SQUID magnetization data, at zero field and between frequencies 10 and 1042 Hz, clearly reveals complex 1 to undergo a frequency dependent of the out-of-phase signal and thus be a single molecular magnet with a thermally activated barrier of Ueff = 32-36 cm−1 (47 - 52 K). Variable temperature Mössbauer data also corroborate a significant temperature dependence in δ and ΔEQ values for 1, which is in agreement with the system undergoing a change in spin state. Likewise, variable temperature X-band EPR spectra of 1 reveals the S = 3/2 to be likely the ground state with the S = 5/2 being close in energy. Multi-edge XAS absorption spectra suggest the electronic structure of 1 to be highly covalent with an effective iron oxidation state that is more reduced than the typical ferric complexes due to the significant interaction of the phosphine groups in PNP and Cl ligands with iron. A variable temperature single crystal X-ray diffraction study of 1 collected between 30-300 K also reveals elongation of the Fe–P bond lengths and increment in the Cl–Fe–Cl angle as the S = 5/2 state is populated. Theoretical studies show overall similar orbital pictures except for the d(z2) orbital which is the most sensitivity to change in the geometry and bonding where the quartet (4B) and the sextet (6A) states are close in energy.

## Measurement of filling factor 5/2 quasiparticle interference with observation of charge e/4 and e/2 period oscillations

Willett, R. L.; Pfeiffer, L. N.; West, K. W.
Tipo: Artigo de Revista Científica
Português
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A standing problem in low-dimensional electron systems is the nature of the 5/2 fractional quantum Hall (FQH) state: Its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be used to manipulate and measure quantum Hall edge excitations. Here we use a small-area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharonov–Bohm effect are observed for integer quantum Hall and FQH states (filling factors ν = 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these factors as charge calibrations, periodic transmission through the device consistent with quasiparticle charge e/4 is observed at ν = 5/2 and at lowest temperatures. The principal finding of this work is that, in addition to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 ν and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference...

## Experimental Evidence for a Spin-Polarized Ground State in the \nu=5/2 Fractional Quantum Hall Effect

Pan, W.; Stormer, H. L.; Tsui, D. C.; Pfeiffer, L. N.; Baldwin, K. W.; West, K. W.
Tipo: Artigo de Revista Científica
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We study the \nu=5/2 even-denominator fractional quantum Hall effect (FQHE) over a wide range of magnetic (B) field in a heterojunction insulated gate field-effect transistor (HIGFET). The electron density can be tuned from n=0 to 7.6 \times 10^{11} cm^{-2} with a peak mobility \mu = 5.5 \times 10^6 cm^2/Vs. The \nu=5/2 state shows a strong minimum in diagonal resistance and a developing Hall plateau at magnetic fields as high as 12.6T. The strength of the energy gap varies smoothly with B-field. We interpret these observations as strong evidence for a spin-polarized ground state at \nu=5/2.; Comment: new references added

## A complete classification of the $(15_4 20_3)$-configurations with at least three $K_5$-graphs

Petelczyc, K.; Prażmowska, M.; Prażmowski, K.
Tipo: Artigo de Revista Científica
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The class of $\left(\binom{n+1}{2}_{n-1} \binom{n+1}{3}_3\right)$-configurations which contain at least $n-2$ $K_n$-graphs coincides with the class of so called systems of triangle perspectives i.e. of configurations which contain a bundle of $n-2$ Pasch configurations with a common line. For $n=5$ the class consists of all binomial partial Steiner triple systems on $15$ points, that contain at least three $K_5$-graphs. In this case a complete classification of respective configurations is given and their automorphisms are determined.

## Strongly Anisotropic Electronic Transport at Landau Level Filling Factor $\nu = 9/2$ and $\nu = 5/2$ Under Tilted Magnetic Field

Pan, W.; Du, R. R.; Stormer, H. L.; Tsui, D. C.; Pfeiffer, L. N.; Baldwin, K. W.; West, K. W.
Tipo: Artigo de Revista Científica
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We have investigated the influence of an increasing in-plane magnetic field on the states at half-filling of Landau levels ($\nu$ = 11/2, 9/2, 7/2, and 5/2) of a two-dimensional electron system. In the electrically anisotropic phase at $\nu$ = 9/2 and 11/2 an in-plane magnetic field of $\sim$ 1-2 T overcomes its initial pinning to the crystal lattice and {\it reorient} this phase. In the initially isotropic phases at $\nu$ = 5/2 and 7/2 an in-plane magnetic field {\it induces} a strong electrical anisotropy. In all cases, for high in-plane fields, the high resistance axis is parallel to the direction of the in-plane field.; Comment: 6 page, 3 figues

## Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)Sigma0 reactions at Egamma=1.5-2.4 GeV

LEPS Collaboration; Zegers, R. G. T.; Sumihama, M.; Ahn, D. S.; Ahn, J. K.; Akimune, H.; Asano, Y.; Chang, W. C.; Date, S.; Ejiri, H.; Fujimura, H.; Fujiwara, M.; Hicks, K.; Hotta, T.; Imai, K.; Ishikawa, T.; Iwata, T.; Kawai, H.; Kim, Z. Y.; Kino, K.; Ko
Tipo: Artigo de Revista Científica
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Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6

## Backward-angle photoproduction of $\pi^0$ mesons on the proton at $E_\gamma$ = 1.5--2.4 GeV

Sumihama, M.; Ahn, J. K.; Akimune, H.; Asano, Y.; Chang, W. C.; Daté, S.; Ejiri, H.; Fujimura, H.; Fujiwara, M.; Hicks, K.; Hotta, T.; Imai, K.; Ishikawa, T.; Iwata, T.; Kawai, H.; Kim, Z. Y.; Kino, K.; Kohri, H.; Kumagai, N.; Makino, S.; Matsumura, T.;
Tipo: Artigo de Revista Científica
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Differential cross sections and photon beam asymmetries for $\pi^0$ photoproduction have been measured at $E_\gamma$ = 1.5--2.4 GeV and at the $\pi^0$ scattering angles, --1 $<$ cos$\Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $\pi^0$ production has been determined. An enhancement at backward angles is found above $E_\gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_\gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.; Comment: 12 pages, 4 figures, submitted to PLB

## Exact Quantization of Even-Denominator Fractional Quantum Hall State at $\nu$=5/2 Landau Level Filling Factor

Pan, W.; Xia, J. -S.; Shvarts, V.; Adams, E. D.; Stormer, H. L.; Tsui, D. C.; Pfeiffer, L. N.; Baldwin, K. W.; West, K. W.
Tipo: Artigo de Revista Científica
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We report ultra-low temperature experiments on the obscure fractional quantum Hall effect (FQHE) at Landau level filling factor $\nu$=5/2 in a very high mobility specimen of $\mu=1.7 \times 10^7$ cm$^2$/Vs. We achieve an electron temperature as low as $\sim$ 4~mK, where we observe vanishing $R_{xx}$ and, for the first time, a quantized Hall resistance, $R_{xy}=h/(5/2e^2)$ to within 2 ppm. $R_{xy}$ at the neighboring odd-denominator states $\nu$=7/3 and 8/3 is also quantized. The temperature dependences of the $R_{xx}$-minima at these fractional fillings yield activation energy gaps $\Delta_{5/2}$=0.11K, $\Delta_{7/3}$=0.10K, and $\Delta_{8/3}$=0.055K.; Comment: 5 pages, 3 figures

## Measurement of filling factor 5/2 quasiparticle interference: observation of charge e/4 and e/2 period oscillations

Willett, R. L.; Pfeiffer, L. N.; West, K. W.
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.57171%
A standing problem in low dimensional electron systems is the nature of the 5/2 fractional quantum Hall state: its elementary excitations are a focus for both elucidating the state's properties and as candidates in methods to perform topological quantum computation. Interferometric devices may be employed to manipulate and measure quantum Hall edge excitations. Here we use a small area edge state interferometer designed to observe quasiparticle interference effects. Oscillations consistent in detail with the Aharanov-Bohm effect are observed for integer and fractional quantum Hall states (filling factors 2, 5/3, and 7/3) with periods corresponding to their respective charges and magnetic field positions. With these as charge calibrations, at 5/2 filling factor and at lowest temperatures periodic transmission through the device consistent with quasiparticle charge e/4 is observed. The principal finding of this work is that in addtion to these e/4 oscillations, periodic structures corresponding to e/2 are also observed at 5/2 and at lowest temperatures. Properties of the e/4 and e/2 oscillations are examined with the device sensitivity sufficient to observe temperature evolution of the 5/2 quasiparticle interference. In the model of quasiparticle interference...

## Search for $K^-pp$ bound state via $\gamma d \rightarrow K^+ \pi^-X$ reaction at $E_\gamma=1.5-2.4$ GeV

Tokiyasu, A. O.; Niiyama, M.; Parker, J. D.; Ahn, D. S.; Ahn, J. K.; Ajimura, S.; Akimune, H.; Asano, Y.; Chang, W. C.; Chen, J. Y.; Daté, S.; Ejiri, H.; Fujimura, H.; Fujiwara, M.; Fukui, S.; Hasegawa, S.; Hicks, K.; Horie, K.; Hotta, T.; Hwang, S. H.;
Tipo: Artigo de Revista Científica
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A search for $K^-pp$ bound state (the lightest kaonic nucleus) has been performed using the $\gamma d \rightarrow K^+ \pi^- \rm{X}$ reaction at E$_\gamma$=1.5-2.4 GeV at LEPS/SPring-8. The differential cross section of $K^+ \pi^-$ photo-production off deuterium has been measured for the first time in this energy region, and a bump structure was searched for in the inclusive missing mass spectrum. A statistically significant bump structure was not observed in the region from 2.22 to 2.36 GeV/$c^2$, and the upper limits of the differential cross section for the $K^-pp$ bound state production were determined to be 0.1$-$0.7 $\mu$ b (95$%$ confidence level) for a set of assumed binding energy and width values.

## Impact of disorder on the 5/2 fractional quantum Hall state

Pan, W.; Masuhara, N.; Sullivan, N. S.; Baldwin, K. W.; West, K. W.; Pfeiffer, L. N.; Tsui, D. C.
Tipo: Artigo de Revista Científica
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We compare the energy gap of the \nu=5/2 fractional quantum Hall effect state obtained in conventional high mobility modulation doped quantum well samples with those obtained in high quality GaAs transistors (heterojunction insulated gate field-effect transistors). We are able to identify the different roles that long range and short range disorders play in the 5/2 state and observe that the long range potential fluctuations are more detrimental to the strength of the 5/2 state than short-range potential disorder.; Comment: PRL 106, 206806 (2011)

## Field-Induced Quasiparticle Excitation in Ca(Al$_{0.5}$Si$_{0.5}$)$_2$: Evidence for unconventional Superconductivity

Kuroiwa, S.; Takagiwa, H; Yamazawa, M.; Akimitsu, J.; Ohishi, K.; Koda, A.; Higemoto, W.; Kadono, R.
Tipo: Artigo de Revista Científica
Português
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The temperature ($T$) and magnetic field ($H$) dependence of the magnetic penetration depth, $\lambda(T,H)$, in Ca(Al$_{0.5}$Si$_{0.5}$)$_2$ exhibits significant deviation from that expected for conventional BCS superconductors. In particular, it is inferred from a field dependence of $\lambda(H)$ ($\propto H$) at 2.0 K that the quasiparticle excitation is strongly enhanced by the Doppler shift. This suggests that the superconducting order parameter in Ca(Al$_{0.5}$Si$_{0.5}$)$_2$ is characterized by a small energy scale $\Delta_S/k_B\le 2$ K originating either from anisotropy or multi-gap structure.; Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jpn

## Magnetic transitions in the spin S=5/2 frustrated magnet BiMn2PO6 and strong lattice softening in BiMn2PO6 and BiZn2PO6 below 200 K

Nath, R.; Ranjith, K. M.; Roy, B.; Johnston, D. C.; Furukawa, Y.; Tsirlin, A. A.
Tipo: Artigo de Revista Científica
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The crystallographic, magnetic and thermal properties of BiMn2PO6 and BiZn2PO6 were investigated by x-ray diffraction, magnetic susceptibility \chi, heat capacity Cp, and 31P NMR measurements as well as by density-functional band-theory calculations. Both compounds show a strong monotonic lattice softening on cooling, where the Debye temperature decreases by a factor of two from \Theta_D=650K at T=300K to \Theta_D=300K at T=2K. The \chi(T) data for BiMn2PO6 above 150K follow a Curie-Weiss law with a Curie constant consistent with a S=5/2 with g=2 and an antiferromagnetic (AFM) Weiss temperature \theta_CW= -78K. The \chi data indicate long-range AFM ordering below TN=30K, confirmed by a sharp lambda-type peak in Cp(T) at 28.8K. The band-theory calculations indicate that BiMn2PO6 is an AFM compound with dominant interactions J1/kB= 6.7K and J3/kB= 5.6K along the legs and rungs of a two-leg spin-ladder, respectively. In addition to the long-range AFM ordering at TN=30K, a second transition at 10 K is observed from the \chi and NMR measurements but is not evident in the Cp data. The Cp data at low T suggest a significant contribution from AFM spin waves moving in three dimensions and the absence of a spin-wave gap. A detailed analysis of the NMR spectra indicates commensurate magnetic order between 10K and 30K and a possible incommensurate modulation and/or spin canting below 10K. The commensurate order is consistent with microscopic simulations that yield a collinear Neel-type AFM spin arrangement both within and between the ladders...

## A spectroscopic study of the cycling transition 4s[3/2]_2-4p[5/2]_3 at 811.8 nm in Ar-39: Hyperfine structure and isotope shift

Williams, W.; Lu, Z. -T.; Rudinger, K.; Xu, C. -Y.; Yokochi, R.; Mueller, P.
Tipo: Artigo de Revista Científica
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Doppler-free saturated absorption spectroscopy is performed on an enriched radioactive Ar-39 sample. The spectrum of the 3s^2 3p^5 4s [3/2]_2 - 3s^2 3p^5 4p [5/2]_3 cycling transition at 811.8 nm is recorded, and its isotope shift between Ar-39 and Ar-40 is derived. The hyperfine coupling constants A and B for both the 4s [3/2]_2 and 4p [5/2]_3 energy levels in Ar-39 are also determined. The results partially disagree with a recently published measurement of the same transition. Based on earlier measurements as well as the current work, the isotope shift and hyperfine structure of the corresponding transition in Ar-37 are also calculated. These spectroscopic data are essential for the realization of laser trapping and cooling of Ar-37 and Ar-39.

## phi photo-production from Li, C, Al, and Cu nuclei at Egamma=1.5 - 2.4 GeV

Ishikawa, T.; Ahn, D. S.; Ahn, J. K.; Akimune, H.; Chang, W. C.; Date, S.; Fujimura, H.; Fujiwara, M.; Hicks, K.; Hotta, T.; Imai, K.; Kawai, H.; Kino, K.; Kohri, H.; Matsumura, T.; Mibe, T.; Miwa, K.; Miyabe, M.; Morita, M.; Murakami, T.; Muramatsu, N.;
Tipo: Artigo de Revista Científica
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The photo-production of $\phi$ mesons from Li, C, Al, and Cu at forward angles has been measured at $E_gamma$=1.5--2.4 GeV. The number of events for incoherent phi photo-production is found to have a target mass number dependence of $A^{0.72\pm 0.07}$ in the kinematical region of $|t|\le 0.6$ ${\rm GeV}^2/c^2$. The total cross section of the $\phi$-nucleon interaction, $\sigma_{\phi N}$, has been estimated as $35^{+17}_{-11}$ mb using the $A$-dependence of the $\phi$ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than $\sigma_{\phi N}$ in free space, suggesting that the $\phi$ properties might change in the nuclear medium.; Comment: 12 pages 4 figures, submitted to Phys. Lett. B

## Fractional quantum Hall effect in a quantum point contact at filling fraction 5/2

Miller, J. B.; Radu, I. P.; Zumbuhl, D. M.; Levenson-Falk, E. M.; Kastner, M. A.; Marcus, C. M.; Pfeiffer, L. N.; West, K. W.
Tipo: Artigo de Revista Científica
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Recent theories suggest that the excitations of certain quantum Hall states may have exotic braiding statistics which could be used to build topological quantum gates. This has prompted an experimental push to study such states using confined geometries where the statistics can be tested. We study the transport properties of quantum point contacts (QPCs) fabricated on a GaAs/AlGaAs two dimensional electron gas that exhibits well-developed fractional quantum Hall effect, including at bulk filling fraction 5/2. We find that a plateau at effective QPC filling factor 5/2 is identifiable in point contacts with lithographic widths of 1.2 microns and 0.8 microns, but not 0.5 microns. We study the temperature and dc-current-bias dependence of the 5/2 plateau in the QPC, as well as neighboring fractional and integer plateaus in the QPC while keeping the bulk at filling factor 3. Transport near QPC filling factor 5/2 is consistent with a picture of chiral Luttinger liquid edge-states with inter-edge tunneling, suggesting that an incompressible state at 5/2 forms in this confined geometry.

## Differential cross section and photon beam asymmetry for the gamma n -> K+ Sigma- reaction at Egamma=1.5-2.4 GeV

Kohri, H.; Ahn, D. S.; Ahn, J. K.; Akimune, H.; Asano, Y.; Chang, W. C.; Date', S.; Ejiri, H.; Fukui, S.; Fujimura, H.; Fujiwara, M.; Hasegawa, S.; Hicks, K.; Hotta, T.; Imai, K.; Ishikawa, T.; Iwata, T.; Kawai, H.; Kino, K.; Makino, S.; Mart, T.; Matsuda
Tipo: Artigo de Revista Científica
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Differential cross sections and photon beam asymmetries have been measured for the gamma n -> K+ Sigma- and gamma p -> K+ Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of Egamma=1.5-2.4 GeV at 0.6

## The nuclear structure of Th-229

Gulda, K.; Kurcewicz, W.; Aas, A. J.; García Borge, María José; Burke, D. G.; Fogelberg, B.; Grant, I. S.; Hagebø, E.; Kaffrell, N.; Kvasil, J.; Løvhøiden, G.; Mach, H.; Mackova, A.; Martínez, T.; Nyman, G.; Rubio, Berta; Taín, José Luis; Tengbla
Tipo: Artículo Formato: 382229 bytes; application/pdf
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25 pages, 5 tables, 9 figures.-- PACS nrs.: 21.10.-k; 23.20.-g; 23.20.Lv; 23.20.Nx.-- Available online Dec 5, 2001.; The γ-rays following the β- decay of Ac-229 have been investigated by means of γ-ray singles and γγ-coincidence measurements using Ge detectors. Multipolarities of 40 transitions in Th-229 have been established by measuring conversion electrons with a mini-orange electron spectrometer. The half-lives of the 146.35, 164.53 and 261.96 keV levels have been measured using the advanced time delayed betagammagamma(t) method. The low-lying states in Th-229 and observed transition rates have been interpreted within the quasiparticle-phonon model with inclusion of Coriolis coupling. Two octupole correlated parity partner bands, with K-π = 5/2(±) and K-π = 3/2(±), were identified in Th-229.; This work was supported in part by the Polish Scientific Research Committee, the Swedish Natural Science Research Council, the Norwegian Research Council, the Spanish CICYT under contracts AEN94–0833-C02–02 and AEN96–1662, the Canadian Natural Sciences and Engineering Research Council, the Grant Agency of Czech Republic under the contract 202/99/1718, and UK Engineering and Physical Science Research Council.; Peer reviewed

## Quenched E1 transition rates in Th-231

Aas, A. J.; Mach, H.; Kvasil, J.; García Borge, María José; Fogelberg, B.; Grant, I. S.; Gulda, K.; Hagebø, E.; Hoff, P.; Kurcewicz, W.; Lindroth, A.; Løvhøiden, G.; Mackova, A.; Martínez, T.; Rubio, Berta; Sánchez-Vega, M.; Smith, J. F.; Taín, J
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24 pages, 5 tables, 5 figures.-- PACS nrs.: 21.10.−k; 21.10.Tg; 21.10.Re; 23.20.−g; 23.20.Lv; 27.90.+b.; The fast timing βγγ(t) method has been used to measure lifetimes of the low-lying levels in Th-231 populated in the β- decay of Ac-231. The half-life of the K-π = 5/2(-) band-head at 185.7-keV was measured as T(1/2) = 1073(79) ps, yielding D-0 = 1.76(8) x 10(-2) e·fm and 1.65(6) x 10(-2) e·fm for the El transitions to the 7/2(+) and 5/2(+) members respectively of the K-π = 5/2(+) ground state band. Furthermore, T(1/2) ≤ 74 ps and ≤ 74 ps were measured for the K-π = 3/2(+) and 1/2(+) bandheads at 221.4- and 247.6-keV, and T-1/2 = 503(12) ps and 98(36) ps for the 1/2(-) and 3/2(-) states at 554.7- and 593.6-keV, members of the K-π = 1/2(-) band. The latter results consistently yield D(0) values of the order of 1.1 x 10-2 e·fm for three transitions connecting the K-π = 1/2(±) bands. The observed transition rates have been interpreted within the quasiparticle-phonon model with the inclusion of Coriolis coupling.; This work was supported in part by the Research Council of Norway, the Nansen Foundation, the Swedish Natural Science Research Council, the Polish Scientific Research Committee under grant KBN-2-P03B-001-11...

## Octupole correlations in Ra-229

Fraile, Luis M.; Aas, A. J.; García Borge, María José; Fogelberg, B.; García Raffi, Luis M.; Grant, I. S.; Gulda, K.; Hagebø, E.; Kurcewicz, W.; Kvasil, J.; Løvhøiden, G.; Mach, H.; Mackova, A.; Martínez, T.; Rubio, Berta; Taín, José Luis; Teije