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

Fonte: PubMed
Publicador: PubMed

Tipo: Artigo de Revista Científica

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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.

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

Fonte: National Academy of Sciences
Publicador: National Academy of Sciences

Tipo: Artigo de Revista Científica

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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...

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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#Condensed Matter - Mesoscale and Nanoscale Physics#Condensed Matter - Strongly Correlated Electrons

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 16/04/2014
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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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 10/03/1999
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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 12/08/2007
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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 23/07/1999
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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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 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...

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 22/06/2013
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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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/09/2011
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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)

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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...

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## 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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 20/12/2010
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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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 09/11/2004
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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

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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.

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

Fonte: Universidade Cornell
Publicador: Universidade Cornell

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

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## The nuclear structure of Th-229

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artículo
Formato: 382229 bytes; application/pdf

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#Radioactivity Th-229 from decay chain of Fr-229, Fr-229 from Th-232(p,4p) and U-238(p,6p4n)#Mass separation#Measured E-γ, I-γ, Ee, I(ce), T(1/2), ATD βγγ(t), eγ-coincidence, γγ-coincidence#Th-229 deduced levels, ICC, multipolarities, I-π, rotational bands, B(XL), dipole moments#Ge,#Si(Li)#Plastic#BaF2 detectors#Mini-orange spectrometer#[PACS] Properties of nuclei#nuclear energy levels

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

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## Quenched E1 transition rates in Th-231

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artículo
Formato: 1283063 bytes; application/pdf

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#Radioactivity#Ac-231#β-#Measured Eγ, Iγ, γ-γ coincidences, T(1/2)#Deduced Th-231 levels#B(XL)#Fast-timing βγγ(t) method#Rotational bands#Quasiparticle-plus-phonon model#[PACS] Properties of nuclei#nuclear energy levels

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...

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## Octupole correlations in Ra-229

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artículo
Formato: 2478405 bytes; application/pdf

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#Radioactivity 229/87Fr [from 238/92U (p,6R4n) mass separation]#Measured E-γ, I-γ, I(CE), γ-γ coincidences, T(1/2)#Deduced 229/88Ra levels, ICC multipolarities, I-π, rotational bands, B(XL)#Ge, Si(Li), BaF2, detectors#Mini-Orange spectrometer#Fast timing βγγ(t) method#Quasiparticle-plus-phonon model#[PACS] Lifetimes, widths#[PACS] Electromagnetic transitions#[PACS] Collective levels#[PACS] Properties of specific nuclei listed by mass ranges: A ≥ 220

36 pages, 5 tables, 9 figures.-- PACS nrs.: 23.20.−g; 21.10.Tg; 21.10.Re; 27.90.+b.; The structure of Ra-229 has been studied in the β- decay of Fr-229. Spins and parities have been determined from the conversion electron measurements, while half-lives for the 137.5, 142.7, 168.8, 213.0 and 479.0 keV levels have been measured in the ps and ns ranges via the fast timing βγγ(t) method. Our data confirm the previous results and enrich the knowledge of the structure of this nucleus by 25 new states and several strong transitions. Structural similarities are established between Ra-229 and its N = 141 isotone Th-231. The experimental results are compared with the theoretical predictions of the quasiparticle-phonon model with inclusion of Coriolis coupling. The reduced transition probabilities, and especially the moderately fast B(E1) rate for the 137.5 keV transition connecting the band-heads of the K-π = 5/2(±) parity doublet bands, reveal the presence of significant octupole correlations in Ra-229.; This work was partially supported by the Spanish CICYT "Plan National de Altas Energias" (under contracts AEN96-1662 and AEN96-1679), the Margit & Folke Pehrzon Foundation, the Swedish Natural Science Research Council, Czech Republic Grant Agency (under contract 202/96/ 1744) and the Polish Scientific Research Committee (under grant KBN-2-P03B-OOl-11).; Peer reviewed

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