31 research outputs found
Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40
The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure
Low collectivity of the 2(1)(+) state of Po-212
International audienceThe lifetime of the state of Po was measured in the Pb(C,Be)Po transfer reaction by Îł -ray spectroscopy employing the recoil distance Doppler shift (RDDS) method. The derived absolute B(E2) value of 2.6(3)W.u. indicates a low collectivity and contradicts previous claims of α-cluster components in the structure of the state. It is demonstrated that a consistent description of the properties of the âââ sequence in Po cannot be achieved in the framework of a single-j shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in Pb and Po
Low collectivity of the first 2âș states of ÂČÂčÂČ,ÂČÂčâ°Po
The lifetimes of the first 2âș excited states of ÂČÂčÂČ,ÂČÂčâ°Po were measured in two transfer reactions ÂČâ°âžPb(ÂčÂČC,âžBe)ÂČÂčÂČPo and ÂČâ°âžPb(ÂčÂČC,Âčâ°Be)ÂČÂčâ°Po by the Recoil Distance Doppler Shift (RDDS) method and by the Doppler Shift Attenuation method (DSAM), respectively. The derived absolute B(E2) values of 2.6(3) W.u. for ÂČÂčÂČPo and 1.83(28) W.u. for ÂČÂčâ°Po indicate low collectivity. It is shown that the properties of the yrast 2ââș, 4ââș, 6ââș and 8ââș states in both nuclei cannot be described consistently in the framework of nuclear shell models. It is also demonstrated in the case of ÂČÂčâ°Po that Quasi-particle Phonon Model (QPM) calculations cannot overcome this problem thus indicating the existence of a peculiarity which is neglected in both theoretical approaches
Mechanisms of T cell organotropism
F.M.M.-B. is supported by the British Heart Foundation, the Medical Research Council of the UK and the Gates Foundation
First Flavor-Tagged Determination of Bounds on Mixing-Induced CP Violation in Bs -> J/psi phi Decays
This Letter describes the first determination of bounds on the CP-violation
parameter 2*beta_s using Bs decays in which the flavor of the bottom meson at
production is identified. The result is based on approximately 2,000 Bs ->
J/psi phi decays reconstructed in a 1.35 fb-1 data sample collected with the
CDF II detector using p-bar p collisions produced at the Fermilab Tevatron. We
report confidence regions in the two-dimensional space of 2*beta_s and the
decay-width difference Delta-Gamma. Assuming the standard model predictions of
2*beta_s and Delta-Gamma, the probability of a deviation as large as the level
of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations.
Dedicated to the memory of our dear friend and colleague, Michael P. Schmidt.Comment: 7 pages, 2 figures, submitted to PR
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Adenosquamous versus Andocarcinoma of the Pancreas: A Population-Based Outcomes Analysis
Adenosquamous versus adenocarcinoma of the pancreas: a population-based outcomes analysis.
BackgroundPancreatic adenosquamous carcinoma has historically been characterized as having a more aggressive clinical course than ductal adenocarcinoma. The natural history of this disease, however, is essentially unknown.MethodsWe evaluated the clinical characteristics of all patients with pancreatic adenosquamous carcinoma recorded in the California Cancer Registry 2000-2007 and compared them to those of patients with ductal adenocarcinoma.ResultsNinety-five patients with pancreatic adenosquamous carcinoma and 14,746 patients with ductal adenocarcinoma were identified. Demographics were similar between subtypes (pâ>â0.05). Disease stage at presentation was also similar; over 50% of each diagnostic group presented with metastatic disease (pâ=â0.62). Surgical resection was more common among patients with locoregional adenosquamous carcinoma than adenocarcinoma (pâ=â0.0004), but rates of adjuvant therapy administration were similar (pâ>â0.05). The cohorts' median overall survival durations were similar in a Cox proportional hazards model (pâ=â0.45); overall survival was also similar when only patients with resected disease were considered (pâ=â0.65). Early stage, resection and receipt of radiation or chemotherapy were favorable independent prognostic factors among patients with adenosquamous carcinoma. The median overall survival duration of patients with resected adenosquamous carcinoma was 12 months (95% CI, 8-52).ConclusionsAdenosquamous carcinoma has a natural history similar to that of ductal adenocarcinoma when treated with prevalent clinical patterns of care
Improvement of the intrinsic time resolving power of the Cologne iron-free orange type electron spectrometers
Conversion electron spectroscopy represents an important tool for nuclear structure analysis of medium and heavy nuclei. Two iron-free magnetic electron spectrometers of the orange type have been installed at the Institute for Nuclear Physics of the University of Cologne. The very large transmission of 15% and the very good energy resolution of 1% makes the iron-free orange spectrometer a powerful instrument. By means of fast timing techniques, lifetimes of nuclear excited states can be measured with an accuracy better than 20 ps. For the first time, the energy dependent centroid position of prompt events yielding the time-walk characteristics (the prompt curve) of the orange spectrometer fast timing setup has been measured using prompt secondary delta-electrons generated in a pulsed beam experiment. The prompt curve calibrated as a function of energy allows precise lifetime determination down to a few tens of picoseconds by the use of the centroid shift method. (C) 2010 American Institute of Physics. [doi:10.1063/1.3499259
Different collectivity in the two signatures of the i13/2 stemming band in Âčâ¶â·Yb
Six lifetimes have been determined in the 5/2âș [642] band from vi13/2 parentage in Âčâ¶â·Yb by means of Recoil distance Doppler-shift (RDDS) measurements carried out at the Cologne FN tandem. The deduced transition strengths and the level scheme are reasonably described by Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the 5/2âș[642] band. In that band, the quadrupole collectivity of the favored signature is appreciably larger than this of the unfavored signature. The effect increases with increasing the spin. Naturally, the rigid PTRM cannot explain these features, but the structure of its wave functions suggests a possible solution. It is associated with the enhanced contribution of low-Ω orbitals from vi13/2 parentage in the favored signature compared to the unfavored one. This could selectively increase the deformation of the favored signature band members and give rise to a dynamic shape coexistence taking place between the two signatures which needs quantitative explanation by future theoretical work
Plunger lifetimes and electromagnetic transition strengths in odd 167Yb
Nine lifetimes have been determined for the first time in the 5/2â[523] and 5/2+[642] bands of 167Yb by means of Recoil distance Doppler-shift measurements carried out at the Cologne FN tandem. For the data analysis, a dedicated version of the Differential decay curve method was used. The newly deduced transition strengths and the level scheme are reasonably described by the Particle plus triaxial rotor model (PTRM) calculations except for the behavior of the quadrupole collectivity in the two signatures of the 5/2+[642] band. The stretched B(E2)ÊŒs in the favored signature are appreciably larger than those in the unfavored signature. The effect increases with spin. In the PTRM calculations, the wave functions of the favored signature levels contain larger contribution of low-Ω orbitals from Îœi13/2 parentage than those of the unfavored levels. This could selectively increase the deformation of the favored signature band members. If so, rotation and Coriolis interaction would give rise to a dynamic shape coexistence taking place between the two signatures