23 research outputs found
Two-neutron transfer reaction mechanisms in C(He,He)C using a realistic three-body He model
The reaction mechanisms of the two-neutron transfer reaction
C(He,He) have been studied at 30 MeV at the TRIUMF ISAC-II
facility using the SHARC charged-particle detector array. Optical potential
parameters have been extracted from the analysis of the elastic scattering
angular distribution. The new potential has been applied to the study of the
transfer angular distribution to the 2 8.32 MeV state in C, using
a realistic 3-body He model and advanced shell model calculations for the
carbon structure, allowing to calculate the relative contributions of the
simultaneous and sequential two-neutron transfer. The reaction model provides a
good description of the 30 MeV data set and shows that the simultaneous process
is the dominant transfer mechanism. Sensitivity tests of optical potential
parameters show that the final results can be considerably affected by the
choice of optical potentials. A reanalysis of data measured previously at 18
MeV however, is not as well described by the same reaction model, suggesting
that one needs to include higher order effects in the reaction mechanism.Comment: 9 pages, 9 figure
High-Precision Branching Ratio Measurement for the Superallowed + Emitter 74Rb
A high-precision branching-ratio measurement for the superallowed β
+ decay of 74Rb was performed at the
TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electronpositron
tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted β
particles; the 8π spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting γ rays
that were emitted following Gamow-Teller and nonanalog Fermi β
+ decays of 74Rb; and the Pentagonal Array
of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring
β-delayed conversion electrons. Twenty-three excited states were identified in 74Kr following 8.241(4) × 108
detected 74Rb β decays. A total of 58 γ -ray and electron transitions were placed in the decay scheme, allowing
the superallowed branching ratio to be determined as B0 = 99.545(31)%. Combined with previous half-life and
Q-value measurements, the superallowed branching ratio measured in this work leads to a superallowed f t value
of 3082.8(65) s. Comparisons between this superallowed f t value and the world-average-corrected Ft value, as
well as the nonanalog Fermi branching ratios determined in this work, provide guidance for theoretical models
of the isospin-symmetry-breaking corrections in this mass region.IS
High-precision branching-ratio measurement for the superallowed β\u3csup\u3e+\u3c/sup\u3e emitter 74Rb
A high-precision branching-ratio measurement for the superallowed β+ decay of 74Rb was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) radioactive ion-beam facility. The scintillating electron-positron tagging array (SCEPTAR), composed of 10 thin plastic scintillators, was used to detect the emitted β particles; the 8π spectrometer, an array of 20 Compton-suppressed HPGe detectors, was used for detecting γ rays that were emitted following Gamow-Teller and nonanalog Fermi β+ decays of 74Rb; and the Pentagonal Array of Conversion Electron Spectrometers (PACES), an array of 5 Si(Li) detectors, was employed for measuring β-delayed conversion electrons. Twenty-three excited states were identified in 74Kr following 8.241(4)×108 detected 74Rb β decays. A total of 58 γ-ray and electron transitions were placed in the decay scheme, allowing the superallowed branching ratio to be determined as B 0=99.545(31)%. Combined with previous half-life and Q-value measurements, the superallowed branching ratio measured in this work leads to a superallowed ft value of 3082.8(65) s. Comparisons between this superallowed ft value and the world-average-corrected Ft̄ value, as well as the nonanalog Fermi branching ratios determined in this work, provide guidance for theoretical models of the isospin-symmetry-breaking corrections in this mass region. © 2013 American Physical Society
High-precision half-life and branching-ratio measurements for superallowed Fermi β \u3csup\u3e+\u3c/sup\u3e emitters at TRIUMF - ISAC
A program of high-precision half-life and branching-ratio measurements for superallowed Fermi β emitters is being carried out at TRIUMF\u27s Isotope Separator and Accelerator (ISAC) radioactive ion beam facility. Recent half-life measurements for the superallowed decays of 14O, 18Ne, and 26Alm, as well as branching-ratio measurements for 26Alm and 74Rb are reported. These results provide demanding tests of the Standard Model and the theoretical isospin symmetry breaking (ISB) corrections in superallowed Fermi β decays. © Owned by the authors, published by EDP Sciences, 2014
Ground-State and Pairing-Vibrational Bands with Equal Quadrupole Collectivity in \u3csup\u3e124\u3c/sup\u3eXe
The nuclear structure of 124Xe has been investigated via measurements of the β+/EC decay of 124Cs with the 8πγ-ray spectrometer at the TRIUMF-ISAC facility. . . .
For the remainder of this abstract, please visit: http://dx.doi.org/10.1103/PhysRevC.91.04432
Conversion electrons from high-statistics β-decay measurements with the 8π spectrometer at TRIUMF-ISAC
The 8π spectrometer, located at TRIUMF-ISAC, was the world\u27s most powerful spectrometer dedicated to β-decay studies until its decommissioning in early 2014 for replacement with the GRIFFIN array. An integral part of the 8π spectrometer was the Pentagonal Array for Conversion Electron Spectroscopy (PACES) consisting of 5 Si(Li) detectors used for charged-particle detection. PACES enabled both γ - e- and e- - e- coincidence measurements, which were crucial for increasing the sensitivity for discrete e- lines in the presence of large backgrounds. Examples from a 124Cs decay experiment, where the data were vital for the expansion of the 124Csm decay scheme, are shown. With sufficient statistics, measurements of conversion coefficients can be used to extract the E0 components of Jπ → Jπ transitions for J ≠ 0, which is demonstrated for data obtained in 110In→110Cd decay. With knowledge of the shapes of the states involved, as obtained, for example, from the use of Kumar-Cline shape invariants, the mixing of the states can be extracted
Two-Neutron Transfer Reaction Mechanisms in \u3csup\u3e12\u3c/sup\u3eC(\u3csup\u3e6\u3c/sup\u3eHe, \u3csup\u3e4\u3c/sup\u3eHe) \u3csup\u3e14\u3c/sup\u3eC using a Realistic Three-Body \u3csup\u3e6\u3c/sup\u3eHe Model
The reaction mechanisms of the two-neutron transfer reaction 12C(6He,4He) have been studied at Elab=30 MeV at the TRIUMF ISAC-II facility using the Silicon Highly-segmented Array for Reactions and Coulex (SHARC) charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 2+2 8.32 MeV state in 14C, using a realistic three-body 6He model and advanced shell-model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30-MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at Elab=18 MeV, however, is not as well described by the same reaction model, suggesting that one needs to include higher-order effects in the reaction mechanism
Far from \u27Easy\u27 Spectroscopy with the 8π and GRIFFIN Spectrometers at TRIUMF-ISAC
The 8π spectrometer, installed at the TRIUMF-ISAC facility, was the world\u27s most sensitive γ-ray spectrometer dedicated to β-decay studies. A description is given of the 8π spectrometer and its auxiliary detectors including the plastic scintillator array SCEPTAR used for β-particle tagging and the Si(Li) array PACES for conversion electron measurements, its moving tape collector, and its data acquisition system. The recent investigation of the decay of 124Cs to study the nuclear structure of 124Xe, and how the β-decay measurements complemented previous Coulomb excitation studies, is highlighted, including the extraction of the deformation parameters for the excited 0+ bands in 124Xe. As a by-product, the decay scheme of the (7+) 124Cs isomeric state, for which the data from the PACES detectors were vital, was studied. Finally, a description of the new GRIFFIN spectrometer, which uses the same auxiliary detectors as the 8π spectrometer, is given
Cellular orientation is guided by strain gradients
The strain-induced reorientation response of cyclically stretched cells has been well characterized in uniform strain fields. In the present study, we comprehensively analyse the behaviour of human fibroblasts subjected to a highly non-uniform strain field within a polymethylsiloxane microdevice. Our results indicate that the strain gradient amplitude and direction regulate cell reorientation through a coordinated gradient avoidance response. We provide critical evidence that strain gradient is a key physical cue that can guide cell organization. Specifically, our work suggests that cells are able to pinpoint the location under the cell of multiple physical cues and integrate this information (strain and strain gradient amplitudes and directions), resulting in a coordinated response. To gain insight into the underlying mechanosensing processes, we studied focal adhesion reorganization and the effect of modulating myosin-II contractility. The extracted focal adhesion orientation distributions are similar to those obtained for the cell bodies, and their density is increased by the presence of stretching forces. Moreover, it was found that the myosin-II activity promoter calyculin-A has little effect on the cellular response, while the inhibitor blebbistatin suppresses cell and focal adhesion alignment and reduces focal adhesion density. These results confirm that similar internal structures involved in sensing and responding to strain direction and amplitude are also key players in strain gradient mechanosensing and avoidance