90 research outputs found
First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
In this letter, we report a new mass for Li using the trapping
experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived
nuclide, , for which a mass measurement has ever been
performed with a Penning trap. Combined with our mass measurements of
Li we derive a new two-neutron separation energy of 369.15(65) keV: a
factor of seven more precise than the best previous value. This new value is a
critical ingredient for the determination of the halo charge radius from
isotope-shift measurements. We also report results from state-of-the-art
atomic-physics calculations using the new mass and extract a new charge radius
for Li. This result is a remarkable confluence of nuclear and atomic
physics.Comment: Formatted for submission to PR
Tensor interaction constraints from beta decay recoil spin asymmetry of trapped atoms
We have measured the angular distribution of recoiling daughter nuclei
emitted from the Gamow-Teller decay of spin-polarized Rb. The
asymmetry of this distribution vanishes to lowest order in the Standard Model
(SM) in pure Gamow-Teller decays, producing an observable very sensitive to new
interactions. We measure the non-SM contribution to the asymmetry to be
= 0.015 0.029 (stat) 0.019 (syst), consistent with the SM
prediction. We constrain higher-order SM corrections using the measured
momentum dependence of the asymmetry, and their remaining uncertainty dominates
the systematic error. Future progress in determining the weak magnetism term
theoretically or experimentally would reduce the final errors. We describe the
resulting constraints on fundamental 4-Fermi tensor interactions.Comment: 11 pages, 13 figures; v2 published in Phys. Rev. C, with referee
clarifications and figures improved for black-and-whit
Isotope Shift Measurements of Stable and Short-Lived Lithium Isotopes for Nuclear Charge Radii Determination
Changes in the mean-square nuclear charge radii along the lithium isotopic
chain were determined using a combination of precise isotope shift measurements
and theoretical atomic structure calculations. Nuclear charge radii of light
elements are of high interest due to the appearance of the nuclear halo
phenomenon in this region of the nuclear chart. During the past years we have
developed a new laser spectroscopic approach to determine the charge radii of
lithium isotopes which combines high sensitivity, speed, and accuracy to
measure the extremely small field shift of an 8 ms lifetime isotope with
production rates on the order of only 10,000 atoms/s. The method was applied to
all bound isotopes of lithium including the two-neutron halo isotope Li-11 at
the on-line isotope separators at GSI, Darmstadt, Germany and at TRIUMF,
Vancouver, Canada. We describe the laser spectroscopic method in detail,
present updated and improved values from theory and experiment, and discuss the
results.Comment: 34 pages, 24 figures, 14 table
Half-life of the superallowed β+ emitter Ne18
The half-life of Ne18 has been determined by detecting 1042-keV γ rays in the daughter F18 following the superallowed-Fermi β+ decay of samples implanted at the center of the 8πγ-ray spectrometer, a spherical array of 20 HPGe detectors. Radioactive Ne18 beams were produced on-line, mass-separated, and ionized using an electron-cyclotron-resonance ionization source at the ISAC facility at TRIUMF in Vancouver, Canada. This is the first high-precision half-life measurement of a superallowed Fermi β decay to utilize both a large-scale HPGe spectrometer and the isotope separation on-line technique. The half-life of Ne18, 1.6656 ± 0.0019 s, deduced following a 1.4σ correction for detector pulse pile-up, is four times more precise than the previous world average. As part of an investigation into potential systematic effects, the half-life of the heavier isotope Ne23 was determined to be 37.11 ± 0.06 s, a factor of 2 improvement over the previous precision. © 2007 The American Physical Society
High precision branching ratio measurement for the superallowed β decay of [Formula Presented] A prerequisite for exacting tests of the standard model
Nonanalog Fermi and Gamow-Teller branches in the superallowed β decay of [Formula Presented] have been investigated using γ-ray and conversion-electron spectroscopy. Nine observed transitions, in conjunction with a recent shell model calculation, determine the branching ratio of the analog transition to be 99.5(1)%. The experimental upper limits for the Fermi decay to the [Formula Presented] and [Formula Presented] levels are in agreement with recent theoretical predictions. The [Formula Presented] value for the [Formula Presented] β decay is predicted to be 10405(9) keV. © 2003 The American Physical Society
Gamma-ray spectroscopy at TRIUMF-ISAC: The new frontier of radioactive ion beam research
High-resolution gamma-ray spectroscopy is essential to fully exploit the unique scientific opportunities at the next generation radioactive ion beam facilities such as the TRTUMF Isotope Separator and Accelerator (TSAC). At IS AC the 871 spectrometer and its associated auxiliary detectors is optimize for p-decay studies while TIGRESS an array of segmented clover HPGe detectors has been designed for studies with accelerated beams. This paper gives a brief overview of these facilities and also presents recent examples of the diverse experimental program carried out at the STI spectrometer. © 2009 American Institute of Physics
Nuclear Charge Radius of Li-9, Li-11: Halo Neutron: the influence of Halo Neutrons
The nuclear charge radius of Li-11 has been determined for the first time by
high precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded
a Li-7 - Li-11 isotope shift (IS) of 25101.23(13) MHz for the Doppler-free 2s -
3s transition. IS precision for all other bound Li isotopes was also improved.
Differences from calculated mass-based IS yield values for change in charge
radius along the isotope chain. The charge radius decreases monotonically from
Li-6 to Li-9, and then increases from 2.217(35) fm to 2.467(37) fm for Li-11.
This is compared to various models, and it is found that a combination of halo
neutron correlation and intrinsic core excitation best reproduces the
experimental results.Comment: 5 pages, 2 figure
Liver-FibroSTARD checklist and glossary: tools for standardized design and reporting of diagnostic accuracy studies of liver fibrosis tests
Chronic liver diseases are highly prevalent and require an accurate evaluation of liver fibrosis to determine patient management. Many efforts have been made over this last decade to develop accurate non-invasive tools for liver fibrosis evaluation as alternative methods to liver biopsy. These non-invasive methods of liver fibrosis assessment including blood markers and liver stiffness measurement by elastography are increasingly well validated and contribute to safer and more practical clinical care for patients [1, 2]. These efforts have led to a dramatic increase in the number of diagnostic accuracy studies of liver fibrosis tests and to a proliferation of reports whose quality is very heterogeneous. [...
High precision branching ratio measurement for the superallowed beta decay of Rb-74: A prerequisite for exacting tests of the standard model
Journals published by the American Physical Society can be found at http://publish.aps.org/Nonanalog Fermi and Gamow-Teller branches in the superallowed beta decay of Rb-74 have been investigated using gamma-ray and conversion-electron spectroscopy. Nine observed transitions, in conjunction with a recent shell model calculation, determine the branching ratio of the analog transition to be 99.5(1)%. The experimental upper limits for the Fermi decay to the 0(2)(+) and (0(3)(+)) levels are in agreement with recent theoretical predictions. The Q(EC) value for the Rb-74 beta decay is predicted to be 10405(9) keV
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