36 research outputs found
Hyperfine Anomalies in Fr: Boundaries of the Spherical Single Particle Model
We have measured the hyperfine splitting of the 7P(1/2) state at the 100 ppm level in Fr isotopes (Fr-206g,Fr-206m,Fr-207,Fr-209,Fr-213,Fr-221) near the closed neutron shell (N = 126 in Fr-213). The measurements in five isotopes and a nuclear isomeric state of francium, combined with previous determinations of the 7S(1/2) splittings, reveal the spatial distribution of the nuclear magnetization, i.e., the Bohr-Weisskopf effect. We compare our results with a simple shell model consisting of unpaired single valence nucleons orbiting a spherical nucleus, and find good agreement over a range of neutron-deficient isotopes (Fr207-213). Also, we find near-constant proton anomalies for several even-N isotopes. This identifies a set of Fr isotopes whose nuclear structure can be understood well enough for the extraction of weak interaction parameters from parity nonconservation studies
Beta asymmetry parameter in the decay of 114In
The beta asymmetry parameter A for the pure Gamow-Teller decay of 114In is
reported. The low temperature nuclear orientation method was combined with a
GEANT4 based simulation code allowing for the first time to address in detail
the effects of scattering and of the magnetic field. The result, A = -0.994 +/-
0.010stat +/- 0.010syst, constitutes the most accurate value for the asymmetry
parameter of a nuclear beta transition to date. The value is in agreement with
the Standard Model prediction of A = -1 and provides new limits on tensor type
charged weak currents.Comment: 11 pages, 2 figures; additional information was added on systematic
effects, the magnetic field map and the calculation of the Qcos(theta) value
Isotope shifts in francium isotopes Fr206-213 and Fr-221
We present the isotope shifts of the 7s(1/2) to 7p(1/2) transition for francium isotopes Fr206-213 with reference to Fr-221 collected from two experimental periods. The shifts are measured on a sample of atoms prepared within a magneto-optical trap by a fast sweep of radio-frequency sidebands applied to a carrier laser. King plot analysis, which includes literature values for 7s(1/2) to 7p(3/2) isotope shifts, provides a field shift constant ratio of 1.0520(10) and a difference between the specific mass shift constants of 170(100) GHz amu between the D-1 and D-2 transitions, of sufficient precision to differentiate between ab initio calculations
Ft values of the T = 1/2 mirror beta transitions
A complete survey is presented of all half-life and branching-ratio
measurements related to the isospin T = 1/2 mirror beta transitions ranging
from 3He to 83Mo. No measurements are ignored, although some are rejected for
cause. Using the decay energies obtained in the 2003 Mass Evaluation
experimental ft values are then determined for the transitions up to 45V. For
the first time also all associated theoretical corrections needed to convert
these results into "corrected" Ft values, similar to the superallowed 0+ -> 0+
pure Fermi beta transitions, were calculated. Precisions of the resulting
values are in most cases between 0.1 % and 0.4 %. These Ft(mirror) values can
now be used to extract precise weak interaction information from past and
ongoing correlation measurements in the beta decay of the T = 1/2 mirror beta
transitions
The half-life of Fr in Si and Au at 4K and at mK temperatures
The half-life of the decaying nucleus Fr was determined in
different environments, i.e. embedded in Si at 4 K, and embedded in Au at 4 K
and about 20 mK. No differences in half-life for these different conditions
were observed within 0.1%. Furthermore, we quote a new value for the absolute
half-life of Fr of t = 286.1(10) s, which is of comparable
precision to the most precise value available in literature
First detection and energy measurement of recoil ions following beta decay in a Penning trap with the WITCH experiment
The WITCH experiment (Weak Interaction Trap for CHarged particles) will
search for exotic interactions by investigating the beta-neutrino angular
correlation via the measurement of the recoil energy spectrum after beta decay.
As a first step the recoil ions from the beta-minus decay of 124In stored in a
Penning trap have been detected. The evidence for the detection of recoil ions
is shown and the properties of the ion cloud that forms the radioactive source
for the experiment in the Penning trap are presented.Comment: 9 pages, 6 figures (9 figure files), submitted to European Physical
Journal
Precision measurements of the Co -asymmetry parameter in search for tensor currents in weak interactions
The -asymmetry parameter for the Gamow-Teller decay of
Co was measured by polarizing the radioactive nuclei with the brute
force low-temperature nuclear-orientation method. The Co activity was
cooled down to milliKelvin temperatures in a He-He dilution
refrigerator in an external 13 T magnetic field. The particles were
observed by a 500 thick Si PIN diode operating at a temperature of
about 10 K in a magnetic field of 0.6 T. Extensive GEANT4 Monte-Carlo
simulations were performed to gain control over the systematic effects. Our
result, , is in agreement with
the Standard-Model value of , which includes recoil-order
corrections that were addressed for the first time for this isotope. Further,
it enables limits to be placed on possible tensor-type charged weak currents as
well as other physics beyond the Standard Model