43 research outputs found
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
A new beamline for laser spin-polarization at ISOLDE
A beamline dedicated to the production of laser-polarized radioactive beams
has been constructed at ISOLDE, CERN. We present here different simulations
leading to the design and construction of the setup, as well as technical
details of the full setup and examples of the achieved polarizations for
several radioisotopes. Beamline simulations show a good transmission through
the entire line, in agreement with observations. Simulations of the induced
nuclear spin-polarization as a function of atom-laser interaction length are
presented for Na, [1] and for Ar, which is studied in this
work. Adiabatic spin rotation of the spin-polarized ensemble of atoms, and how
this influences the observed nuclear ensemble polarization, are also performed
for the same nuclei. For Ar, we show that multiple-frequency pumping
enhances the ensemble polarization by a factor 1.85, in agreement with
predictions from a rate equations model.
[1] J. Phys. G: Nucl. Part. Phys./174408400
Confirmation of Parity Violation in the Gamma Decay of
This paper reports measurements using the technique of On Line Nuclear
Orientation (OLNO) which reexamine the gamma decay of isomeric Hf and specifically the 501 keV 8 -- 6
transition. The irregular admixture of E2 to M2/E3 multipolarity in this
transition, deduced from the forward-backward asymmetry of its angular
distribution, has for decades stood as the prime evidence for parity mixing in
nuclear states. The experiment, based on ion implantation of the newly
developed mass-separated Hf beam at ISOLDE, CERN into an
iron foil maintained at millikelvin temperatures, produces higher degrees of
polarization than were achieved in previous studies of this system. The value
found for the E2/M2 mixing ratio, = -0.0324(16)(17), is in close
agreement with the previous published average value = - 0.030(2), in
full confirmation of the presence of the irregular E2 admixture in the 501 keV
transition. The temperature dependence of the forward-backward asymmetry has
been measured over a more extended range of nuclear polarization than
previously possible, giving further evidence for parity mixing of the 8 and 8 levels and the deduced E2/M2 mixing ratio.Comment: 28 pages, 9 figures, accepted for publication in Physical Review
Magnetic moments of short-lived nuclei with part-per-million accuracy: Towards novel applications of -detected NMR in physics, chemistry and biology
We determine for the first time the magnetic dipole moment of a short-lived
nucleus with part-per-million (ppm) accuracy. To achieve this two orders of
magnitude improvement over previous studies, we implement a number of
innovations into our -detected Nuclear Magnetic Resonance (-NMR)
setup at ISOLDE/CERN. Using liquid samples as hosts we obtain narrow, sub-kHz
linewidth, resonances, while a simultaneous in-situ H NMR measurement
allows us to calibrate and stabilize the magnetic field to ppm precision, thus
eliminating the need for additional -NMR reference measurements.
Furthermore, we use ab initio calculations of NMR shielding constants to
improve the accuracy of the reference magnetic moment, thus removing a large
systematic error. We demonstrate the potential of this combined approach with
the 1.1 s half-life radioactive nucleus Na, which is relevant for
biochemical studies. Our technique can be readily extended to other isotopic
chains, providing accurate magnetic moments for many short-lived nuclei.
Furthermore, we discuss how our approach can open the path towards a wide range
of applications of the ultra-sensitive -NMR in physics, chemistry, and
biology.Comment: re-submitte
LOW-TEMPERATURE NUCLEAR ORIENTATION ON THE KONDO SYSTEM CEXND1-XNI
The isotope Nd147 has been oriented by means of low-temperature nuclear orientation on the pseudobinary series CexNd1-xNi for x=0.0, 0.1, 0.25, 0.5, and 0.8. The results show that the compounds are magnetically ordered due to Nd-Nd interactions and no magnetic moment exists on cerium. The Kondo effect is present (for x 0) as revealed by measurements of electical resistivity and thermoelectric power. © 1994 The American Physical Society
HPGe detectors for low-temperature nuclear orientation
Using the low-temperature nuclear orientation (LTNO) technique one can study various interesting properties of atomic nuclei and nuclear decay which can be deduced from the measurements of the angular distributions of charged particles emitted during the decay. However, the use of particle detectors working in conditions of LTNO devices (which are generally not available commercially) is a necessary precondition for the realization of these experiments. Planar HPGe detectors for detection of charged particles at "liquid helium" temperatures were developed and produced at NPI Rez. Relatively simple technology using vacuum evaporation and diffusion was employed. The performance of detectors at low temperatures was tested and their characteristics measured in a testing cryostat before using them in real experiments. The HPGe detectors were extensively used in a whole range of LTNO experiments with various physical objectives - in offline (IKS Leuven) as well as online (CERN-ISOLDE, Louvain-la- Neuve - LISOL) experiments. In the framework of the project "Meson-Exchange Enhancement of First-Forbidden -Transitions in the Lead Region", the measurements of angular distribution of emitted -particles allowed to determine experimentally the "meson-exchange currents" contribution to the -decay. In the project "Isospin Mixing in N~Z nuclei", the isospin-forbidden -transitions of the nuclei in region (A = 50-100) were studied in order to obtain information on the isospin structure of the nuclear states. A new project looking for the possible presence of the tensor currents contribution to the -decay is being prepared for the CERN-ISOLDE facility
Large Area Silicon Drift Detector Prototypes for Experiment
Linear Silicon Drift detectors with an active area of 33.5cm