F. Wauters

Precision measurements of the

The {beta}-asymmetry parameter A-tilde for the Gamow-Teller decay of {sup 60}Co was measured by polarizing the radioactive nuclei with the brute-force low-temperature nuclear-orientation method. The {sup 60}Co activity was cooled down to milliKelvin temperatures in a {sup 3}He-{sup 4}He dilution refrigerator in an external 13-T magnetic field. The {beta} particles were observed by a 500-{mu}m-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, A-tilde=-1.014(12){sub stat}(16){sub syst}, is in agreement with the standard-model value of -0.987(9), 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.

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The β-asymmetry parameter A for the pure Gamow-Teller decay of 114 In is reported. The low-temperature nuclear orientation method was combined with a GEANT4-based simulation code allowing us, for the first time, to address in detail the effects of scattering and the magnetic field. The result, A = -0.994 ± 0.010 stat ± 0.010 syst , constitutes the most accurate value for the asymmetry parameter of a nuclear β 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.

Co

Abstract The measurement of the β asymmetry parameter in nuclear β decay is a potentially very sensitive tool to search for non V – A components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the β radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of β particles as well as (back)scattering in the source, on the sample holder and on the detector, have to be correctly taken into account in the analysis of the data. A thorough study of these effects and a new method based on detailed GEANT4 Monte-Carlo simulations that was developed for this purpose is presented here. The code was developed for β asymmetry measurements by means of the Low Temperature Nuclear Orientation (LTNO) method, but can in principle be generalized to other experimental setups using other polarization techniques.

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The half-life of the {alpha}-decaying nucleus {sup 221}Fr was determined in different environments, that is, 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 value for the absolute half-life of {sup 221}Fr of t{sub 1/2}=286.1(10) s that is of comparable precision to the most precise value available in the literature.

-asymmetry parameter in search for tensor currents in weak interactions

This paper reports measurements using the technique of On Line Nuclear Orientation (OLNO) which reexamine the gamma decay of isomeric 180Hfm 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 180Hfm 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, ǫ = -0.0324(16)(17), is in close agreement with the previous published average value ǫ = 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. PACS numbers: 21.10.HW,23.20.En,23.40.Bw,27.70.+q,29.30.Lw,150≤A≤189

β asymmetry parameter in the decay of In 114

It has been claimed recently that half-lives of radioactive nuclei embedded in metals would be significantly affected by electron screening provided by the metal. The effect would further be strengthened at low temperatures. We have determined the half-life-of {sup 253}Es nuclei embedded in iron at temperatures between 4 K and 50 mK. Our results agree with the room temperature literature value within about 2% and show no dependence on temperature over a range of almost two orders of magnitude.

A GEANT4 Monte-Carlo simulation code for precision β spectroscopy

A new value for the hyperfine magnetic field of copper impurities in iron is obtained by combining resonance frequencies from experiments involving {beta}-NMR on oriented nuclei on {sup 59}Cu, {sup 69}Cu, and {sup 71}Cu with magnetic moment values from collinear laser spectroscopy measurements on these isotopes. The resulting value, i.e., B{sub hf}(CuFe) = -21.794(10) T, is in agreement with the value adopted until now but is an order of magnitude more precise. It is consistent with predictions from ab initio calculations. Comparing the hyperfine field values obtained for the individual isotopes, the hyperfine anomalies in Fe were determined to be {sup 59{Delta}69}=0.15(9)% and {sup 71{Delta}69}=0.07(11)%.

Half-life of 221Fr in Si and Au at 4 K and at millikelvin temperatures

Nuclear magnetic resonance (NMR/ON) measurements with

Confirmation of parity violation in the gamma decay of Hf-180(m)

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{alpha}-decay half-life of {sup 253}Es in metallic Fe at temperatures between 4 K and 50 mK

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