The 6He nucleus is an ideal candidate to study the weak interaction. To this end we have built a high-intensity source of 6He delivering ~10^10 atoms/s to experiments. Taking full advantage of that available intensity we have performed a high-precisi
on measurement of the 6He half-life that directly probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a measurement of the beta-neutrino angular correlation in 6He beta decay that will allow to search for new physics beyond the Standard Model in the form of tensor currents.
Studies of 6He beta decay along with tritium can play an important role in testing ab-initio nuclear wave-function calculations and may allow for fixing low-energy constants in effective field theories. Here, we present an improved determination of t
he 6He half-life to a relative precision of 3x10^(-4). Our value of 806.89 pm 0.11(stat)^{+0.23}_{-0.19}(syst) ms resolves a major discrepancy between previous measurements. Calculating the statistical rate function we determined the ft-value to be 803.04 ^{+0.26}_{-0.23} s. The extracted Gamow-Teller matrix element agrees within a few percent with ab-initio calculations.
We report results of air monitoring started due to the recent natural catastrophe on 11 March 2011 in Japan and the severe ensuing damage to the Fukushima Dai-ichi nuclear reactor complex. On 17-18 March 2011, we registered the first arrival of the a
irborne fission products 131-I, 132-I, 132-Te, 134-Cs, and 137-Cs in Seattle, WA, USA, by identifying their characteristic gamma rays using a germanium detector. We measured the evolution of the activities over a period of 23 days at the end of which the activities had mostly fallen below our detection limit. The highest detected activity amounted to 4.4 +/- 1.3 mBq/m^3 of 131-I on 19-20 March.
We performed ultracold neutron (UCN) storage measurements to search for additional losses due to neutron (n) to mirror-neutron (n) oscillations as a function of an applied magnetic field B. In the presence of a mirror magnetic field B, UCN losses wou
ld be maximal for B = B. We did not observe any indication for nn oscillations and placed a lower limit on the oscillation time of tau_{nn} > 12.0 s at 95% C.L. for any B between 0 and 12.5 uT.
