Spin Echo, Fidelity, and the Quantum Critical Fan in TmVO_{4}.

Using spin-echo nuclear magnetic resonance in the model transverse field Ising system TmVO_{4}, we show that low frequency quantum fluctuations at the quantum critical point have a very different effect on ^{51}V nuclear spins than classical low-frequency noise or fluctuations that arise at a finite temperature critical point. Spin echoes filter out the low-frequency classical noise but not the quantum fluctuations. This allows us to directly visualize the quantum critical fan and demonstrate the persistence of quantum fluctuations at the critical coupling strength in TmVO_{4} to high temperatures in an experiment that remains transparent to finite temperature classical phase transitions. These results show that while dynamical decoupling schemes can be quite effective in eliminating classical noise in a qubit, a quantum critical environment may lead to rapid entanglement and decoherence.

Measurements of nematic susceptibility with phase sensitive nuclear magnetic resonance in pulsed strain fields.

We present nuclear magnetic resonance data in BaFe2As2 in the presence of pulsed strain fields that are interleaved in time with the radio frequency excitation pulses. In this approach, the preceding nuclear magnetization acquires a phase shift that is proportional to the strain and pulse time. The sensitivity of this approach is limited by the homogeneous decoherence time, T2, rather than the inhomogeneous linewidth. We measure the nematic susceptibility as a function of temperature and demonstrate a three orders of magnitude improvement in sensitivity. This approach will enable studies of the strain response in a broad range of materials that previously were inaccessible due to inhomogeneous broadening.

Inverse Laplace transformation analysis of stretched exponential relaxation.

We investigate the effectiveness of the Inverse Laplace Transform (ILT) analysis method to extract the distribution of relaxation rates from nuclear magnetic resonance data with stretched exponential relaxation. Stretched-relaxation is a hallmark of a distribution of relaxation rates, and an analytical expression exists for this distribution for the case of a spin-1/2 nucleus. We compare this theoretical distribution with those extracted via the ILT method for several values of the stretching exponent and at different levels of experimental noise. The ILT accurately captures the distributions for ß≲0.7, and for signal to noise ratios greater than ∼40; however the ILT distributions tend to introduce artificial oscillatory components. We further use the ILT approach to analyze stretched relaxation for spin I>1/2 and find that the distributions are accurately captured by the theoretical expression for I=1/2. Our results provide a solid foundation to interpret distributions of relaxation rates for general spin I in terms of stretched exponential fits.

Radon and health--an update.

BACKGROUND: The National Radiological Protection Board (NRPB) estimated in 1990 that radon causes 5 per cent of lung cancer in the United Kingdom. The estimate was not based on direct evidence. Since then a number of epidemiological studies have been reported. In addition, various policies have been formulated and some implemented, including the mounting of public campaigns to reduce radon in houses in parts of the United Kingdom. METHODS: A review of the scientific literature, policy documents and results of the campaigns has been undertaken. RESULTS: New data on miners support previous evidence that radon, at the levels found in mines, does cause lung cancer. The one study to add to the two previous case control studies looking at domestic radon tips the scales slightly towards radon being incriminated in homes as well. The effect of smoking, a multiplicative or additive risk with radon, is still unclear. Radon can be calculated to cause up to 383 lung cancer deaths per year in the five currently designated 'radon affected' areas. Approximately 287 of these deaths will be in cigarette smokers, and the most effective way for smokers exposed to radon to reduce their lung cancer risk is to stop smoking. CONCLUSION: Evidence of the risk from residential radon is still insufficient to justify the current NRPB advice. If it were, a much more effective radon campaign would be needed. Such a campaign would concentrate on reducing lung cancer in people by tackling both radon exposure and cigarette smoking, rather than simply reducing radon in houses.