Achievements of ISIS neutron science 2001-2007

Highlights in ISIS science 2001-2007.

Mapping stresses in engineering components

The control of residual stresses is critical for the design and safe operation of many engineering components.  These stresses arise during various production stages, for example during welding.  The development of new welding technologies such as inertia friction welding is important for the future of the civil aerospace industry. Neutron diffraction at ISIS has enabled the stresses resulting from this process to be mapped, leading to the tailoring of stress-relieving heat treatments.

M Preuss et al., Met. Mater. Trans. A33 (2002) 3227

Behaviour of alcohol-water mixtures

The behaviour of alcohol-water mixtures, sometimes very different from what might be predicted, is determined by the molecular-level organisation of the water and alcohol molecules. Neutron diffraction at ISIS has shown that the unexpected properties of water-alcohol systems arises from incomplete mixing at the molecular level together with  some retention of the local structure found in pure water.

JL Finney et al., Phys. Rev. Lett. 71 (1993) 4346, S Dixit et al., Nature 416 (2002) 829.

Small molecule structure under pressure

An understanding of formation mechanisms for large solar system bodies requires knowledge of how molecular materials behave under pressure. High pressure neutron diffraction studies of methane hydrate are of direct relevance to modeling Saturn’s largest moon Titan.

JS Loveday et al., Nature 410 (2001) 661.

Strain measurements on electroceramics

The in-situ engineering testing facilities at ISIS have led to improved understanding of mechanical properties in a wide range of materials, from steels to shape memory alloys to rocks.  Studies of piezoelectric ceramics have led to insights into the internal structure and behaviour of these smart materials, contributing towards their successful application as sensors and micromechanical actuators.

RC Rogan et al., J. Appl. Phys. 93 (2003) 4104

Crystal structure of  ice phases

Ice can assume a large number of different crystal structures, more than any other material known.  Neutrons can provided detailed information on ice molecule arrangement, including amorphous phases and those which occur under extreme pressure.

RJ Nelmes et al., Phys. Rev. Lett. 71 (1993) 1192; JL Finney et al., Phys. Rev. Lett. 88 (2002) 225503; Phys. Rev. Lett. 89 (2002) 205503.

The secrets of storing hydrogen

Concern over climate change and a dwindling supply of fossil fuels mean that there is increasing interest in alternative forms of energy. Hydrogen shows much promise as a clean, green fuel. However, storing hydrogen is not easy. ISIS has enabled studies of materials that have the potential to store hydrogen cheaply and efficiently. One of the most exciting materials they have looked at so far is Li4BN3H10. This material can store hydrogen at a much higher weight percent – around 12%. Using neutron diffraction, David and his colleagues were able to analyse the structure of the material and see exactly where the hydrogen is stored and how mobile it is.

W.I.F. David et al The Fuel Cell Review. Volume 3, Issue 1, Feb/Mar 2006.

Cut and paste enzymes

One of the main mechanisms of genetic change involves enzymes called recombinases which catalyse the re-arrangement of DNA sequences by breaking the DNA and rejoining the ends in new ways. This cutting and recombination is responsible for genetic diversity arising in sexual reproduction, and is also crucial for DNA repair and other cellular processes. Recombinant techniques are, of course, a key component in genetic engineering.

The researchers chose to work on a laboratory-made, highly-active variant of Tn3.

Small angle scattering, with both X-rays and neutrons, was used to analyse the synapse structure in its natural watery environment. The research team was able to ascertain the relative positions and conformation of the resolvase enzyme and DNA molecules by comparing the results with those predicted from computer models.

Solution Structure of the Tn3 Resolvase-Crossover Site Synaptic Complex, M Nöllmann et al, Molecular Cell 16 (2004) 127.

Behavior of Tn3 Resolvase in Solution and its Interaction with res, M Nöllmann, O Byron and W Marshall Stark, Biophysical Journal 89 (2005) 1920.

Stopping pollution in its tracks

Phenol and its derivatives are common chemical compounds, found in many everyday products, from weed-killer to antiseptic solution. Unfortunately phenols are also toxic and can be a serious form of pollution if they reach a water system. It is therefore important to understand how effective clay particles are at mopping up and containing phenol contamination.

Unlike other methods of detecting organic particles, neutron scattering still works when the clays are in their natural wet state and can see the behaviour at high pressures and temperatures, mimicking the effect of burial down to around 10 km

Neutrons revealed that phenol remains relatively mobile, even inside clays with tiny, nanometre-sized, pores. Trapping the phenol required minuscule pores, just one molecular layer thick, but even then there is a chance for escape if the clay dries and shrinks and cracks appear letting the phenol out.

The structure and dynamics of 2-dimensional fluids in swelling clays, NT Skipper et al., Chemical Geology, 230(3) (2006) 182 

Frustration!

Minerals prefer to form a perfectly ordered crystal structure when they are cooled, but for some, known as ‘frustrated systems, this is a hard task. Studying frustrated systems using neutrons at ISIS has enabled scientists to discover new classes of magnets and exotic forms of matter, with wide-ranging applications.

Multiferroics are minerals that are both ferroelectric (their atoms can order electrically, just like a ferromagnet’s atoms order magnetically) and magnetic. Such materials are exceedingly rare and until recently it was unclear what caused this novel magnetic-ferroelectric coupling.

Using neutron diffraction, Radaelli and his colleagues have found that the properties of multiferroic materials were intimately related to their frustration geometry. Potentially multiferroic minerals could be used as an alternative form of data storage for computer memories. Understanding how the frustration geometry controls the mineral properties brings applications like this one step closer

Spin structure and magnetic frustration in multiferroic RMn2O5 (R=Tb,Ho,Dy) GR Blake et al., Phys Rev B 71 (21) (2005) 214402

Structural anomalies and multiferroic behavior in magnetically frustrated TbMn2O5 LC Chapon et al., Phys Rev Lett 93 (17) (2004) 177402

Superconductors take a spin

Despite a great deal of study, there is still much we do not know about how high-temperature superconductivity works. The Maps spectrometer, installed at ISIS in 2001, can uniquely record the spin fluctuations over a wide spectrum of energies. Recently, an international collaboration studied two of the cuprates - one containing yttrium and barium (YBa2Cu3O6+x), and the other lanthanum and strontium ( La2-xSrxCuO4) obtaining a comprehensive picture of their magnetic behaviour. They were able to calculate the change in magnetic energy in going from the normal to the superconducting state, and show that it was more than enough to cause the collective pairing that is the signature of superconductivity.  In the case of the lanthanum strontium cuprate, the team showed that there were two sets of fluctuations associated with the collective magnetic behaviour. The higher-energy set matched features seen in a different type of experiment using ultraviolet light to explore the electron energies, which had been linked to the formation of a superconducting state in these puzzling materials.

The structure of the high-energy spin excitations in a high-transition temperature superconductor, SM Hayden et al., Nature 429 (2004) 531

Magnetic energy change available to superconducting condensation in optimally doped YBa2Cu306.95, H Woo et al., Nature Physics 2 (2006) 600.

Two energy scales in the spin excitations of the high-temperature superconductor

La2-xSrxCuO4, B Vignolle et al., Nature Physics 3 (2007) 163

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