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The Glasgow group is involved in the construction of the GE0600 interferometer as well as in R&D activity on technology for advanced gravitational wave detectors, GE0600 will be the first GW detector using quasi-monolithic silica suspensions in order to decrease thermal noise significantly with respect to steel wire suspensions. The results concerning GE0600 suspension mounting and performance will be shown in the first section. Section 2 is devoted to the present results from the direct measurement of thermal noise in mirrors mounted in the 10 m interferometer in Glasgow which has a sensitivity limit of 4 x 10(-19) m Hz(-1/2) above I kHz. Section 3 presents results on the measurements of coating losses. R&D activity has been carried out to understand better how thermal noise in the suspensions affects the detector sensitivity, and in section 4 a discussion on the non-linear thermoelastic effect is presented.

The GEO 600 laser interferometer with 600 m armlength is part of a worldwide network of gravitational wave detectors. Due to the use of advanced technologies like multiple pendulum suspensions with a monolithic last stage and signal recycling, the anticipated sensitivity of GEO 600 is close to the initial sensitivity of detectors with several kilometres armlength. This paper describes the subsystems of GEO 600, the status of the detector by September 2001 and the plans towards the first science run.

We report experiments in which laser-induced fluorescence detection is incorporated into a flowing afterglow helium plasma to study the kinetics and dynamics of excited helium atoms. Following excitation of helium in the 3 3P-2 3S band at 388.9 nm, dispersed fluorescence spectra show major features at 388.9, 706.5 and 587.6 nm corresponding to emission from the 3 3P, 3 3S and 3 3D states as observed in previous studies. In addition to these major features, we also observe weaker, molecular emissions in the 430-500 and 710-725 nm regions which we assign to fluorescence from He2 states. Similar experiments in which the 3 1P-2 1S band at 501.6 nm is excited afford strong atomic fluorescence from the 3 1P and 3 1D states at 501.6 and 667.8 nm, respectively. A weak emission feature can also be assigned to 3 1S-2 1P emission at 728.1 nm. Weak molecular emissions are again observed but in this case in the 440-470 and 535-600 nm regions.

Unit-cell parameters of RbTi2(PO4)3, a framework structure (space group R3c) with alternating corner-linked Ti octahedra and P tetrahedra that define six-coordinated alkali cation sites, were determined at eight pressures from 0.0 to 6.2 GPa, and crystal structure refinements were obtained at 0.0 and 6.2 GPa. The structure remains dimensionally rhombohedral at all pressures, with the a axis more than four times more compressible than c. Compressibilities of both axes increase abruptly above about 1.7 GPa; the bulk modulus decreases from 104(3) GPa (K'=4) to approximately 60 GPa. Furthermore, the appearance of reflections that violate the c glide-plane symmetry above 1.7 GPa signals the occurrence of a reversible phase transition involving distortion of the framework. From the pressure dependence of the intensities of critical X-ray reflections, the phase transition is revealed as being continuous and close to second order in character. Structure refinements of the 6.2 GPa data reveal R3 symmetry, an acentric space group, for the high-pressure form. Average Ti-O-P angles decrease from 151.5 to 140 degrees between room pressure and 6.2 GPa. These changes result in a coordination change for Rb from one centric six-coordinated site (Rb-O=2.855 AA) at room pressure, to two symmetrically distinct acentric 12-coordinated sites (mean Rb-O approximately=3.01 AA) at 6.2 GPa.

By reverse-bias capacitance-voltage measurements on Schottky diode samples the authors have determined the immobile-charge concentrations N+ at 85 K and 120 K on n-type VPE GaAs, before and after 1.0 MeV proton irradiation at the low temperature and after progressive heating to 300 K, so as to study the proton-irradiation-induced defects that anneal at low temperatures in this semiconductor and to obtain information on their carrier-trapping energy levels. They find that the irradiation-induced decrease in the N+ value is considerably removed, by a total of about 40%, in three defect-annealing stages, A, B and C, centred at approximately 180, 235 and 280 K respectively. The annealing kinetics of stages B and C are consistent with those of the annealing stages I and II found by Thommen (1970) in studies of resistivity changes in electron-irradiated bulk n-GaAs. In contrast, they report stage A as a new annealing stage at a temperature lower than any previously known for defects in gallium arsenide. By consideration of the sensitivity of the N+ value at low measurement temperature to the natures and energy levels of electron trapping defects they deduce that the three stages A, B and C are all predominantly due to the removal of acceptor levels that lie below about Ec-0.2 eV. They deduce also that the stage C levels are close to or below the middle of the energy-band gap. They suggest that the stage A, B and C defects may include defects produced by the displacement of gallium atoms.

A NASA mission that almost never saw the light of day is now being readied for take-off. Dawn, which is designed to intercept the asteroids Vesta and Ceres, had previously been cancelled after problems with its novel propulsion system. But with the faults now corrected, mission scientists hope Dawn will embark on its eight-year voyage at the end of this month.

A group of physicists in the UK thinks it knows how to create beams of neutronsa thousand times brighter than those at any existing facility. Their technique involves using the neutrons that emerge when deuterium and tritium are made to fuse. Although their study is only theoretical, the physicists say that such a facility could be built within 20 or 30 years (Science 315 1092).

Ever since the days of Maxwell, Thomson and Rutherford, the University of Cambridge has been rightly recognized for the quality of its physics research. But physics at Cambridge, which is centred on the world-famous Cavendish Laboratory, is about to boosted by the building of a new centre for the physics of medicine and a cosmology institute. The university is also making a string of new appointments in physics.

Right now, millions of researchers around the world are working on countless exciting and as-yet unsolved scientific problems. Students are slaving, postdocs pondering, supervisors wrinkling. But the odds are that many of them are doing it wrongly in exactly the same way.

A medical physicist from Ireland has devised a deceptively simple technique that could provide salvation for many of the billion or so people without access to clean drinking water. The technique, developed by Kevin McGuigan from the Royal College of Surgeons in Ireland, involves placing dirty water in clear plastic bottles and leaving them out in the Sun. Ultraviolet radiation from the Sun can kill water-borne pathogens, particularly if the water heats up.

The authors report measurements by deep-level transient spectroscopy (DLTS) and immobile-space-charge profiling on lattice-defect production in VPE n-GaAs at 80K by 1.0 MeV electron irradiation, and on the annealing behaviour of the defects at 80-300K. It is shown that the electron traps E1, E2 and E3 are produced by the irradiation, before anneal at 300K, and that an additional electron-trapping defect 'E(0.23)', with an apparent activation energy of 0.23+or-0.02 eV to the conduction band, is created by the irradiation and is removed in the 235K annealing stage found previously by Thommen (1970) in electron-irradiated bulk-grown n-GaAs. The authors suggest that the E(0.23) level arises from a plural-defect structure, and that it anneals by dissociation or internal recombination. The results also indicate the irradiation production of below-mid-gap electron-trapping levels at a concentration much larger than the concentration of electron traps observed, as DLTS levels, in the upper half of the energy gap, and that about 50% annealing of the total net electron trap concentration occurred at 80-300K. Increased at 80-300K in the concentrations of the E1 and E2 defects were also observed in this range of annealing temperature.

Thick natural targets of Ru, Pd, and Cd have been bombarded with 4He, 16O and 32S ions. The relative intensities of the 2+ to 0+ decay gamma rays resulting from the Coulomb excitation of the even isotopes were measured. For each set of isotopes the quadrupole moments of the first excited states were deduced assuming a previously published measurement for one of the isotopes. Where the present results could be checked against previous absolute results in the Ru, Pd and Cd isotopes, reasonable agreement was found. However, the results are not in good agreement with those from a previous relative measurement in the Cd isotopes. The practical limitations of the relative method of quadrupole-moment measurement are discussed.

The B(E2) values of some of the low-lying levels in 135Ba have been measured by means to Coulomb excitation using 8 and 10 MeV alpha particles. An attempt has been made to describe 135Ba as a neutron quasiparticle coupled to an anharmonic 135Ba core using the intermediate-coupling unified nuclear model. The agreement between the experimental and calculated energy levels and E2 transition strengths is good, especially if the quadrupole moment of the first excited state of the core is taken to be strongly negative.

The nuclei 129Xe and 131Xe have been studied by Coulomb excitation and by ( alpha ,n) reactions on 126Te and 128Te. The authors report eleven new levels for 129Xe and six for 131Xe and B(E2) spin up values for some of the low-lying states. The present Coulomb excitation experiments together with published beta -decay work enable some spin-parity assignments and restrictions to be made. The data are broadly consistent with the predictions of the particle-vibrator coupling model, although a thorough comparison requires further spectroscopic measurements and more detailed theoretical calculation.

The theory and design of a neutron velocity selector for use in the wavelength range 7-15 A are discussed. The selector takes the form of seven thin circular disks rigidly mounted on a rotating shaft. Each disk is opaque to neutrons and has 80 slots machined at regular intervals about its circumference. In order to simplify construction the positions of the disks have been determined so that the slots can be machined parallel to the axis of rotation. The theoretical resolution which can be expected of the device is discussed.

By a development of the method of Frisch a general treatment has been given of the time lag for diffusion in a multiple laminate ABCD... where each lamina is composed of a different material. The treatment relates to flow of heat or matter in laminated slabs, hollow cylinders or spherical shells, under conditions where the diffusion coefficients are independent of concentration in each lamina, and where Henry's law governs the distribution of diffusant between each pair of laminae. Several special cases have been treated numerically which demonstrate some properties of the time lag in laminates.

The creation of lattice defects in crystalline solids by atomic displacement during irradiation with electrons, ions and neutrons has been studied for many years. Much of this work has used measurement techniques, such as the electrical resistivity of metals and semiconductors, and electron spin resonance in semiconductors and insulators, which are sensitive only to or predominantly to the presence of point defects – single interstitial atoms and vacant sites – or of very small complexes of these.

An efficient monochromator is made by imaging a single graded filter on to itself so that the variation from red to blue is reversed in the image. This system transmits a large flux of continuously variable wavelength and narrow bandpass. It is compact and can be adapted for use with a circular filter.

A continuously variable monochromator with a half-width bandpass of 7.2 nm is described. Two graded filters are used, and although the transmittance is low, the exit slit can be opened to emit a flux of monochromatic light not easily obtainable with the same purity from a single graded filter, nor from a conventional prism of grating instrument of comparable dimensions.

In the usual moire fringe measuring system, practical difficulties arise in the use of very fine gratings. An optical system is described in which the use of a separate index grating is avoided, the moire fringes being formed between the scale grating and the image formed by its reflexion in a concave mirror. This arrangement has the particular advantage that the sensitivity is doubled. A working model has been constructed to demonstrate the principle.

Completely pure and perfect semiconductors, even if such existed, would be of no use as electronic devices since they would have no rectifying properties, no excess of electrons or holes, no energy levels in the energy bandgap, etc, necessary for the active and effective operation of semiconductor devices. In fact, these requirements are usually fulfilled by incorporating particular impurities to produce p-type or n-type electrical conductivities and other special properties.