Measurement of gamow-teller strength for 176Yb --> 176Lu and the efficiency of a solar neutrino detector

We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem.     

The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

Coherent optical control of the spin of a single hole in an InAs/GaAs quantum dot

We demonstrate coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. A superposition of hole-spin states is created by fast (10-100?ps) dissociation of a spin-polarized electron-hole pair. Full control of the hole spin is achieved by combining coherent rotations about two axes: Larmor precession of the hole spin about an external Voigt geometry magnetic field, and rotation about the optical axis due to the geometric phase shift induced by a picosecond laser pulse resonant with the hole-trion transition.     

The rapid deposition of moiré grids

This technical note describes a simple method for using the nickel meshes with up to 2000 lines/in. (lpi) as masks for producing moiré grids. The main advantages, when compared with other methods, are the substantial increase in the speed of application and the precision of the reproduced grid.     

Application of profile projectors to moiré analysis

Two profile projectors have been modified for moiré applications by the addition of adjustable screens which contain magnified master grids. The instruments have been examined for any errors they may introduce into the measurements and the screen adjustments have been calibrated. Their use and application are described briefly.     

Breakup of 8B and the 7Be(p, γ)8B reaction

The calculated rate of events in some of the existing solar neutrino detectors is directly proportional to the rate of the ⁷Be(p, γ)⁸B reaction measured in the laboratory at low energies. However, the low-energy cross sections of this reaction are quite uncertain as various measurements differ from each other by 30–40%. The Coulomb dissociation process which reverses the radiative capture by the dissociation of ⁸B in the Coulomb field of a target, provides an alternate way of accessing this reaction. While this method has several advantages (like large breakup cross sections and flexibility in the kinematics), the difficulties arise from the possible interference by the nuclear interactions, uncertainties in the contributions of the various multipoles and the higher order effects, which should be considered carefully. We review the progress made so far in the experimental measurements and theoretical analysis of the breakup of ⁸B and discuss the current status of the low-energy cross sections (or the astrophysical S-factor) of the ⁷Be(p, γ)⁸B reaction extracted therefrom. The future directions of the experimental and theoretical investigations are also suggested. Work supported by EPSRC, UK, grant nos J/95867 and L/94574.     

The production of high-density moiré grids

The basic principles and methods of the moiré method are well known. Here, some of the procedures and equipment developed by the authors for the production and reproduction of high-line-density grids for strain-measurement purposes are described.     

Spatio-temporal characterization of double plasma mirror for ultrahigh contrast and stable laser pulse

An ultrahigh contrast laser pulse of over 10¹¹ for 6 ps before the main pulse was achieved by employing a double plasma mirror installed at the end of a 100 TW Ti:sapphire laser system. Spatial beam qualities such as focusability and stability were found to be extremely sensitive in the range of 14–360 J/cm² on the double plasma mirror, while ultrahigh contrast was maintained. At the fluence of 90 J/cm² the focusability of the ultrahigh contrast laser was not degraded, and the stability was very close to that obtained without the double plasma mirror when the 2-dimensional normalized standard deviation and the correlation function for several laser beam profiles were analyzed. These results are requisites for carrying out relativistic laser-plasma interactions with ultrahigh contrast laser pulses, enabling the use of ultrathin solid targets.