ALBERT

Notes: In plasma immersion ion implantation, a target is immersed in a plasma and a series of negative, high-voltage pulses are applied to implant ions into the target. An approximate analytical model in one-dimensional planar geometry is developed to determine the time-varying implantation current, the total dose, and the energy distribution of the implanted ions for a voltage pulse with finite rise and fall times. Scaling rules are presented for the implanted current and energy distribution with respect to plasma density, peak applied voltage, and ion mass. Comparisons with numerical simulations are used to demonstrate that the accuracy of the model is well characterized by a single parameter: the ratio of the ion flight time to the pulse rise time.

Notes: We have constructed a high-resolution x-ray image intensifier (XRII) for use in atomic physics. The XRII consists of an alkali halide scintillator crystal coupled by a fiber optic to a proximity focused microchannel plate stack with a bialkali photocathode and wedge and strip readout. The useful area of the detector is 12 cm2. We have measured full width half maximum spatial resolutions at 22 keV of 300 μm and at 122 keV of 600 μm with 0.5-mm-thick and 1.6-mm-thick CsI(Na) crystals, respectively. With NaI(Tl) crystals, x-ray arrival times can be determined with sub-100 ns resolution. In this paper we present the detailed performance of the XRII as well as a brief discussion of the theory of photoelectron limited fast timing.

Notes: We have measured the 8–11-keV emission spectra from plasmas produced by impinging 0.53-μm, 100- and 200-ps FWHM Gaussian laser pulses on targets of different materials. The experimental spectra from W and Zn are identified by comparison with local thermodynamic equilibrium plasma emission calculations.

Notes: SANS experiments of an amorphous Fe90Zr10 alloy were carried out in the temperature region 20–300 K with and without the application of a magnetic field. The scattering versus temperature for different Q values (zero field cooled magnetization) shows two transitions at Tc=240 K and Tf=40 K. However, both transitions are not observed in magnetic field (2.6 kG) cooling down curves. By switching off the magnetic field and warming up the sample only the transition at Tf=40 K is observed. Application of a magnetic field at different temperatures in a zero field cooled sample reduces the scattering; the scattering returns to its initial value after switching off the field.

Notes: The characterization of subpicosecond laser produced plasmas is currently being investigated by the Livermore ultrashort pulse laser group. A 800-nm, 150-fs, 35-mJ laser is focused to a 7-μm spot on solid aluminum targets, producing XUV (〈1 keV), K shell (1.5–30 keV), and hard (≥3.0 keV) x-ray emission. The K-shell emission is studied using a Von Hamos crystal spectrograph with a KAP crystal curved to an 80-mm radius, resulting in a calculated resolution of E/ΔE≈400. The dispersed x rays are detected with a microchannel plate intensified reticon detector which relays the images out of the chamber and displayed on a computer monitor. The hard x rays are monitored with an array of filter x-ray diodes, covering energies from 3 to 75 keV. The XUV emission is monitored with a variably spaced line grating, flat field spectrometer, and a grazing incidence spectragraph. The diagnostics will be presented along with current data from experiments. This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.

Notes: This longitudinal study of the relations between 20 general managers and their chairmen in the UK National Health Service has wider implications despite its distinctive setting. It showed that the two roles are very dependent upon each other, and occupy overlapping domains, so that what each can do is considerably affected by the other's behaviour. the chairman has more power to determine their relative domains so that studies of individual chief executives should take account of this relationship. the ways in which both chairmen and general managers played their roles differed widely. One reason for the differences in the chairmen's roles was the wide variation in the time that they gave to the job. Different types of relationship are described. the most common was that of partners where the two complemented each other. the study crosses different literatures: corporate management, leadership, role theory and managerial work and behaviour. Its main concern is with managerial work and behaviour but it also has some implications for corporate management.

Notes: P seismograms recorded in Europe from some of the earthquakes that occur at depths of around 100 km in northern Chile show three prominent arrivals P, bP and pP; bP being interpreted as a conversion of downward radiated S to P at a discontinuity in wavespeed beneath the source. On broad-band seismograms the duration of the P pulse is around 5s, that of bP around 2s and that of pP around 12s. These differences in duration have been interpreted as Doppler effects due to the motion of the source of seismic radiation, this being assumed to be a near-unilateral fracture propagating downwards on a steeply-dipping fault-plane. For the downward radiated pulses (P and bP) the source is travelling towards the observer whereas for the upward radiated pulse (pP) the source is receding from the observer.The near-unilateral fracture interpretation of the differences in pulse duration is based on data from the earthquake of 1976 November 30 recorded on effectively one azimuth (∼30-40°), which is towards Europe. To give further support to the interpretation requires data from a wider range of azimuths but this is not available for the 1976 earthquake. However, data from the northern Chile earthquake of 1980 May 26 are available from four stations covering an azimuthal range of 180°: Eskdalemuir, Scotland (EKA, azimuth 31.6°); Blacknest, England (BNA, azimuth 35.6°); Gauribidanur, India (GBA, azimuth 95.2°) and Warramunga, Australia (WRA, azimuth 212.0°). The 1980 earthquake, which appears to have a very similar mechanism to that of the 1976 earthquake, is investigated here to see if the observations are consistent with the near-unilateral fracture mechanism.The first motion of P and pP where these can be observed and the general form of the broad-band seismograms are consistent with the presence of a nodal plane dipping steeply towards the east. P is observed to be small relative to the surface reflection pP at EKA, BNA and GBA where P leaves the source close to a node, and P is large relative to pP at WRA where P leaves the source away from the node and the take-off of pP is close to a node.Taking the steeply-dipping nodal plane to be the fault plane, the fault dimensions and fracture speeds compatible with the pulse durations are estimated. Using one of the compatible solutions (fault length 40 km, maximum width, 18 km, fracture speed 0.5P wavespeed, maximum dimension oriented downdip) seismograms are computed and compared to the observed. The computed seismograms simulate the pulse durations and relative amplitudes of most of the main pulses. The detailed form of the main pulses is not modelled possibly because the fault model used is oversimplified. The complexity of the observed pulses presumably indicates that the distribution of slip on the fault plane varies less smoothly than assumed in the model.To determine the detailed distribution and time history of slip on the fault requires data from a larger number of well-distributed stations than is available here. However, if it is accepted that the pulse durations of P, bP and pP given are reliable and that hP is an S-to-P conversion at a boundary below the source then the conclusion seems to be inescapable that the source was a near-unilateral fracture propagating downwards on a steeply-dipping fault-plane.

Notes: Theory predicts that pulses that propagate on stationary non-minimum time paths, such as the PP path, undergo phase shifts such that the onset is emergent and the observed pulse is non-causal relative to the arrival time predicted by ray theory. The phase shift isπ/2 radians, at least at high frequencies, so that the observed pulses should approximate to the Hilbert transform of the pulse recorded over a minimum time path. Although onsets of phases that follow non-minimum time paths (usually called mini-max phases) are predicted to be emergent, those observed often seem clear and no more difficult to read than those of arrivals that follow minimum time paths. An example of a PP seismogram which is clearly emergent is shown here. Simulations obtained by Hilbert transforming the impulse responses of conventional long-period and short-period seismographs convolved with attenuation operators. show that the first half-cycle of mini-max phases which should have the emergent onset will usually be of low amplitude relative to the second half-cycle. This suggests that on observed seismograms the first half-cycle of mini-max phases may be obscured by earlier arrivals. The second half-cycle will then be taken as the first motion and could appear to have a well-defined onset. The effects of phase shifts that result in emergent onsets can be corrected for to some extent, and ideally onset times of mini-max phases would be read from such corrected records. However. onset times of PP read directly from conventional seismograms are reported in bulletins and these times have been assumed by some to be reliable enough to be used to determine anomalies in wavespeed in the upper mantle in the vicinity of the reflection point. Perhaps surprisingly the assumption appears to be justified in that the apparent onset time of a mini-max phase on a conventional short-period seismograph may be little different from the onset time read after correction for the π/2 phase shifts.

Notes: Small-angle neutron scattering is used to study the precipitation behaviour of dissolved oxygen in dislocation-free Czochralski-grown single crystals of silicon doped with boron and compared with those for similar undoped material. The presence of boron dramatically alters the nature of precipitates in silicon. Heat treatment at 1023 K no longer leads to the formation of the large cushion-shaped precipitates observed in essentially undoped material. The precipitates are much smaller, and do not exhibit any anisotropic small-angle scattering. Furthermore, the precipitation process is over in less than 24 h. Subsequent treatment at 1323 K leads to the formation of cushion-shaped regions which are much larger than those formed in the absence of boron.