The instrument is the result of the development work started three years ago when we introduced the Vernier method (1), (2), (3), (4), but since then other instruments, based on the Vernier technique, have been developed (5), (6) and used (7). The block scheme of the instrument is shown in Fig. 1.

A system for gain and drift stabilisation of a sampling oscilloscope is described, useful for accurate measurements of average shape and fluctuations of random waveforms.

Here we describe the methods employed for the analysis of digitized data produced by electron time-of-flight and gamma spectrometers that are part of the recently completed advanced positron beam system at the University of Texas at Arlington. The digitization of the data acquisition methods enabled the coincident measurement of the energies of the positron-induced electrons and the Doppler shifted annihilation gamma. Additionally, the digitization of data acquisition methods has led to the development of a multi-stop time-of-flight spectrometer. The digital analysis methods employed in the extraction of timing and energy information from the detector traces have resulted in (i) a digital time-of-flight spectrum of positron-induced secondary electrons utilizing signals from a micro-channel plate (MCP) electron detector and a high-purity germanium gamma detector (HPGe); (ii) a two-dimensional spectrum representing the correlation between the energy of the annihilation gamma and the times-of-flight of positron-induced secondary electrons; and (iii) the first spectra of positron-induced multiple secondary electrons. The digital analysis methods, when applied to positron annihilation-induced Auger electron spectroscopy (PAES), will be capable of providing the energy and momentum of the electron with which the positron annihilates. This information will allow the determination of the contribution of individual atomic orbital levels to the total Doppler broadening spectrum, and may contribute to the understanding of the interaction of positrons with novel two-dimensional materials. The digital multi-stop time-of-flight spectrometer is expected to aid in the quest to unravel the complex decay pathways associated with the Auger decay of annihilation-induced core holes.

The decay features of positrons in anthracene have been experimentally investigated using both single- and poly-crystals at temperatures ranging between −196°C and 295°C. In solid specimens annihilation lifetime was equal to 3.7 × 10−10 sec independently of the measuring tempera- ture. A very notable effect was however found near the melting point (218°C) a complex decay appearing at about 210°C. Neutron irradiated specimens showed a complex decay even at room temperature.

A high accuracy non-overload amplifier particularly suited to gamma-ray spectroscopy is described. Very high counting rates are allowed without distortion of the spectra. (auth)

SPICAV VIS-IR spectrometer on-board the Venus Express mission measured the H2O abundance above Venus’ clouds in the 1.38 µm band, and provided an estimation of the cloud top altitude based on CO2 bands in the range of 1.4–1.6 µm. The H2O content and the cloud top altitude have been retrieved for the complete Venus Express dataset from 2006 to 2014 taking into account multiple scattering in the cloudy atmosphere. The cloud top altitude, corresponding to unit nadir aerosol optical depth at 1.48 µm, varies from 68 to 73 km at latitudes from 40ºS to 40ºN with an average of 70.2 ± 0.8 km assuming the aerosol scale height of 4 km. In high northern latitudes, the cloud top decreases to 62–68 km. The altitude of formation of water lines ranges from 59 to 66 km. The H2O mixing ratio at low latitudes (20ºS-20ºN) is equal to 6.1 ± 1.2 ppm with variations from 4 to 11 ppm and the effective altitude of 61.9 ± 0.5 km. Between 30º and 50º of latitude in both hemispheres, a local minimum was observed with a value of 5.4 ± 1 ppm corresponding to the effective altitude of 62.1 ± 0.6 km and variations from 3 to 8 ppm. At high latitudes in both hemispheres, the water content varies from 4 to 12 ppm with an average of 7.2 ± 1.4 ppm which corresponds to 60.6 ± 0.5 km. Observed variations of water vapor within a factor of 2-3 on the short timescale appreciably exceed individual measurement errors and could be explained as a real variation of the mixing ratio or/and possible variations of the cloud opacity within the clouds. The maximum of water at lower latitudes supports a possible convection and injection of water from lower atmospheric layers. The vertical gradient of water vapor inside the clouds explains well the increase of water near the poles correlating with the decrease of the cloud top altitude and the H2O effective altitude. On the contrary, the depletion of water in middle latitudes does not correlate with the H2O effective altitude and cannot be completely explained by the vertical gradient of water vapor within the clouds. Retrieved H2O mixing ratio is higher than those obtained in 2.56 µm from VIRTIS-H data (Cottini et al., [2015] Planet. Space Sci., 113, 219–225 ) at altitudes of 68–70 km which is well consistent with the lower altitudes of water mixing ratio from the 1.38 µm band. Observations for different solar and emission angles allowed to constrain also the average vertical distribution of H2O mixing ratio in the clouds with 2 ppm at 66 km and 7–7.5 ppm at 59–61 km. The water vapor latitudinal-longitudinal distribution does not show any direct correlation with the cloud tops. Yet a strong asymmetry of H2O longitudinal distribution has been observed with a maximum of 7–7.5 ppm from −120º to 30º of longitude and shifted to the southern hemisphere (20ºS-10ºN). To the east, the minimum is observed with values not in excess of 6 ppm and over a wide range of longitudes from 30º to 160º. Bertaux et al. (2015) announced a correlation between the zonal wind pattern in the equatorial region and underlying topography of Aphrodite Terra as the result of stationary gravity waves produced at the ground level near the mountains. The water minimum corresponds to the Aphrodite Terra highlands and can be also associated with the influence of Venus topography. No prominent long-term on the time scale of 8.5 years nor local time variations of water vapor and the cloud top altitude were detected.

A fast, low-noise, pulse amplifier is described, which has an input stage consisting of a cascode of two triode-connected E83F tubes. Its rms noise voltage is equivalent to a pulse of 280 electronic charges injected on an input capacity of 21 ΜΜF, the frequency response of the amplifier being defined by two RC circuits having both a time constant of 1.5 Μs. On a capacity of 34 ΜΜF and a frequency response given by time constants of 3 Μs, the rms noise is equivalent to a pulse of 380 electronic charges.