26 research outputs found
Development of high-gain gaseous photomultipliers for the visible spectral range
We summarize the development of visible-sensitive gaseous photomultipliers,
combining a semitransparent bi-alkali photocathode with a state-of-the-art
cascaded electron multiplier. The latter has high photoelectron collection
efficiency and a record ion blocking capability. We describe in details the
system and methods of photocathode production and characterization, their
coupling with the electron multiplier and the gaseous-photomultiplier operation
and characterization in a continuous mode. We present results on the properties
of laboratory-produced KCsSb, CsSb and NaKSb photocathodes and
report on their stability and QE in gas; KCsSb photocathodes yielded QE
values in Ar/CH(95/5) above 30% at wavelengths of 360-400 nm. The novel
gaseous photomultiplier yielded stable operation at gains of 10, in
continuous operation mode, in 700 Torr of this gas; its sensitivity to single
photons was demonstrated. Other properties are described. The successful
detection of visible light with this gas-photomultiplier pave ways towards
further development of large-area sealed imaging detectors, of flat geometry,
insensitive to magnetic fields, which might have significant impact on light
detection in numerous fields.Comment: 22 pages, 12 figures, for submission to JINS
The Photon-Assisted Cascaded Electron Multiplier: a Concept for Potential Avalanche-Ion Blocking
We present a Photon-Assisted Cascaded Electron Multipliers (PACEM) which has
a potential for ion back-flow blocking in gaseous radiation detectors: the
avalanche from a first multiplication stage propagates to the successive one
via its photons, which in turn induce photoelectron emission from a
photocathode deposited on the second multiplier stage; the multiplication
process may further continue via electron-avalanche propagation. The
photon-mediated stage allows, by a proper choice of geometry and fields,
complete blocking of the ion back-flow into the first element; thus, only ions
from the latter will flow back to the drift region. The PACEM concept was
validated in a double-MHSP (Micro-Hole & Strip Plate) cascaded multiplier
operated in xenon, where the intermediate scintillation stage provided optical
gain of ~60. The double-MHSP detector had a total gain above 10^4 and energy
resolution of 18% FWHM for 5.9 keV x-rays.Comment: 13 pages, 5 figures. Submitted to JINST - electronic Journal of
Instrumentation, June 25, 200
Thermodynamics and kinetics of boundary friction
A deterministic theory describing the behavior of an ultrathin lubricant film
between two atomically-smooth solid surfaces is proposed. For the description
of lubricant state the parameter of excess volume arising due to chaotization
of solid medium structure in the course of melting is introduced. Thermodynamic
and shear melting is described consistently. Dependences of friction force on
temperature of lubricant, shear velocity of rubbing surfaces, and pressure upon
surfaces are analyzed. Within the framework of a simple tribological model the
stick-slip mode of friction, when the lubricant periodically melts and
solidifies, is described. The obtained results are qualitatively compared with
the experimental data.Comment: 14 pages, 6 figures, 33 reference
A Comparative Numerical Study on GEM, MHSP and MSGC
In this work, we have tried to develop a detailed understanding of the
physical processes occurring in those variants of Micro Pattern Gas Detectors
(MPGDs) that share micro hole and micro strip geometry, like GEM, MHSP and MSGC
etc. Some of the important and fundamental characteristics of these detectors
such as gain, transparency, efficiency and their operational dependence on
different device parameters have been estimated following detailed numerical
simulation of the detector dynamics. We have used a relatively new simulation
framework developed especially for the MPGDs that combines packages such as
GARFIELD, neBEM, MAGBOLTZ and HEED. The results compare closely with the
available experimental data. This suggests the efficacy of the framework to
model the intricacies of these micro-structured detectors in addition to
providing insight into their inherent complex dynamical processes
MHSP in reversed-biased operation mode for ion blocking in gas-avalanche multipliers
We present recent results on the operation of gas-avalanche detectors
comprising a cascade of gas electron multipliers (GEMs) and Micro-Hole and
Strip Plates (MHSPs) multiplier operated in reversed-bias (R-MHSP) mode. The
operation mechanism of the R-MHSP is explained and its potential contribution
to ion-backflow (IBF) reduction is demonstrated. IBF values of 4E-3 were
obtained in cascaded R-MHSP and GEM multipliers at gains of about 1E+4, though
at the expense of reduced effective gain in the first R- MHSP multiplier in the
cascade.Comment: 23 pages, 8 figure
The COMPASS Experiment at CERN
The COMPASS experiment makes use of the CERN SPS high-intensitymuon and
hadron beams for the investigation of the nucleon spin structure and the
spectroscopy of hadrons. One or more outgoing particles are detected in
coincidence with the incoming muon or hadron. A large polarized target inside a
superconducting solenoid is used for the measurements with the muon beam.
Outgoing particles are detected by a two-stage, large angle and large momentum
range spectrometer. The setup is built using several types of tracking
detectors, according to the expected incident rate, required space resolution
and the solid angle to be covered. Particle identification is achieved using a
RICH counter and both hadron and electromagnetic calorimeters. The setup has
been successfully operated from 2002 onwards using a muon beam. Data with a
hadron beam were also collected in 2004. This article describes the main
features and performances of the spectrometer in 2004; a short summary of the
2006 upgrade is also given.Comment: 84 papes, 74 figure
Fauna of Mollusks of the Lower Reaches of the Danube River within the Territory of Ukraine
MILK PRODUCTIVITY OF DAUGHTERS OF DIFFERENT SIRES OF THE HOLSTEIN BREED
The productive and breeding abilities of animals are largely determined by their origins. Sires, especially those belonging to the leading lines of the Holstein breed, have a great impact on the cow production in dairy cattle breeding. According to the purpose of work, the article present data of a comparative assesment of the Holsteins breed's cow productivity of milk of different sires' daughters of Wis Burke Ideal 1013415 line. The research was conducted under the conditions of intensive technology of a modern dairy complex with a cow population of more than 13 ths. animals, total production of 175 ths. tons and milk yield per cow of 11900 kg of milk. The results of the research prove the valuable breeding abilities of the sires, which are confirmed by the high milk productivity of their daughters. In two completed lactations the milk yield of the daughters (n = 510) of four sires averaged from 8964.1 kg to 10171.5 kg of milk. The mass fraction of fat in milk ranged from 3.59 to 3.84 % and the mass fraction of protein – from 3.12 to 3.18 %. When comparing daughters of different bulls in terms of milk production, there is a reliable difference in individual key indicators for a full lactation and 305 days of lactation. Concerning the lactation period, there are differences in the sires' daughters productivity: all daughters of the Wis Burke Ideal 1013415 bulls are characterized by high productivity qualities. The dairy output level indicates purposeful breeding and selection work with the herd