A new kind of positron sources for future linear colliders, where the converter is an aligned tungsten crystal, oriented on the 〈111〉-axis, has been studied at CERN in the WA103 experiment with ...tertiary electron beams from the SPS. In such sources the photons resulting from channeling radiation and coherent bremsstrahlung create the e+e− pairs.
Electron beams, of 6 and 10GeV, were impinging on different kinds of targets: a 4mm thick crystal, a 8mm thick crystal and a compound target made of 4mm crystal followed by 4mm amorphous disk. An amorphous tungsten target 20mm thick was also used for the sake of comparison with the 8mm crystal and to check the ability of the detection system to provide the correct track reconstruction. The charged particles coming out from the target were detected in a drift chamber immersed partially in a magnetic field. The reconstruction of the particle trajectories provided the energy and angular spectrum of the positrons in a rather wide energy range (up to 150MeV) and angular domain (up to 30°). The experimental approach presented in this article provides a full description of this kind of source. A presentation of the measured positron distribution in momentum space (longitudinal versus transverse) is given to allow an easy determination of the available yield for a given momentum acceptance. Results on photons, measured downstream of the positron detector, are also presented. A significant enhancement of photon and positron production is clearly observed. This enhancement, for a 10GeV incident beam, is of 4 for the 4mm thick crystal and larger than 2 for the 8mm thick crystal. Another important result concerns the validation of the simulations for the crystals, for which a quite good agreement was met between the simulations and the experiment, for positrons as well as for photons. These results are presented after a short presentation of the experimental setup and of the track reconstruction procedure.
Laser technologies that are used for the development of sensor elements for Remotely Operated Vehicles (ROVs) are presented, as well as the latest developments in underwater robotics where laser ...spectroscopy methods are applied to environmental monitoring. A submersible laser spectrometer unit intended for studying Raman scattering and laser-induced fluorescence (LIF) spectra is presented. The spectrometer was developed as an element of an ROV sensor system for remote detection and measurements of organic matter concentrations in sea water and underwater objects. The results of environmental tests of the submersible LIF spectrometer in various marine areas, including the Arctic, are described.
The project of using the SND NaI(Tl) calorimeter as an antineutron detector Bukin, A.D.; Bukin, D.A.; Golubev, V.B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2009, 2009-1-00, Letnik:
598, Številka:
1
Journal Article
Recenzirano
We present the project of neutron electromagnetic form factor measurements in the
e
+
e
-
→
n
n
¯
process with SND detector at VEPP-2000
e
+
e
-
-collider. Time-of-flight technique is vital for the ...forthcoming study of
e
+
e
-
→
n
n
¯
process. The results of time resolution measurement of NaI(Tl) counter using Flash-ADC for cosmic muons and
n
n
¯
events detection efficiency estimations are presented.
The
e
+
e
−
→ ω, ρ → π
0
e
+
e
−
processes have been investigated in the experiments with Spherical Neutral Detector at the VEPP-2M
e
+
e
−
collider. The measurements provide the probability ℬ(ω → π
...0
e
+
e
−
) = (0.761 ± 0.053 ± 0.064) × 10
−3
of the ω → π
0
e
+
e
g-
conversion decay and the upper limit ℬ(ρ → π
0
e
+
e
−
) < 1.2 × 10
−5
(at 90% CL) for the ρ → π
0
e
+
e
−
decay. The transition form factor was measured at three values of the 4-momentum transfer squared.
A comparative study of the efficiency of the hydrophobic catalyst RCTU-3SM in chemical isotope exchange reactions of hydrogen with water and the oxidation of trace amounts of hydrogen in relation to ...the detritiation tasks of technological streams was carried out. It is shown that, depending on the equilibrium conditions of the isotope exchange process, there is an optimum temperature at which the reaction rate has a maximum. It was found that the rate of oxidation reaction of trace hydrogen depends on the content of oxygen in the purified stream. With oxygen concentration reducing, the oxidation rate initially increases, and when the ratio of oxygen and hydrogen concentrations is less than 100, the rate remains constant within the experimental error.
The new tracking system of the Spherical Neutral Detector for experiments at the VEPP-2000
e
+
e
-
collider in Novosibirsk is described. The system consists of a 9-layer drift chamber with 24 jet ...cells and a proportional chamber in a common gas volume. Main system features are its small size and high density of readout channels for gaseous tracking systems at colliding experiments.
The drift chamber provides at least four measurements along the track for charged particles within 94% solid angle and nine measurements for particles propagating at large angle relative to the beam axis.
R
-
ϕ
coordinates (in a plane perpendicular to the beam axis) are obtained using the ionization drift time measurement. Longitudial coordinates are measured using charge division on anode wires and charge distribution on cathode strips. Design angular resolutions for radial tracks are
σ
ϕ
=
0
.
26
∘
,
σ
θ
=
0
.
3
∘
, the vertex resolution is
σ
R
=
0.2
mm
.
The full-size prototype of the tracking system has been assembled and tested. The wire structure of the prototype represents one quadrant of the chamber. Results of the prototype assembly quality control and tests with radioactive sources and cosmic rays are presented. They are in a good agreement with expected system parameters.
We have experimentally determined the threshold energy for filamentation in THEOS-based hybrid silicate nanocomposite materials containing polysaccharides and hyperbranched polyglycidols and the ...conversion efficiency from the femtosecond Ti : sapphire laser output to a supercontinuum in the range . The addition of sodium hyaluronate (polysaccharide) and low concentrations of Au nanoparticles or CdS quantum dots with an average diameter of has been shown to considerably reduce the threshold energy for filamentation and improve the laser output to supercontinuum conversion efficiency.
The cross section for the
e
+
e
−
→ ωπ
0
→ π
0
π
0
γ process has been measured in the energy range of 1.1–1.9 GeV. The measurement has been made with the Spherical Neutral Detector at the VEPP-2000
e
...+
e
−
collider. The data in the energy range of 1.1–1.4 GeV are in agreement with the earlier measurements with the SND and CMD-2 detectors. The cross section has also been measured above 1.4 GeV.
Tungsten crystals oriented on their 〈111〉 axis, were submitted to 6 and 10 GeV electron beams on the SPS-CERN transfer lines. The crystals, 4 and 8 mm thick, used alone or associated to 4 mm thick ...amorphous disk, were studied as positron sources. The emerging positrons were detected by a Drift Chamber partially immersed in a magnetic field, where their trajectories were reconstructed providing the energy spectrum and the angular distribution. Significant enhancements were observed for the crystal source when compared to the amorphous one of the same thickness. The gain was larger than 3 and 2 for the 4 mm and 8 mm targets, respectively. The presented results look very promising for e+e− linear colliders.
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