A 10B-based neutron detector with stacked Multiwire Proportional Counters and macrostructured cathodes

We present the results of the measurements of the detection efficiency for a 4.7 \r{A} neutron beam incident upon a detector incorporating a stack of up to five MultiWire Proportional Counters (MWPC) with Boron-coated cathodes. The cathodes were made of Aluminum and had a surface exhibiting millimeter-deep V-shaped grooves of 45{\deg}, upon which the thin Boron film was deposited by DC magnetron sputtering. The incident neutrons interacting with the converter layer deposited on the sidewalls of the grooves have a higher capture probability, owing to the larger effective absorption film thickness. This leads to a higher overall detection efficiency for the grooved cathode when compared to a cathode with a flat surface. Both the experimental results and the predictions of the GEANT4 model suggests that a 5-counter detector stack with coated grooved cathodes has the same efficiency as a 7-counter stack with flat cathodes. The reduction in the number of counters in the stack without altering the detection efficiency will prove highly beneficial for large-area position-sensitive detectors for neutron scattering applications, for which the cost-effective manufacturing of the detector and associated readout electronics is an important objective. The proposed detector concept could be a technological option for one of the new chopper spectrometers and other instruments planned to be built at the future European Spallation Source in Sweden. These results with macrostructured cathodes generally apply not just to MWPCs but to other gaseous detectors as well.Comment: 14 pages, 9 figure

Projectile fragmentation of 129Xe at Elab=790 AMeV

We have measured production yields and longitudinal momentum distributions of projectile-like fragments in the reaction 129Xe + 27Al at an energy of Elab=790 AMeV. Production cross sections higher than expected from systematics were observed for nuclei in the neutron-deficient tails of the isotopic distributions. A comparison with previously measured data from the fragmentation of 136Xe ions shows that the production yields strongly depend on the neutron excess of the projectile with respect to the line of beta-stability. The momentum distributions exhibit a dependence on the fragment neutron-to-proton ratio in isobaric chains, which was not expected from systematics so far. This can be interpreted by a higher excitation of the projectile during the formation of neutron-deficient fragments.Comment: 21 pages, 8 figures, 1 tabl

The High-Acceptance Dielectron Spectrometer HADES

HADES is a versatile magnetic spectrometer aimed at studying dielectron production in pion, proton and heavy-ion induced collisions. Its main features include a ring imaging gas Cherenkov detector for electron-hadron discrimination, a tracking system consisting of a set of 6 superconducting coils producing a toroidal field and drift chambers and a multiplicity and electron trigger array for additional electron-hadron discrimination and event characterization. A two-stage trigger system enhances events containing electrons. The physics program is focused on the investigation of hadron properties in nuclei and in the hot and dense hadronic matter. The detector system is characterized by an 85% azimuthal coverage over a polar angle interval from 18 to 85 degree, a single electron efficiency of 50% and a vector meson mass resolution of 2.5%. Identification of pions, kaons and protons is achieved combining time-of-flight and energy loss measurements over a large momentum range. This paper describes the main features and the performance of the detector system

男子技巧“双重倒立坠落成颈上倒立”高难创新动作的可行性分析

将现役世界冠军作为研究对象,采用文献资料法和专家访问法,对此动作的创新性和动作性质进行了较为深入的研究和探讨,得出的结论为:一方面,此动作不仅完全具备作为难度储备动作的条件,即超前性和创新性,而且还为继续开发此类新的超高难创新系列动作奠定基础;另一方面,此动作性质的“特殊性”为拓宽技巧领域的动作范围和丰富动作形式创造了先决条件,在世界大赛中运用具有一定的可行性

Layout and performance of the polarizing guide system for the J-NSE spectrometer at the FRM II

The neutron spin-echo instrument, J-NSE, that has been moved from the ELLA guide hall at the FRJ-2 in Julich to the guide hall of the new FRM II reactor, needs an intense beam of polarized neutrons. Polarization of the short wavelengths is achieved in a bent section of about 8 m and radius 160 m, with a m = 3 FeSi multilayer coating. Due to the total reflection of Fesi, longer wavelengths (lambda similar or equal to 10-20 (A) over circle) pass unpolarized and need an additional short polarizer at the entrance of the instrument. After the bent section within a 10 m straight guide section a turn of vertical polarization to longitudinal guide field is performed and a selector is inserted. Then about 10m of tapered Ni-58 covered guide follows, which end with a cross-section of 60 x 60 mm(2). We present the design criteria and first measurements on the performance of this guide concept. (c) 2007 Elsevier B.V. All rights reserved

Geant4 based simulations for novel neutron detector development

A Geant4-based Python/C++ simulation and coding framework, which has been developed and used in order to aid the R&D efforts for thermal neutron detectors at neutron scattering facilities, is described. Built upon configurable geometry and generator modules, it integrates a general purpose object oriented output file format with meta-data, developed to facilitate a faster turn-around time when setting up and analysing simulations. Also discussed are the extensions to Geant4 which have been implemented in order to include the effects of low-energy phenomena such as Bragg diffraction in the polycrystalline support materials of the neutron detectors. Finally, an example application of the framework is briefly shown