Performance of the Micromegas detector in the CAST experiment

The gaseous Micromegas detector designed for the CERN Axion search experiment CAST, operated smoothly during Phase-I, which included the 2003 and 2004 running periods. It exhibited linear response in the energy range of interest (1-10keV), good spatial sensitivity and energy resolution (15-19% FWHM at 5.9keV)as well as remarkable stability. The detector's upgrade for the 2004 run, supported by the development of advanced offline analysis tools, improved the background rejection capability, leading to an average rate 5x10^-5 counts/sec/cm^2/keV with 94% cut efficiency. Also, the origin of the detected background was studied with a Monte Carlo simulation, using the GEANT4 package.Comment: Prepared for PSD7: The Seventh International Conference on Position Sensitive Detectors, Liverpool, United Kingdom, 12-16 Sep. 200

Estimating soil plasticity properties from pedological data

Abstract: A number of pedological soil classification systems have been developed worldwide. These include an internationally accepted system and various national systems, some of which have been incorporated into databases which include maps. Such information is used primarily for agricultural purposes. Various physical and chemical soil properties are used for classifying soils according to these pedological systems. This paper proposes an approach, based on a research project, which may be used to statistically significantly determine the plasticity characteristics of soils from the physical and chemical properties that are used to pedologically classify soils by systems, such as the South African Binomial System. These plasticity characteristics may be used to establish the engineering soil classification groups which may, in turn, be used as a means of rapidly determining the general suitability of areas for proposed developments, particularly during the preliminary stages of transportation route locations and township developments, with a resultant saving of time and money

The effect of site practices on the integrity of large diameter bored piles

In South Africa, concrete in large diameter bored piles is generally placed by discharging a high flow concrete mix directly from the truck mixer and allowing the concrete to fall freely to the base of the pile hole. While certain site practices have been used by piling contractors for years, many engineers are not convinced of their acceptability. This paper discusses the results of an investigation which assessed the effect of site practices on the integrity of cast in-situ bored piles. Such practices include the method of concrete placement and the amount of water and/or loose spoil in the pile hole at the time of casting. The results of this investigation dispel the myth that the free fall placement of concrete in clean, dry pile holes has a detrimental effect on the degree of compaction and compressive strength of the concrete

The influence of aggregate stiffness on the creep of concrete

Abstract: Creep is the time dependant increase in strain of a solid body under sustained stress. In concrete, the negative effects of creep are often responsible for excessive defl ection at service loads which can result in cracking, creep buckling of long columns and loss of prestressing force. While it is conceptually easy to appreciate that the stiffness of the aggregate in concrete will infl uence the magnitude of creep, the extent of this effect across the range of commonly used aggregates in South Africa has not been assessed. This paper discusses the results of an investigation that was aimed at quantifying the infl uence of aggregate stiffness on the measured creep behaviour of plain concrete. The experimental programme included measurements of total creep on concrete specimens of two different strength grades for each of three different but commonly used South African aggregate types (quartzite, granite and andesite). In addition, elastic modulus tests were conducted on cores of the aggregate types assessed. The test results revealed that no clear correlation exists between the creep of concrete and the stiffness..

An assessment of the accuracy of nine design models for predicting creep in concrete

Abstract: Creep of concrete is a complex phenomenon that has proven difficult to model. Nevertheless, for many reinforced and prestressed concrete applications, a reasonably accurate prediction of the magnitude and rate of creep strain is an important requirement of the design process. Although laboratory tests may be undertaken to determine the deformation properties of materials, these are time consuming, often expensive and generally not a practical option. In addition, this is not often an option at the design stage of a project when decisions about the actual concrete to be used have not yet been taken. National design codes therefore rely on empirical prediction models to estimate the magnitude and development of the creep strain. This paper considers the suitability of nine ‘design code type’ creep prediction models when compared with the actual strains measured on a range of concretes under laboratory control conditions. The concretes tested incorporate three aggregate types and two strength grades for each aggregate type. The results are compared with the predictions of creep using models contained in BS 8110 (1985), SABS 0100 (1992), SABS 0100 (1992) modified, ACI 209 (1992), AS 3600 (1988), CEB-FIP (1970, 1978 & 1990), the RILEM Model B3 (1995) methods. The results indicate that the CEB-FIP (1970) and BS 8110 (1985) methods provide suitably accurate predictions over all the concretes tested. These methods yielded overall coefficients of variation of approximately 18 % and 24 %, respectively. The least accurate method was the CEB-FIP (1978) which yielded a coefficient of variation of approximately 96 %. The results of this investigation led to recommending the BS 8110 (1985) model for South African conditions

Performances of Anode-resistive Micromegas for HL-LHC

Micromegas technology is a promising candidate to replace Atlas forward muon chambers -tracking and trigger- for future HL-LHC upgrade of the experiment. The increase on background and pile-up event probability requires detector performances which are currently under studies in intensive RD activities. We studied performances of four different resistive Micromegas detectors with different read-out strip pitches. These chambers were tested using \sim120 GeV momentum pions, at H6 CERN-SPS beam line in autumn 2010. For a strip pitch 500 micrometers we measure a resolution of \sim90 micrometers and a efficiency of ~98%. The track angle effect on the efficiency was also studied. Our results show that resistive techniques induce no degradation on the efficiency or resolution, with respect to the standard Micromegas. In some configuration the resistive coating is able to reduce the discharge currents at least by a factor of 100.Micromegas technology is a promising candidate to replace Atlas forward muon chambers -tracking and trigger- for future HL-LHC upgrade of the experiment. The increase on background and pile-up event probability requires detector performances which are currently under studies in intensive RD activities. We studied performances of four different resistive Micromegas detectors with different read-out strip pitches. These chambers were tested using \sim120 GeV momentum pions, at H6 CERN-SPS beam line in autumn 2010. For a strip pitch 500 micrometers we measure a resolution of \sim90 micrometers and a efficiency of \sim98%. The track angle effect on the efficiency was also studied. Our results show that resistive techniques induce no degradation on the efficiency or resolution, with respect to the standard Micromegas. In some configuration the resistive coating is able to reduce the discharge currents at least by a factor of 100.Comment: "Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 6 figures.

Micromegas in a Bulk

In this paper we present a novel way to manufacture the bulk Micromegas detector. A simple process based on the PCB (Printed Circuit Board) technology is employed to produce the entire sensitive detector. Such fabrication process could be extended to very large area detectors made by the industry. The low cost fabrication together with the robustness of the electrode materials will make it extremely attractive for several applications ranging from particle physics and astrophysics to medicineComment: 6 pages, 4 figure

The influence of slag fineness on the workability of cementitious pastes

Abstract: In South Africa the fineness of Ground Granulated Blastfurnace Slag (GGBS) has remained the same for nearly forty years. In 1999, producers of GGBS were considering the use of relatively finer ground GGBS with a view to improving the strength performance of concrete. The concomitant increase in compressive strength of concrete with an increase in GGBS fineness was confirmed in an extensive investigation carried out by Slagment (Pty) Ltd (Slagment, 1999). However, the effect of relative fineness of South African GGBS on the workability of concrete mixes had not been assessed. This paper discusses the results of an investigation that was aimed at quantifying the influence of finer ground GGBS on the workability of concrete, based on the work of Page (2001). Traditionally, GGBS was ground to a fineness of 3 600 cm2/g, GGBS (3600), and it was proposed to increase its fineness to 5000 cm2/g, GGBS (5 000). The experimental programme included four binder types, namely, CEM I 42,5 alone or in combination with either GGBS (3 600) or GGBS (5 000) or Fly Ash (FA). To eliminate the effects of aggregates on workability, only binder pastes were tested. The results revealed that, as expected, the binder containing the Fly Ash was the most workable. In general, the finer slag, GGBS (5 000), exhibited a higher viscosity and hence lower workability than the GGBS (3 600), due to its relatively higher surface area

CAST microbulk micromegas in the Canfranc Underground Laboratory

During the last taking data campaigns of the CAST experiment, the micromegas detectors have achieved background levels of $\approx 5 \times 10^{-6}$keV$^{-1}$cm$^{-2}$s$^{-1}$ between 2 and 9 keV. This performance has been possible thanks to the introduction of the microbulk technology, the implementation of a shielding and the development of discrimination algorithms. It has motivated new studies towards a deeper understanding of CAST detectors background. One of the working lines includes the construction of a replica of the set-up used in CAST by micromegas detectors and its installation in the Canfranc Underground Laboratory. Thanks to the comparison between the performance of the detectors underground and at surface, shielding upgrades, etc, different contributions to the detectors background have been evaluated. In particular, an upper limit $< 2 \times 10^{-7}$keV$^{-1}$cm$^{-2}$s$^{-1}$ for the intrinsic background of the detector has been obtained. This work means a first evaluation of the potential of the newest micromegas technology in an underground laboratory, the most suitable environment for Rare Event Searches.Comment: 6 pages, 8 figures. To appear in the proceedings of the 2nd International Conference on Technology and Instrumentation for Particle Physics (TIPP 2011

A low background Micromegas detector for the CAST experiment

A low background Micromegas detector has been operating on the CAST experiment at CERN for the search of solar axions during the first phase of the experiment (2002-2004). The detector operated efficiently and achieved a very low level of background rejection ($5\times 10^{-5}$ counts keV$^{-1}$cm$^{-2}$s$^{-1}$) thanks to its good spatial and energy resolution as well as the low radioactivity materials used in the construction of the detector. For the second phase of the experiment (2005-2007), the detector will be upgraded by adding a shielding and including focusing optics. These improvements should allow for a background rejection better than two orders of magnitude.Comment: 6 pages, 3 figures To appear on the proceedings of the 9th ICATPP Conference on AStroparticle, Particle, Space Physics, Detectors and Medical Physics Application