Performance evaluation of novel square-bordered position-sensitive silicon detectors with four-corner readout

We report on a recently developed novel type of large area (62 mm x 62 mm) position sensitive silicon detector with four-corner readout. It consists of a square-shaped ion-implanted resistive anode framed by additional low-resistivity strips with resistances smaller than the anode surface resistance by a factor of 2. The detector position linearity, position resolution, and energy resolution were measured with alpha-particles and heavy ions. In-beam experimental results reveal a position resolution below 1 mm (FWHM) and a very good non-linearity of less than 1% (rms). The energy resolution determined from 228Th alpha source measurements is around 2% (FWHM).Comment: 13 pages, 10 figures, submitted to Nucl. Instr. and Meth.

Toward a Framework for Understanding Object-Oriented Development Practices

This paper describes specific object-oriented system development cases that resulted from interviews with system developers in a variety of large Midwestern firms. Four object-oriented projects are described, reflecting thediversity of the types of systems and types of technology involved. A few typical issues are discussed. This is the first phase of a research project that seeks to understand issues related to object-oriented development. Additional research is planned todefine and measure key development issues, and this will require developing a instrument based on the findings from these cases

Demonstration of a Lightguide Detector for Liquid Argon TPCs

We report demonstration of light detection in liquid argon using an acrylic lightguide detector system. This opens the opportunity for development of an inexpensive, large-area light collection system for large liquid argon time projection chambers. The guides are constructed of acrylic, with TPB embedded in a surface coating with a matching index of refraction. We study the response to early scintillation light produced by a 5.3 MeV alpha. We measure coating responses from 7 to 8 PE on average, compared to an ideal expectation of 10 PE on average. We estimate the attenuation length of light along the lightguide bar to be greater than 0.5 m. The coating response and the attenuation length can be improved; we show, however, that these results are already sufficient for triggering in a large detector

Demonstration and Comparison of Operation of Photomultiplier Tubes at Liquid Argon Temperature

Liquified noble gases are widely used as a target in direct Dark Matter searches. Signals from scintillation in the liquid, following energy deposition from the recoil nuclei scattered by Dark Matter particles (e.g. WIMPs), should be recorded down to very low energies by photosensors suitably designed to operate at cryogenic temperatures. Liquid Argon based detectors for Dark Matter searches currently implement photo multiplier tubes for signal read-out. In the last few years PMTs with photocathodes operating down to liquid Argon temperatures (87 K) have been specially developed with increasing Quantum Efficiency characteristics. The most recent of these, Hamamatsu Photonics Mod. R11065 with peak QE up to about 35%, has been extensively tested within the R&D program of the WArP Collaboration. During these testes the Hamamatsu PMTs showed superb performance and allowed obtaining a light yield around 7 phel/keVee in a Liquid Argon detector with a photocathodic coverage in the 12% range, sufficient for detection of events down to few keVee of energy deposition. This shows that this new type of PMT is suited for experimental applications, in particular for new direct Dark Matter searches with LAr-based experiments

Absorption of Scintillation Light in a 100 ℓ\ell Liquid Xenonγ\gamma Ray Detector and Expected Detector Performance

An 800L liquid xenon scintillation $\gamma$ ray detector is being developed for the MEG experiment which will search for $\mu^+\to\mathrm{e}^+\gamma$ decay at the Paul Scherrer Institut. Absorption of scintillation light of xenon by impurities might possibly limit the performance of such a detector. We used a 100L prototype with an active volume of 372x372x496 mm$^3$ to study the scintillation light absorption. We have developed a method to evaluate the light absorption, separately from elastic scattering of light, by measuring cosmic rays and $\alpha$ sources. By using a suitable purification technique, an absorption length longer than 100 cm has been achieved. The effects of the light absorption on the energy resolution are estimated by Monte Carlo simulation.Comment: 18 pages, 10 figures (eps). Submitted to Nucl. Instr. and Meth.

Design and Performance of the XENON10 Dark Matter Experiment

XENON10 is the first two-phase xenon time projection chamber (TPC) developed within the XENON dark matter search program. The TPC, with an active liquid xenon (LXe) mass of about 14 kg, was installed at the Gran Sasso underground laboratory (LNGS) in Italy, and operated for more than one year, with excellent stability and performance. Results from a dark matter search with XENON10 have been published elsewhere. In this paper, we summarize the design and performance of the detector and its subsystems, based on calibration data using sources of gamma-rays and neutrons as well as background and Monte Carlo simulations data. The results on the detector's energy threshold, energy and position resolution, and overall efficiency show a performance that exceeds design specifications, in view of the very low energy threshold achieved (<10 keVr) and the excellent energy resolution achieved by combining the ionization and scintillation signals, detected simultaneously

Selected reactive oxygen species and antioxidant enzymes in common bean after Pseudomonas syringae pv. phaseolicola and Botrytis cinerea infection

Phaseolus vulgaris cv. Korona plants were inoculated with the bacteria Pseudomonas syringae pv. phaseolicola (Psp), necrotrophic fungus Botrytis cinerea (Bc) or with both pathogens sequentially. The aim of the experiment was to determine how plants cope with multiple infection with pathogens having different attack strategy. Possible suppression of the non-specific infection with the necrotrophic fungus Bc by earlier Psp inoculation was examined. Concentration of reactive oxygen species (ROS), such as superoxide anion (O2 -) and H2O2 and activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were determined 6, 12, 24 and 48 h after inoculation. The measurements were done for ROS cytosolic fraction and enzymatic cytosolic or apoplastic fraction. Infection with Psp caused significant increase in ROS levels since the beginning of experiment. Activity of the apoplastic enzymes also increased remarkably at the beginning of experiment in contrast to the cytosolic ones. Cytosolic SOD and guaiacol peroxidase (GPOD) activities achieved the maximum values 48 h after treatment. Additional forms of the examined enzymes after specific Psp infection were identified; however, they were not present after single Bc inoculation. Subsequent Bc infection resulted only in changes of H2O2 and SOD that occurred to be especially important during plant–pathogen interaction. Cultivar Korona of common bean is considered to be resistant to Psp and mobilises its system upon infection with these bacteria. We put forward a hypothesis that the extent of defence reaction was so great that subsequent infection did not trigger significant additional response

Experimental Bounds on Masses and Fluxes of Nontopological Solitons

We have re-analyzed the results of various experiments which were not originally interested as searches for the Q-ball or the Fermi-ball. Based on these analyses, in addition to the available data on Q-balls, we obtained rather stringent bounds on flux, mass and typical energy scale of Q-balls as well as Fermi-balls. In case these nontopological solitons are the main component of the dark matter of the Galaxy, we found that only such solitons with very large quantum numbers are allowed. We also estimate how sensitive future experiments will be in the search for Q-balls and Fermi-balls.Comment: 19 pages, 7 eps figures, RevTeX, psfig.st

The scintillation and ionization yield of liquid xenon for nuclear recoils

XENON10 is an experiment designed to directly detect particle dark matter. It is a dual phase (liquid/gas) xenon time-projection chamber with 3D position imaging. Particle interactions generate a primary scintillation signal (S1) and ionization signal (S2), which are both functions of the deposited recoil energy and the incident particle type. We present a new precision measurement of the relative scintillation yield \leff and the absolute ionization yield Q_y, for nuclear recoils in xenon. A dark matter particle is expected to deposit energy by scattering from a xenon nucleus. Knowledge of \leff is therefore crucial for establishing the energy threshold of the experiment; this in turn determines the sensitivity to particle dark matter. Our \leff measurement is in agreement with recent theoretical predictions above 15 keV nuclear recoil energy, and the energy threshold of the measurement is 4 keV. A knowledge of the ionization yield \Qy is necessary to establish the trigger threshold of the experiment. The ionization yield \Qy is measured in two ways, both in agreement with previous measurements and with a factor of 10 lower energy threshold.Comment: 8 pages, 9 figures. To be published in Nucl. Instrum. Methods

Self-shielding effect of a single phase liquid xenon detector for direct dark matter search

Liquid xenon is a suitable material for a dark matter search. For future large scale experiments, single phase detectors are attractive due to their simple configuration and scalability. However, in order to reduce backgrounds, they need to fully rely on liquid xenon's self-shielding property. A prototype detector was developed at Kamioka Observatory to establish vertex and energy reconstruction methods and to demonstrate the self-shielding power against gamma rays from outside of the detector. Sufficient self-shielding power for future experiments was obtained.Comment: 8 pages, 8 figure