A MWPC with a cathode coupled delay line read-out as radioactivity detector for DNA repair studies

A non selective method for the isolation of DNA repair-deficient mutants in mammalian cells is discussed. The method requires radioactive labelling of the short DNA sequences synthesized during repair of damaged regions. Mutants should be recognized by the absence of radioactive incorporation into thier DNA. A multiwire proportional chamber (MWPC) is proposed as a suitable radioactivity detector. The performance of a MWPC prototype with a cathode coupled delay line read-out is described and is shown to be adequate for this application. The main avaantages of a MWPC are reviewed with respect to other methods used for β− radioactivity counting of biological samples, such as liquid scintillators or autoradiography: the proposed detection method is non destructive for the cells, which are being kept alive for further biological studies; furthermore many cell clones can be screened within a reasonable time

ELECTRONIC AUTORADIOGRAPHY OF LIVING HUMAN-CELLS WITH A MWPC

Abstract The use of multiwire proportional chamber (MWPC) for mapping the incorporation of a radioactive precursor of DNA biosynthesis by aggregates of cells is discussed. The resolving power, sensitivity and linearity of the developed system are shown, together with preliminary "electronic autoradiograms" of 14C-labelled cells

DNA-repair deficient cells identification with a multiwire proportional chamber

Abstract Tritium labelled mammalian cells with defective repair of UV-induced damage have been identified by using a MWPC as a position sensitive radioactivity detector. The resolving power (≅1.5mm FWHM), sensitivity (≅101Bq/cm2), efficiency (≅10%) and uniformity (≅4%) of the detection system are shown and "electronic autoradiograms" of normal and mutant cultures are presented; cells, rescued after the radioactivity measurement, retain their cloning ability

Gas pixel detectors

Abstract With the Gas Pixel Detector (GPD), the class of micro-pattern gas detectors has reached a complete integration between the gas amplification structure and the read-out electronics. To obtain this goal, three generations of application-specific integrated circuit of increased complexity and improved functionality has been designed and fabricated in deep sub-micron CMOS technology. This implementation has allowed manufacturing a monolithic device, which realizes, at the same time, the pixelized charge-collecting electrode and the amplifying, shaping and charge measuring front-end electronics of a GPD. A big step forward in terms of size and performances has been obtained in the last version of the 0.18 μm CMOS analog chip, where over a large active area of 15×15 mm 2 a very high channel density (470 pixels/mm 2 ) has been reached. On the top metal layer of the chip, 105,600 hexagonal pixels at 50 μm pitch have been patterned. The chip has customable self-trigger capability and includes a signal pre-processing function for the automatic localization of the event coordinates. In this way, by limiting the output signal to only those pixels belonging to the region of interest, it is possible to reduce significantly the read-out time and data volume. In-depth tests performed on a GPD built up by coupling this device to a fine pitch (50 μm) gas electron multiplier are reported. Matching of the gas amplification and read-out pitch has let to obtain optimal results. A possible application of this detector for X-ray polarimetry of astronomical sources is discussed

The silicon-strip tracker of the Gamma ray Large Area Space Telescope

Abstract The Gamma ray Large Area Space Telescope (GLAST) is an astro-particle mission that will study the mostly unexplored, high energy ( 20 MeV – 1 TeV ) spectrum of photons coming from active sources in the universe. Construction of the GLAST silicon tracker, by far the largest ever built for a space mission, is now well on the way, as it is scheduled for launch by NASA in autumn 2006. We report on the basic technology adopted for the silicon detectors, particularly in connection to their use in space, on the first results of sensors testing and on the status of tracker assembly

X-ray polarimetry with a micro pattern gas detector with pixel readout

In astronomy there are basically four kinds of observations to extract the information carried by electromagnetic radiation: photometry, imaging, spectroscopy, and polarimetry. By optimal exploitation of the first three techniques, X-ray astronomy has been able to unveil the violent world of compact high-energy sources. Here, we report on a new instrument that brings high efficiency also to X-ray polarimetry, the last unexplored field of X-ray astronomy. It will then be possible to resolve the internal structures of compact objects, which otherwise would remain inaccessible even to X-ray interferometry. The new instrument derives the polarization information from the track of the photoelectron imaged by a finely subdivided gas pixel detector. Its great improvement of sensitivity (at least two order of magnitude) will allow direct exploration of the most dramatic objects of the X-ray sky

Gas Pixel Detectors for X-ray Polarimetry applications

We discuss a new class of Micro Pattern Gas Detectors, the Gas Pixel Detector (GPD), in which a complete integration between the gas amplification structure and the read-out electronics has been reached. An Application-Specific Integrated Circuit (ASIC) built in deep sub-micron technology has been developed to realize a monolithic device that is, at the same time, the pixelized charge collecting electrode and the amplifying, shaping and charge measuring front-end electronics. The CMOS chip has the top metal layer patterned in a matrix of 80 micron pitch hexagonal pixels, each of them directly connected to the underneath electronics chain which has been realized in the remaining five layers of the 0.35 micron VLSI technology. Results from tests of a first prototype of such detector with 2k pixels and a full scale version with 22k pixels are presented. The application of this device for Astronomical X-Ray Polarimetry is discussed. The experimental detector response to polarized and unpolarized X-ray radiation is shown. Results from a full MonteCarlo simulation for two astronomical sources, the Crab Nebula and the Hercules X1, are also reported.Comment: 16 pages, 20 figures, accepted for publication in Nuclear Instruments and Methods in Physics Research Section

The On-orbit Calibrations for the Fermi Large Area Telescope

The Large Area Telescope (LAT) on--board the Fermi Gamma ray Space Telescope began its on--orbit operations on June 23, 2008. Calibrations, defined in a generic sense, correspond to synchronization of trigger signals, optimization of delays for latching data, determination of detector thresholds, gains and responses, evaluation of the perimeter of the South Atlantic Anomaly (SAA), measurements of live time, of absolute time, and internal and spacecraft boresight alignments. Here we describe on orbit calibration results obtained using known astrophysical sources, galactic cosmic rays, and charge injection into the front-end electronics of each detector. Instrument response functions will be described in a separate publication. This paper demonstrates the stability of calibrations and describes minor changes observed since launch. These results have been used to calibrate the LAT datasets to be publicly released in August 2009.Comment: 60 pages, 34 figures, submitted to Astroparticle Physic