[show abstract][hide abstract] ABSTRACT: The paper reports the first successful results of a simple new MOS device for injecting electrons at given sites in silicon drift
chambers. The device allows on-line calibration of the time of flight of electrons within the detector, making the reconstruction of their position independent of the temperature-dependent mobility of electrons. Several of these auxiliary devices can be implemented in silicon drift chambers without additional steps in the fabrication process.
[show abstract][hide abstract] ABSTRACT: Differential elliptic flow spectra v2(pT) of \pi-, K0short, p, \Lambda have
been measured at \sqrt(s NN)= 17.3 GeV around midrapidity by the
CERN-CERES/NA45 experiment in mid-central Pb+Au collisions (10% of
\sigma(geo)). The pT range extends from about 0.1 GeV/c (0.55 GeV/c for
\Lambda) to more than 2 GeV/c. Protons below 0.4 GeV/c are directly identified
by dE/dx. At higher pT, proton elliptic flow v2(pT) is derived as a
constituent, besides \pi+ and K+, of the elliptic flow of positive pion
candidates. The retrieval requires additional inputs: (i) of the particle
composition, and (ii) of v2(pT) of positive pions. For (i), particle ratios
obtained by NA49 were adapted to CERES conditions; for (ii), the measured
v2(pT) of negative pions is substituted, assuming \pi+ and \pi- elliptic flow
magnitudes to be sufficiently close. The v2(pT) spectra are compared to
ideal-hydrodynamics calculations. In synopsis of the series \pi- - K0short - p
- \Lambda, flow magnitudes are seen to fall with decreasing pT progressively
even below hydro calculations with early kinetic freeze-out (Tf= 160 MeV)
leaving not much time for hadronic evolution. The proton v2(pT) data show a
downward swing towards low pT with excursions into negative v2 values. The
pion-flow isospin asymmetry observed recently by STAR at RHIC, invalidating in
principle our working assumption, is found in its impact on proton flow
bracketed from above by the direct proton flow data, and not to alter any of
our conclusions. Results are discussed in perspective of recent viscous
dynamics studies which focus on late hadronic stages.
[show abstract][hide abstract] ABSTRACT: The CERES/NA45 experiment at the CERN SPS has previously measurede
- pair production in 160 A.GeV Pb-Au collisions. In the mass regionm > 02 GeV/c2, an enhancement of 2.7±04(stat.)±0.5(syst.) compared to the expectation from known hadronic decay sources was observed. In
the 40 A.GeV data taken in 1999, an enhancement is again found; a preliminary analysis gives an even larger value of 50 ±13(stat.).
The results are compared to theoretical model calculations based on π+π- annihilation with a modified ρ-propagator; they may be related to chiral symmetry restoration.
[show abstract][hide abstract] ABSTRACT: A detector for the X-ray Correlation Spectroscopy (XCS) instrument at the Linac Coherent Light Source (LCLS) in Stanford (CA) is being developed at Brookhaven National Laboratory (BNL). The LCLS is the first operational X-ray free electron laser. It provides extremely bright coherent laser-like X-ray pulses with energy up to 8 keV, shorter than 100 fs and with a repetition rate that will go up to 120 Hz.An ideal detector for XCS experiments should cover a large angular range with high efficiency and provide a proper resolution to resolve the speckle. The requirement for dynamic range is not particularly stringent while a fast readout is needed. In particular, the Charge Pump Detector has to be highly efficient at the energy of 8 keV, provide a dynamic range of 100 photons and a readout noise much better than one photon. The 1024×1024 pixels have to be read within the repetition rate of the laser pulses, that is faster than 8 ms. The pixel size of 56 mum×56 mum is a compromise between charge sharing and small pixel.Working principle and details of the detector will be discussed.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 649:75-77. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: A number of critical active and passive components of optical links have been tested at 77 K or lower temperatures, demonstrating potential development of optical links operating inside the liquid argon time projection chamber (LArTPC) detector cryostat. A ring oscillator, individual MOSFETs, and a high speed 16:1 serializer fabricated in a commercial 0.25-mm siliconon- sapphire CMOS technology continued to function from room temperature to 4.2 K, 15 K, and 77 K respectively. Three types of laser diodes lase from room temperature to 77 K. Optical fibers and optical connectors exhibited minute attenuation changes from room temperature to 77 K. yes yes
Journal of Instrumentation 12/2010; · 1.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present an application-specific integrated circuit (ASIC) for high-resolution x-ray spectrometers (XRS). The ASIC reads out signals from pixelated silicon drift detectors (SDDs). The pixel does not have an integrated field effect transistor (FET); rather, readout is accomplished by wire-bonding the anodes to the inputs of the ASIC. The ASIC dissipates 32 mW, and offers 16 channels of low-noise charge amplification, high-order shaping with baseline stabilization, discrimination, a novel pile-up rejector, and peak detection with an analog memory. The readout is sparse and based on custom low-power tristatable low-voltage differential signaling (LPT-LVDS). A unit of 64 SDD pixels, read out by four ASICs, covers an area of 12.8 cm<sup>2</sup> and dissipates with the sensor biased about 15 mW/cm<sup>2</sup>. As a tile-based system, the 64-pixel units cover a large detection area. Our preliminary measurements at -44°C show a FWHM of 145 eV at the 5.9 keV peak of a <sup>55</sup>Fe source, and less than 80 eV on a test-pulse line at 200 eV.
IEEE Transactions on Nuclear Science 07/2010; · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: The higher density of Germanium (Ge) makes it an ideal candidate for high energy x-ray detectors. The higher mobility of carriers combined with a low effective mass in Ge as compared to Silicon has generated a lot of interest in Ge based devices for high speed devices. However the challenge associated with native oxide makes pixel isolation in a diode array very challenging. Furthermore suitable implants and activation of the implants with temperature constrain is also an issue. We have made a simple Ge diode with Boron and Phosphor as p and n implant. Low temperature grown high k oxide by direct metal sputtering and atomic layer deposition was used. Details of the Ge wafer processing and the effect of different interface layer on the capacitance-voltage characteristics will be discussed.
[show abstract][hide abstract] ABSTRACT: Arrays of Silicon Drift Detectors (SDD) were designed, produced and tested. These arrays are the central part of an X-Ray Spectrometer (XRS) for measuring the abundances of light surface elements (C–Fe) fluoresced by ambient radiation on the investigated celestial object. The basic building element (or cell) of the arrays consists of a single hexagonal SDD. Signal electrons drift toward the center of the hexagon where a very low capacitance anode is located. The hexagonal shape of an individual SDD allows for a continuous covering of large detection areas of various shapes. To match the number of SDD cells with the external Application Specific Integrated Circuit (ASIC), two arrays, one with 16 and another with 64 cells were developed. One side of SDDs, called the window side, is a continuous thin rectifying junction through which the X-ray radiation enters the detector. The opposite side, called the device side contains electron collecting anodes as well as all other electrodes needed to generate the drift field and to sink leakage current produced on Si–SiO2 interface. On both sides of the detector array there is a system of guard rings, which smoothly adjusts the voltage of the boundary cells to the ground potential of the silicon outside the sensitive volume. The drift voltage inside the detector is generated by an implanted rectifying contact, which forms a hexagonal spiral. This spiral produces the main valley where signal electrons drift as well as the voltage divider to produce the drift field. System performance is shown by a spectrum of Mn X-rays produced by the decay of 55Fe.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; 624(2):260-264. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have developed a new method to produce thin-entrance-window Silicon Drift Detectors. To produce the desired thin-entrance-window a double implantation was used. This implantation consists of Boron ions (dose of 1Ã10<sup>14</sup>/cm<sup>2</sup> at 10 keV) plus a second implant of Phosphorus ions (with a dose of 4Ã1012/cm<sup>2</sup> at 50 keV or dose of 9Ã1011/cm<sup>2</sup> at 80 keV) through 500 Â¿ of silicon dioxide. The second Phosphorus implantation compensates for the tail portion of the Boron ion implantation, so that the net Boron ion distribution will result in a thinner Â¿deadÂ¿ silicon layer and an elevated electric field near the silicon surface. We will compare test results from this newly developed thin-window with those from our previous development, where the thin junction was created using a single implantation of Boron ions (dose of 1Ã10<sup>14</sup>/cm<sup>2</sup> at 10 keV) through a 500 Â¿ thick silicon dioxide. All testing was done in the U3C beam line at the National Synchrotron Light Source at Brookhaven National Laboratory.
Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009