Development of a telescope for medium-energy gamma-ray astronomy

The Advanced Energetic Pair Telescope (AdEPT) is being developed at GSFC as a future NASA MIDEX mission to explore the medium-energy (5–200 MeV) gamma-ray range. The enabling technology for AdEPT is the Three- Dimensional Track Imager (3-DTI), a gaseous time projection chamber. The high spatial resolution 3-D electron tracking of 3-DTI enables AdEPT to achieve high angular resolution gamma-ray imaging via pair production and triplet production (pair production on electrons) in the medium-energy range. The low density and high spatial resolution of 3-DTI allows the electron positron track directions to be measured before they are dominated by Coulomb scattering. Further, the significant reduction of Coulomb scattering allows AdEPT to be the first medium-energy gamma-ray telescope to have high gamma-ray polarization sensitivity. We review the science goals that can be addressed with a medium-energy pair telescope, how these goals drive the telescope design, and the realization of this design with AdEPT. The AdEPT telescope for a future MIDEX mission is envisioned as a 8 m3 active volume filled with argon at 2 atm. The design and performance of the 3-DTI detectors for the AdEPT telescope are described as well as the outstanding instrument challenges that need to be met for the AdEPT mission

Simulated Performance of 3-DTI Gamma-Ray Telescope Concepts

We present Monte Carlo simulations of two astronomical gamma-ray telescope concepts based on the ThreeDimensional Track Imager (3- DTI) detector. The 3-DTI consists of a time projection chamber with two-dimensional, crossedstrip micro-well detector readout. The full three- dimensional reconstruction of charged-particle tracks in the gas volume is obtained from transient digitizers, which record the time signature of the charge collected in the wells of each strip. Such detectors hold great promise for advanced Compton telescope (ACT) and advanced pair telescope (APT) concepts due to the very precise measurement of charged particle momenta that is possible (Compton recoil electrons and electron-positron pairs, respectively). We have investigated the performance of baseline ACT and APT designs based on the 3-DTI detector using simulation tools based on GEANT3 and GEANT4, respectively. We present the expected imaging, spectroscopy, polarimetry, and background performance of each design

Simulation of Heavily Irradiated Silicon Pixel Sensors and Comparison with Test Beam Measurements

Charge collection measurements performed on heavily irradiated p-spray DOFZ pixel sensors with a grazing angle hadron beam provide a sensitive determination of the electric field within the detectors. The data are compared with a complete charge transport simulation of the sensor which includes signal trapping and charge induction effects. A linearly varying electric field based upon the standard picture of a constant type-inverted effective doping density is inconsistent with the data. A two-trap double junction model implemented in the ISE TCAD software can be tuned to produce a doubly-peaked electric field which describes the data reasonably well. The modeled field differs somewhat from previous determinations based upon the transient current technique. The model can also account for the level of charge trapping observed in the data.Comment: 8 pages, 11 figures. Talk presented at the 2004 IEEE Nuclear Science Symposium, October 18-21, Rome, Italy. Submitted to IEEE Transactions on Nuclear Scienc

Medium-Energy Gamma-Ray Astrophysics with the 3-DTI Gamma-Ray Telescope

Gamma-ray observations in the medium energy range (0.50-50.0 MeV) are central to unfolding many outstanding questions in astrophysics. The challenges of medium-energy gamma-ray observations, however, are the low photon statistics and large backgrounds. We review these questions, address the telescope technology requirements, and describe our development of the 3-Dimensional Track Imaging (3-DTI) Compton telescope and its performance for a new mediumenergy gamma-ray mission. The 3-DTI is a large-volume time projection chamber (TPC) with a 2-dimensional gas micro-well detector (MWD) readout

A pair production telescope for medium-energy gamma-ray polarimetry

We describe the science motivation and development of a pair production telescope for medium-energy (∼5–200 MeV) gamma-ray polarimetry. Our instrument concept, the Advanced Energetic Pair Telescope (AdEPT), takes advantage of the Three-Dimensional Track Imager, a low-density gaseous time projection chamber, to achieve angular resolution within a factor of two of the pair production kinematics limit (∼0.6° at 70 MeV), continuum sensitivity comparable with the Fermi-LAT front detector (<3 × 10−6 MeV cm−2 s−1 at 70 MeV), and minimum detectable polarization less than 10% for a 10 mCrab source in 106 s.submittedVersionFil: Hunter, Stanley D. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Bloser, Peter F. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Depaola, Gerardo Osvaldo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Dion, Michael P. Department of Energy. Office of Science. Pacific Northwest National Laboratory; Estados Unidos de América.Fil: DeNolfo, Georgia A. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Hanu, Andrei. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Iparraguirre, Lorenzo Marcos. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Legere, Jason. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Longo, Francesco. Università Degli Studi de Trieste. Dipartimento di fisica; Italia.Fil: McConnell, Mark L. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Nowicki, Suzanne F. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Nowicki, Suzanne F. University of Maryland, Baltimore County. Department of Physics; Estados Unidos de América.Fil: Ryan, James M. University of New Hampshire. Institute for the Study of Earth, Oceans, and Space. Space Science Center; Estados Unidos de América.Fil: Son, Seunghee. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Fil: Son, Seunghee. University of Maryland, Baltimore County. Department of Physics; Estados Unidos de América.Fil: Stecker, Floyd W. National Aeronautics and Space Administration. Goddard Space Flight Center; Estados Unidos de América.Física de Partículas y Campo

The development of silicon detectors for the CMS experiment and future experiments

A hybrid pixel detector will be installed as the inner most layer of the tracking system of the CMS experiment, currently under construction at the Large Hardron Collider (LHC) at CERN (Geneva, Switzerland) to provide high resolution tracking and vertex identification. Due to the severe radiation environment of the LHC, the performance of the sensors must be carefully evaluated up to a fluence of 6 × 1014 1-MeV equivalent neutrons per square centimeter. The sensors were fabricated n on n , which means highly segmented n+ implants with 150 × 100 μm2 pitch are in n-type bulk material and p+ implants are used to isolate pixels. The electrical properties of these sensors has been studied. Studies of charge collection efficiency were carried out with a 1064 nm wavelength laser. Comparisons of charge collection efficiency among different sensor designs is presented. In addition, present and future possibilities for the production of thin silicon detectors are discussed. The electrical characteristics and the performance of thin silicon sensors with thickness of 150 μm, 200 μm, 300 μm respectively have been studied. We show that thin silicon sensors are intrinsically more radiation hard than thicker sensors since there is less bulk, and hence less bulk damage in the former

The Development of silicon detectors for the CMS experiment and future experiments

A hybrid pixel detector will be installed as the inner most layer of the tracking system of the CMS experiment, currently under construction at the Large Hardron Collider (LHC) at CERN (Geneva, Switzerland) to provide high resolution tracking and vertex identification. Due to the severe radiation environment of the LHC, the performance of the sensors must be carefully evaluated up to a fluence of 6 × 1014 1-MeV equivalent neutrons per square centimeter. The sensors were fabricated "n on n", which means highly segmented n+ implants with 150 × 100 μm2 pitch are in n-type bulk material and p+ implants are used to isolate pixels. The electrical properties of these sensors has been studied. Studies of charge collection efficiency were carried out with a 1064 nm wavelength laser. Comparisons of charge collection efficiency among different sensor designs is presented. In addition, present and future possibilities for the production of thin silicon detectors are discussed. The electrical characteristics and the performance of thin silicon sensors with thickness of 150 μm, 200 μm, 300 μm respectively have been studied. We show that thin silicon sensors are intrinsically more radiation hard than thicker sensors since there is less bulk, and hence less bulk damage in the former

Thermodynamic modeling of sulfate attack on carbonated Portland cement blended with blast furnace slag

Sulfate attack on concrete induces volumetric changes resulting in a severe damage to the structure. The structural deterioration can be coupled with carbonation in practice, while such coupled effect is relatively unknown. Herein, thermodynamic calculations are used to study the combined effect of sulfate attack and carbonation on slag-blended Portland cement. The results show that the resultant product of sulfate attack varies according to the cations being used. Gypsum and M-S-H are the major products when Mg2+ is present in the sulfate solution, while ettringite and gypsum are predominant in the presence of Na+. Higher levels of carbonation are found to accelerate the effects of sulfate attack, while slag replacement tends to lower the carbonation degree required for destabilization and precipitation of certain phases

Phytochemical and Antioxidant Characterization of Extracts from Unexplored Medicinal Plants <i>Salix schwerinii</i> and <i>Salix kochiana</i>

For a long time, species of the genus Salix have been widely utilized and studied as medicinal plants; however, the biological activity and phytochemical composition of Salix schwerinii (SS) and S. kochiana (SK) have not been studied at all. This study investigated the antioxidant properties of SS and SK extracts and detected phytochemical compounds in the extracts. The results showed that the antioxidant activities (IC50) of SS extract, SK extract, and ascorbic acid (reference) were as follows, respectively: 169.8, 79.8, and 71.2 μg mL−1 for ABTS cation radical scavenging and 38.4, 26.2, and 9.3 μg mL−1 for DPPH free radical scavenging. The results imply that SK has a high potential as a natural antioxidant. The phytochemical compositions of extracts (mg g−1) were analyzed as follows: SS extracts, 217.7 phenolics (1.54 catechin, 0.86 syringic acid, 0.46 luteolin, and others) and 5.06 salicin; SK extracts, 71.0 phenolics (0.54 catechin, 0.28 myricetin, 0.12 salicylic acid, and others) and 2.11 salicin. Compared to previous studies, the present findings go further to highlight that SS deserves attention as a novel source of salicin. The present study highlights the need for further studies on the aspects of medicinal functions of the extracts, bioprocess design for efficient phytochemical extraction, and applications of bioactive substances