Gamma rays from giant molecular clouds

Giant Molecular Clouds (GMCs) are massive, bounded, cool, dense regions containing mostly H2, but also H I, CO, and other molecules. These clouds occupy less than 1 percent of the galactic volume, but are a substantial part of the interstellar mass. They are irradiated by the high energy cosmic rays which are possibly modulated by the matter and magnetic fields within the clouds. The product of cosmic-ray flux and matter density is traced by the emission of high energy gamma-rays. A spherical cloud model is considered and the gamma ray flux from several GMCs within 1 kpc of the sun which should be detectable by the EGRET (Energetic Gamma-Ray Experimental Telescope) instrument on GRO (Gamma Ray Observatory)

The Advanced Energetic Pair Telescope for Gamma-Ray Polarimetry

The Advanced Energetic Pair Telescope (AdEPT), a future NASA/GSFC MIDEX mission, is being developed to perform high-sensitivity medium-energy (5-200 MeV) astronomy and revolutionary gamma-ray polarization measurements. The enabling technology for AdEPT is the Three- Dimensional Track Imager (3-DTI), a large volume gaseous time projection chamber with 2- dimentional micro-well detector (MWD) readout. The low density and high spatial resolution of the 3-DTI allows AdEPT to achieve high angular resolution (~0.5 at 67.5 MeV) and, for the first time, exceptional gamma-ray polarization sensitivity. These capabilities enable a wide range of scientific discovery potential for AdEPT. The key science goals of the AdEPT mission include: 1) Explore fundamental processes of particle acceleration in active astrophysical objects, 2) Reveal the magnetic field configuration of the most energetic accelerators in the Universe, 3) Explore the origins and acceleration of cosmic rays and the Galactic MeV diffuse emission, 4) Search for dark matter in the Galactic center, and 5) Test relativity with polarization measurements. We report on the latest developments of the MWDs for the 3-DTI

Polarimetry in X- and Gamma-Ray Astronomy: The Ultimate Dimension

Polarization has been a powerful diagnostic tool in radio, microwave, and visible astronomy, providing details of photonproduction mechanisms on much smaller scales than can bedirectly imaged or deduced from photon intensity and energyalone. While polarimetry at other these wavebands (radio,microwave, and optical) is an established technique, highenergy astrophysics lags far behind in this respect. Yet polarizationanalysis has the potential of revealing many detailsabout the magnetic fields, geometries, and emission mechanismsfound in high energy emitting sources. Deviations fromspherical symmetry and/or the presence of ordered magneticfields give rise to polarized radiation: some examples includeanisotropy in solar flares, the presence of jets in microquasarsand blazars, accretion disks around stellar and massive blackholes, accreting and rotation-powered pulsars, and beams ingamma-ray bursts. In addition, null polarization detectionsfrom gamma-ray bursts at x-ray energies have been usedas a test of fundamental physics by placing limits on the possibleviolation of Lorentz invariance

The Energetic Gamma-Ray Experiment Telescope (EGRET) Science Symposium

The principle purpose of this symposium is to provide the EGRET (Energetic Gamma-Ray Experiment Telescope) scientists with an opportunity to study and improve their understanding of high energy gamma ray astronomy. The Symposium began with the galactic diffusion radiation both because of its importance in studying galactic cosmic rays, galactic structure, and dynamic balance, and because an understanding of its characteristics is important in the study of galactic sources. The galactic objects to be reviewed included pulsars, bursts, solar flares, and other galactic sources of several types. The symposium papers then proceeded outward from the Milky Way to normal galaxies, active galaxies, and the extragalactic diffuse radiation

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

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

Tissue multifractality and Born approximation in analysis of light scattering: a novel approach for precancers detection

Multifractal, a special class of complex self-affine processes, are under recent intensive investigations because of their fundamental nature and potential applications in diverse physical systems. Here, we report on a novel light scattering-based inverse method for extraction/quantification of multifractality in the spatial distribution of refractive index of biological tissues. The method is based on Fourier domain pre-processing via the Born approximation, followed by the Multifractal Detrended Fluctuation Analysis. The approach is experimentally validated in synthetic multifractal scattering phantoms, and tested on biopsy tissue slices. The derived multifractal properties appear sensitive in detecting cervical precancerous alterations through an increase of multifractality with pathology progression, demonstrating the potential of the developed methodology for novel precancer biomarker identification and tissue diagnostic tool. The novel ability to delineate the multifractal optical properties from light scattering signals may also prove useful for characterizing a wide variety of complex scattering media of non-biological origin

Impact mass flow sensor for monitoring peanut harvest yields

Yield monitoring systems for harvesting machines and methods that can provide yield monitoring of crops are described. Machines include those that pneumatically convey crop through the machine such as peanut harvesting machines. The yield monitoring system includes a force sensor that can be located in conjunction with a duct of the harvesting machine such that impact of the crop materials on an impact plate within the duct will be registered by the force sensor. This registration can be used to determine a mass flow rate for the crop, which can be correlated to yield of the crop. The systems can include additional components such as optical monitors, moisture sensors, and pressure sensors