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Yang, G.

Publications and source records attributed to Yang, G..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Growth and characterization of detector-grade CdMnTe by the vertical Bridgman Technique

Here, we grew Cd1-xMnxTe crystals with a nominal Mn concentration of 5% by the vertical Bridgman growth technique. The compositional variation along the length of the grown ingot was studied by powder X-ray diffraction. The composition was found to be uniform along the growth direction. The achieved resistivity was 1-2.5 x10 10 ohm-cm with a mobility-lifetime (μτ) product value for electrons of ~1.7x10 -3 cm 2 /V. An energy resolution of ~7.5% at 662 keV was achieved or a 9-mm long Frisch grid detector fabricated from an ingot grown using as-received starting materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A 4 x 4 array module of position-sensitive virtual Frisch-grid CdZnTe detectors for gamma-ray imaging spectrometers

Arrays of position-sensitive virtual Frisch-grid CdZnTe (CZT) detectors offer an economical approach to making high efficiency and high energy resolution gamma cameras for spectroscopy and imaging of radioactive sources. There are many application areas for such instruments including gamma-rays astronomy, medical and industrial imaging, nonproliferation and nuclear safeguards. We present the test results from a 4x4 array module coupled to the front-end ASIC. The array houses 16 detectors made of 6x6x20 mm 3 CZT crystals. Each crystal is encapsulated inside an ultrathin polyester shell and furnished with four 5-mm-wide charge-sensing pads placed near the anode on each side of the detector. The pad’s signals are used to measure X-Y coordinates while the cathode signals give the interaction depths (Z coordinates). Combined together the signals provide 3D position information of the interaction points which can be used to correct the detector response non-uniformity. This allows developers to use standard grade (unselected) CZT crystals while retaining high spectroscopic performance comparable with that of the H3D pixelated detectors. The array’s design provides flexibility to replace individual detectors and extend their sizes, potentially increasing upwards of 4 cm in height. We started development of position-sensitive VFG detectors several years ago and today this technology has reached a high-maturity level and is ready to use in practical applications.

3D charge-loss correction↗
DOE OSTI2018

Direct detection of MeV-scale dark matter utilizing germanium internal amplification for the charge created by the ionization of impurities

Light, MeV-scale dark matter (DM) is an exciting DM candidate that is undetectable by current experiments. A germanium (Ge) detector utilizing internal charge amplification for the charge carriers created by the ionization of impurities is a promising new technology with experimental sensitivity for detecting MeV-scale DM. We analyze the physics mechanisms of the signal formation, charge creation, charge internal amplification, and the projected sensitivity for directly detecting MeV-scale DM particles. We present a design for a novel Ge detector at helium temperature (~4 K) enabling ionization of impurities from DM impacts. With large localized E-fields, the ionized excitations can be accelerated to kinetic energies larger than the Ge bandgap at which point they can create additional electron–hole pairs, producing intrinsic amplification to achieve an ultra-low energy threshold of ~0.1 eV for detecting low-mass DM particles in the MeV scale. Correspondingly, such a Ge detector with 1 kg-year exposure will have high sensitivity to a DM-nucleon cross section of ~5 × 10 -45 cm 2 at a DM mass of ~10 MeV/c 2 and a DM-electron cross section of ~ 5 × 10 -46 cm 2 at a DM mass of 1 MeV/c 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Study of sub-pixel position resolution with time-correlated transient signals in 3D pixelated CdZnTe detectors with varying pixel sizes

Here, we evaluated the sub-pixel position resolution achievable in large-volume CdZnTe pixelated detectors with conventional pixel patterns and for several different pixel sizes: 2.8 mm, 1.72 mm, 1.4 mm and 0.8 mm. Achieving position resolution below the physical dimensions of pixels (sub-pixel resolution) is a practical path for making high-granularity position-sensitive detectors, <100 μμm, using a limited number of pixels dictated by the mechanical constraints and multi-channel readout electronics. High position sensitivity is important for improving the imaging capability of CZT gamma cameras. It also allows for making more accurate corrections of response non-uniformities caused by crystal defects, thus enabling use of standard-grade (unselected) and less expensive CZT crystals for producing large-volume position-sensitive CZT detectors feasible for many practical applications. We analyzed the digitized charge signals from a representative 9 pixels and the cathode, generated using a pulsed-laser light beam focused down to 10 m (650 nm) to scan over a selected 3×3 pixel area. We applied our digital pulse processing technique to the time-correlated signals captured from adjacent pixels to achieve and evaluate the capability for sub-pixel position resolution. As an example, we also demonstrated an application of 3D corrections to improve the energy resolution and positional information of the events for the tested detectors.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Arrays of Position-Sensitive Virtual Frisch-Grid CdZnTe Detectors: Results From a $4\times 4$ Array Prototype

Position-sensitive virtual Frisch-grid (VFG) CdZnTe (CZT) detectors offer a unique capability for correcting the response nonuniformities caused by crystal defects. This allowed us to achieve high energy resolution, while using typical-grade commercial CZT crystals with relaxed requirements to their quality, thus reducing the overall cost of detectors. Another advantage of the VFG detectors is that they can be integrated into arrays and used in small compact hand-held instruments or large-area gamma cameras that will enhance detection capability for many practical applications, including nonproliferation, medical imaging, and gamma-ray astronomy. Here in this paper, we present the results from testing small array prototypes coupled with front-end application-specified integrated circuit. Each detector in the array is furnished with 5-mm-wide charge-sensing pads placed near the anode. The pads signals are converted into XY coordinates, which combined with the cathode signals (for Z coordinates) provide 3-D position information of all interaction points. The basic array consists of a number of detectors grouped into 2×2 subarrays, each having a common cathode made by connecting together the cathodes of the individual detectors. Lastly, these features can significantly improve the performance of detectors while using typical-grade low-cost CZT crystals to reduce the overall cost of the proposed instrument.

3-D position-sensitive virtual Frisch-grid (VFG) d↗
DOE OSTI2017

Black Hole Growth Is Mainly Linked to Host-galaxy Stellar Mass Rather Than Star Formation Rate

We investigate the dependence of black hole accretion rate (BHAR) on host-galaxy star formation rate (SFR) and stellar mass (M {sub *}) in the CANDELS/GOODS-South field in the redshift range of 0.5⩽z<2.0. Our sample consists of ≈18,000 galaxies, allowing us to probe galaxies with 0.1M{sub ⊙}yr{sup −1}≲SFR≲100 M{sub ⊙} yr{sup −1} and/or 10{sup 8}M{sub ⊙}≲M{sub ∗}≲10{sup 11} M{sub ⊙}. We use sample-mean BHAR to approximate long-term average BHAR. Our sample-mean BHARs are derived from the Chandra Deep Field-South 7 Ms observations, while the SFRs and M {sub *} have been estimated by the CANDELS team through spectral energy distribution fitting. The average BHAR is correlated positively with both SFR and M {sub *}, and the BHAR–SFR and BHAR–M {sub *} relations can both be described acceptably by linear models with a slope of unity. However, BHAR appears to be correlated more strongly with M {sub *} than SFR. This result indicates that M {sub *} is the primary host-galaxy property related to supermassive black hole (SMBH) growth, and the apparent BHAR–SFR relation is largely a secondary effect due to the star-forming main sequence. Among our sources, massive galaxies (M{sub ∗}≳10{sup 10}M{sub ⊙}) have significantly higher BHAR/SFR ratios than less massive galaxies, indicating that the former have higher SMBH fueling efficiency and/or higher SMBH occupation fraction than the latter. Our results can naturally explain the observed proportionality between M{sub BH} and M {sub *} for local giant ellipticals and suggest that their M{sub BH}/M{sub ∗} is higher than that of local star-forming galaxies. Among local star-forming galaxies, massive systems might have higher M{sub BH}/M{sub ∗} compared to dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Teaming with Brookhaven National Laboratory

BNL has started growing CdZnTeSe crystals for room-temperature radiation detector applications. The addition of Se to CdTe reduces the concentration of secondary phases and sub-grain boundary networks. The addition of Zn increases the energy band gap. Material characterization to understand the limiting factors of radiation detection material and to improve the properties continues to be a core element of an extensive R&D program at the LBNL’s ALS and BNL’s NSLS-II synchrotron facilities. ALS’s Beamline 3.3.2 is available for 60% of its beamtime and allows us to perform both White Beam X-ray Diffraction Topography and Micron Scale X-ray Detector Mapping. The latter technique is extremely useful when measuring scintillators because it allows us to subtract contributions from the variability in the counting statistics, and also the fluctuations due to delta electrons, and non-proportionality. BNL has recently developed a new type of thermal neutron detector using pad technology in combination with 3 He gas operated in ionization mode. The new detector is used for coded aperture thermal neutron imaging.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗