The Nuclear Compton Telescope (NCT) is a balloon-borne soft
gamma-ray (0.2MeV-10MeV) telescope designed to study astrophysical
sources of nuclear line emission and polarization. A prototype
instrument was successfully launched from Ft. Sumner, NM on June 1,
2005. The NCT prototype consists of two 3D position sensitive
High-Purity-Germanium (HPGe) strip detectors fabricated with
amorphous Ge contacts. The novel ultra-compact design and new
technologies allow NCT to achieve high efficiencies with excellent
spectral resolution and background reduction. Energy and positioning calibration data was acquired pre-flight in Fort Sumner, NM after the full instrument integration. Here we discuss our calibration techniques and results, and detector efficiencies. Comparisons with simulations are presented as well.
We flew a prototype of the Nuclear Compton Telescope (NCT) on a high altitude balloon from Fort Sumner, New Mexico on 2005 June 1. The NCT prototype is a soft gamma-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and gamma-ray polarization. Our program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope satellite, while studying gamma-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. The NCT prototype utilizes two, 3D imaging germanium detectors (GeDs) in a novel, ultra-compact design optimized for nuclear line emission (0.5-2 MeV) and polarization in the 0.2-0.5 MeV range. Our prototype flight was a critical test of the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes.
We are developing a 2-detector high resolution Compton telescope utilizing 3D imaging germanium detectors (GeDs) to be flown as a balloon payload in Spring 2004. This instrument is a prototype for the larger Nuclear Compton Telescope (NCT), which utilizes 12-GeDs. NCT is a balloon-borne soft γ-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and γ-ray polarization. The NCT program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope, while studying γ-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. NCT has a novel, ultra-compact design optimized for studying nuclear line emission in the critical 0.5-2 MeV range, and polarization in the 0.2-0.5 MeV range. The prototype flight will critically test the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes. In this paper we present the design and preliminary results of laboratory performance tests of the NCT flight electronics.
Our collaboration is developing a 2-detector prototype high resolution Compton telescope utilizing 3D imaging germanium detectors (GeDs) for a test balloon flight in Spring 2003. This instrument is a prototype for a full 12-GeD instrument, the Nuclear Compton Telescope. NCT is a balloon-borne soft gamma-ray (0.2-15 MeV) telescope designed to study astrophysical sources of nuclear
line emission and polarization. The NCT program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope, while studying gamma-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. NCT has a novel, ultra-compact design optimized for studying nuclear line emission in the critical 0.5-2 MeV range, and polarization in the 0.2-0.5 MeV range. This prototype flight will critically test the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes. We present the design and expected performance of this prototype NCT instrument.
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a
NASA Small Explorer satellite designed to study hard x-ray and
gamma-ray emission from solar flares. In addition, its
high-resolution array of germanium detectors can see photons
from high-energy sources throughout the Universe. Here we discuss
the various algorithms necessary to extract spectra, lightcurves,
and other information about cosmic gamma-ray bursts, pulsars,
and other astrophysical phenomena using an unpointed, spinning
array of detectors. We show some preliminary results and discuss
our plans for future analyses. All RHESSI data are public, and
scientists interested in participating should contact the
principal author.
KEYWORDS: Sensors, Calibration, Germanium, Electrodes, Spectral resolution, Monte Carlo methods, Prototyping, Electronics, Telescopes, Signal detection
We have developed germanium detector technologies for use in the Nuclear Compton Telescope (NCT) - a balloon-borne soft γ-ray (0.2-10 MeV) telescope to study astrophysical sources of nuclear line emission and polarization. The heart of NCT is an array of twelve large volume cross strip germanium detectors, designed to provide 3-D positions for each photon interaction with ~1mm resolution while maintaining the high spectral resolution of germanium. Here we discuss the detailed performance of our prototype 19x19 strip detector, including laboratory tests, calibrations, and numerical simulations. In addition to the x and y positions provided by the orthogonal strips, the interaction depth (z-position) in the detector is measured using the relative timing of the anode and cathode charge collection signals. We describe laboratory calibrations of the depth discrimination using collimated sources with different characteristic energies, and compare the measurements to detailed Monte Carlo simulations and charge collection routines tracing electron-hole pairs from the interaction site to the electrodes. We have also investigated the effects of charge sharing and loss between electrodes, and present these in comparison to charge collection simulations. Detailed analysis of strip-to-strip uniformity in both efficiency and spectral resolution are also presented.
The scientific objectives, status, and future instrumental requirements of high energy X-ray astronomy (20 to 200 keV) are discussed. Two particularly compelling requirements are: (1) an improvement in sensitivity to a level of about 5 microCrab and (2) a survey of the sky at a sensitivity of about 0.1 milliCrab, which will discover and characterize about 10,000 new sources. The first requirement can be fulfilled by imaging telescopes that use large-area focusing X-ray mirrors, which are effective over 5-30 arcminute fields, and the second requirement can be met by arrays of large area coded mask imagers with wide fields, about 50 deg. Multilayer mirror and CdZnTe detector technology now in development offers the potential to meet these objectives. Position-sensitive CdZnTe detectors are well-suited to both of these imaging techniques, and instrument concepts that use these detectors are described. Detectors with pixel readout are better suited for focusing telescopes, and those with crossed-strip readout are better suited for coded mask imagers. Technical aspects of these detectors are discussed. Recent work at UCSD and WU on CdZnTe strip detectors is described in detail. Studies with small, 40 micron, X-ray beams have mapped a crossed-strip detector's spatial response with fine spatial resolution.
The scientific objectives and future requirements of high energy x-ray astronomy are discussed and concepts for imaging instruments based on CdZnTe detectors and coded masks are reviewed. An instrument concept based on CdZnTe strip detectors, HEXIS, is described in detail. Technical requirements for large area CdZnTe strip detectors are discussed and recent work at UCSD and WU on the capabilities of CdZnTe strip detectors is described in detail. Studies with small, approximately 50 micron beams demonstrate that crossed strip detectors have good properties for both spatial and spectral measurements.
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