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 m<sup>3</sup> 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.
Progress in high-energy gamma-ray science has been dramatic since the launch of INTEGRAL, AGILE and FERMI.
These instruments, however, are not optimized for observations in the medium-energy (~0.3< E<sub>γ</sub> < ~200 MeV) regime
where many astrophysical objects exhibit unique, transitory behavior, such as spectral breaks, bursts, and flares. We
outline some of the major science goals of a medium-energy mission. These science goals are best achieved with a
combination of two telescopes, a Compton telescope and a pair telescope, optimized to provide significant improvements
in angular resolution and sensitivity. In this paper we describe the design of the Advanced Energetic Pair Telescope
(AdEPT) based on the Three-Dimensional Track Imager (3-DTI) detector. This technology achieves excellent, mediumenergy
sensitivity, angular resolution near the kinematic limit, and gamma-ray polarization sensitivity, by high resolution
3-D electron tracking. We describe the performance of a 30×30×30 cm<sup>3</sup> prototype of the AdEPT instrument.
The Neutron Imaging Camera (NIC) is based on the Three-dimensional Track Imager (3_DTI) technology developed at
GSFC for gamma-ray astrophysics applications. The 3-DTI, a large volume time-projection chamber, provides accurate,
~0.4 mm resolution, 3-D tracking of charged particles. The incident direction of fast neutrons, En > 0.5 MeV, are
reconstructed from the momenta and energies of the proton and triton fragments resulting from 3He(n,p)3H interactions
in the 3-DTI volume. The performance of the NIC from laboratory is presented.
We describe a gamma-ray imaging camera (GIC) for active interrogation of explosives being developed by
NASA/GSFC and NSWC/Carderock. The GIC is based on the
Three-dimensional Track Imager (3-DTI) technology
developed at GSFC for gamma-ray astrophysics. The 3-DTI, a large volume time-projection chamber, provides
accurate, ~0.4 mm resolution, 3-D tracking of charged particles. The incident direction of gamma rays, E > 6 MeV, are
reconstructed from the momenta and energies of the electron-positron pair resulting from interactions in the 3-DTI
volume. The optimization of the 3-DTI technology for this specific application and the performance of the GIC from
laboratory tests is presented.
The high-energy antimatter telescope (HEAT) instrument has been flown successfully by high-altitude balloon in 1994 and 1995, in a configuration optimized for the detection and identification of cosmic-ray electrons and positrons at energies from about 1 GeV up to 50 GeV and beyond. It consists of a two-coil superconducting magnet and a precision drift-tube tracking hodoscope, complemented with a time-of-flight system, a transition radiation detector and an electromagnetic shower counter. We review the design criteria for optimal e<SUP>+/- </SUP> detection and identification, and assess the instruments' performance and background rejection during its first two flights. We also review the adaptation of HEAT for measurements of high-energy cosmic- ray antiprotons and for isotopic composition studies.