The Upcoming Long Duration Balloon Flight of the Nuclear Compton Telescope Mark E. Bandstra, Eric Bellm, Steven E. Boggs, Jason D. Bowen, Daniel Perez-Becker, Cornelia B. Wunderer, Andreas Zoglauer, Mark Amman, Paul N. Luke, Hsiang-Kuang Chang, Jeng-Lun Chiu, Jau-Shian Liang, Yuan-Hann Chang, Zong-Kai Liu, Chih-Hsun Lin, Minghuey A. Huang, Pierre Jean Abstract—The Nuclear Compton Telescope (NCT) is a balloon- borne soft γ-ray (0.2 MeV–10 MeV) telescope designed to study astrophysical sources of nuclear line emission and polarization. A prototype instrument was successfully launched from Fort Sumner, New Mexico on June 1, 2005. The NCT prototype consisted of two 3D position sensitive high-purity germanium strip detectors (GeDs) fabricated with amorphous Ge contacts. We are currently working toward two balloon flights: another conventional balloon flight from Fort Sumner, New Mexico in September 2008, and a long-duration balloon flight (LDBF) from Alice Springs, Australia in December 2009. The NCT instrument is being upgraded to include all twelve planned GeDs. The electronics for all twelve detectors have been redesigned for smaller size, lower power consumption, and lower noise, and are now being fabricated and tested. Here we present our current progress in preparing for the flights. I. I NTRODUCTION T HE Nuclear Compton Telescope (NCT) is a balloon- borne soft γ -ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and γ - ray polarization (see, e.g., [1]–[4]). It employs a novel Comp- ton telescope design (Fig. 1), utilizing twelve high spectral resolution germanium detectors (GeDs) with the ability to record in three dimensions the location of each individual photon interaction. Tracking individual interactions serves three purposes: imaging the sky using Compton imaging tech- niques, measuring polarization, and very effectively reducing background. The entire set of detectors and their cryostat are enclosed inside an active BGO well (Fig. 2), giving an overall field of view of 3.2 sr (although a collimator will be added for the flight, reducing the field of view; see Section IV). The instrument is mounted in a pointed, autonomous balloon platform (gondola). NCT is designed to optimize sensitivity to nuclear line emission over the crucial 0.5-2 MeV range, and sensitivity to polarization in the 0.2-0.5 MeV range. M. E. Bandstra, E. Bellm, S. E. Boggs, J. D. Bowen, D. Perez-Becker, C. B. Wunderer, and A. Zoglauer are at the University of California Space Sciences Laboratory, Berkeley, CA. M.Amman and P. N. Luke are at Lawrence Berkeley National Laboratory, Berkeley, CA H.-K. Chang, J.-L. Chiu, and J.-S. Liang are at National Tsing Hua University, Taiwan Y.-H. Chang and Z.-K. Liu are at National Central University, Taiwan C.-H. Lin is at the National Space Organization (NSPO), Taiwan M. A. Huang is at National United University, Taiwan P. Jean is at Centre d’Etude Spatiale des Rayonnements (CESR), Toulouse, France (M.E.B.’s email: bandstra@ssl.berkeley.edu) Fig. 1. The heart of NCT is an array of 12 cross-strip GeDs with 3D position resolution, excellent spectroscopy, sensitivity to γ-ray polarization, and high efficiency. The prototype NCT flew from the National Scientific Bal- loon Facility (NSBF, now Columbia Scientific Balloon Facility – CSBF) site in Fort Sumner, New Mexico on June 1, 2005. The flight lasted 6 hours with the instrument at approximately 40 km altitude. Due to the relatively short flight and a malfunctioning of the pointing system, limited scientific data was obtained. However, with the prototype flight we were able both to demonstrate the successful integration of the flight systems and instrument and to qualify NCT for a future long- duration balloon flight (LDBF). More details of the prototype flight can be found in [3], [5]. Two upcoming flights are planned for NCT in 2008 and 2009. The first flight, planned for September 2008 from Fort Sumner, New Mexico, will be a conventional balloon flight similar to the prototype flight, but will focus on observing northern hemisphere γ -ray point sources like the Crab pulsar and Cygnus X-1. As a conventional flight, its duration will be ∼24-48 hours. The second flight will be an LDBF from Alice Springs, Australia (23.7 ◦ S, 133.9 ◦ E) in December 2009. The goal of the LDBF is for a flight duration of 20 days at approximately a 40 km altitude. The flight will focus on observing and mapping diffuse galactic nuclear line emission. 2007 IEEE Nuclear Science Symposium Conference Record N59-3 1-4244-0923-3/07/$25.00 ©2007 IEEE. 2532