A Compton telescope for remote location and identification of radioactive material

Authors

James M. Ryan, University of New HampshireFollow
Justin Baker, University of New Hampshire - Main CampusFollow
John R. Macri, University of New Hampshire - Main CampusFollow
Mark L. McConnell, University of New Hampshire - Main CampusFollow
Richard Carande, Neva Ridge Technologies, Inc.

Abstract

The spare detectors from NASA Compton Gamma-Ray Observatory COMPTEL instrument have been reconfigured to demonstrate the capability at ground level to remotely locate and identify sources of g radiation or the movement of material that might shield γ-ray sources. The Gamma-Ray Experimental Telescope Assembly (GRETA) employs two 28 cm diameter scintillation detectors separated by 81 cm: one 8.5 cm thick liquid scintillator detector and one 7.5 cm thick NaI(Tl) detector. The assembly electronics and real-time data acquisition system measures the energy deposits and time-of- flight for each coincident detection and compiles histograms of total energy and incident angle as computed using the kinematics of Compton scattering. The GRETA field of view is a cone with full angle approximately 120°. The sensitive energy range is 0.3 to 2.6 MeV. Energy resolution is ~10% FWHM. The angular resolution, ~19° in the simplified configuration tested, will improve to better than 5° with well-defined enhancements to the data acquisition hardware and data analysis routines. When operated in the mode that was used in space, the instrument is capable of measuring and imaging up to 30 MeV with an angular resolution of 1.5°. The response of the instrument was mapped in the laboratory with 14 Ci ²²Na source 3 m from the instrument. Later, we conducted demonstrations under two measurement scenarios. In one, the remotely located instrument observed an increase of background radiation counts at 1.4 MeV when a large amount of lead was removed from a building and a corresponding decrease when the lead was replaced. In the other scenario, the location and isotope-identifying energy spectrum of a 500 μCi¹³⁷Cs source 3-5 m from the instrument with two intervening walls was determined in less than one minute. We report details of the instrument design and these measurements.

Department

Space Science Center, Physics

Publication Date

4-16-2008

Journal Title

SPIE Proceedings

Publisher

SPIE

Digital Object Identifier (DOI)

10.1117/12.777711

Document Type

Conference Proceeding

Recommended Citation

James M. Ryan ; Justin Baker ; John R. Macri ; Mark L. McConnell and Richard Carande "A Compton telescope for remote location and identification of radioactive material", Proc. SPIE 6943, Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Security and Homeland Defense VII, 694312 (April 16, 2008); doi:10.1117/12.777711; http://dx.doi.org/10.1117/12.777711

Rights

© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering.