Imaging of gamma rays with the WINKLER high-resolution germanium spectrometer

Abstract

The WINKLER spectrometer is a matrix of nine highpurity n-type germanium detectors developed for astrophysical observations and terrestrial radiation monitoring. The spectrometer has been fitted with a set of modulation collimator grids designed for imaging hard X-ray and gamma-ray sources by the Mertz, Nakano, and Kilner method. This technique employs a pair of gridded collimators in front of each detector with the number of grid bars varying from one to N, where N is the number of detectors. When the collimator pairs are rotated through a full 360-degree angular range, the detector signals provide the information for a two-dimensional band-limited Fourier reconstruction of orderN. Tests of the spectrometer with single and multiple point sources as well as continuous source distributions are reported. The spectrometer field-of-view is 20 degrees, and the observed FWHM of the point spread function is 1.6 degrees, in good agreement with simulation results. Images have been obtained for gamma-ray energies from 60 keV to 1.3 MeV, although transmission through the grids reduces contrast at the higher energies. Potential capabilities of the spectrometer for locating the position of single point sources or resolving structure in closely spaced source distributions are discussed, as well as proposed upgrades to improve angular resolution.

3 Semiconductor Detectors

“…It can be better than 1.8 keV for very good large volume detectors. Detection efficiencies of more than 25% (as compared with a 3" χ 3" Nal(Tl) scintillation counter for 1.33 MeV γ-rays from a 60 Co source placed at 25 cm in front of the detector) have been measured for detectors of at least 100 cm 3 Spectrometry of charged particles with thin entrance window Ge(Li) detectors has been limited to particles whose range does not exceed about one centimetre. Attempts to detect protons, deuterons or α-particles in the range 40-160 MeV by using side-entry Ge(Li) counters have shown resolution losses due to the presence of a thick surface dead layer [24],…”

“…Starting with the initial point contact diode and p-n junctions, the main developments have been concerned with lithium compensated crystals (Ge (Li)) and more recently high purity material (HP-Ge). Present evolutions are oriented towards the preparation of germanium-based multidetector arrays involving a great number of large volume high purity counters leading to high detection efficiency and high energy resolution γ-ray imaging [2][3][4]. Gammasphere, Eurogam or Euroball programs represent the most advanced projects in this field for nuclear physics.…”

Dual-Particle Imaging Performance of a Cs2LiYCl6:Ce (CLYC)-Based Rotational Modulation Collimator (RMC) System

“…In comparison to common radiation imagers, the RMC has the advantage of not requiring a position-sensitive detector, which is a main cause of the complexity and high fabrication cost. RMC technique has been used on several missions for observing astronomical sources of gamma rays [16][17][18]. Since then, the RMC imaging system, which was used in the field of astronomy (far-field imaging), has had its application scope expanded to include homeland security.…”