1. Development of a Large Area Gamma-ray Detector
Camden Ertley, Christopher Bancroft, Peter Bloser, Taylor Connor, Jason Legere, Mark McConnell, and James Ryan
Space Science Department
Abstract:
Experimental Results:
Event Location Algorithm:
We have been working on the development a large area gamma ray detector operating in the keV energy range. The detector design is based on an array of detector modules, each consisting of a scintillator directly coupled to a multi-anode photomultiplier tube. This poster focuses on the development of a computer simulation to aid in the optimization of the detector module design. The simulations have been validated by comparisons with various laboratory data taken with a prototype detector module. Parallel to the simulation effort, an algorithm for the localization of individual gamma ray event is being developed. Using data taken with the prototype detector, a spatial resolution (1σ) in the lateral (x,y) directions of 1-3 mm has been successfully demonstrated.
Algorithms used to determine the position of the gamma ray interaction in the scintillator range from very simply to very complex. We have compared a simple weighted average (WA) algorithm with a more complex artificial neural network (ANN).
57Co Gamma-Ray Source
Anode 4-4
Anode 4-8
Weighted Average:
The WA algorithm computes the average position of the gamma ray interaction using the position of each anode and its signal as a weight. The WA causes information at the edge of the detector to be distorted. The squared weighted average (SWA) uses the square of the signal to correct for some of the edge distortion. The SWA also gives better results for events occurring near the center of the detector.
CASTER:
The Coded Aperture Survey Telescope for Energetic Radiation (CASTER) is one of two proposed concepts for NASA’s Black Hole Finder Probe (BHFP). The goals of this mission are to determine how blacks holes are formed, how they evolve, and to perform an all sky census of black holes throughout the universe over a range of masses and accretion rates. Using an array of anger camera modules, CASTER would have a large, 60 × 120, field of view and be sensitive in the keV energy band. The imager detection plane in each anger camera module consists of an array of multi-anode photomultiplier tubes coupled to a scintillator.
Simulation Results:
122 keV monoenergetic particle source
Reflectivity of scintillator surfaces: 0.98
Artificial Neural Network:
An ANN processes information similar to the way the network of neurons in the brain does. The ANN uses interconnected nodes arranged in layers to solve problems that linear programs cannot. There is an input layer (the signal from each anode), several hidden layers, and an output layer (the calculated position). To be effective, the ANN first needs to be trained using a data set with known solutions. The ANN causes less distortion for events occurring near the edge of the detector.
Coded Aperture Module
Detector Plane
Monte Carlo Simulation:
Collimator
Glass
Teflon
Aluminum Enclosure
Photocathode
Scintillator
Photon Tracks
Gamma Track
Based on the Geant4 software toolkit
50 x 50 x 10 mm scintillator crystal
0.3 mm photon reflector (Teflon) at the front surface and lateral surfaces of the scintillator
1.5 mm glass optically coupled to the LaBr3
Example of an artificial neural network
10 Training Iterations