Abstract of my Master's Thesis
Feasibility Study of SONTRAC - a Neutron Tracking Telescope for Solar, Atmospheric and other Applications
University of New Hampshire , Space Science Center , Dec. 1997
The SONTRAC Solar Neutron TRACking telescope is designed to measure neutrons in the energy range of 20 - 250 MeV in order to obtain temporal and spectral information about high energy protons produced by solar flares. The detector consists of a block of organic plastic scintillating fibers stacked in orthogonal layers and viewed by image intensified CCD cameras. Neutrons are detected through neutron-proton double scatters in the scintillating fiber block. Neutron energies and incident directions can be determined from stereoscopic images of the scintillation tracks from recoil protons. The SONTRAC detector is also capable of measuring the incident direction and energy of gamma rays above 20 MeV by imaging tracks of electron-positron pairs.
A small prototype of the detector designed for a proof-of-concept study has been operational at UNH since April 1997. The core of the prototype is a 12.7 x 12.7 x 100 mm scintillating fiber bundle. The fibers are all parallel, therefore only 2-D imaging is possible. The prototype was exposed to 14 MeV neutrons at SDSU. The resulting images served as a first proof of concept. More detailed calibrations using neutrons between 14 and 30 MeV as well as 20 - 35 MeV protons were done at the cyclotron facility at UC Davis. In addition, we recorded track images of minimum ionizing cosmic-ray muons.
The proton calibrations indicate a proton energy resolution of about 1.5 MeV for 30 MeV protons. The Bragg peak can be detected, allowing one to determine the proton direction (in addition to orientation) from the track images. The results of the neutron measurements are consistent with the expectations; but a detailed analysis is complicated because of the prototype's restriction to 2-D imaging. The muon images demonstrate sufficient sensitivity of the detector to image the tracks from the highest energy protons of interest (~200 MeV), as well as tracks from relativistic electron-positron pairs. We present predicted detection efficiencies for neutrons and gamma-rays as well as predicted angular resolution for neutron detection.
Finally, we discuss other applications for this detector concept, including atmospheric physics, the GLAST concept, nuclear waste monitoring and imaging for proton therapy.