e-RPT: Ecuadorian radioactive particle tracking. Proposal and evaluation of a low-budget RPT system with GEANT4

Radioactive Particle Tracking (RPT) is a non-invasive measurement technique used to reconstruct the Lagrangian particle field inside a fluid flow. This technique tracks the trajectories followed by radioactive particles that move along the fluid, and it is based on the counts registered by radiation detectors that are placed strategically around the boundaries of the system. The aim of this paper is to develop a low-budget RPT system proposed by the Departamento de Ciencias Nucleares of the Escuela Politécnica Nacional and to generate a GEANT4 model of it for optimizing its design. This system is based on the usage of the minimum amount of radiation detectors required to track a tracer and on the innovative idea of calibrating them with moving particles. To achieve this, energy and efficiency calibrations were performed with a single NaI detector, and their results were compared with the results generated with a GEANT4 model simulation. As a result of this comparison, another methodology was proposed to add the effects of the electronic detector chain in the simulated results by a Detection Correction Factor (DCF) without further C++ coding in GEANT4. Next, the NaI detector was calibrated for moving particles. For this purpose, a single NaI was used in different experiments to analyze the influence of particle velocity, data acquisition systems, and radiation detector position along the x-axis, y-axis, and z-axis. Finally, these experiments were simulated in GEANT4 to improve the digital models. Particle positions were reconstructed based on the generation of Trajectory Spectrum (TS) which gives a specific count rate for each particle position as it moves on the x-axis. The magnitude and shape of TS were compared with DCF corrected simulated data and experimental results. This comparison showed that the variation of detector position along the x-axis changed the shape of TS, while the variation of the location along the y-axis and z-axis reduced the sensitivity of the detector. The existence of an effective zone of the detector location was identified. At this zone, the TS shows high changes in the count rate for low changes of particle position. Based on the overhead of the TS, it was demonstrated that this RPT system must employ at least 3 detectors to have capabilities to predict particle positions.