Evaluation and mathematical analysis of performances of gamma detector based on photosensor

Gamma detectors including gas-filled detectors, scintillation detectors, and solid-state detectors are still widely used and developed depending on the purpose. An indirect detectors that combines a scintillators and... [ view full abstract ]

Gamma detectors including gas-filled detectors, scintillation detectors, and solid-state detectors are still widely used and developed depending on the purpose. An indirect detectors that combines a scintillators and photosensors are used to visualize the gamma rays. Gamma camera is an indirect photosensors, which consist of a collimator, an analog signal processing board, data acquisition bard, and software. Spatial resolution and detection efficiency, which are important performance factors of the gamma camera, are determined by various factors. The purpose of this study is to evaluate the factors influencing major performances by Monte Carlo simulation and analyze mathematically. For this study, the spatial resolution and the detection efficiency were evaluated by changing the height and diameter of the collimator, the energy of the gamma ray, and the position of the radioactive sources emitting the gamma ray using Monte Carlo N-Particle Transport code, version 6. The geometry for the simulation consisted of a con-shaped pinhole collimator with a tungsten aperture, lead septa, NaI (Tl) scintillator, and Silicon photomultiplier (SiPM). Acceptance angle and focal length were 37° and 15 cm, respectively. Various point sources including ¹⁵²Eu, ¹³⁷Cs, ⁶⁰Co, and ⁴⁰K were located 70 cm above the center of the collimator aperture. The NaI (Tl) crystal having a size of ф4x3, energy resolution of 6.9 % about ¹³⁷Cs, light yield of 41x10³ photons/MeV, and decay time of 230 ns and the photosensor having pixel pitch of 3.36 mm were used for the simulation. As the height of collimator increases and the diameter of collimator decreases, the spatial resolution and efficiency were improved and decreased, respectively. The spatial resolution showed a tendency to improve as the energy of the gamma ray was small. Angle-dependent efficiency showed a tendency to decrease by more than 7 % from the center of the collimator aperture to the edge in the useful field of view. These results were related to the penetration effect fo the gamma particle in the edge of the collimator. The mathematical analysis of the simulation results including interactions of the gamma particle with matter will be presented.