Solar Monitoring by Ions of Light Elements (SMILE) Payload Prototype and Validation by Altitude Surveys of Cosmic Ray Fluxes

Solar Monitoring with Ions of Light Elements (SMILE) is a space-based charged particle detector payload using the $\Delta$E–E technique on the dual 3U CubeSat mission called SMILING. The objectives of the SMILE payload are to measure the variation of cosmic rays depending on magnetic latitude and asymptotic direction and monitor the temporal variations of solar energetic particle and Galactic cosmic ray flux. The payload prototype comprises plastic scintillator fibers to measure the direction of incoming ions. We use a silicon PIN detector as a $\Delta$E detector to measure the energy deposited by penetrating particles, while BGO scintillators of varying thickness were chosen to detect the total energy of the incoming charged particles (E). A bottom plastic scintillator was designed to be the anti-coincidence detector and cover the angular acceptance of the penetrating particles. In this work, we focus on testing the SMILE prototype to confirm the payload’s functionality for space flight. Detector signals were calibrated from radioactive sources as well as cosmic rays and secondaries in Earth’s atmosphere. High-altitude cosmic ray surveys using short-term balloon flights and various locations on Doi Inthanon, Thailand's highest mountain, were conducted to test the instrument’s capability to measure particle fluxes over a wide energy range. We will report experimental results on cosmic ray flux variation with altitude, along with the SMILE prototype's geometrical acceptance and estimated cosmic ray count rates at different altitudes from Geant4 simulations. Comparison of experimental and simulation results verifies that the hardware system performs as expected.