Calibration of Silicon-Based Detectors to Measure Lunar Surface Particles Using Heavy Ion Beams

초록

To assess the biological effects of lunar surface radiation, two silicon-based detectors, a dosimeter and a spectrometer, were developed as science payloads for the Commercial Lunar Payload Services (CLPS) program. They were designed to measure the linear energy transfer (LET) and energy spectra of charged particles originating from galactic cosmic rays (GCRs) and solar energetic particles (SEPs). The dosimeter uses a thick and a thin silicon sensor to measure lower and higher LET particles, respectively. The spectrometer uses the same silicon sensors and adds a cesium iodide (CsI) scintillator behind them, followed by a third silicon sensor. They were tested with the He, C, Si, and Fe ion beams modulated by different thicknesses of polymethyl methacrylate (PMMA) at the Heavy Ion Medical Accelerator in Chiba (HIMAC) to simulate heavy ions with a wide range of LET present on the lunar surface. Monte Carlo simulations were performed with the same geometry as the experimental setup to calibrate the analog-to-digital converter (ADC) channels of the sensors to LET values. A fairly linear relationship was observed between the measured peak channels and the simulated LET values across a broad LET range. However, a slight deviation from linearity was observed in the high LET region for the heavily modulated Fe ion beams. The energy calibration of the spectrometer showed that the incident proton energies could be reconstructed from the energy deposits in the stacked sensors. These results indicate that the developed dosimeter and spectrometer are suitable for measuring the LET and energy spectra of charged particles from GCRs and SEPs on the lunar surface and can provide valuable information on the biological effects of lunar surface radiation.

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