LET spectra measurements on LDEF: variations with shielding and location

Area of Science:

• Space physics
• Radiation detection
• Particle physics

Background:

• Passive plastic nuclear track detectors (PNTDs) were used to measure Linear Energy Transfer (LET) spectra.
• Previous calculations of LET spectra deviated from measurements, especially for high LET particles.

Purpose of the Study:

• To investigate the factors influencing LET spectra measurements.
• To understand the contributions of primary and secondary particles to LET spectra.
• To analyze the impact of detector orientation, shielding, and location on LET measurements.

Main Methods:

• LET spectra measurements were conducted at various locations on the Long Duration Exposure Facility (LDEF) satellite.
• Experiments included P0006 LETSME, P0004 Seeds in Space, A00l5 Free Flyer Biostacks, and M0004 Fiber Optics Data Link.
• Detector orientation and shielding effects were studied using orthogonal stacks in the P0006 experiment.
• Ground-based accelerator experiments with CR-39 detectors and 154 MeV protons were performed for comparison.

Main Results:

• LET spectra measurements showed significant dependence on detector orientation, shielding, and location (east, west, Earth sides of LDEF).
• High LET spectra were primarily attributed to short-range inelastic secondary particles from trapped proton interactions.
• Lower LET spectra were mainly due to stopping primary protons and GCR particles.
• Higher particle production rates were observed on the west side of LDEF due to increased trapped proton flux in the South Atlantic Anomaly (SAA).
• Track density increased with shielding depth, indicating a significant contribution from secondary particles.

Conclusions:

• Detector orientation, shielding, and location are critical factors in PNTD LET spectra measurements.
• Secondary particles play a dominant role in high LET spectra, particularly from trapped proton interactions.
• Understanding these factors is crucial for accurate radiation environment characterization and modeling.
• 1-D modeling of proton beams provides a useful basis for understanding secondary particle production in space radiation environments.