The Radiation Assessment Detector (RAD) is an energetic particle analyzer designed to characterize the full spectrum of energetic particle radiation at the surface of Mars, including galactic cosmic rays (GCRs), solar energetic particles (SEPs), secondary neutrons and other particles created both in the atmosphere and in the Martian regolith.
RAD consists of the RAD Sensor Head (RSH) and the RAD Electronics Box (REB) integrated together in a small, compact volume. The RSH contains a solid-state detector telescope with three silicon PIN diodes for charged particle detection, a thallium doped Cesium Iodide scintillator, plastic scintillators for neutron detection and anti-coincidence shielding, and the front-end electronics. The REB contains three circuit boards, one with a novel mixed-signal ASIC for processing analog signals and an associated control FPGA, another with a second FPGA to communicate with the rover and perform onboard analysis of science data, and a third board with power supplies and power cycling or “sleep”-control electronics. The latter enables autonomous operation, independent of commands from the rover.
The RAD particle and energy coverage is shown in the figure below. Also shown is a cross section of the RAD instrument showing each of the individual detectors and other internal components. The RAD instrument is mounted just below the top deck of the rover with the charged particle telescope pointed in the zenith direction.Measurement Capabilities
- Charge particles (protons & heavy ions up to Fe) (1 ≤ Z ≤ 26) vs energy & time
- Neutral particles (neutrons and γ-rays) (1-100 MeV neutrons) vs energy & time
- Absorbed Dose & Dose rate (LET of 0.3 to 1000 keV/mm) as a function of time
- Dose Equivalent (time-resolved Si LET spectra to determine LET-based Quality Factors)
- Mass = 1.56 kg
- Power = 4.2 W
- Volume = 10.3 x 12.2 x 20.4 cm³
- Field-of-View = 65° (view cone)
- Geometric Factor = 1 cm² * sr
Charged Particles: Charged particles entering RAD from the top deposit energy in solid-state detectors A, B, and C. Valid charged particle events occur in a view cone of about 65 degrees (full angle), defined by the A and B detector telescope geometry (see animation below).
Neutral Particles: Neutral particles are detected when energy is deposited only in the D and/or E detectors. An anticoincidence shield (F) surrounds the D and E detectors to discriminate valid neutral particle events and charged particle events which deposit energy in F as well as D and/or E (see animation below).