Radiation Assessment Detector

About the size of a small toaster, the Radiation Assessment Detector will look skyward and use a stack of silicon detectors and a crystal of cesium iodide to measure galactic cosmic rays and solar particles that pass through the Martian atmosphere. Image credit:
NASA/JPL-Caltech/SwRI

The Radiation Assessment Detector (RAD) will be one of the first instruments sent to Mars specifically to prepare for future human exploration. The size of a small toaster or six-pack of soda, RAD will measure and identify all high-energy radiation on the Martian surface, such as protons, energetic ions of various elements, neutrons, and gamma rays. That includes not only direct radiation from space, but also secondary radiation produced by the interaction of space radiation with the martian atmosphere and surface rocks and soils.

To prepare for future human exploration, RAD will collect data that will allow scientists to calculate the equivalent dose (a measure of the effect radiation has on humans) to which people would be exposed on the surface of Mars. RAD will also assess the hazard presented by radiation to potential microbial life, past and present, both on and beneath the martian surface. In addition, RAD will investigate how radiation has affected the chemical and isotopic composition of martian rocks and soils. (Isotopes are atoms of the same element having the same number of protons but a different number of neutrons.)

A stack of paper-thin, silicon detectors and a small block of cesium iodide measure high-energy charged particles coming through the Martian atmosphere. As the particles pass through the detectors, they lose energy, producing electron or light pulses. An internal signal processor analyzes the pulses to identify each high-energy particle and determine its energy. In addition to identifying neutrons, gamma rays, protons, and alpha particles (subatomic fragments consisting of 2 protons and 2 neutrons, identical to helium nuclei), RAD will identify heavy ions up to iron on the periodic table. The RAD will be lightweight and energy efficient so as to use as little of the Mars Science Laboratory's available mass and energy resources as possible.