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Mars Science Laboratory

Radiation Assessment Detector (RAD)

Radiation Assessment Detector
About the size of a small toaster, the Radiation Assessment Detector looks skyward and uses 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. Credit: NASA/JPL-Caltech/SwRI

The Radiation Assessment Detector (RAD) is 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 measures and identifies 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 collects data that allows 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 also assesses the hazard presented by radiation to potential microbial life, past and present, both on and beneath the martian surface. In addition, RAD investigates 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 identifies heavy ions up to iron on the periodic table. The RAD is lightweight and energy efficient so as to use as little of the Mars Science Laboratory's available mass and energy resources as possible.

Curiosity's First Radiation Measurements on Mars
Like a human working in a radiation environment, NASA's Curiosity rover carries its own version of a dosimeter to measure radiation from outer space and the sun.

Radiation Assessment Detector for Mars Science Laboratory
This instrument, shown prior to its September 2010 installation onto NASA's Mars rover Curiosity, will aid future human missions to Mars by providing information about the radiation environment on Mars and on the way to Mars. Credit: NASA/JPL-Caltech/SwRI