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Radiation-Induced Computer Malfunction

Dateline: 05/22/00

By Alan Bruzel

Although computer glitches will result from catastrophic releases of radiation (such as nuclear warfare), naturally occurring radiation has thus far posed the greater threat to the computer user. And, although the average user may naively blame software alone for errors and crashes, the guilt must be shared with natural, ever-present, environmental radiation.

Hard Errors and Soft Errors

A hard error results from permanent damage, such as a defect in the silicon that comprises a computer chip. Incident ionizing radiation causes those temporary aberrations in computer performance known as soft errors.

Alpha Particles and Cosmic Rays

Computer components are most likely to encounter ionizing radiation in the form of alpha particles and cosmic rays. Alpha particles are of low energy, and, to cause problems, must be produced by radioactive decay events occurring in immediate proximity to a computer device. It was discovered in the late 1970's that memory chips were failing due to alpha particles released by miniscule amounts of radioactive impurities (for example, thorium or uranium) in the silicon and in the chip packaging materials. Further purification of raw materials by chip manufacturers corrected this problem and significantly reduced soft errors caused by alpha particles.

Cosmic rays are also particles, and range from the size of a proton to more than the size of an iron nucleus. (Alpha particles are the size of a helium nucleus, and are thus at the smaller end of this scale.) Furthermore, unlike alpha particles, cosmic rays can be immensely energetic and therefore don't need to be generated close to a computer chip for their effects to be felt. They are believed to originate in the sun and in regions outside the solar system; they have enough energy to reach Earth and collide with oxygen and nitrogen molecules in Earth's atmosphere. The collision produces electrons, protons, neutrons, pions, and photons, with the most substantial effects on computers delivered by the neutrons, protons, and pions. The interaction of sensitive computer components with these particles may flip a logic bit from one to zero, or vice versa.

As chip semiconductor features shrink below 0.25 microns in size (and they are), soft errors are expected to become more and more prevalent. In addition, because a thinner atmosphere affords less protection, individuals using laptop computers aboard aircraft are most at risk of experiencing radiation-induced soft errors. Those using their laptops in salt mines are least at risk.

What the Web Has to Say about:
Radiation-Induced Computer Malfunction

Benefits of Chipkill-Correct ECC for PC Server Main Memory
Using error correction code to prevent soft errors in PC servers. Includes a history of alpha particle and cosmic ray interactions with computer memory components. From Timothy J. Dell, IBM Microelectronics Division.

Cosmic Rays, High Energy Phenomena
History, properties, and detection of cosmic rays. From Jack Guercio, University of Alberta.

Mitsubishi Electric Corporation Introduces New Soft Error-Resistant Memory Chip
New SRAM design provides greater protection against cosmic ray and alpha particle induced errors. News item from ChipCenter.com.

Radiation Hardening of Electronics
Radiation damage and its prevention. From Virginia Polytechnic Institute and State University.

Radiation, Not Software, May Be the Cause of Many PC Errors
As chips get smaller, soft errors pose more of a problem. From Jack Robertson, EDTN Network.

Spacecraft Anomalies due to Radiation Environment in Space
Susceptibility of satellite electronics to space radiation. From M. Lauriente and A.L. Vampola.

Terrestrial Cosmic Rays and Soft Errors
Collection of papers from the IBM Journal of Research and Development.

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