Long Duration Exposure Facility
(LDEF) Archive System

NASA Langley Research Center
Hampton, Virginia

Ionizing Radiation Results

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Page Content: William H. Kinard
Page Construction: Thomas H. See


... we have to remember that what we observe is not nature in itself but nature exposed to our method of questioning.

Werner Karl Heisenberg

Physics and Philosophy (1955)


The LDEF satellite provided the unique opportunity to investigate long-term radiation exposure of spacecraft materials in the low-Earth orbit (LEO) environment. These experiments were subjected to the space environment, neutron and proton fluence, and half of one solar cycle, from solar minimum to solar maximum. Dosimetric measurements, radiation effects and astrophysics were studied in these experiments. The LDEF Ionizing Radiation Experiments have impacted the scope and extended the knowledge of cosmic-ray research, radiation dosimetry, induced radioactivity, and radiation environment modelling. Overall, there were thirteen ionizing radiation experiments that were located throughout various LDEF trays. The following table summarizes these experiments, their locations on LDEF, the titles and Principal Investigators for the experiments.

The cosmic-ray experiments are an example of the importance and success of the LDEF mission. These experiments address fundamental questions about the nucleosynthesis of heavy elements in the galaxy and accerlation of the nuclei to high energies. AO178 measured the elemental abudances of galactic cosmic rays above atomic number 65. It is the most signifcant study yet of the actinides (e.g., thorium and uranium) in the cosmic rays, and will define their abudance relative to lighter elements (e.g., platinum and lead). This data will reveal the importance of rapid (explosive) nucleosynthesis for heavy-element production in the galaxy. M0001 was designed to study both galactic and anomalous cosmic rays. The low energy "anomalous" nuclei are now thought to be from the interstellar gas which enters the solar system, becomes partially ionized, and is then accelerated (by shock waves) up to a few tens of MeV. These particles carry information about the interstellar medium and particle acceleration in the solar system. In addition to anomalous cosmic rays, experiment M0002-2 also studies low-energy heavy ions that are trapped in the inner radiation belt. The trapping mechanism for these particles is not understood. These three LDEF ionizing radiation experiments are just a small subset of the LDEF experiments and yet, this small subset demonstrates the significant contribution that the LDEF experiments have in the ionizing radiation field of study.

LDEF demonstrates the power of experiments with passive radiation detectors and induced activity measurements, exposed for a long period in space, to make significant advances in cosmic-ray astrophysics, radiation dosimetry, and environment modelling. The radiation experiments were not designed as an ensemble, nor was the long exposure anticipated, but every experiment that has been analyzed has made a significant contribution, some with unexpected and remarkable results.

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