NASA Langley Research Center
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Ionizing Radiation SIG Charter

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The LDEF Ionizing Radiation Special Investigation Group (IR SIG) was chartered to perform measurements and analyses that were not a part of the LDEF experiments objectives but are important for application to future missions. The IR SIG must ensure that relevant and applicable information for design and development of future missions is reported and archived, and that the results will be in a form useful to those programs. Each SIG defined specific objectives toward these general goals, in accordance with programmatic constraints. The IR SIG members produced a document which lists the tasks that were to be completed.

1. Pre-recovery predictions of radiation dose, particle fluences, LET spectra, and radioactivity.

2. A post-recovery radiation safety inspection. This inspection was performed soon after Columbia's payload bay doors were opened in the Orbiter Processing Facility (OPF) with hand-held survey detectors and dry wipes of small areas. No radioactivity enhancements above background were detected with the survey instruments. KSC personnel performed these surveys.

3. A full spacecraft activation measurement. This measurement was performed for two months in the SAEF II building, while experiment trays were removed, with a very sensitive germanium spectrometer array.

4. Provide radiation environment predictions (booklet).

5. Analyze supporting radiation data and induced radioactivity and compare to calculations. A program was organized to measure the induced activity in about 400 samples of the spacecraft structure and experiments materials selected at many locations and shielding depths. The activation measurement data set provides an excellent test of calculational methods such as the directional trapped proton environment model, the High Energy Transport Code (HETC) and other methods to predict activation in spacecraft. Furthermore, the activation measurements and prediction methods are of great interest to the gamma ray astronomy community (e.g., GRO and Mars Orbiter).

6. Provide detailed calculations of radiation dose, linear energy transfer (LET) spectra and secondary components (including neutrons) as a function of position around LDEF and shielding depth. Provide detailed calculations of induced activity. Update calculation methods and environment models as warranted by data. The main models and calculations to be applied are the AP8 trapped proton model, AE8 trapped electron model, a new model for trapped protons which combines AP8 with the directional properties of the protons, methods for calculating induced radioactivity (e.g., the HETC), the cosmic-ray environment and methods for calculating LET spectra (e.g., the Cosmic Ray Effects on Microelectronics [CREME] code and the HETC code). The definitve application of these methods requires a detailed mass model of the LDEF structure and selected experiment trays.

7. Compare radiation data, when available, from experiments with calculations.

8. Disseminate results of 4-7 as available.

9. Accumulate the radiation data and analysis results from experiments as available, and supply the experimenters with environment calculations and analyses as they become available. Coordinate data exchange among LDEF investigators with radiation measurements.

10. Provide calculations/estimates for specific locations in LDEF, or for specific components with suspected radiation effects.

11. Advise experiment investigators and other SIGs about potential radiation effects and methods of post-flight radiation testing. The LDEF IR SIG supported a number of post-recovery radiation analysis efforts which required accelerator exposures for the calibration of detectors or for the assessment of possible radiation effects. Due to the low altitude and inclination orbit, and the relatively low-radiation dose, significant radiation effects were not anticipated.

12. Provide final report on LDEF radiation environment and effects. The documentation and archival of data, models, and methods is a major task of the IR SIG. In addition to written reports and summaries of results, the environment models and calcuation methods will be documented and placed in accessible networks. The induced activity data and prediction methods will be a major subset of the archive. Activation results (including the occurrence of unusual amounts of nuclides in the original materials that have been discovered) will be archived in the Materials and Processes Technical Information System (MAPTIS).

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