NASA Langley Research Center
Hampton, Virginia

Ionizing Radiation Detectors

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The LDEF Ionizing Radiation Experiments utilized a broad range of detectors: thermoluminscent detectors, plastic nuclear track detectors, activation and fission foils. There were 190 TLDs, more than 500 PNTDs and 400 activated materials, 22 fission foils and 4 other detectors (microsphere and AgCl) on the LDEF structure. A reference chart is provided to indicate which detectors the experiments used and the area of study.



Experiments P0004, P0006, M0004 and AO015 contained a variety of passive detectors to measure the radiation dose, heavy particle fluence, linear energy transfer (LET) spectra and several aspects of the secondary radiations including neutrons and the concentration of heavily ionizing recoil nuclei. These experiments contained detectors at various shielding depths typically encountered in manned spacecraft. The P0004 detectors were distributed at various depths in the seeds experiments. P0006 comprised a comprehensive set of dosimetric detectors at precisely defined shielding depths in the seeds experiments tray. AO015 carried many detectors to characterize the radiation exposure of biological samples. Some of these detectors were used to locate the tracks of heavy nuclei which passed through the biological samples. Experiments M0003, M0006 and AO138-07 also carried detectors for local radiation dose monitoring.

A set of five metal samples (Co, Ni, Ta, V, In) of approximately 100 gm each were placed in five separate locations around LDEF. The metals were selected for specific activation products and cross-sections to study the activation process and to measure the flux of the activating particles (trapped protons, cosmic rays and neutrons). The flux and spectra of neutrons, which have not been frequently nor definitively measured in spacecraft, can be studied through activation reactions which are exclusively, or partially, caused by neutrons.

It should be noted that LDEF carried no radiation detectors at sufficiently shallow shield depths (< 0.1 cm Al) to measure trapped electrons. Attempts to measure the electron dose in some surface samples with electron paramagnetic resonance (EPR) techniques are planned.

The set of passive radiation detectors on LDEF is the most comprehensive yet flown on a low Earth orbit mission. The value of these detector measurements is enhanced by the spacecraft's Earth-fixed flight altitude (which is nearly the same as that planned for the International Space Station). This allows the directional characteristics of the ambient radiation and its effects at various shielding depths to be studied. The large number and variety of detectors at various locations and shielding depths, the orbit, the altitude stability, and the long duration make this a valuable and unique data set for studies of the LEO radiation environment.

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