Radiation survey of the LDEF spacecraft

The authors report the first complete gamma-ray survey of a large spacecraft, the Long Duration Exposure Facility (LDEF). The survey was conducted using an array of germanium detectors from the US Naval Research Laboratory and individual detectors from the Institute for Space Science and Technology to study the accumulation and distribution of radioisotopes induced in the wide variety of materials present on the LDEF. ²²Na, ⁷Be, ⁵⁴Mn/el, and the positron annihilation line were all strongly observed. Traces of ⁵⁶ Co, ⁵⁷Co, and ⁶⁰Co were also observed The most striking feature of the data was the unexpected distribution of ⁷Be, which was predominately present on the leading surfaces of the spacecraft. The evidence clearly indicates an accretion of the ⁷Be onto the surface of the LDEF. This is the first known observation of the deposition of a radioisotope onto the surface of a spacecraft. ⁷Be is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. To explain the surface density of 5.4×10⁵ atoms/cm², it must be assumed that the light ⁷Be atom is transported up from lower altitudes