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1 June 1992 H Lya transmittance of thin foils of C, Si/C, and Al/C for keV particle detectors
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A class of instruments designed for remote sensing of space plasmas by measuring energetic neutral atoms (ENA) uses a thin foil as both a signal generator and a light shield. An ENA imager must look directly at the ENA source region, which is also usually in intense source of H Ly(alpha) (1216 angstroms) photons. ENA are produced by charge exchange between energetic ions and the ambient neutrals, and both charge exchange cross section s and ion populations decrease with increasing ion energy. Therefore it is desirable to minimize the energy threshold for ENA detectors, at the same time maximizing the blocking of H Ly(alpha) . Optimizing filter design to meet these two contrary requirements has led us to measure the transmittance of thin C, Si/C, and Al/C foils at H Ly(alpha) . Our results indicate that (1) transmittance of < 7 X 10-4 can be achieved with (mu) g/cm2 Si on 1.7 (mu) g/cm2 C; (2) an Si/C composite foil with a thin carbon layer is more effective in blocking UV radiation while having the lowest energy threshold of all the foils measured; and (3) transmittance of Si/C foils of known Si and C thicknesses cannot be accurately predicted, but must be measured.
© (1992) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Virginia Ann Drake, Bill R. Sandel, David G. Jenkins, and Ke Chiang Hsieh "H Lya transmittance of thin foils of C, Si/C, and Al/C for keV particle detectors", Proc. SPIE 1744, Instrumentation for Magnetospheric Imagery, (1 June 1992);


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