1 June 1992 H Lya transmittance of thin foils of C, Si/C, and Al/C for keV particle detectors
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Abstract
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.
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Virginia Ann Drake, Bill R. Sandel, David G. Jenkins, 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); doi: 10.1117/12.60588; https://doi.org/10.1117/12.60588
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