Photoelectric Effect

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These condensation trails from photoelectrons were produced in a Supersaturated Environments Cloud Chamber. An Iron-55 source of 5.9 keV K-shell capture X-rays was located to the right of the photograph field, and slightly above the chamber’s sensitive plane. The low energy X-rays interact with air primarily through the photoelectric effect. Each dot was caused by a single photoelectron, often accompanied by a lower energy Auger electron. Because the X-rays typically travel many centimeters before interacting, and the photoelectron range is much shorter, a fairly uniform array of dots were observed. Point source divergence (inverse square law) and air attenuation account for decreased photoelectron density on the left side of the photograph.