X-ray detector typical of those used in solar observation satellites such as OSO-5. This commercial unit, manufactured by LND Inc., is a proportional counter. It converted impinging x-rays to an electrical signal and amplified that for further processing. It comprises a hollow metal gas-filled cylinder equipped with a window transparent to x-rays at one end. Electrons released by impinging x-rays will travel to the oppositely charged electrode. During the course of their travels, they collide with gas molecules which results in the release of further electrons. This process leads to a cascade of charge and the effective amplification of the electrical signal generated by the initial x-ray. The x-ray frequency detection range of the instrument is determined by choice of gas and the imposed electrical potential and the nature of the entrance window. This detector was transferred to NASM by NASA (GSFC) in 1988.