Photoelectric Photometer, "Oke Box", Kitt Peak National Observatory

This is an insulated container to stabilize a multi-stage photoelectric photomultiplier. It was used with telescopes at the Kitt Peak National Observatory. The photoelectric photometer is a device for measuring the amount of light gathered by a telescope from point-like sources such as a star or galaxy. Light that had been processed by the diaphragm and filters in the photometer head was routed to the photomultiplier tube inside the "Oke Box". A half-aluminized hemisphere in front of the cathode, designed by J. B. Oke caused the light to be repeatedly bounced onto the cathode surface of the tube enhancing its red sensitivity. The electrons released from the gallium arsenide coated surface of the tube were then accelerated by an electric field onto a series of electrodes called dynodes. Additional electrons were released by each sequential impact of electrons on a dynode leading to a cascade of charge and thus amplification of the initial signal. This box was built at KPNO in 1974 and used for measuring light from astronomical objects for nearly 20 years; the Observatory donated this to NASM in 2000.