Photomultiplier, Open Cathode, OAO-III

This open-faced photomultiplier tube was manufactured by EMR PhotoElectric Co. of Princeton, New Jersey. It is one of a set delivered to a Princeton team led by astronomer Lyman Spitzer in the late 1960s for use in the Princeton Experiment Package, the primary instrument planned for the third Orbiting Astronomical Observatory (OAO III). This was a spectrometer flown on OAO ("Copernicus" after launch). Ultraviolet detectors of this design contain 18 dynode stages that amplify the electric signal from a potassium bromide coated photocathode that sits at the bottom of the tube. Each dynode is made of beryllium copper strips looking like a little grill. A voltage-dividing network keeps each dynode at its proper electrical potential. This tube was used in the laboratory for testing purposes and was taken out of service in 1971. It was donated to NASM in 1982, where it was exhibited in the "Stars" gallery from 1983 through 1997. It is now on display in the "Explore the Universe" gallery.