Memorandum
TO:
FROM:
DATE:
SUBJECT: Description of the Spectrograph (Monochromator) Body
The spectrograph is an optical instrument used to perform qualitative or semiquantitative chemical analyses based on intensities of spectral lines emitted by excited atoms.
The body of the spectrograph consists of a large brass cylinder, 48 inches long, 16-1/2 inches outside diameter, and 1/4 inch wall thickness. This cylinder is closed at each end and has provision for attaching a diffusion pump and a vacuum gauge (an ionization gauge).
The two END PLATES on the cylinder and the two 1-5/8-inch-wide FLANGES, 19 inches in diameter, are made of 1/4-inch-thick Muntz metal. Muntz metal is an alloy consisting of 60 percent copper and 40 percent zinc.
Each FLANGE contains a 1/4-inch-deep groove so it can be fit snugly over the ends of the cylindrical body. On the opposite side of each flange is a groove, 0.206 x 0.003 inch wide. A Parker O-ring seal, size 2-461, 16 inch inside diameter, 1/4 inch thickness, made of butyl rubber base (material number E 515-8), can be placed into the groove for proper vacuum sealing with the end plate.
Each flange and end plate has 12 equally spaced 1/4 inch holes drilled through it. These holes are centered on an 18-1/2-inch-diameter bolt circle. Each flange is secured to the cylindrical body with tin-lead solder.
The end plates are held in alignment with the flanges by means of two large steel HINGES. These hinges enable one person to open the spectrograph and swing the end plates out of the work area without strain. Each hinge is fastened to the back side of an end flange with four 1/4-inch-diameter, 1-1/4-inch-long bolts.
When an O-ring has been seated in the groove of a flange, the end plate swings into position so its machined surface is flat against the O-ring. The 12 bolts can then be tightened to a torque of 8-1/2 foot-pounds so the O-ring is compressed into the groove by the end plate, thus making a vacuum-tight seal.
Two pieces of 1/4-inch-thick aluminum, alloy 2024-T351, are used to provide a SHELF. The aluminum pieces are held together, side by side, by three cleats on the underside. The shelf is 15 inches wide and therefore rests below the center of the cylindrical cross section of the body. The shelf’s length is 42-1/2 inches. This length allows 1 inch of space between the end of the shelf and the front-end plate and 4 inches’ space at the rear end. Thus, pumping speed is not retarded by the presence of the shelf.
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