A Model Demonstrating the Cyclotron Principle EUGENE E. GRASSEL Blackburn College, Olrlinvilb. Illinois
INTERESTING original device was used reANcently at a science open house a t Blackburn College, to explain the movement of protons or denterons between the "dees" of a cyclotron. This device shows the relative position of the moving particles as the dees change in charge, and the increase in speed of a projectile as it travels from the center to the outer edge of the dees.
This device, shown in the figures, consists of a box lighted from the inside, the top of which is a piece of plywood in which a spiral slit and two sets of negative and positive signs have been sawed. Between the spiral and the source of light is a slotted circular plywood disc, which is turned by a small motor. A paper top containing a picture of the dees is laid over the plywood top. Two sets of plus and minus signs are placed one above the other, above the spiral. The top set is in the order, plus-minus, and the bottom set is in the order, minus-plus. The motor-turned disc, which is placed directly below the spiral, has an annular slot cut close to the edge, extending half way around the disc. A second annular slot is cut closer to the center, extending around the other half of the disc, and a third slot is cut along a radius of that diameter which passes through the ends of the first two slots. The disc is placed below the top containing the spiral, so that the center of the spiral coincides with the center of the disc; then the outer slot falls directly under the top set of signs, and when the disc is turned, the inner slot coincides with the bottom set of signs. The disc is placed with the side turned up that causes the radial slot to fall on the side of the box where the negative sign is lit. This disc is held on a vertical axle made of a dowel pin fastened se'curely between the center of the spiral and the bottom of the box, and kept from moving sideways by guide wires fastened around the dowel and to the sides of the box The disc is grooved around the edge, and a string belt extends from the pulley on the motor around the disc in the groove. The box is lighted by an electric light placed under the
revolving disc. Between the disc and the light is placed a sheet of tissue paper to diffuse the light and get rid of undesirable shadows.
The principles of the cyclotron are demonstrated by the movement of spots of l i ~ hwhich t show through the paper top. This is-caused by the changing in the'alipment of openings as the revolving disc turns under the plywood top.
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