Robert Jemison Van de Graaff

Born on December 20, 1901 in Tuscaloosa, Alabama, Robert, of a Cherokee mother and Dutch father. Graduated from University of Alabama in 1923, MS in mechanical engineering, and went to work for the Alabama Power Company. Became interested in nuclear physics after attending a lecture by the great Marie Curie. He learned of Ernest Rutherford's hope that someday particles could be accelerated to do better experiments in nuclear physics. He decided that he was the one who could make that happen. Earned his Ph. D. in physics in 1928 and, in 1929 built the first electrostatic machine, producing 80,000 V. 

(Since the dielectric strength of air is 3,000,000 V/m, Van de Graaff, first machine would only throw a spark of about 2.5 cm. The one I demonstrated in class threw sparks of over 10 cm.)

By 1931, he had a dual sphere machine that produced 1 MV of potential difference, enough to smash an atom.

The idea is to run an insulating belt between two pulleys to carry charge to a collecting comb inside a metal sphere. In his first machine, Van de Graaff used a silk belt, but our demonstration machine uses a rubber belt. In his first machine, Van de Graaff used a charged comb to charge the belt, but our demonstration machine uses a grounded "charged comb" with a metal pulley at one end and a plastic pulley at the other. One way will charge the sphere positive while the other will charge the sphere negative. In Van de Graaff's first million volt machine, he used both. 

(The excellent schematic picture
above is from Eugenii Katz of the
Hebrew University of Jerusalem)

By 1933, Van de Graaff was producing 7 MV with a pair of 15 foot diameter aluminum spheres mounted on railway carts so they could be wheeled outside in good weather. Nuclear physics in those days was a fair weather sport.

The spheres shown at the left still exist. While they are no longer used to do nuclear physics, they are used every day. The main gallery of the Boston Science Museum was built around them, and the museum gives daily lightning shows.