An External Beam Bunch Selector for a 60-Inch Cyclotron

An external beam-bunch selector has been built to modulate the beam of the NASA 60-inch cyclotron for neutron time-of-flight studies. Electrostatic deflection at one-fourth the cyclotron frequency is used to lengthen the beam burst period, so that longer flight times can be used. The design and performance of this apparatus are described. With this equipment, flight times up to 400 nanoseconds are available, without distortion of the cyclotron beam burst width. Energy resolutions of the order of 2 percent are thus possible.