Measurement of Time of Flight in the Millimicrosecond Region

The Hanford system for measurement of neutron time of flight differs from conventional techniques only in the use of a vernier chronotron for time interval measurements. The chronotron consists of two circulating transmission lines with a single fast coincidence circuit between them. The line lengths are adjusted to give slightly different circulation periods. By counting the number of circulations necessary to bring two noncoincident pulses into coincidence, a number is obtained which is a measure of the time interval in terms of the difference in circulation periods. This number is used as the channel address for storage in a Radiation Counter Laboratories 256 channel analyzer. Discussion of the vernier chronotron includes: 1) The factors determining channel width, stability and uniformity, 2) use of the RCA 6810 for starting circulation directly, 3) performance of the system as determined with prompt gamma ray cascades, and 4) performance of the instrument in conjunction with the other components of the time of flight system.