Issues

Time‐of‐flight experiments, conventionally dependent on neutrons from an accelerator, have long been used in the slow grinding out of cross‐section data. Last December, at the AEC's Test Station in Nevada, the vastly larger supply of neutrons from an underground nuclear explosion was employed in a scaled‐up time‐of‐flight experiment. The results of that experiment, which are regarded as preliminary, were reported to the American Physical Society in April, during the 1965 spring meeting in Washington, D.C., and the following article is based on the invited paper presented by Dr. Hemmendinger at that time. More precise results are expected from an experiment carried out on June 11, 1965, data from which are still being processed. The author is a group leader at the Los Alamos Scientific Laboratory in New Mexico.

New interest has arisen in the wavefront reconstruction process of Gabor. With the aid of the laser, photographic imagery has been produced in which the image is, to all appearances, a three‐dimensional reconstruction of the original, complete with parallax and other visual effects.

The current international standard for the physical measurement of time is based on the use of atomic‐frequency control devices that are now being studied intensively in the search for an ultimate basis for the precise definition of time. The author is assistant chief of the Physics Division of the NBS Radio Standards Laboratory, Boulder, Colo., where the atomic‐frequency standard is being actively investigated.