detectors. The region between break and peak has overlapping coverage. Turee photocell and two photomultiplier detectors will’ de used with four 5X, tnree TW, and three 1056 indicators. For Project 2.5 a dual transit-time transmitter will be installed on a tail-plate on King prior to its departure from tne-ZI. Dual . transit-time receivers will be installed in eaca of two B-50's prior to taeir leaving tne ZI. Upon arrival of the King unit and the Be50's at Kwajalein, tie transmitters and receivers will be checked, using the C-12+ and tze islend's (and/or Curtiss') facilities. PROGRAM 3 SCIENTIFIC PiOTOGRAPHY Pilot experiments at Tumbler-Snapper have led to minor changes in tne uotespot experiment for Operation Ivy. Tne collimating pipes out from the bomb will be 35 ft long instead of 20 ft and will be filled wits nelium. The changes are made in order to reduce tne probability of interference from light attenuation in the air and from Teller light. An additional observation will be made at the top endof the deuterium section in order to obtain three points on the shock position vs time curve at that level. It has been decided tnat the fabrication of the collimating tubes will be accomplisied at Los Alamos. This will have the advantage of close control in anticipation of minor revisions that may be deemed necessary. Since tne specifications for these tubes have been revised, tney will not be available for the work at Buffalo, N. Y. Tne collimating~ tube scaffold nas been completed by the Patent Scaffolding Co., Inc., Long Island, N. Y., inspected, crated for overseas shipment, and -27- # 10