Radio in the Atom Tests
July 1946 Radio-Craft

July 1946 Radio-Craft [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Craft, published 1929 - 1953. All copyrights are hereby acknowledged.

A year after the two atom bombs were dropped to end World War II, the newly formed Atomic Energy Commission conducted detailed detonation tests at the Bikini Atoll, in the South Pacific. Most people more than 40 years old are very familiar with the images of the giant mushroom cloud that formed over the site. This "Radio in the Atom Tests" article from the July 1946 issue of Radio−Craft magazine reports on plans being made to measure and record sound pressure, nuclear radiation, radio and radar signatures, temperature, light spectrum and intensity, and other parameters. The information would be used for improved bomb making, nuclear power generation, medical imaging and treatment, and general research on nuclear fission and fusion (a fission implosion is to initiate a fusion reaction).

Radio in the Atom Tests

By E. A. Witten

Electronic Specialists Will Learn Much at Bikini Atoll

Probably the most elaborate scientific tests ever carried out as far as the number of people, amount of equipment and total expense are concerned will be the atomic energy tests this summer. For the gigantic task of measuring and determining the amount of damage an atomic bomb can do, Joint Army-Navy Task Force One will send three elaborately equipped laboratory ships to Bikini Atoll (Fig. 1). These ships will carry many of the nation's top-ranking scientists with all equipment and instruments necessary for conducting the tests. One ship will be devoted entirely to electronics and will carry such equipment as radar units of the most advanced design, Geiger counters, radiology equipment, long-range television apparatus, seismographs; all in addition to the standard radio transmitting and receiving apparatus.

The technical staff will consist of over 1000 technicians. These men will be divided up into nine specialist groups or divisions: bomb operation; blast pressure and shock; wave motion and oceanography; electromagnetic propagation and electronics; radiological safety; radiometry; radiation; remote measurements; and technical photography.

In the field of wave motion, supersonic echo sounders will measure the vertical motion of both the target ships and the buoys at a distance from the explosion, while pressure recorders on the bottom will record water depth versus time by measurement of hydraulic pressure. In addition, seismographs will be set up on the islands around the atoll to observe the propagation of shock waves through the earth and thus obtain information on the geological structure of the atoll.

The electromagnetic propagation and electronics division will make studies of the effect of the atomic bomb explosion on the propagation of electromagnetic waves. These tests are planned to show the influence of the intense local ionization resulting from the detonation on both sky and ground wave transmission. Other experiments will show the radar reflective properties of the bomb cloud and the intensity of the atmospheric electrical disturbances developed by the explosion.

Standard Navy, Signal Corps, and Air Force radar equipment as well as special devices constructed for the tests will be used to measure electromagnetic propagation. The area to be tested, the distance covered by the blast, and a time base are shown on the diagrammatical chart in Fig. 2.

Army Air Force "drones" will carry Geiger counter warning circuits and special transmitters to determine the effect of the bomb explosion in the 5-to-9-megacycle region. It is not known at present what effect the bomb cloud will have in radio or radar interference or reflection.

The radiological safety section is charged with protection of personnel from radiological hazards after the blast. This includes responsibility for measurement of radiological phenomena in the areas to be entered by various personnel and for tracking the movement of radioactive air and water masses caused by the explosion. The primary safety device is the Geiger counter which indicates radioactivity by a clicking sound, a cathode-ray tube or the movement of a hand on a dial. Additional safety devices are ionization chambers, specially sensitized films, and chemical capsules which indicate total radioactivity from the measurement of induced radioactivity.

Radiometry is the subject of study of another staff section. Radiometry is defined for the purposes of the atom bomb tests, as a measurement of light in the visible spectrum and adjacent wave bands (ultra-violet and infra-red). This is distinguished from the staff section which is concerned with radiation or the measurements of gamma rays, neutrons, etc.

Among the instruments used by this section are: spectrographs to obtain the spectral distribution of the first flash; photo-electrical units to record the intensity of the first flash as a function of time; and bolometers to measure the total radiant energy emitted by the first flash. Unfortunately, the findings in this field only, the instruments used and the techniques employed are classified under the security regulations of the Manhattan Engineer District and will not be released for publication till some time after the tests are completed.

Four Army Air Force's B-29's will be prepared to track and photograph the cloud resulting from the blast to determine its persistency and radiological activity. Ground photographs will be made from fixed installations on 75-foot steel towers, placed at strategic points on Bikini Atoll. All these cameras will be radio controlled.

Radio and television-equipped aircraft will play an important part in the tests. Radio-controlled drones (Photo A) carrying radiological instruments will be directed to the scene of the blast and information will either be radioed back to the observation ships or the drones will be directed back to the ships. A new type of long-range, high-altitude, high definition television system (See Radio-Craft, May 1946) installed in the nose and waist of reconnaissance planes equipped with transmitting apparatus will enable Task Force One officers to view at close hand the destruction and effects of the bomb, which would otherwise be impossible, (or at least highly impractical in terms of lives.)

The drones are scheduled to fly close enough to the atomic bomb blast so that sensitive scientific and photographic instruments stowed in their cockpits will record what happens when an atom bomb explodes on its target. Each of these drones is controlled by a plane from which a Navy pilot will maneuver his drone, keeping it always in sight and able to identify it by its colored tail. The drones are red, overall, with a colored fin and rudder matching a color painted on the engine cowling of the Queen Bee plane which controls its flight.

The drones will take off under the control of a Navy radio specialist in a radio control truck (photo B) parked on the carrier flight deck. When they are 100 feet in the air, the Queen Bee pilot takes over from the truck. After the explosion, the Queen Bee planes and those drones that come through the tests will fly to Roi Island where they will be landed and the data which was recorded by their sensitive instruments removed for study by the atomic scientists.

All AAF men participating in the tests are required to take refresher courses in subjects pertinent to their specialty. Radio operators and technicians will be schooled in the intricacies of radar and loran, both of which will be used in the tests. (Photo C)

Posted October 22, 2021