Introduction

They are some of the most famous and eerie images to emerge

from the Cold War: atmospheric nuclear tests captured one

millisecond after detonation. Using a rapatronic camera

developed by Harold Edgerton of Edgerton, Germeshausen &

Grier Inc. (EG&G), a company specializing in electronic

technology, the rapatronic camera was capable of photographing

still images at the rate of 1/1,000,000 of a second. 

Background

Dr. Harold Edgerton, a pioneer in strobe photography, developed

the concept for the rapatronic camera in the 1940s. With partners

Germeshausen and Grier, Edgerton made the first rapatronic

camera capable of recording still images of rapidly-changing

subject matter from as far as seven miles away. Called

‘rapatronic’ for its rapid action electronic shutter, the cameras

were used to photograph atmospheric nuclear tests at the Nevada

Test Site primarily during the Tumbler-Snapper series in 1952,

and Operation Upshot-Knothole in 1953. The rapatronic

photographic technique enabled very early capture on film of the

nuclear fireball immediately after detonation. The exposures

were often as short as 10 billionths of a second, and each camera

could take only one photograph. As a result, banks of four to 10

cameras were set up to take sequences of photographs during a

single nuclear test.

The images

Valuable data about nuclear tests resulted from the rapatronic images.

Photos resulting from the rapatronic technique revealed, for the first

time, misshapen fireballs immediately after detonation of atmospheric

nuclear tests - many of which were detonated atop 300-foot towers.

Many of the photos reveal two striking features: glowing spikes

projecting from the bottom of the fireball, and a peculiar mottling of

the actual fireball. 

The spikes protruding from the lower part of the fireball result from

the fire extending and burning along ropes or cables that stretch from

the shot cab (the housing for the test device at the top of the tower) to

the ground. Physicist Dr. John Malik researched this phenomenon and

appropriately named it a "rope trick." The effect had been observed in

earlier tests when spikes were seen extending along cables that

moored the shot towers to the ground. During the Snapper phase of

the Tumbler-Snapper series, Malik conducted experiments using

different kinds of cables and ropes, and with different surface

treatments. 

This rapatronic image, captured during the TumblerSnapper series at the Nevada Test Site in 1952,

illustrates the phenomenon known as the “rope trick.”

A rapatronic photo captures a tower test

during Tumbler-Snapper immediately after

detonation, but before the “rope trick” is

visible.
Malik observed that if the rope was painted black, the spike formation

was augmented, and if it was painted with reflective paint or wrapped

in aluminum foil, no spikes were observed in the rapatronic images.

Malik's experimentation confirmed the hypothesis that it is the heating

and vaporization of the rope induced by exposure to high intensity

visible light radiation which caused the "rope trick" effect. 

The cause of the surface mottling in the rapatronic images is more

complex. Immediately after detonation, the growth of the fireball is

due to radiative transport - thermal x-rays "outpacing" the actual

expanding bomb debris. Milliseconds later, a hydrodynamic shock

front forms, and the fireball

expansion is caused by the

shock front-driven

hydrodynamic pressure. As the

shock compression heats the air,

the fireball grows far more

slowly than it did directly after

detonation. The debris from the

actual bomb and shot cab is

vaporized, and the vapors are

initially accelerated to very high

velocities before the shock

front forms. Once the shock

front forms, clumps of the

material splash against the

back of the shock front in an irregular pattern creating the mottled appearance.

In addition to rapatronic images captured during the Tumbler-Snapper series and

Operation Upshot Knothole at the Nevada Test Site, rapatronic images were also taken

during Operation Greenhouse in 1951 and Operation Redwing in 1956, both conducted

in the Pacific; and Operation Hardtack II in 1958, conducted at the Nevada Test Site.

Conclusion

Rapatronic images provided a valuable tool for scientists to understand the events that

occur in the milliseconds after the

detonation of a nuclear bomb. The images

prompted research and validation of new

concepts, and brought Dr. Harold

Edgerton, the father of rapatronic

photography, acclaim for his contributions

to science and photography. He received

the Medal of Freedom, the National Medal

of Science, the National Medal of

Technology, and the International Center

of Photography's Lifetime Achievement

Award. 

Because the rapatronic

camera could only take one

photo, banks of cameras

were needed to photograph

a single nuclear test. 

For more information, contact:

U.S. Department of Energy

National Nuclear Security Administration

Nevada Site Office

Office of Public Affairs

P.O. Box 98518

Las Vegas, NV 89193-8518

phone: 702-295-3521

fax: 702-295-0154

email: nevada@nv.doe.gov

http://www.nv.doe.gov

DOE/NV - -1136

June 2006

Rapatronic images captured in succession during an atmospheric tower test in the Snapper

phase of the Tumbler-Snapper series.

Lea, part of Operation Hardtack II, was

detonated at the Nevada Test Site on

October 13,1958.