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For Immediate Release:
September 16, 1997

News Media Contacts:
Darwin Morgan, NV, 702/295-3521
Greg Cook, NV, 702/295-4628
David Schwoegler, Livermore, 510/422-6900
Chris Kielich, DOE HQ, 202/586-5806

Second Subcritical Experiment Scheduled for September 18

The Department of Energy has scheduled the second of two planned subcritical experiments—physics experiments to learn the properties of nuclear materials—for Thursday, September 18. The experiment, named Holog, will be conducted by the Department of Energy's Lawrence Livermore National Laboratory at the U1a Complex at the Nevada Test Site.

These experiments are essential to the department's Stockpile Stewardship and Management Program, the plan to maintain the safety and reliability of the nuclear weapons stockpile in the absence of underground nuclear testing. This confidence in safety and reliability is required by the President in order for the United States to support the Comprehensive Test Ban Treaty.

The name Holog is taken from the lab-developed laser-holography technology that allows scientists to capture three-dimensional images of the particles ejected from the surface of materials shocked by high explosives.

The object of the experiment is to characterize this "particle cloud." Information about the mass, particle-size distribution and mass-velocity distribution will allow scientists to understand more clearly the properties of plutonium.

The Holog experiment will consist of two simultaneous non-nuclear explosions in a chamber sealed with a two-foot concrete and steel plug from the rest of the tunnel complex. In the first, a 77-gram plutonium disk, a little smaller than a 50-cent piece, will be bolted onto a target holder attached to a steel cylinder containing 50 grams of a chemical explosive. The second will use a smaller 50 gram quantity of plutonium and 50 grams of high explosive.

Both the shape and the small amount of plutonium used in the experiments are designed to prevent a self-sustaining nuclear reaction. Thus, these experiments are consistent with the Comprehensive Test Ban Treaty. They are called "subcritical" experiments because no self-sustaining nuclear fission chain reaction will occur.

Scientific data obtained from the experiment will allow scientists to answer basic questions about the way plutonium reacts when it's shocked – which cannot be determined with the required precision by experimenting with substitute materials. The data will help to bench-mark complex computer simulations of nuclear weapons performance that will be used to certify the safety and reliability of the Nation's nuclear weapons stockpile, without nuclear testing.

The JASONs, an independent group of scientists, reviewed the design of this subcritical experiment. They concluded it "will add valuable scientific information to our database relevant to the performance of our nuclear weapons, and that there is no conceivable scenario in which it will lead to criticality."

Subcritical experiments are essential to the United States' commitment to a reliable nuclear deterrent in a world free of nuclear testing. The first subcritical experiment, Rebound, was successfully conducted at the Nevada Test Site by the Department of Energy's Los Alamos National Laboratory on July 2.

Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy.

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