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Legal Notice

May 2001

The Laboratory
in the News

Commentary by
Jeff Wadsworth

Hidden Defects
with Neutrons

The Human in the Mouse Mirror

The NIF Target Chamber—Ready
for the Challenge

Indoor Testing Begins Soon at
Site 300



Jeff Wadsworth
Deputy Director for
Science and Technology

Advanced Technology for
Stockpile Stewardship

ONE of the greatest challenges facing Lawrence Livermore is helping to assure the safety and reliability of the nation's nuclear stockpile. This effort, called stockpile stewardship, demands our best technologies as well as our most creative thinking, especially in the absence of nuclear testing.
The Laboratory has been deeply involved in many aspects of stockpile stewardship. One of them is the Enhanced Surveillance Campaign, an effort to develop advanced diagnostic systems for the nondestructive surveillance of stockpiled nuclear weapons. Nondestructive surveillance is far more cost-effective and efficient than disassembling a weapon and its many components.
One of our most promising nondestructive surveillance technologies is described in the article entitled Uncovering Hidden Defects with Neutrons. The article details how a team of Lawrence Livermore researchers is demonstrating the use of high-energy neutrons as a way to inspect thick, heavily shielded objects such as nuclear warheads. This technology is needed because current methods, such as x-ray imaging, cannot easily reveal defects in materials like plastics and ceramics when they are shielded by thick metal parts such as uranium.
The team has conducted experiments at Ohio University over the past four years. Because of the experiments' highly promising results, we hope to see a prototype system installed at Livermore that would ultimately be transferred to other National Nuclear Security Administration (NNSA) facilities.
Once in operation, high-energy neutron radiography's primary mission will be the surveillance of nuclear weapons. However, neutron imaging could also be used to perform such tasks as identifying warheads that need refurbishment or for inspecting refurbished warheads before they are returned to the stockpile. In this manner, the technology could serve as a valuable tool for carrying out any changes in the size of the nation's stockpile by helping scientists to make informed decisions based on the condition of weapons.
It is important to note that neutron imaging is designed to complement, not replace, existing nondestructive evaluation tools used in stockpile surveillance. In analyzing the state of the U.S. stockpile, researchers want as much data as they can possibly produce. Neutron imaging may be the only way that researchers can learn anything about the internal structure of some heavily shielded components. In this respect, neutron imaging will simply help us do a better job of stockpile surveillance.
The success of high-energy neutron radiography demonstrates how we can leverage our experience in underground nuclear testing, which stopped in 1992. The initial idea for the project (that is, neutron imaging in the 10- to 15-megaelectronvolt energy range) and basic details of our current system design were derived from Monte Carlo simulations that used advanced neutron and gamma-ray transport codes first developed to support underground testing. Also, the design of the imaging detector is based on technology Livermore scientists originally developed for use at NNSA's Nevada Test Site.
High-energy neutron radiography is one of a number of enhanced nondestructive evaluation technologies under development at Lawrence Livermore. Another promising technology is high-energy x-ray tomography for high-resolution imaging of a nuclear warhead's plutonium pit. Our scientists are exploring other ideas as well, in response to high-level requests for new diagnostics that support stockpile stewardship. We hope these new ideas, like neutron radiography, will be successful so that they will also serve the nation's stockpile stewardship needs.






































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UCRL-52000-01-5 | May 25, 2001