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For a 10-centimeter-thick slab of material, a beam of x rays is payday loans online by roughly one million (one in a million x rays makes it through the slab), whereas one in three payday advance protons makes it through. Because many more protons make it through than x rays, scientists say payday advance that protons are more penetrating.

Seemingly Simple Technology "At first glance," says Lawrence Livermore physicist Edward Hartouni, "proton radiography seems simple and obvious. High-energy protons are used directly as a radiographic probe to illuminate an object, are absorbed and scattered by payday loans online object, and then are brought to a focused image by a magnetic lens system for recording by an imaging detector. He notes that the Laboratory is well positioned to assess proton radiography because of its expertise in accelerators and detectors obtained in payday loans online and high-energy physics research.

Hartouni says protons offer several advantages over x rays for studying the dynamics of imploding systems. For example, about 10,000 times fewer protons than x rays are needed to make the same quality radiograph. The greater penetrating ability of protons gives a much higher signal-to-noise ratio, which translates to higher resolution. Protons also have a better capacity to discriminate between two similar materials. X rays are sensitive to density only, so if the densities of two dissimilar materials are close, the radiograph will fail to differentiate the two clearly.

What's more, Hartouni says, using magnets to focus beams of charged particles is an established practice at accelerator laboratories. If is quite easy to split a single proton beam into a large number of separate beams for penetrating an object from different angles. Also, because protons are naturally pulsed in the accelerator, it is easy to produce pulsed beams that would permit multiple, stop-action radiographs to be taken during a single dynamic experiment.

Finally, x rays are produced by first creating and accelerating a beam of electrons. These electrons are directed onto a target, where they decelerate, damaging the target in the process. The deceleration produces photons with a broad energy spectrum and with only some of the photons in the x-ray band. Protons offer a more efficient direct source of penetrating radiation. Radiography Remains the Top Tool In the absence of nuclear testing, advanced radiography is the most important experimental tool currently available to help maintain the nation's aging nuclear stockpile.

Hydrotests use high explosives and surrogate nuclear materials to make up a mock primary (the first stage of a nuclear weapon). During the test, explosive pressures become so great that materials flow like liquids, that is, hydrodynamically. X-radiographs taken during the experiment allow physicists to study what happens to the different materials on very short time scales and deep within the mock primary.

Livermore's newly upgraded Flash X-Ray (FXR) machine, located at the remote Site 300 test center, will continue to be one of the premier flash x-ray capabilities once the Contained Firing Facility is completed in 2001.

The upgraded machine will be able to take two radiographs along the same vantage point about a microsecond apart. Los Alamos National Laboratory's Dual Axis Radiographic Hydrodynamic Test (DAHRT) facility, when fully operational, will offer higher resolution radiographs than FXR. The first arm of the facility, which uses a single-phase accelerator, is scheduled to become fully operational in the late fall of 2000.

A second arm (for which Livermore scientists provided most of the design) will be situated 90 degrees to the first and is scheduled for completion in about two years. Although additional arms can be added, the expense would be considerable and the number of pulses per view is severely limited. The work of the last five years by physicists from Lawrence Livermore and Los Alamos national laboratories has helped to advance proton radiography to the point where the technology is a serious candidate for the Advanced Hydrotest Facility (AHF).

Planning the Next-Generation Facility Still in the conceptual stages, the AHF would be an important long-term goal of the Stockpile Stewardship Program. The facility would better reveal the evolution over time of a weapon primary under normal conditions and in accident scenarios. The AHF would be constructed at either Los Alamos or DOE's Nevada Test Site (NTS).

The facility would provide radiographs from between 8 and 16 directions and between 5 and 12 fleeting pulses per experiment.

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