By Bill Cook
|Physicist Peter Heimberg assembles a neutron spectrometer he designed and built for the Department of Energy to test neutron splatter on board USNS Seay.|
Bill Cook photos
Even before Sept. 11, 2001, experts in the Department of Defense and U.S. maritime industry were becoming increasingly concerned about the possibility of radioactive material being slipped into the United States via any of the hundreds of cargo ships that visit the nation's ports each year.
Today, Military Sealift Command, the DOD's sea transportation provider, plays a vital role in homeland security and has used three of its ships as test platforms to evaluate the latest state-of-the-art calibrating equipment designed to detect hidden radioactive material.
MSC first played a part when fast sealift ship USNS Regulus was used as a platform for Department of Energy testing in Norfolk, Va., in January 2003. More recently, DOE used MSC's large, medium-speed roll-on/roll-off ships USNS Mendonca and USNS Seay for testing in the port of Philadelphia during the loading of U.S. Army cargo in support of Operation Iraqi Freedom.
|Physicist Peter Heimberg demonstrates the neutron spectrometer equipment during a ship visit to USNS Seay by Vice Adm. David L. Brewer III, USN, Commander, Military Sealift Command. A radioactive test source was placed in a nearby location, and the equipment is picking up its signature.|
In the past, the use of radioactive detection devices met with mixed results. Inaccurate readings led investigators to interrupt seagoing commerce to search for shipboard radioactive devices that did not exist. DOE scientists eventually pegged the cause of several false positive readings to the special effect that a ship's hull has on atmospheric radiation, called the neutron ship effect.
Measuring the effect of a ship's hull has been challenging, since ships come in all shapes and sizes, are loaded with a variety of cargo that frequently changes from port to port, and are hard to find empty in a controlled environment for any length of time.
Enter MSC, owner of huge cargo ships that can mimic their commercial counterparts. When needed, MSC ships can be empty for the required testing time and can be kept in a controlled environment. In short, MSC ships have proven to be the perfect platform for DOE studies.
|Physicist Peter Heimberg on board USNS Mendonca with the many pieces that make up the one-of-a-kind, full-range neutron spectrometer that collected data during Mendonca's trans-Atlantic voyage to Crete. This spectrometer has also seen service on a U-2 spy plane, gathering similar data at the edge of Earth's atmosphere.|
Peter Heimberg, a senior physicist with DOE's Remote Sensing Laboratory at Andrews Air Force Base in the Washington, D.C., region, said the study of the neutron ship effect was initiated in 2003. The major focus of the study was why neutron background rates increase aboard large ships and cause survey equipment to behave erratically.
"The ship effect occurs when high energy cosmic rays, protons, interact with earth's atmosphere, leading to showers of neutrons at surface level," Heimberg explained. "In the presence of large quantities of steel, such as on a ship, these high energy neutrons are converted to many more lower energy neutrons, which has the effect of turning a ship into a floating neutron source. This phenomenon is harmless, but it makes measurement difficult."
The sensitivity of the detection equipment must be turned down to overcome the radiation static that exists in most everyday environments. Unfortunately, reducing the sensitivity of detection equipment can interfere with the maximum detection capabilities needed to search for illegal nuclear devices or raw materials.
Heimberg said, "We hope to develop tremendously sensitive equipment that can actually discern between the naturally occurring cosmic ray-induced background neutrons and those that should not be there — those of man-made sources. We don't, however, know yet if that is even possible.
|Five-gallon containers hold radioactive source material used during equipment testing onboard USNS Seay.|
"Using Mendonca and Seay during loading operations and later when underway was perfect," Heimberg pointed out. "We brought gross-count detectors and constructed portable neutron spectrometers on board to really capture the treasure trove of data present when the ships were loaded to the gills with heavy equipment."
Once USNS Mendonca was fully loaded, three scientists of Heimberg's team sailed with the ship and continued taking detailed neutron measurements with the spectrometers during the 11-day voyage to the island of Crete in the Mediterranean Sea. Steve Aspiotis, a retired MSC master and now a port agent there, assisted the team in departing the ship and getting their equipment safely shipped stateside.
"The data obtained during this voyage represents one of the most complete series of measurements of the neutron background spectrum at sea and will provide critical input to future computer modeling efforts," advised Heimberg. "We couldn't be happier with what we collected. The data was simply superb.
"These experiments have greatly expanded the knowledge of neutron and ship interactions, especially as they relate to national security issues, and we have MSC to thank for that," Heimberg concluded.