Lessons Learned











Symmetry Analyzer



Under some circumstances, it may be important to know if the object in a storage container is spherical. A way to do this was suggested in Moscow by Vitaliy Dubinin of VNIIEF during discussions on the Mutual Reciprocal Inspections initiative in 1996. A homogeneous radioactive item should have an isotopic radiation field. Dubinin suggested placing the item before a neutron detector then rotating it incrementally about two orthogonal axes. The neutron counts would then be recorded at each incremental position. If the counts were nearly equal in each position, the item could be declared to be spherical. The method was successfully tested in joint U.S.–Russian Federation experiments at Lawrence Livermore National Laboratory in late 1996.

For the FMTTD, a number of different plutonium attributes needed to be measured simultaneously with both an improvised neutron multiplicity counter and two gamma-ray detectors. The item to be measured was placed in the cavity of the neutron multiplicity counter and all of the measurements were done simultaneously—with the gamma-ray detectors viewing the item through the walls of the multiplicity counter. This arrangement precluded measurement about two axes but did allow measurements about one axis to check for cylindrical symmetry. This was deemed to be adequate for the purpose of the FMTTD. During the measurement, the axes of symmetry of the items measured were aligned with the axis of symmetry of the multiplicity counter. The multiplicity counter has eight identical banks of neutron detectors equally distant from its axis of symmetry. This made it possible to conduct eight neutron measurements around the item simultaneously precluding the need to rotate the item. This method was quite successful for detecting deviations from cylindrical symmetry.


Symmetry System


     Solid State Disk Module  

     Power Supply


Symmetry Acquisition and Analysis

  •      Acquisition Hardware: 

     Software Installation Manual

     Universal Library Users Guide 

     Universal Library, Function Reference

     Extended Software Installation Manual



Department of Energy

 Defense Threat Reduction Agency | Los Alamos National Laboratory

Lawrence Livermore National Laboratory | Pacific Northwest National Laboratory