Seeing Through Steel:  Nondestructive Evaluation of Deadly Substances by Spectroscopy of Neutron-Induced Gamma Rays

Dr. A.J. Caffrey
Idaho National Laboratory

Seeing the unseen has been a recurring theme in applied physics since the 1895 discovery of x radiation by Roentgen.   A bit over a century later in 1990, the United States government sought a nondestructive identification method for the chemicals inside military stockpile munitions and containers in anticipation of the 1994 Chemical Weapons Convention.  A team of Idaho National Laboratory (INL) physicists responded by designing a neutron-based instrument that can “see” through the thick steel casing of an artillery projectile and determine the chemical within, eliminating the need for drilling, sampling, and chemical analysis of lethal substances like nerve agent sarin.  The Portable Isotopic Neutron Spectroscopy (PINS) system was operational and adopted by the U.S. military by 1992. 

Initially, PINS was thought useful just for treaty monitoring applications.  The accidental discovery of a cache of buried World War I-era chemical munitions in Washington, D.C. in January 1993 made it clear that PINS could play an important role in the identification of “non-stockpile” munitions, that is, projectiles recovered from burial sites and firing ranges.  Non-stockpile munitions frequently have lost their identifying markings due to corrosion, and yet their contents must be known for safe and lawful disposal.  Besides chemical warfare agents like nerve agents and mustard gas, non-stockpile munitions may contain explosives, smoke generating chemicals, e.g. white phosphorus, or practice fills like plaster-of-Paris.

Today PINS development continues at INL, and in 2013, third-generation PINS instruments became commercially available.  In this talk, the evolution of PINS hardware and software will be explained, along with the supporting physics that permits the instrument to “see through steel.”