NCJ Number
58399
Date Published
1978
Length
13 pages
Annotation
AN ANALYSIS OF FOUR RADIOFREQUENCY RESONANCE ABSORPTION SPECTROSCOPY (RRAS) TECHNIQUES SUGGESTS THAT TWO OF THE TECHNIQUES CAN AND SHOULD BE USED AS DETECTORS FOR HIDDEN EXPLOSIVES.
Abstract
THE FOUR BASIC RRAS TECHNIQUES ARE NUCLEAR MAGNETIC RESONANCE (NMR), NUCLEAR QUADRUPOLE RESONANCE (NQR), ELECTRON SPIN RESONANCE (ESR) OR ELECTRON PARAMAGNETIC RESONANCE (EPR), AND MICROWAVE MOLECULAR ABSORPTION (MMA). FOR THE LAST 15 YEARS, SOUTHWEST RESEARCH INSTITUTE HAS BEEN STUDYING THE USE OF ONE OR MORE OF THESE FOUR TECHNIQUES TO DETECT HIDDEN EXPLOSIVES. PARTICULARLY CONSIDERED WERE THE SIGNALS FROM THE NUCLEI IN THE EXPLOSIVES, ANY FREE ELECTRONS IN THE EXPLOSIVES, OR THE MOLECULES FROM THE GASES GIVEN OFF BY THE EXPLOSIVES. THE TECHNIQUES WERE COMPARED AS TO SENSITIVITY OR RELATIVE SIGNAL/NOISE RATIO. AFTER SELECTING THE BEST TECHNIQUES, A CHOICE HAD TO BE MADE AS TO WHICH OF THE FOUR OPERATIONAL MODES TO USE: STEADY STATE, TRANSIENT, ADABATIC RAPID PASSAGE, OR DYNAMIC POLARIZATION. TRANSIENT NMR AND EPR CAN AND SHOULD BE USED AS DETECTORS FOR HIDDEN EXPLOSIVES. HIDDEN UNTAGGED EXPLOSIVES CAN BE DETECTED BY A ONE-INSTRUMENTAL COMBINATION OF HYDROGEN NMR FOR ALL OF THE EXPLOSIVES EXCEPT BLACK POWDER, AND ESR FOR THE BLACK POWDER. THE DETECTION OF EXPLOSIVES CAN BE ACCOMPLISHED AT MAGNETIC FIELDS AS LOW AS 590 GAUSS WITH USEFUL SIGNAL/NOISE RATIOS AND FILLING FACTORS OF 0.1, USING HYDROGEN TRANSIENT NMR SIGNALS. A HYDROGEN NMR INSTRUMENT CAN BE USED TO DIFFERENTIATE THE HYDROGEN NMR SIGNALS FROM EXPLOSIVES AND THE HYDROGEN NMR SIGNALS FROM OTHER MATERIALS USING DIFFERENCES IN THEIR RELAXATION TIMES AND THE EFFECTS OF LEVEL CROSSING OR THERMAL MIXING. ILLUSTRATIONS, CHARTS, GRAPHS, AND REFERENCES ARE PROVIDED. (KCP)