John M. Dale

Principal Component Analysis of Diffuse Near-Infrared Reflectance Data From Paper Currency

Product tampering and product counterfeiting are increasing the need for methods to quickly determine product authenticity. One of the concepts that we are investigating for the detection of counterfeit objects involves the use of pattern recognition techniques to analyze multivariant data acquired from properties intrinsic to the object. The near-infrared reflectance spectra of currency and other paper stock were used as a test system. The sample population consisted of authentic currency, circulated and uncirculated, and cotton and rag paper stock as stand-ins for counterfeit currency. Reflectance spectra were obtained from a spot that was essentially void of printing on both sides of the currency specimens. Although the reflectance spectra for all of the samples were very similar, principal component analysis separated the samples into distinct classes without there being any prior knowledge of their chemical or physical properties. Class separation was achieved even for currency bills that differed only in their past environment. Leave-One-Out procedures resulted in 100% correct classification of each member of the sample set. A K-Nearest-Neighbor test or a linear discriminate can be used to correctly classify unknown samples.

A design for a high intensity slow positron facility using forward scattered radiation from an electron linear accelerator

A tungsten moderator will be placed behind the target of the Oak Ridge Electron Linear Accelerator (ORELA) to convert gamma radiation to slow positrons. These will be extracted and led through evacuated solenoids to an experiment room. A Penning trap will be used to extend the slow positron pulses to achieve duty factors of 10% or greater. The facility will be used for atomic and molecular physics studies, positron microscopy, and materials research. Operations will be inexpensive and will not interfere with the normal function of ORELA, the measurement of neutron cross sections by flight-time spectrometry.

The characterizations of solid specimens: Approaching the whole problem

The purpose of this paper is to demonstrate that complicated mixtures of solids can be characterized to a rather high degree if a coordinated examination by non-destructive methods is used. The techniques discussed are X-ray fluorescence, scanning electron microscopy, photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction. The application of these methods to the characterization of corrosion scale on an inconel coupon is illustrated. The types of information accumulated were elemental composition, chemical forms of elements, special distributions of elements and compounds in the scale, sizes of particles that made up the scale, variations in composition of particle surfaces from that of their interiors, and composition of scale-alloy interface.

Analytical applications of positrons

In using positrons as analytical tools the experimenter has two quite different options. The first and more obvious is to duplicate electron methods with positrons and see what differences (if any) result. The second is to exploit a unique characteristic of positrons, such as the formation and decay of the positronium atom, to study chemical composition and surface characteristics. Because positrons do not exist freely in our world, they must be obtained from radioactive sources or nuclear interactions. Source intensity has consequently been a limiting factor in experiments that attempt to duplicate electron applications. Some methods of producing and moderating positrons that have been developed here (and elsewhere) are described as well as results from studies using the sources. Surface measurements require less intense sources and yield useful data on materials such as xeolites, silica gels, graphite and alumina. Experimental apparatus, data and interpretation will be discussed.