M. Leslie Carman

Recent developments in PSD plastics: optimization, attenuation, and additives (Conference Presentation)

Pulse shape discrimination in plastic scintillators has been of much interest in recent years. As with many innovative technologies, initial formulations for PSD plastics provided new capabilities that required much in-depth research to fully develop and refine. Herein we describe results from extensive optimization studies which have led to the development of PSD plastics with markedly improved scintillation performance and physical properties. Results of exploring different plastic matrices as well as a variety of secondary dyes are reported and optimum components are described. Due to the large concentration of additives required to manifest optimal PSD properties in plastic scintillators, the physical stability can be limited and the mechanical properties of PSD plastics are inferior to standard engineering plastics. Practical and theoretical solutions have been developed to address the physical stability and mechanical deformation problems in PSD plastics, and this work has resulted in physically stable scintillators with robust mechanical properties. Performance deterioration on increasing the size of PSD plastics is also addressed. At large sizes, physical and performance characteristics are much more sensitive to preparation conditions and compositional alterations as compared with small scintillators, and efforts to improve these properties are described. Finally, efforts to incorporate aromatic lithium compounds into PSD plastics are summarized and the effects of the lithium compounds on scintillation, stability, and attenuation are discussed.

Organic scintillators with pulse shape discrimination for detection of radiation(Conference Presentation)

The detection of neutrons in the presence of gamma-ray fields has important applications in the fields of nuclear physics, homeland security, and medical imaging. Organic scintillators provide several attractive qualities as neutron detection materials including low cost, fast response times, ease of scaling, and the ability to implement pulse shape discrimination (PSD) to discriminate between neutrons and gamma-rays. This talk will focus on amorphous organic scintillators both in plastic form and small-molecule organic glass form. The first section of this talk will describe recent advances and improvements in the performance of PSD-capable plastic scintillators. The primary advances described in regard to modification of the polymer matrix, evaluation of new scintillating dyes, improved fabrication conditions, and implementation of additives which impart superior performance and mechanical properties to PSD-capable plastics as compared to commercially-available plastics and performance comparable to PSD-capable liquids. The second section of this talk will focus on a class of small-molecule organic scintillators based on modified indoles and oligophenylenes which form amorphous glasses as PSD-capable neutron scintillation materials. Though indoles and oligophenylenes have been known for many decades, their PSD properties have not been investigated and their scintillation properties only scantily investigated. Well-developed synthetic methodologies have permitted the synthesis of a library of structural analogs of these compounds as well as the investigation of their scintillation properties. The emission wavelengths of many indoles are in the sensitive region of common photomultiplier tubes, making them appropriate to be used as scintillators in either pure or doped form. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work has been supported by the U.S. Department of Energy Office of Nonproliferation Research and Development (NA-22) and by the Defense Threat Reduction Agency (DTRA).

Portable thin layer chromatography for field detection of explosives and propellants

A field deployable detection kit for explosives and propellants using thin layer chromatography (TLC) has been developed at Lawrence Livermore National Laboratory (LLNL). The chemistry of the kit has been modified to allow for field detection of propellants (through propellant stabilizers), military explosives, peroxide explosives, nitrates and inorganic oxidizer precursors. For many of these target analytes, the detection limit is in the μg to pg range. A new miniaturized, bench prototype, field portable TLC (Micro TLC) kit has also been developed for the detection and identification of common military explosives. It has been demonstrated in a laboratory environment and is ready for field-testing. The kit is comprised of a low cost set of commercially available components specifically assembled for rapid identification needed in the field and identifies the common military explosives: HMX, RDX, Tetryl, Explosive D or picric acid, and TNT all on one plate. Additional modifications of the Micro TLC system have been made with fluorescent organosilicon co-polymer coatings to detect a large suite of explosives.