This proposal is for an interdisciplinary research effort of experimental work to develop a dilute aqueous "green" liquid scintillator. The proposed scintillator is based on an entirely new mechanism taking advantage of the high chemical-energy content of OH-radicals which are copiously produced in water by radiation interactions. The research approach is to identify compounds which are reactive with OH radicals to form excited states of known fluorescent products, or are susceptible to use as sensitizers in dye-sensitizer systems. Preliminary results have already shown weak light output from one model system in response to OH radical reactions. Such a dilute aqueous scintillator would result in significant reduction in mixed waste (radioactive hazardous chemical mixtures) production in biomedical applications of liquid scintillation counting for tracer work; and also dramatic cost savings in large scintillation detectors such as those used for portal monitoring or as vetoes/buffers in low background experiments conducted underground.

"Green" liquid scintillator suitable for widespread deployment in large volume gamma ray and neutron screening detectors. The scintillator is "green" because it is a dilute water solution, unlike the toxic, flammable benzenoid systems of conventional liquid scintillators. The proposed research would enhance the nation's threat detection posture. Aqueous scintillators would also be highly useful in biomedical applications involving "liquid scintillation counting", where they would ease or eliminate the mixed waste problem encountered in this technique.

Graduate and undergraduate students at Temple University, an urban research university with substantial minority enrollment, would be actively involved in the research.

Project Report

The purpose of this project is to develop a water-based alternative to conventional liquid scintillators, which are made from toxic, carcinogenic, flammable organic solvents. This report concerns the first year of a two-year funding period. A scintillator is a substance used to detect nuclear radiation, by virtue of visible light it emits when it absorbs ionizing radiation such as x-rays or gamma rays. Scintillators are widely used to detect radioactive substances in biochemical tracer studies, and to scan for nuclear radiation as in cargo screening at ports of entry. In the modern era, use of conventional scintillators made from flammable solvent chemicals is disfavored for reasons of toxicity, flammability, and difficulty of disposal. A water-based scintillator would be highly desirable, especially if it could be a dilute solution (~1%) of relatively non-toxic agents. The solvent chemicals used in conventional scintillators were chosen for their unique chemical reaction to absorption of radiation, which enables them to produce light efficiently. The radiation chemistry of water is well understood but it is fundamentally different, requiring a completely different approach to designing a scintillator. We have approached this problem by screening water-soluble compounds known to emit light ("chemiluminescent" compounds) for light emission in simulated radiation experiments. We have had to develop methods and calibrate instruments to make these measurements. Our initial findings can be summarized as follows: We have found that light emission in simulated radiation experiments is not a rare phenomenon. Most of the simple fluorescent compounds we tested emit easily measurable amounts of light in these experiments. Calibration of instruments for measuring absolute chemiluminescence yield is nearly finished. It is becoming clear that light yields for early candidate emitters, though measurable with sensitive equipment, are still quite low Development is continuing on apparatus and methods for simulating the chemistry of ionizing radiation in water (using ultrasound and reactive chemicals) and also for studies with actual radiation sources. Thees methods will be used to screen more candidate emitters as the work progresses. Literature searches have revealed several classes of promising emitters to test going forward, which may lead to higher light output and a successful conclusion to the work. This work is being carried out at Temple University, an urban research university, with significant involvement o fundergraduate students from the Chemistry, Physics, Biology and Engineering majors. At the present time, six undergraduate students including one female are doing important work for pay on this project. These students attend weekly group meetings and are individually mentored by the PI, a weekly one-on-one meeting with each student.

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Temple University
United States
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