Organic Glass Scintillators for Nuclear Physics Experiments

The nuclear physics community relies on state-of-the-art detector systems to explore exotic nuclei at the limits of nuclear stability. Understanding the structure and properties of nuclei at the neutron dripline provides insight into nature’s fundamental interactions and astrophysical processes. Important criteria for neutron detectors include a high detection efficiency, neutron spectroscopy, a fast response, efficient discrimination between neutrons and the gamma rays, scaleup to large sizes and low cost. Discrimination between neutrons and gamma-rays is typically achieved with liquid scintillators. Unfortunately, liquid scintillators are rather bulky and hazardous to work with due to their low flash points, toxicity, and are difficult to transport. On the other hand, plastic scintillators such as those used in the Low Energy Neutron Detector Array (LENDA) at NSCL, and the Versatile Array of Neutron Detectors at Low Energy (VANDLE) at HRIBF offer efficient neutron detection but lack neutron/gamma pulse shape discrimination (PSD). Also, the low light yield, and therefore the energy threshold at which these plastic scintillation detectors can operate, leaves much to be desired. Multi-mode Organic Glass Scintillators (OGS) developed at RMD and Sandia National Laboratory (SNL) have faster decay than plastic scintillators, high light yield and neutron/gamma PSD comparable to trans-stilbene, as well as gamma-ray spectroscopy capabilities due to tin loading. Moreover, these can be fabricated in large sizes via a melt-casting process at a low cost. The multi-mode OGS will increase the output of the FRIB experiments not only in astrophysics experiments, but also in other nuclear structure studies such as high-spin physics, fast-timing lifetime measurements, and beta-delayed and fast neutron spectroscopy at the limits of stability. In Phase I, RMD and SNL have developed and selected OGS composition with the goal of its suitability in nuclear physics experiments. Our collaborator Dr. Zegers group at Michigan State University (MSU) have validated its superior performance compared to commercially available organic scintillators, particularly for its adaptability in the LENDA neutron array. We have demonstrated high light yield, fast decay, excellent PSD, and potential for scalability in a single OGS composition. In addition, increased gamma-ray sensitivity has been achieved by adding tin compound to OGS. The goal of the Phase II project is to optimize polymer and tin compound in the selected OGS, and scale it up to large bar-size detectors to replace current neutron detectors in the arrays used in FRIB experiments. The potential applications for the proposed OGS include nuclear physics, nuclear non-proliferation - large portal monitors, high energy particle physics research, nuclear waste characterization, industrial non-destructive evaluation, biological and materials research, astronomy, and health physics.