High Performance LuYAG Crystal Scintillating Fibers for Nuclear Physics Experiments

The Facility for Rare Isotope Beams (FRIB) will provide an unprecedented beam flux requiring new instruments with enhanced detection capabilities, particularly for beam diagnostics, tracking, and total energy measurements. Tracking detectors capable of withstanding FRIB intensities while providing high position, timing, and energy resolutions are needed for almost every experiment. Currently, gaseous detectors based on parallel plate chambers (PPAC) are being deployed, but they do not meet all the requirements of the application. More specifically, they have a maximum counting rate capability of around 100 kHz, but FRIB intensity will command higher counting rates, at least 1 MHz or more. PPAC, as gas filled detectors, are prone to gas leaks or windows breakage, with release of gas in the beam line, which is dangerous for the machine. For the Re-accelerator facility, diagnostics imaging where the energy of the beam is low (~ 5-10 MeV/u) and the rates are low (< 106), low outgassing is important (pressure as low as 10-9 - 10-10 torr), which prohibits use of PPAC, and therefore, no diagnostics tools currently exist for this purpose. For these applications, detector transparency to the beam is not required, and solid matter solutions, in particular scintillating fibers, are being considered. However, existing fibers (based on plastic scintillators) are prone to radiation damage. We propose to solve this problem by developing radiation hard, fast scintillating fibers and fiber assemblies capable of high-count rates, high positional resolution, and at relatively low cost, when compared to existing PPAC detectors. YAG:Ce and LuAG:Ce are fast scintillators with count rate capability over 1 MHz, and are the most radiation-hard scintillator materials tested to date; however, they are not available in the form factor needed for PPAC replacement and also new beam diagnostics tool. Thin arrays of fibers, each <0.5 mm thick, 1 mm wide, and 10-20 cm long, are needed to replace PPAC active area of 10 cm x10 cm or 20 cm x20 cm (depending on the position in the beam). This proposal addresses the very challenging FRIB requirements by developing cost-effective scintillating fibers of cerium-doped yttrium aluminum garnet (YAG:Ce) and lutetium yttrium aluminum garnet (LuYAG:Ce), with exceptional tolerance to ionizing radiation, high stopping power, and fast decay time of 70 ns, allowing acquisition rates of up to 15 MHz. The high speed of these scintillators would allow for time-of-flight measurements, which is not possible with current detectors. These thin scintillating fibers can be arranged in a row to enable spatial sampling and fine timing resolution. The fibers will be cut out of single crystals and will have an initial cross section of 0.8mm x0.8mm and required length up to 20 centimeters and will be arranged in a 20 cm x 20 cm matrix. The scintillator fibers can be also arranged in a “ribbon” or orthogonal “ribbons” configuration, depending on the specific detector requirements. The LuYAG:Ce scintillating materials with tunable Lu:Y ratio developed in this work will be cheaper LuAG:Ce scintillators while retaining most of the performance benefits. Crystal compositions most suitable for large scale production and FRIB deployment will be established and compared to PPAC performance and cost. The ability to manufacture novel LuYAG:Ce scintillating crystal and fibers will prove useful not only for FRIB, but also for electromagnetic calorimeters and homeland security applications where such scintillators would significantly reduce the false alarm rate in passive nuclear detection systems and allow for a large range of deployment. Fast response time and radiation hard LuYAG:Ce scintillators will find use in the scintillator market for applications such as oil and gas exploration, space-borne detectors, nuclear power plant safety, and medical applications.