TECHNOLOGY AREA(S): Materials, Nuclear, SensorsOBJECTIVE: To investigate and develop fast scintillation materials that can be operated under nuclear battlefields for nuclear search, identification, and dose rate estimation.The new scintillators must have ultra-fast decay time, with very limited to no slower decay components, good luminosity, and capable of radioisotope identification.Demonstrate materials performance in prototype detector and develop a cost model and commercial production path. DESCRIPTION: Most radiation detection systems utilize scintillators as detectors.However in high dose rate environment the majority of scintillators are too slow and often subject to radiation damage.Hence, the alternative sensors used under these conditions are often limited to GM-tubes or silicon diodes.While simple and effective, these detectors have their drawbacks: They provide count rates only rather than spectroscopic information which leads to inaccurate isotope identification and dose rate estimation [1]. In addition, the high dead time under high radiation environment will result in the loss of triggers, or lead to detector paralysis. The inoperability of the advanced scintillators at high dose environment has severely limited the mission capabilities in search and identification of radioactive materials in the nuclear battlefield.In order to improve radioisotope identification and dose rate estimation for very high dose rate environment, new detector materials are sought.Potential solutions include the development of fast and high radiation-tolerant spectroscopic scintillators.Such scintillators shall possess very fast decay time (shorter than 5 ns), very low to absence of slower decay components, high enough light yield (> 1,000 photons/MeV) to allow the detection of photons down to 60 keV, sufficient energy resolution for spectroscopy based dose measurement, and high enough radiation hardness to survive and operate in intense dose rate environment, up to 1,000 cGy/h.Examples of existing fast scintillators include halide scintillators [2], e.g. BaF2, CLYC, etc.These scintillators decay with < 1 ns time constant and have good luminosity of ~2,000 photons/MeV.However, these scintillators often have slower scintillation decay components that would create significant baseline detrimental for the detector under high radiation fields.In addition, halides are also prone to radiation damage during prolonged exposure to high radiation doses.Oxides, on the other hand, can be radiation hard and provide fast decay time, such as PbWO4 (PWO) commonly used in high energy physics experiments [3].PWO has high density and fast decay time, but the light yield is not high enough [4].Even more interesting are the rare earth oxides, such as Lu2O3, have exhibited much higher light yield and faster decay time than PWO.These oxides are often prepared in the form of ceramic scintillators, which makes them more robust and radiation hard than single crystals [5].To leverage the ongoing research momentum in fast and radiation hard scintillator materials, DTRA seeks innovative ideas for ultra-fast scintillation materials capable of achieving high count rate with sufficient energy resolution for dose evaluation and isotope identification at both low dose rate environments and nuclear battlefield conditions.The materials must be rugged and can operate over DoD's wide range of environments.Phase I development must demonstrate feasibility of selected materials to provide high count rate, acceptable energy resolution for reliable dose calculation and isotope identification, and adequate radiation hardness.Phase II development will further optimize the down selected materials to achieve the following performance thresholds {objectives}: 1) Decay time: < 5 ns {< 1 ns} 2) Light yield: > 1,000 photons/MeV {> 2,000 photons/MeV}3) FWHM energy resolution at 662 keV: 10-15% {7-10%, or approaching that of NaI:Tl} 4) Capable of operating in high dose rate environment: up to 1,000 cGy/h {3,000 cGy/h} 5) Materials unit cost: less than the cost of PWO {similar to the cost of the NaI:Tl} 6) Materials must be environmentally rugged for DoD applications 7) Neutron detection: optional {required} The materials performance must be demonstrated in the prototype detector configuration by the end of Phase II program.PHASE I: Identify the scintillator materials and their potential.Demonstrate pathways for meeting the Phase II performance goals through feasibility studies at the end of Phase I.Demonstrate radiation hardness capabilities.By the end of the Phase I, single or multiple candidate materials shall be down selected for further development in Phase II.PHASE II: Further optimize the selected material(s) to produce detector-size samples at the targeted performance parameters.Demonstrate the performance in prototype detectors that accomplish the goals of reliable gamma-ray (and/or neutron) detection and identification under both low dose rate environments and fallout conditions.The detectors shall demonstrate radioisotope identification capabilities consistent with ANSI N42.34 [6].Demonstrate ability to measure dose/dose rate under fallout conditions accurate to 20% or 15 cGy.Develop manufacturing and commercialization plans for implementing the research in production and dissemination of the scintillators, respectively.PHASE III: Further optimize the selected material(s) to produce detector-size samples at the targeted performance parameters.Demonstrate the performance in prototype detectors that accomplish the goals of reliable gamma-ray (and/or neutron) detection and identification under both low dose rate environments and fallout conditions.The detectors shall demonstrate radioisotope identification capabilities consistent with ANSI N42.34 [6].Demonstrate ability to measure dose/dose rate under fallout conditions accurate to 20% or 15 cGy.Develop manufacturing and commercialization plans for implementing the research in production and dissemination of the scintillators, respectively.KEYWORDS: scintillation materials, high radiation field, dose measurements, gamma-ray detection, radio-isotope identification, RIIDReferences:[1] National Urban Security Technology Laboratory for the U.S. Department of Homeland Security, Science and Technology Directorate, June 2016. Radiation Dosimeters for Response and Recovery Market Survey Report. Homeland Security [2] P. Rodnyi, Core-valence luminescence in scintillators, Rad. Meas., Vol. 38, p. 343, 2004. [3] P. Lecoq and M. Korzhik, Scintillator developments for high energy physics and medical imaging, NIM A Vol. 47, p. 1311, 2000. [4] L. van Peiterson, et al., Charge transfer luminescence of Yb3+, J. Lum Vol. 91, p. 177, 2000. [5] T. Yanagida, et al., Optical and scintillation properties of transparent ceramic Yb:Lu2O3 with different Yb concentrations, Optical Material, Vol. 36, p. 1044, 2014. [6] ANSI N42.34, American National Standard Performance Criteria for Hand-Held Instruments for the Detection and Identification of Radionuclides.
