Strontium iodide scintillators for high energy resolution gamma ray spectroscopy Cody M. Wilson a , Edgar V. Van Loef a , Jarek Glodo a , Nerine Cherepy b , Giulia Hull b , Stephen Payne b , Woon-Seng Choong c , William Moses c , Kanai S. Shah a a Radiation Monitoring Devices, Inc., 44 Hunt Street, Watertown, MA, USA 02472; b Lawrence Livermore National Laboratory, Livermore, CA, USA 94551; c Lawrence Berkeley National Laboratory, Berkeley, CA 94720 ABSTRACT Recently SrI 2 , a scintillator patented by Hofstadter in 1968, has been rediscovered and shown to possess remarkable scintillation properties. The light output of SrI 2 :Eu 2+ has been measured to be even higher than previously observed and exceeds 120,000 photons/MeV, making it one of the brightest scintillators in existence. The crystal also has excellent energy resolution of less than 3% at 662 keV. The response is highly linear over a wide range of gamma ray energies. The emission of SrI 2 :Eu 2+ and SrI 2 :Ce 3+ /Na + is well-matched to both photomultiplier tubes and blue-enhanced silicon photodiodes. While SrI 2 :Eu 2+ is relatively slow, SrI 2 :Ce 3+ /Na + has a fast response. SrI 2 crystals with many different dopant concentrations have been grown and characterized. In this presentation, crystal growth techniques as well as the effects of dopant concentration on the scintillation properties of SrI 2 , over the range 0.5% to 8% Eu 2+ and 0.5% to 2% Ce 3+ /Na + , will be discussed in detail. Keywords: SrI2, gamma ray spectroscopy, scintillation, high energy resolution, alkaline earth halide 1. INTRODUCTION Current spectroscopy applications, such as non-invasive chemical assaying and low energy nuclear physics experiments, require a scintillator that has a high light yield, good energy resolution, fast scintillation decay, and high effective atomic number. NaI:Tl is currently the most widely used scintillator despite the non-linearity of its response to gamma ray excitation energy and relatively poor energy resolution 1 . Newer generation scintillators like LaBr 3 :Ce 3+ provide a better combination of the desired qualities 2,3 . In 1968, Hofstadter patented SrI 2 :Eu 2+ , however the device has never been developed as a radiation detector and until recently its scintillation properties had not been explored 4 . Additionally, Hofstadter et al. reported on CaI 2 :Eu 2+ , another alkaline earth halide scintillator 5 . At that time CaI 2 :Eu 2+ was found to have a light output of over 100,000 photons/MeV, and recent studies have found that total to be even higher 6 . Unfortunately, CaI 2 :Eu 2+ is extremely difficult to grow in substantial volumes and its scintillation capabilities have gone unexploited. Recently SrI 2 :Eu 2+ has been revisited and SrI 2 doped with 0.5% Eu 2+ was found to possess exceptional scintillation properties including a light output in excess of 85,000 photons/MeV and an energy resolution of less than 4% at 662 keV 7 . In this investigation we continue the exploration into the properties of SrI 2 :Eu 2+ , looking at the effect of dopant concentration and finding even higher light output totals and improved energy resolution; making it one of the most promising scintillators in existence for nuclear spectroscopy applications. Additionally, SrI 2 doped with Ce 3+ /Na + is investigated and found to have a much faster response, though it is yet unable to match the high light output totals of SrI 2 :Eu 2+ . SrI 2 crystals with many different dopant concentrations have been grown and characterized. In this paper, crystal growth techniques as well as the effect of dopant concentration on the scintillation properties of SrI 2 , over the range 0.5% to 8% Eu 2+ and 0.5% to 2% Ce 3+ /Na + , will be discussed in detail. Invited Paper Hard X-Ray, Gamma-Ray, and Neutron Detector Physics X, edited by Arnold Burger, Larry A. Franks, Ralph B. James, Proc. of SPIE Vol. 7079, 707917, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.806291 Proc. of SPIE Vol. 7079 707917-1 2008 SPIE Digital Library -- Subscriber Archive Copy