Dysprosium-Containing Nanocrystals for Thermal Neutron Detection
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Dysprosium-Containing Nanocrystals for Thermal Neutron Detection Antonio C. Rivera1, Natasha N. Glazener1, Nathaniel C. Cook1, Nathan J. Withers1, John B. Plumley1, Brian A. Akins1, Ken Carpenter2, Gennady A. Smolyakov1, Robert D. Busch2, and Marek OsiĔski1 1
Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, NM 87106-4343 Tel. (505) 272-7812; Fax (505) 272-7801; E-mail: [email protected] 2
Department of Chemical and Nuclear Engineering, 1 University of New Mexico, Albuquerque, NM 87131 ABSTRACT We propose a novel concept of optical detection of thermal neutrons in a passive device that exploits transmutation of Dy-164, a dominant, naturally occurring isotope of dysprosium, into a stable isotope of either holmium Ho-165 or erbium Er-166. Combination of the high thermal neutron capture cross section of ~2,650 barns and transmutation into two other lanthanides makes Dy-164 a very attractive alternative to traditional methods of neutron detection that will be completely insensitive to gamma irradiation, thus reducing greatly the likelihood of false alarms. The optically enabled neutron detection relies on significant differences in optical properties of Dy, Ho, and Er that are not sensitive to a particular isotope, but change considerably from one element to another. While the concept applies equally well to bulk materials and to nanocrystals, nanocrystalline approach is much more attractive due to its significantly lower cost, relative ease of colloidal synthesis of high quality nanocrystals (NCs), and superior optical and mechanical properties of NCs compared to their bulk counterparts. We report on colloidal synthesis of DyF3 NCs, both doped and undoped with Ho and co-doped with Ce and Eu to enhance their optical properties. We also report on DyF3:10%Ce and DyF3:10%Eu NCs irradiated with thermal neutrons from a Cf-252 source and their optical characterization. INTRODUCTION Standard detectors of slow neutrons rely on the 10B(n,α), 6Li(n,α), or 3He(n,p) reactions [1]. The thermal neutron cross section for the 10B(n,α) reaction is 3840 barns, and the natural abundance of 10B is 19.8%. The most common detector based on the boron reaction is a BF3 gas tube. Boron-loaded scintillators are also used, although they encounter the challenge of discriminating between gamma rays backgrounds and gamma rays due to neutrons. The thermal neutron cross section for the 6Li(n,α) reaction is 940 barns, and the natural abundance of 6Li is only 7.4%. This requires enrichment of 6Li isotope. Moreover, detectors using 6Li suffer from their sensitivity to gamma radiation. The thermal neutron cross section for the 3He(n,p) reaction is 5330 barns, but its natural abundance of only 0.0001% results in a very high cost ($1,000 per liter for US commercial use [2]). Currently, all 3He production comes solely from the refurbishment and dismantlement of the nuclear stockpile as a byproduct from the radioactive decay of tritium, where it is separated during the tritium cleaning process. A further proble
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