C.G. Chilom (Univ Bucharest, Fac Phys, Dept Elect Solid State & Biophys, Magurele, Romania) B. Zorila, M. Bacalum (Horia Hulubei Natl Inst Phys & Nucl Engn, Magurele, Romania); R. Yaroslavtsev, S.V. Stolyar (Siberian Fed Univ, Krasnoyarsk, Russia; SB RAS, Kirensky Inst Phys, Krasnoyarsk, Russia)

YuMO facility (IBR-2 pulsed reactor, Dubna, Russia); other methods: IFIN-HH, Romania; SB RAS KIP, Krasnoyarsk, Russia