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Report No.

Nuclear resonance fluorescence in U-238 using LaBr detectors for nuclear security

Hayakawa, Takehito; Negm, H.*; Ogaki, Hideaki*; Daito, Izuru*; Kii, Toshiteru*; Zen, H.*; Omer, M.*  ; Shizuma, Toshiyuki; Hajima, Ryoichi

Recently, a nondestructive measurement method of shielded fissional isotopes such as $$^{235}$$U or $$^{239}$$Pu has been proposed for the nuclear security. These isotopes are measured by using nuclear resonance fluorescence (NRF) with monochromatic energy $$gamma$$-ray beams generated by laser Compton-scattering (LCS). We have proposed that one measure scattered $$gamma$$-rays from NRF with LCS $$gamma$$-ray beams using the LaBr$$_{3}$$(Ce) detectors. The LaBr$$_{3}$$(Ce) crystals include internal radioisotopes of a meta-stable isotope $$^{138}$$La and alpha decay chains from some actinides as $$^{227}$$Ac. There is a broad pump at about 2 MeV. This pump is considered to be an overlap of $$alpha$$-rays from decay chains of some actinides but its detailed structure has not been established. Here we have measured NRF spectra of $$^{238}$$U using the LCS $$gamma$$-rays with energy of about 2.5 MeV at the HIgS facility of the Duke University. The background has been evaluated using a simulation code GEAT4. The 9 peaks, 8 NRF $$gamma$$-rays plus the Compton scattered $$gamma$$-ray of the incident beam, are finally assigned in an energy range of about 200 keV at about 2.5 MeV. The 8 integrated NRF cross-sections measured by LaBr$$_{3}$$(Ce) have been consistent with results by an HPGe detector. The three levels are newly assigned using the HPGe detector. Two of them are also measured by LaBr$$_{3}$$(Ce).



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