This paper presents calculation results based on Monte-Carlo method to select an appropriate neutron moderator and design four configurations for a 252Cf irradiation system. These configurations provide six neutron spectra with the various average energies (1.04 MeV, 1.38 MeV, 1.69 MeV, 2.05 MeV, 2.46 MeV and 2.93 MeV) suitable for the calibration of neutron survey meters and personal dosimeters.

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Nuclear level scheme permits to determine nuclear level density, gamma strength function, and to evaluate nuclear models. In comparison to light nuclei, the structure of heavy nuclei is much more complicated because of their strong deformation. In order to study nuclear level scheme, gamma – gamma coincidence spectrometer with advantages of low Compton background and the ability of identifying correlated gamma transitionshas been often used. This paper presents the first results of an experimentalstudy of level scheme of 172Yb using gamma – gamma coincidence spectrometer at the Dalat Nuclear Research Institute.

The event-event coincidence spectroscopy system was successfully established and operated on thermal neutron beam of channel N0. 3 at Dalat Nuclear Research Reactor (DNRR) with resolving time value of about 10 ns. The studies on level density, gamma strength function and decay scheme of intermediate-mass and heavy nuclei have been performed on this system. The achieved results are opening a new research of nuclear structure based on (n, 2ɣ) reaction.