K₀ Method Of Prompt-gamma Neutron Activation Analysis And Its Application

Neutron-induced prompt-gamma activation analysis, PGNAA, is a highly sensitive and nondestructive nuclear analytical technique for the determination of multielements in diversified materials. In PGNAA, an element can be identified and quantified by measuring (he energy and intensity of gamma rays promptly emitted (within 10^-14 seconds or less) from the compound nucleus formed by the element after the absorption of neutrons. For elements with indicator nuclides of pure β^- emitters or very weak y branching ratios, consequently cannot be readily determined by conventional NAA (i.e. DGNAA), especially light elements such as hydrogen, boron, nitrogen, silicon, and the elements with high neutron capture cross sections, PGNAA is an important complementary method.In this work, a series of preliminary studies on PGNAA are conducted at No.O horizontal channel of the 15 MW heavy water research reactor (HWRR) in China Institute of Atomic Energy (CIAE). One of the main aims of the work is to lay the foundation for more intensive PGNAA studies using high quality thermal and cold neutron beams at China Advanced Research Reactor (CARR), which will be set up at CIAE in the near future.There are five chapters in this thesis. The first chapter expounds the significance of prompt gamma-ray neutron activation analysis, and gives a brief introduction to the history and current status of PGNAA at home and abroad. The second chapter explains the basic principle of neutron activation analysis (both PGNAA and DGNAA), including the procedures of qualitative and quantitative analysis, the detection limits for multielements, main characteristics, and major applications of PGNAA. The third chapter introduces the facilities used in PGNAA and efficiency calibration of high purity germanium detector (HPGe). The facilities include the high purity thermal neutron beam system, the shielding for measurement system and the measurement system itself. The principle and procedures of efficiency calibration for wide range of gamma energy (90 to 7500 keV) are introduced for HPGe detectorsystem. The concept of effective interaction depth (EID) for coaxial HPGe and calculation method are recommended for the normalization of efficiencies from different counting positions.The whole process of analysis, from sampling and sample preparation to data reduction and evaluation, is summarized in the forth chapter. The application of direct counting rate measurement and measurement of ko factors of multielements for PGNAA, and the determination of multielements in reference materials by using conventional NAA (DGNAA) are described in this chapter.Finally, a brief introduction to the database of PGNAA together with a brief summary of this work and an expectation for future research on PGNAA is given at the end of this thesis.