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Radiation Measurements and Spectroscopy
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Generally, the samples used in a neutron activation analysis (NAA) are small and their mass can be accurately measured and, because one is usually seeking concentrations of trace elements, a NAA analysis is well approximated as a linear process and application of linear LS technique is appropriate. However, for bulk samples, a prompt-gamma neutron activation analysis (PGNAA) is non-linear, primarily for the following reasons: Sample mass, which often is not known, affects the flux density and the macroscopic capture cross section of the sample.The composition of the sample, which is unknown in advance, affects the spectrum. In particular, moisture content strongly affects the thermal-neutron flux density, which is what gives rise to the prompt gamma rays. Also, neutron absorbers affect the thermal flux density.
Electrical, Physical, and Chemical Characterization
Published in Robert Doering, Yoshio Nishi, Handbook of Semiconductor Manufacturing Technology, 2017
Dieter K. Schroder, Bruno W. Schueler, Thomas Shaffner, Greg S. Strossman
Purpose. The radiochemical techniques most commonly applied to semiconductor materials are listed in Table 28.9. Of these, neutron activation analysis (NAA) is the most sensitive for trace element analysis. It is predominantly applied to bulk silicon (CZ and float zone) and can provide ppb or better sensitivities for many impurities of importance to semiconductor manufacturers. The other activation methods are more suited for profiling thin film structures.
An Overview of the Application of Pulsed Neutron Activation in Flow Measurements
Published in Nuclear Technology, 2020
Neutron activation analysis (NAA) is a nuclear technique that relies on the measurement of gamma rays emitted from a sample that is irradiated by a beam of neutrons.1 The energy of the emitted gamma rays from a sample exposes the element contents of the sample, and the intensity of the gamma rays are directly proportional to the concentration and abundance of the elements. NAA has a wide range of applications from chemistry to geology, archeology, soil science, environmental analysis, semiconductor industry, medicine, agriculture, and even forensic science. In this paper, we review applications of the neutron activation technique for flow velocity measurements based on tracing the activity in the medium flowing in a pipeline. As shown in Fig. 1, the NAA analysis process starts with bombarding the sample with a beam of neutrons. The neutron capture process by the elements of the sample produces unstable compound nuclei followed by gamma-ray emission (called prompt gamma with energies up to 11 MeV in a very short time of about 10−12 to 10−9 s) creating radioactive isotopes. Finally, the radionuclides decay to stable nuclei with the emission of beta particles along with gamma rays (called delayed gamma). Detection of the gamma rays provides the precise identification and quantification of elements in the sample. The rate at which gamma rays are emitted with particular energies can be measured by high-resolution semiconductor detectors. If the prompt gamma rays (measured during neutron irradiation) are used to determine the presence and amount of elements in the sample, then NAA is called prompt gamma neutron activation analysis (PGNAA). If the analysis is based on the delayed gamma rays (measured at some time after neutron irradiation), it is called delayed gamma neutron activation analysis (DGNAA). Both PGNAA and DGNAA are illustrated in Fig. 1. PGNAA applies to elements with extremely high neutron capture cross sections and short irradiation time, often on the order of seconds or minutes. While DGNAA is applicable for the vast majority of elements that produce radioactive nuclides, PGNAA concentrates on elements that produce stable isotopes or elements with weak decay gamma-ray intensities.2