Isotope mapping capabilities using prompt gamma emission from epithermal neutrons
The time resolved Prompt Gamma Activation Analysis (T-PGAA) consists in the measurement of gamma energy spectrum induced by the radioactive capture as a function of incident neutron Time Of Flight. The PGAA spectrum in resonance or off-resonance conditions in the thermal-epithermal-fast ranges is presented to increase the elemental sensitivity and potential capabilities with respect to the NRCA and PGAA techniques. Moreover, the proposed method will introduce element specific sensitivity through incident neutron energy selection in PGAA spectra for multicomponent samples.
The strength of neutron imaging techniques is related to the unique properties of the neutron-matter interaction, such as large penetration depth into bulk materials, sensitivity to light atoms, and high contrast between adjacent elements in the periodic table (Neutron Imaging and A...). The advent of advanced pulsed neutron sources has made available intense fluxes of epithermal neutrons, with energies from above 0.5 eV to the \(\sim\) keV range (Windsor 1981). These sources offer the additional advantage to use the neutron energy dependence of the neutron cross sections, which allow to enhance the sensitivity to specific elements and isotopes as a function of the neutron energy. State of the art technologies available for neutron-based methods, using cold, thermal and epithermal/fast neutron beams, are currently being applied to study Cultural Heritage artifacts at numerous neutron beam facilities throughout the world (Hilger 2006, Maekawa 2009). FRASE PIU’ GENERALE
PGAA E DETTAGLI SULLA TECNICA (COSA SI FA GIà) STESSA COSA PER NRCA The gamma ray energy spectrum, following radiative absorption, also contains a wealth of information, being element/isotope specific, and shows photo (Belgya 2008) n energy-dependent attenuation due to the spatial location of the emitting nucleus inside the sample [9, 10]. At reactor sources, these properties are at the basis of the Prompt Gamma Activation Analysis (PGAA) technique with thermal and cold neutrons, where high resolution gamma ray energy spectra are recorded [9, 11, 12] without any TOF information. Some of these techniques use neutron resonances for element and isotope identification such as Neutron Resonance Capture Analysis (NRCA) [ref]. This technique use gamma-ray detector to measure the gamma ray emission that follows a resonant neutron capture event in the sample: (n, gamma). The Time Of Flight (TOF) of the recorded event provides information on the specific element in which the resonant radiative absorption takes place. Different elements, and their relative abundances, are therefore distinguished according to element-specific characteristic TOF patterns.
COSA FACCIAMO NOI IN PIù E DI DIVERSO A dual TOF-photon energy resolved analysis will go beyond the current state of the art of both PGAA and NRCA, with the potential to enhance the capabilities of both techniques, providing a simultaneous element/spatial sensitivity not currently available. Gamma energy emission spectra for bi-parametric measurements can be recorded by a gamma detector (as germanium detector) equipped with a fast electronics. The bi-parametric acquisition procedure aims to the elemental identification and localization inside extended samples, without recurring to multiple rotations/exposures.
Descrizione apparato e modalità di acquisizione. descrizione di ISIS
Presentimao semplicemente i grafici: - Figura 1: spettro PGAA dello Stagno integrato su tutti i tempi e con taglio attorno alla risonanza (vediamo se esteticamente preferiamo i due spettri sovrapposti nello stesso grafico o due figure una sotto l’altra)
- Figura 2: spettro NRCA in TOF integrato su tutte le energie e con taglio attorno alla risonanza (vediamo se esteticamente preferiamo due spettri sovrapposti nello stesso grafico o due figure una sotto l’altra)