Improvement of early warning monitoring using gamma spectrometry
- Autores: Anna Camp Brunés
- Directores de la Tesis: Arturo Vargas Drechsler (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Alexandros Clouvas (presid.), M. Amor Duch Guillen (secret.), Néstor Armando Cornejo Díaz (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The present thesis is focused on the improvement of radiological surveillance networks using gamma spectrometry. Tipically they are equipped with gamma dose rate monitors, while they do not have gamma spectrometry monitors. These measure the effects of gamma radiation, but do not provide any nuclide-specific information. Nowadays new materials have been developed in the spectrometry research field and the implementation of gamma spectrometry detectors is being actively considered in European gamma-dose stations (more than 5000).
In this thesis the lanthanum bromide, LaBr3(Ce), detector has been selected as the reference instrument to study the possibility of installing it in early warning networks. The reasons for its choice were its resolution, which improves from 7 % to 3 % at 662 keV, its availability and the fact that these detectors are already being used at institutions such as STUK, the nuclear safety authority in Finland. Selected monitors have been characterized by irradiation at a reference laboratory at the Institute of Energy Technologies (INTE). Furthermore, the study of their inherent background and the influence of cosmic radiation have been investigated by means of exposures in lakes, underground laboratories and the use of Monte Carlo (MC) simulations.
In addition to its main function, gamma spectroscopy, these detectors allow the possibility of calculating values of ambient dose equivalent H*(10). In this thesis two different methods have been developed and applied to spectra measured using LaBr3(Ce) crystals in long-term measurements and intercomparison campaigns, the stripping method and the conversion coefficients method. The first is based on obtaining the external flux that reaches the monitor and involves the subtraction of all partial absorptions produced by scatterings in the monitor itself. This methodology, which has been already studied and usually applied to HPGe detectors, proved that it can also offer good results in LaBr3(Ce) detectors. The second methodology is based on splitting the spectra into several energy regions, and a coefficient to ¿convert¿ from measured counts to H ¿*(10) values for each region is defined. Results obtained have been compared with classical dose rate monitor values. The long-term measurements were performed at surveillance stations in Barcelona and Madrid. Since, fortunately, there were no radiological emergencies during research for this thesis, H*(10) diurnal and seasonal variations at these stations are studied from the viewpoint of the influence of cosmic radiation and variations of 222Rn daughter concentration. Intercomparison campaigns were performed at Physikalisch-Technische Bundesanstalt (PTB) facilities to study both detector sensibility and the accuracy of H*(10) calculated values.
Use of new technological advances in the determination of high levels of H*(10) led us to study the viability of installing gamma radiation detectors on an unmanned aerial vehicle. In this thesis a drone prototype has been developed which uses a 3¿ x 3¿ NaI installed in an RPAS helicopter. The first flights took place at different altitudes and over a pond in order to study detector sensitivity. Although the prototype it is still at an initial stage and more flights are required, preliminary results obtained are promising, showing that the system is able to detect variations in terrestrial radioactivity.
