In the event of possible nuclear or radiological emergencies, governments or international organizations must develop an emergency response preparedness to ensure the protection of workers, public, intervention personnel and environment. In addition, there is growing concern about possible terrorist attacks or malicious acts using radioactive or orphan sources, so a proper emergency management is necessary. In particular, the assessment of environmental contamination should be carried out to establish which areas have been affected and determine the level of contamination in each of the matrices or environmental compartments, such as air, water, soil, food or vegetation. This is the main objective of the emergency environmental radiological surveillance plans. This PhD thesis provides the development of rapid testing procedures to evaluate the contamination produced by a radiological or nuclear emergency in different environmental matrices. Firstly, a study of the methodology of radiological emergencies response has been developed, taking into account, on the one hand, the environmental matrices to be analyzed, and on the other hand, the term source or radionuclides to be determined in an emergency. Specifically, several source terms are studied produced as a consequence of an accident at a nuclear power plant, a malicious act using orphan sources, "dirty bombs" or improvised nuclear devices, and an accident in a radioactive facility in the Valencian Community. From the results of this study, the procedures to be developed in the PhD thesis have been selected.

Background: In recent events of the coronavirus disease 2019 (COVID-19) pandemic, computed tomography (CT) scans are being globally used as a complement to the reverse-transcription polymerase chain reaction (RT-PCR) tests. It will be important to be aware of major organ dose levels, which are more relevant quantity to derive potential long-term adverse effect, for Korean pediatric and adult patients undergoing CT for COVID-19. Materials and Methods:We calculated organ dose conversion coefficients for Korean pediatric and adult CT patients directly from Korean pediatric and adult computational phantoms combined with Monte Carlo radiation transport techniques. We then estimated major organ doses delivered to the Korean child and adult patients undergoing CT for COVID-19 combining the dose conversion coefficients and the international survey data. We also compared our Korean dose conversion coefficients with those from Caucasian reference pediatric and adult phantoms.Results and Discussion: Based on the dose conversion coefficients we established in this study and the international survey data of COVID-19-related CT scans, we found that Korean 7-yearold child and adult males may receive about 4-32 mGy and 3-21 mGy of lung dose, respectively. We learned that the lung dose conversion coefficient for the Korean child phantom was up to 1.5-fold greater than that for the Korean adult phantom. We also found no substantial difference in dose conversion coefficients between Korean and Caucasian phantoms. Conclusion:We estimated radiation dose delivered to the Korean child and adult phantoms undergoing COVID-19-related CT examinations. The dose conversion coefficients derived for different CT scan types can be also used universally for other dosimetry studies concerning Korean CT scans. We also confirmed that the Caucasian-based CT organ dose calculation tools may be used for the Korean population with reasonable accuracy.