Well-established emergency preparedness for radiological and nuclear events is essential for minimizing risks and consequences to public health, safety, and the environment. Such events may give rise to complex exposure scenarios that challenge existing frameworks for risk assessment, medical response, and decision-making, regardless of whether the incident is accidental or deliberate. Effective preparedness therefore requires technical capabilities for dose assessment, an integrated understanding of biological effects, training for relevant exposure scenarios, as well as a clear regulatory and organizational framework for emergency response.

In addition to the technical and biological challenges addressed in the papers included in this thesis, emergency preparedness for radiological and nuclear events is strongly shaped by national legislation and regulatory frameworks issued by relevant authorities. The exercise of public authority, legal responsibilities, mandated roles during emergency situations, and coordination between agencies define how preparedness measures are implemented in practice and how response actions are initiated and managed. Radiological and nuclear events are governed by partly overlapping legal and organizational frameworks, which may complicate emergency preparedness and response. Radiological events are mainly handled within civil emergency preparedness structures, whereas nuclear events may require additional legal mechanisms related to national security and governmental decision-making. Moreover, the nature of the scenario, whether accidental or deliberate, may require involvement of law enforcement and other security actors, extending the scope of emergency response beyond radiation-related considerations alone. 

The overall aim of this licentiate thesis is to contribute to improved emergency preparedness for large-scale radiological and nuclear events by integrating technical, biological, and organizational perspectives. This aim is addressed through two complementary studies: one investigating the applicability of a biological dosimetry technique for exposure to mixed radiation fields, representative of those expected in nuclear emergency scenarios, and one assessing the consequences of a radiological dispersal scenario in an urban environment, with particular focus on the geographical distribution of radioactive contamination under varying local urban conditions. Together, these studies are placed within a broader framework of emergency preparedness, with particular attention to the Swedish regulatory and organizational context governing radiological and nuclear emergencies.

The results show that both radiological emergency scenarios and nuclear-related exposure situations involve considerable complexity in terms of exposure patterns and dose assessment. The biological dosimetry study indicates that gene expression–based methods can provide useful information for retrospective dose assessment following mixed radiation exposures, supporting their potential application in large-scale triage situations. The radiological dispersal study shows that local conditions, such as urban landscape and meteorological factors, strongly influence the spatial distribution of radioactive contamination and potential population exposure. In large-scale emergency scenarios, the geographical extent of contamination can therefore have a significant impact on the selection of individuals for further medical examination.

The findings of this thesis emphasise the importance of integrating technical assessments, biological dosimetry, and regulatory considerations in radiological and nuclear emergency preparedness. By addressing both consequence assessment and retrospective dose estimation, the work contributes knowledge that can support planning, decision-making, and prioritization of resources during large-scale emergency situations. The results may therefore provide analytical support to authorities and organizations involved in preparedness and response to radiological and nuclear emergencies.