Although the question of energy security is regarded as an integral part of the contemporary political agenda, there is no single definition that has been agreed among the international community. The term itself has been evolving for more than 40 years of use. This article reviewes and compares existing definitions of the concept at global, regional, and national levels as well as from scientific point of view. It is commonly accepted that security is related to risk. Identifying and measuring energy security risks is a difficult task as the term contains elements whose meaning often depends on the context. Since the energy system cannot be fully protected, it is appropriate to consider energy security as a risk management problem. This article analyses existing energy security assessment literature and proposes a complemented approach for measuring and evaluating national energy security.

The paper studies world markets of stable and radioactive isotopes. Isotopes have found various applications in science, industry, agriculture and other sectors of the economy, but especially - in medicine. Nuclear medicine is developing intensively all over the world thanks to the success in the treatment of various diseases with the help of radioactive pharmaceuticals (radiopharmaceuticals). The article uses empirical data from a forecast study of the global radiopharmaceuticals market made in 2015 by a research company «Markets and Markets» for the European, North American and global markets. The paper also analyzes the statistical data on the global export and import of natural uranium, enriched and depleted uranium, plutonium, thorium and some stable isotopes of non-medical purposes, presented by a company «Trend economy» in 2014. Despite a unique industrial base for the production of isotopes created in the Soviet Union Russia occupies a modest position on the world market of nuclear medicine except for certain areas. More than 80% of isotopes, produced in USSR were consumed domestically, the export of the stable and radioactive isotopes was in equal proportions. Now the country's domestic radiopharmaceuticals market is poorly developed. To radically change the situation, it is necessary to carry out reforms that stimulate the development of nuclear medicine.