The application of various sources of ionizing radiations in the practical activity of man has become routine. The scope of application of the radiations in scientific investigations, in industry, in agriculture, and in medicine is continuously expanding. The priority investigations in science and engineering are those that are related to atomic science and technology, to the development and introduction of progressive radiation technologies, protection of the environment, development of the fuel-energy complex, nuclear energetics, etc. All this has led to the creation of means of measurement of x-ray, gamma, beta, alpha, neutron, proton, and electron radiations, including those that are pulsed. Various radiation accidents and the Chernobyl atomic electric station catastrophe have acutely raised the problem of radiological protection of the personnel and population. As a result, dosimetric measurements and radiometric measurements of the activity of radionuclides have assumed a mass character. The unity of radiological measurements is based on the national systems of primary, secondary, and reference standards and working standards and means of measurement; an important role is also played by the system of reproduction of the standard units in the reference and working standards by means of the existing testing procedures, by the system of scientific-technical documentation of the methods for testing the means of measurement and by the system of certification testing of the means of measurement [i]. The standards of the physical units pertaining to the metrology of ionizing radiations kept in the Mendeleev AllUnion Scientific Research Institute of Metrology (VNIIM) and in the All-Union Scientific Research Institute of Physical-Technical and Radiological Measurements (VNIIFTRI) are presented in Table i. The current system for ensuring the unity of measurements in the Russian Federation and countries of the former Soviet Union ensures a high quality of dosimetric, radiometric, and spectrometric measurements in accordance with the recommendations of the Consultive Committee on Standards for Measurements of Ionizing Radiations of the International Bureau of Weights and Measures (IBWM), International Commission on Radiological Units (ICRU), International Commission on Radiological Protection (ICRP), International Organization on Legislative Metrology (IOLM), International Atomic Energy Agency (IAEA), World Health Organization (WHO), etc. Frequent collation of the national primary and secondary standards of Russia with those of IBWM and the leading national laboratories of the world, e.g., NBS (USA), PTI (Germany), NPL (UK), etc. facilitate mutual verification of the results of measurement of ionizing radiations.