In the beginning of the 70th decade, the IRD already had laboratories that developed activities in the area of ionizing radiation metrology, by means of its laboratories of neutrons, of dosimetry, and radionuclides calibration. These laboratories later on would compose the National Laboratory of Metrology of the Ionizing Radiations, LNMRI.

Since 1976, IRD started to integrate the Secondary Standard Laboratories SSDL network, coordinated by the International Atomic Energy Agency, AIEA, with support of the World Health Organization, WHO. This worldwide network was established with the purpose of guaranteeing the quality of the measurements made in the field of ionizing radiations.
As a consequence of the development of research activities and academic improvement accomplished in IRD/CNEN, in 1986 a researcher of LNMRI started to integrate the International Committee of Radionuclide Metrology, ICRM; participating in the first key comparison organized by BIPM, using a primary method for calibration of the quantity activity.

In 1989, INMETRO designated, by means of agreement, LNMRI responsible for the activities of a National Laboratory in the field of Ionizing Radiation, recognizing the relevance of the works developed in the laboratory of metrology of IRD.
In those years, the dosimetry laboratory was receiving a growing demand for calibrations of instruments in the radiation protection area, as consequence of the radiological accident of Goiânia, in 1987. Them, the IRD submitted in 1991 a research project to the International Atomic Energy Agency to implement a Brazilian calibration network for radiation protection to guarantee the traceability of the measurements in the field of the worker's safety.
In 1996, BIPM donated to Brazil a sphere of steel used for the sulfate of manganese bath method, used for the primary standardization of neutron sources. This method is used in research and development and in comparisons organized by BIPM.

In October 14th , 1999, the president of INMETRO and the coordinator of LNMRI, together with 38 countries signatories of the Convention of the Meter, they signed the Mutual Recognition Arrangement, MRA. Nowadays, 45 countries has already jointed to the agreement. The main objective of the MRA is to establish the degree of metrological equivalence of the standards maintained by the national laboratories of metrology, to provide the mutual recognition of the calibration certificates and to supply a technical base, and it holds, for wide scientific and technological agreements, as well as agreements related to the international trade. The technical base for the recognition of the certificates is the equivalence of the national standards established by means of the key-comparisons organized by BIPM and for the regional organizations of metrology.

In 2003, the two researchers' of LNMRI curricula were submitted to BIPM to compose its Committee Consultatif for Ionizing Radiation, CCRI. Today Brazil possesses representatives in the three sections of the advisory committee (Dosimetry, Neutrons and Radioactivity).

In 2004, LNMRI-IRD implemented the requirements of the NBR ISO 17025 standard for calibration laboratories. In this phase, LNMRI was submitted to a peer review evaluation to validate the implementation of the requirements of the standard. The quality system of the LNMRI was soon after evaluated in a meeting of the Interamerican System of Metrology, SIM, and was considered approved.