Japanese Measurement System of Ionizing Radiation

 Calibrations of measuring instruments for ionizing radiation dose survey require standard radiation sources. These measuring instruments used on site are calibrated with standard radiation sources which have been already calibrated by higher standards. Figure 1 shows the international traceability system of ionizing radiation dose survey.

 In the Japanese traceability system, the standards of Japan Radioisotope Association and Japan Chemical Analysis Center are traceable to the national standards of National Metrology Institute of Japan (NMIJ), AIST.

 The standards of International Atomic Energy Agency (IAEA) are traceable to the primary standards of national metrology institutes (NMIs). The equivalency of national measurement standards and calibration capabilities of NMIs has been recognized through international comparison under the global MRA.

 Figures 2, 3 and 4 show the results of international comparison on radioactivity measurements of cesium 137(Cs-137), etc. The results of NMIJ, AIST well agree with those of other NMIs. This fact leads to the mutual recognition among Japan and other countries.

 (Note : The vertical axis on the left hand side in Figures 2 - 4 is the deviation of the measurement result of each participant, x_i, from the key comparison reference value, x_R. The vertical axis on the right hand side provides the scale for reading the relative deviation with respect to x_R. The ”blue” bars indicate the range of ±1 % of deviation.)

 (You can find the results of international comparison of NMIs in the Key Comparison Database (KCDB) of BIPM Website.)