Base Information Q&A SiteJAEA

Radioactivity and Air Dose Rate


How is the concentration of radioactive Cs measured?

The Ge semiconductor detector and NaI scintillation detector are used for measurement. We use different instruments depending on our study purpose, e.g., a Ge semiconductor detector is used primarily when detailed tests are required; a NaI scintillation detector is primarily used for conducting simple tests at a massive scale.

  • To understand the movement of radioactive Cs in the environment, highly precise measurements of the concentrations must be performed. Therefore, CLADS of the Japan Atomic Energy Agency uses Ge semiconductor detectors to obtain radioactive Cs concentration data.
  • CLADS of Japan Atomic Energy Agency is certified as a test laboratory for radioactivity measurement (object nuclide: 134Cs and 137Cs) based on international standard ISO/IEC 17025:2005 (General requirements for the competence of testing and calibration laboratories) in October 2015.

Table 1 Comparison of Ge semiconductor and NaI scintillation detectors

Analytical instrument Ge semiconductor detector NaI scintillation detector
External view Ge semiconductor detector NaI scintillation detector
Price Ten and several millions to tens of millions of yen Several hundred thousand to several millions of yen
Weight 1–2 tons Approx. 100 kg
Measurement environment Cooling by liquid nitrogen and an electric system is required. As long as it is stable, measurements can be performed at room temperature
  • Detailed analysis capabilities
  • High price; additional cost for maintenance
  • Heavy; requires a floor with load-carrying capacity treatment
  • Lower price than Ge semiconductor detectors
  • Can be installed anywhere with air-conditioning
  • Usage example
  • Study of the environmental dynamics of radioactive Cs in Fukushima (Japan Atomic Energy Agency))
  • Detailed tests of agricultural products (local governments)
  • Simple screening of agricultural products (local governments)