• 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
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
Features	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)

Related articles

• How can the radioactive Cs distribution at the bottom of lakes or rivers be measured?
• How can radioactive Cs in a solid phase material such as soil be analyzed?

Reference

1. 原子力百科事典ATOMICA “ゲルマニウム半導体検出器”
2. 原子力百科事典ATOMICA “NaI(Tl)シンチレーション検出器”
3. 日本原子力研究開発機構　福島廃炉安全工学研究所「Ge測定（ISO認証の取得）」
4. 日本原子力研究開発機構　福島廃炉安全工学研究所広報誌「明日へ向けて　私たちの取り組み」 No.8（2016年1月）
5. 長尾ほか(2019), 福島における放射性セシウムの環境動態研究の現状（平成30年度版）, JAEA-Research 2019-002, 235p.