Field photon energy spectra in Fukushima after the nuclear accident

Figures & data

Figure 1. Measurement setup for angular dependence for the CdZnTe detector.

Figure 2. Measured photon energy spectra at the angles of 0°, 45°, and 90°.

Table 1. Comparison of ambient dose rate at the National Metrology Institute of Japan (NMIJ) reference X-ray fields.

Mean energy (keV)	253	208	166	118	83	64
Dose rates by reference ionization chamber	4.44E–5	4.59E–5	3.28E–5	3.24E–5	1.81E–5	1.91E–5
Dose rates by CZT	4.34E–5	4.21E–5	3.36E–5	3.44E–5	1.91E–5	1.99E–5
Ratio (CZT/standard)	0.98	0.92	1.02	1.06	1.06	1.04

Figure 3. Comparison of measured and calculated spectra by EGS5 for a Cs-137 source.

Table 2. Information of measurement points.

Point A	Roadside in Iidate village. There is no decontamination area around this point.
Point B	Point in large flat field (100 m×5 0 m） at Iidate village. There is no decontamination area around this point.
Point C	Point in large flat decontaminated field (100 m×50 m） at Iidate village.
Point D	Roadside in Fukushima city near Fukushima station.

Table 3. Measured ambient dose rate using CdZnTe detector and NaI(Tl) survey meter. Italic value means a ratio of each energy region against a total dose.

	NaI(Tl) survey
	meter	CdZnTe detector
			Ambient dose	Ambient dose	Ambient dose
	Ambient dose	Total ambient	rate for below	rate from 250	rate above 500
	rate (Sv/h)	dose rate (Sv/h)	250 keV (Sv/h)	to 500 keV (Sv/h)	keV (Sv/h)
Point A	6.00E–6	6.16E–6	1.08E–6	8.17E–7	4.26E–6
			0.18	0.13	0.69
Point B	3.66E–6	3.52E–6	4.64E–7	3.61E–7	2.69E–6
			0.13	0.10	0.77
Point C	4.0E–7	3.63E–7	1.70E–7	7.46E–8	1.18E–7
			0.47	0.21	0.33
Point D	8.6E–7	8.68E–7	1.01E–7	1.03E–7	6.64E–7
			0.12	0.12	0.77

Figure 4. Normalized photon flux at each point. Flux is normalized at the peak of Cs-137 gamma rays.

Figure 5. Normalized ambient dose rate distribution at each point. Dose rate is normalized at the peak of Cs-137 gamma rays.