Estimation of surface anthropogenic radioactivity concentrations from NaI(Tl) pulse-height distribution observed at monitoring station

Abstract

A method of estimating surface radioactivity concentrations of key anthropogenic radionuclides from NaI(Tl) pulse-height distribution observed at a monitoring station (MS) was discussed. In the estimation, a realistic assumption on geometric distribution of source and obstacles around the detector of the MS including the infiltration of radionuclides into the ground was used and the results were compared with ones with a commonly used assumption of a uniformly distributed plane source. The surface radioactivity concentration was determined by comparing the count rates at the full-energy peak ranges between observation and calculation with an electron-photon transport code EGS5. It was shown that the estimated absolute values of concentration differed by a factor of ∼1.5 depending on the assumption of infiltration depth. The estimated surface concentrations of (131)I, (134)Cs and (137)Cs were in good agreement with ones determined by the in situ measurements with an HPGe detector and the cumulative values of daily surface depositions.

Study on Method for Simultaneous Determination of Ambient Dose Equivalent Rates and Activity Concentration in Air for Environmental Radiation Monitoring

“…For instance, the NaI(Tl) scintil-lation spectrometers have been used for monitoring the surroundings of nuclear facilities in Japan. 1,2) In European countries, the so-called spectro-dosimetry system for the radiological early warning networks has been developed and ready for installation. 3) Installing the NaI(Tl) scintillation spectrometers around nuclear facilities depends mainly on the emergency radiological monitoring strategy in Japan, which focuses on information about abnormal doi: 10.3769/radioisotopes.70.1 RADIOISOTOPES increase of dose rates.…”

“…Determination of radioactive concentration in air of radioiodine from the pulse height spectra obtained the NaI(Tl) scintillation spectrometers has been published in several years after the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP). 1,2,4) Just after the nuclear accident at the FDNPP, a realtime dose rate mapping system called KURAMA was developed. 5) The KURAMA system helped decision makers establish the rehabilitation strategy from the contamination due to the radioactive materials released from the FDNPP.…”