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  • Aerial monitoring system

    Methods

    Aerial radiological monitoring of East Japan after the Fukushima Daiichi NPP accident

    Yukihisa SANADA a, Takeshi SUGITAa, Aatsuya KONDO a and Tatsuo TORII a Headquaters of Fukushima Partnership Operations Center of Fukushima Partnership Environmental Safety Research and Development, Japan Atomic Energy Agency, 2-2-2,Uchisaiwai-cho, Chiyoda,Tokyo,100-8577, JAPAN E-mail: sanada.yukihisa@jaea.go.jp

    Introduction

    II. Correction factor

    Comparison with the ground survey Summary

    Results II. 3D map of the deposition

    II. Prediction of dose rate

    I. Map of dose rate and the deposition

    5年後に換算1年後に換算

    IV. Discrimination between radiocesium and natural radionuclides

    0.001

    0.01

    0.1

    1

    10

    100

    0 100 200 300 400 500 600 700

    Calculated (Cs134/C137=0.9)

    Observed (0.0063 West Japan Average)

    Observed (0.0073 Fukushima)

    C or

    re ct

    io n

    fa ct

    or o

    f h ei

    gh t

    (n or

    m al

    iz ed

    o f d

    os e

    ra te

    a t 3

    00 m

    )

    Height(m)

    Normalization

    I. Procedure of data analysis

    threshold

    Table Aerial monitoring system System Install Det. size(inch), quantity Energy range Channel Altimeter

    A Inside 16"×4"×2", 6 detector 0.02 - 3 MeV 1,024 ch GPS

    B Outside 16"×4"×4", 4 detector 0.05 - 3 MeV 256 ch Laser

    C Outside 16"×4"×4", 8 detector 0.2 - 3 MeV 256 ch Radio wave

    D Inside 16"×4"×4", 4 detector 0.05 - 3 MeV 256 ch GPS

    10-1 100 101 102 10-1

    100

    101

    102

    y = 1.01x

    Dose rate by AMS(µSv/h)

    D os

    e ra

    te b

    y N

    aI s

    ur ve

    y m

    et er

    o n

    th e

    gr ou

    nd (µ

    S v/

    h) RS701

    RS701

    RS501

    PDU*

    * Power Distribution Unit (PDU) Input 28VDC, 115VDC

    Computer +RadAssist

    GPS Sub-

    monitor

    Battery

    Battery

    Detector RSX-3

    Detector RSX-3

    - Count rate was obtained by helicopter with large detector - Height above the ground 150-300m - Flight space: 3km - Acquisition rate: 1 second interval

    We measured the ambient dose-rate and the deposition amount of radioactive cesium by using four helicopters in the whole area of East Japan to investigate the influence of the radioactivity that released in the atmosphere due to the disaster of the Fukushima Daiichi NPP (Nuclear Power Plant), Tokyo Electric Power Company (TEPCO), occurred by the East Japan earthquake and tsunami on March 11, 2011.

    Mission Goals are …. - to create the radiation map of East Japan for

    grasp on the influence of a radiocesium. - to establish the method of aerial radiological

    monitoring

    Achievement of aerial radiation monitoring

    Date Mission Note 25 Mar. 2011 MEXT Press release of plan

    for aerial radiation monitoring 5 Apr. 2011 60km zone from

    NPP(DOE)+60-80km zone from NPP(NUSTEC)

    17 May. 2011 80-100km zone from NPP(NUSTEC)

    17 May. 2011 40km zone from NPP(DOE+JAEA*1)+40-80km zone from NPP(NUSTEC)

    *1:DOE system in helicopter of the Self- Defence Forces

    21 Jun. 2011 Miyagi-pref., Toshigi-pref., and Ibaraki-pref. (NUSTEC+JAEA*2)

    *2: DOE system in helicopter of the air- rescue

    2 Aug. 2011 MEXT project

    After 1 year After 5 year

    101

    102

    103

    104

    105

    106

    0.1 1 10

    150m 300m 450m

    C ou

    nt ra

    te

    Dose rate at 1m on the ground( µSv/h)

    y = 31032 x y = 8904 x y = 2883 x

    keV900

    keV450

    C CSI

    >

    >=

    ( ) HFCdBGGCD m1 ××−= ( )( )Flysd HHexpHF −µ=

    GC: Gross count rate (cps) BG: Cosmic-ray, Body contamination (cps) Cd: Dose conversion factor (cps/µSv/h) HF: Height correction factor µ: Attenuation factor (m-1) Hsd: Standard height (approximaetly 300m) Hfly: Flight height

    Attenuation factor Dose conversion factor Example of SI distribution Comparison of contamination map by SI method

    Spectrum index (SI) method was applied for discrimination between radiocesium and natural radionuclides. 1

    10

    100

    1000

    10000

    100000

    0 500 1000 1500 2000 2500 3000

    Co un

    t

    Gamma energy (keV)

    1

    10

    100

    1000

    10000

    100000

    0 500 1000 1500 2000 2500 3000

    Co un

    t

    Gamma energy (keV)

    Radiocesium

    K-40

    U-series Th-series

    Radiocesium that emitted into the atmosphere was deposited along Ou Mountains, Iide Mountains, Echigo Mountains, Shimotsuke Mountains and Kanto Mountains.

    Based on the created map, the prediction map was made in consideration of half-life. - Area of above 0.23 uSv/h(=1.9 mSv/y) was

    limited to Fukushima, Tochigi* and Gunma* after 5 years. (* mountainous region)

    AMS data was compared to ground survey data (NaI survey meter). - On the whole, it was well in agreement. - In the following cases, the data of AMS

    may not match ground survey data. (1) Area of a fold of hills horizontal effects (2) Cosmic ray time, season and weather

    It has been understood for the region where the dose-rate is high to extend from the NPP for northwestward, and wide to Gunma Prefecture from the vicinity of Fukushima City in the direction of the southwest. This map is utilized to determine the decontamination area and estimate the variation of contamination areas.

    - The radiation map which can be used for the plan of decontamination or the determination of a refuge zone was able to be made.

    - The method of aerial radiological monitoring was established. * the conversion method to a dose rate * discrimination between radiocesium and natural radionuclides

    http://ejje.weblio.jp/content/threshold

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