Annals of Nuclear Energy 47 (2012) 21–27

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Annals of Nuclear Energy

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Measurement and quantitative analysis of radioactivity concentration in soilon playgrounds of Korean elementary schools

Mi-Hyun Kim a,b, Jae-Hwan Cho c,d, Kyung-Rae Dong b,e, Woon-Kwan Chung e,⇑, Jong-Woong Lee f,g,Seong-Gyu Shin h

a Department of Radiation Science & Technology, Chonbuk National University, Republic of Koreab Department of Radiological Technology, Gwangju Health College University, Republic of Koreac Department of Radiological Science, Gyeongsan University College, Republic of Koread Department of Computer Science and Engineering, Soonchunhyang University, Republic of Koreae Department of Nuclear Engineering, Chosun University, Republic of Koreaf Department of Radiology, Kyung Hee University Hospital at Gang-dong, Republic of Koreag Department of Electronics and Communications Engineering, Gwangwoon University, Republic of Koreah Department of Radiological Technology, Busan dong-a University Medical Center, Republic of Korea

a r t i c l e i n f o a b s t r a c t

Article history:Received 16 January 2012Received in revised form 2 April 2012Accepted 4 April 2012Available online 10 May 2012

Keywords:School playgroundHigh purity Ge semiconductor detectorRadioactivity concentration

0306-4549/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.anucene.2012.04.011

⇑ Corresponding author. Address: Department ofUniversity, 375, Seosuk-dong, Dong-gu, Gwangju 501+82 62 230 7166; fax: +82 62 232 9218.

E-mail addresses: tkprins@nate.com (M.-H. Kim),Cho), krdong@hanmail.net (K.-R. Dong), wkchung@woongkosbi@hanmail.net (J.-W. Lee), ssg200@yahoo.c

The aim of this study is to obtain nationwide basic data on the distribution of environmental radiationand radioactivity in normal times and to draw a comparison of chart characteristics and distribution invarious areas for contributing to the improvement in radioactivity analysis technology, people’s healthand national environment in the future. Soil sampling points from 160 elementary schools were selectedbased on the division of the Korean Peninsula by area before samples of soil were taken on playgrounds ofthe selected schools for analysis. The soil radioactivity concentrations in the investigated areas were mea-sured by means of high purity Ge (HPGe) detector. The results obtained show that K-40 (potassium-40)value ranged from 654.49 ± 365.05 Bq/kg in Jeju Island to 1287.00 ± 299.81 Bq/kg in Incheon Metropoli-tan City, Cs-137 (caesium-137) value ranged from 0.819 ± 0.164 Bq/kg in North Jeolla Province to0.140 ± 0.080 Bq/kg in Ulsan Metropolitan City, Be-7 (beryllium-7) value ranged from 979.5 ±123.22 Bq/kg in Seoul Metropolitan City to 11.81 ± 3.29 Bq/kg in South Jeolla Province, Tl-208 (thoriumC) value ranged from 90.82 ± 14.66 Bq/kg in Incheon Metropolitan City to 24.03 ± 8.25 Bq/kg in BusanMetropolitan City, Pb-212 (thorium B) value ranged from 91.99 ± 25.94 Bq/kg in Incheon MetropolitanCity to 25.23 ± 18.11 Bq/kg in Busan Metropolitan City, Bi-214 (radium C) value ranged from42.70 ± 16.79 Bq/kg in Incheon Metropolitan City to 14.79 ± 10.30 Bq/kg in Jeju Island, Ra-226 (radium-226) value ranged from 96.63 ± 32.12 Bq/kg in Incheon Metropolitan City to 36.77 ± 9.30 Bq/kg in BusanMetropolitan City.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

As science and technology have advanced in the 21st century,radioactive materials are increasingly used in nuclear powerplants, diverse research and medical institutions, as well as in var-ious industries. And, as the size of such plants, institutions andindustries become bigger, it has become more likely that peopleare exposed to radiation in their everyday life. In line with theincreasing concern of issues related to the living environment such

ll rights reserved.

Nuclear Engineering, Chosun-759, Republic of Korea. Tel.:

8452404@hanmail.net (J.-H.chosun.ac.kr (W.-K. Chung),o.kr (S.-G. Shin).

as air or water pollution, people are now raising their voice toexpress concern on radioactive contamination (Ahn, 2001). In par-ticular, a huge amount of radioactive materials were released tothe air in the wake of the Chernobyl nuclear power plant accidentin 1986 (Yarilin et al., 1993). In addition, yellow sand storms fromChina, which spread diverse pollutants over South Korea, havebeen on the rise. Recently, China has been planning to build manynuclear power plants on its coast in the Yellow Sea while EastAsian countries are active in establishing business plans for nuclearpower. As a result, there is always a possibility that accidentsinvolving radioactive contamination may occur in countries neigh-boring South Korea; the radioactive materials, which are releasedto the air, fall to the ground along with fallout and rainwater beforebeing deposited in the soil, hence increasing its radioactivity (Chaet al., 2004). Artificial radioactive nuclides, which are generateddue to nuclear explosions or in nuclear power plants, are the

Fig. 1. Sampling points of soil in elementary schools across the nation.

22 M.-H. Kim et al. / Annals of Nuclear Energy 47 (2012) 21–27

products of nuclear fission in most cases except for a few nuclidessuch as 3H, 14C, and others. Among them, 137Cs is the nuclide thatdraws particular attention in dose assessment. 90Sr along with137Cs is readily found in the environment. Since the nuclide has along half-life, it may have an influence on the terrestrial ecosystemas it is absorbed by plants (Lee et al., 1998, 1995).

Soil is a direct radiation source in the environment. Soil con-tains major radiation sources such as decay products of 238U seriesand 232Th series as well as 40K, while artificial radioactive nuclidesare also strewn across the environment. Therefore, radioactivityconcentration in soil is very critical to assessing the influence onterrestrial ecosystems and further, on humans because distributionof and change in concentration are used as basic data for examin-ing what increases in radioactivity in the case of a nuclear powerplant accident, figuring out characteristics and behavior of theradiation environment, and conducting research on geological fea-tures and soil (Barci-Funel et al., 1995).

The Korea Atomic Energy Research Institute, Korea Institute ofNuclear Safety, and Nuclear Power Laboratory of the Korea ElectricPower Research Institute have measured radioactivity in air, waterand soil in the surroundings of nuclear power plant facilities (KoreaInstitute of Nuclear Safety, 2009). In addition, radioactivity mea-surement stations across the nation have measured radioactivityin air, water, soil, and some kinds of grain and vegetables everyyear as a way to monitor radioactive materials nationwide(Korea Institute of Nuclear Safety, 2009). Unfortunately, there aresignificantly insufficient data on the measurement of naturalradioactivity in the living environment for children who haveundifferentiated cells.

Against this background, soil samples were taken on play-grounds of elementary schools nationwide that were living spacefor children who were sensitive to radioactivity. After preprocess-ing the samples, a high purity Ge (HPGe) detector was used to mea-sure radioactivity concentration in the soil samples. The purpose ofthis study was to obtain nationwide basic data on the distributionof environmental radiation and radioactivity under normal condi-tions and draw a comparison chart for characteristics and distribu-tion by area. Eventually, this study intended to contribute to theimprovement in radioactivity analysis technology in the futureand provide a basic data reference for the improvement of humanhealth and environment.

2. Materials and methods

2.1. Sampling and preprocessing

Soil shows diverse values of pore size and humidity, and radio-activity concentration in soil is significantly influenced by factorssuch as the condition of organic matter contained on the soil sur-face and the type of parent rock that determines the macroscopiccharacteristics of soil (Chang et al., 2009). Therefore, the radioac-tivity concentration shows significant changes according to area.

After the division of the Korean Peninsula by area and latitude,soil samples were taken on the playgrounds of 160 elementaryschools that were considered to have almost no disturbance anderosion of soil over a long period and have frequent contact withchildren before the analysis was made. Fig. 1 shows the soil sam-pling points.

In order to secure representativeness of the selected samplingpoints, 10 spots or more were singled out from one sampling pointbefore sampling and mixing. Such a mixed sample was consideredas the soil sample for this point. For soil sampling, organic matter(fallen leaves, twigs, and so on), which was not decomposed on theground surface in each selected sampling point, was removed be-fore an auxiliary sampler, a plastic hammer and a small entrench-

ing shovel were used to take surface soil samples to a depth of0–5 cm, weight of 2 kg, subsoil depth of 5–30 cm, and weight of2 kg.

After weighing the sampled soil, it was air-dried in the shade forabout 1 week. The soil was then sieved, air-dried again, shakenwith a 2 mm mesh sieve to exclude larger soil particles. After theselected soil was spread as evenly as possible over a wide pieceof paper, it was divided into nine equal parts in the shape of a grid.A certain amount of soil was taken from each part before beingmixed. The soil was mixed a few times to ensure equal representa-tiveness. To spread a certain amount of soil evenly in a container,mortar was used to grind the soil sufficiently. After the samplewas dried in an oven at temperature of 105 �C for 24 h, the U-8container was filled with the sample and at a height of 5 cm foranalysis of gamma nuclide. The container was sealed with Parafilmbefore the net weight of soil sample analyzed should be specified.

2.2. Measurement and analysis of radioactivity of a sample

The sample, which was preprocessed as explained above, wasput on the high purity Ge (HPGe) detector that is a semiconductordetector shielded with lead. Then, the multi-channel pulse heightanalyzer (MCA) was used to perform gamma-ray spectrometryfor analysis.

The gamma-ray spectrometer used in this study consists of theHPGe detector (Canberra, USA) and the MCA (ORTEC, USA).

In order to measure the concentrations of radioactive nuclidesin the soil-filled sample, the measurement time for one samplewas set at 80,000 s to analyze the concentration of gamma radioac-

M.-H. Kim et al. / Annals of Nuclear Energy 47 (2012) 21–27 23

tive nuclides and obtain a spectrum file. According to the measure-ment of the five samples first, subsoil and surface soil showed nodifference in the spectrum file, which led to the decision to conductmeasurement only for surface soil.

To determine the radioactivity concentration of each nuclide byusing the measured spectrum, measurement time and chargequantity were entered to the APTEC (Aptec Co., New York, USA)which is a program to analyze gamma radioactive nuclides, in or-der to calculate the radioactivity concentration for each type of nu-clide. And, with a focus on 137Cs (661.66 keV) and 40K (1460.8 keV),the existence of other nuclides examined as channels, were exam-ined in the peaks of 238.6 keV, 352 keV, 609.1 keV, 911.9 keV,1460.8 keV, and 1764.5 keV that were shown in the environmentalsample. Based on the results, radioactivity concentration for eachnuclide was calculated before correction for errors in volume anda density was made, which led to the finalization of radioactivityconcentration.

In general, the total energy of 3 MeV and channel 8192 wereused for environmental sample analyses. The energy per channelcan be calculated as follows:

EnergyðkeVÞChannel

¼ 3000 keV8192

¼ 0:3662 ð1Þ

Among the 11 values of energy, the number of channels for 137Cs(661.66 keV) energy can be calculated as follows:

661:66 keV0:3662 keV=Channel

¼ 1;807 Channel ð2Þ

The number of channels for 40K (1460.8 keV) energy can be calcu-lated as follows:

1460:8 keV0:3662 keV=Channel

¼ 3;989 Channel ð3Þ

The number of channels for 7Be (485 keV) energy can be calculatedas follows:

485 keV0:3662 keV=Channel

¼ 1;324 Channel ð4Þ

The number of channels for 208Tl (2620 keV) energy can be calcu-lated as follows

2620 keV0:3662 keV=Channel

¼ 7;154 Channel ð5Þ

The number of channels for 212Pb (590 keV) energy can be calcu-lated as follows:

590 keV0:3662 keV=Channel

¼ 1;611 Channel ð6Þ

The number of channels for 214Bi (5502 keV) energy can be calcu-lated as follows:

5502 keV0:3662 keV=Channel

¼ 15;024 Channel ð7Þ

The number of channels for 226Ra (250 keV) energy can be calcu-lated as follows:

250 keV0:3662 keV

¼ 690 Channel ð8Þ

After peaks were confirmed in gamma ray spectrum that wasobtained for each channel, the peaks other than the one that hadenergy (11 Line) that was included in certificate were deleted.

The deleted peaks are as follows:

� 511 keV: Ann peak� 1325 keV: Single escape peak at 1836 keV of Y-88.� 814 keV: Double escape peak at 1836 keV of Y-88.

� 2505 keV: Sum peak at 1173 keV + 1332 keV of Co-60.� 2734 keV: Sum peak at 898 keV + 1836 keV of Y-88.

In addition, tail was generated in the surroundings of peak,which was attributable mostly to undershoot or overshoot.As a result, pole zero was set up to remove undershoot andovershoot, which aimed at getting rid of tail. In the stagesmentioned above, the final radioactivity concentration wasdetermined.

2.3. Measurement of radioactivity concentration in soil

In order to determine the radioactivity concentration based onthe gamma ray spectrum that was measured from the soil samplesobtained at the sampling points, the calculation of area for themeasured photoelectric peak or full-energy absorption peak wasrequired. Methods to calculate the area of the peak can be dividedto the sum and the fitting method. In this paper, the sum methodwas used for the peak calculation. The sum method is used to cal-culate the sum of the coefficient values of the channel to find outthe area of the spectrum peak. Since such methods require noparameter for analysis of the spectrum peak, it is often used for or-dinary and repetitive measurements. The net area of the peak (n),excluding the background area, can be expressed as follows (KoreaElectric Power Corporation, 1992):

N ¼ G� CðB1 þ B2Þ

2að9Þ

where G = coefficient value of spectrum peak; C = number of peakchannels; B1 = coefficient value for a channels below the peak;B2 = coefficient value for a channels on the right of the peak.

The photoelectric peak follows a Gaussian distribution in com-bination with a statistical fluctuation and random noise measure-ment system. Therefore, it is most common to assume that therange of the peak is 3 standard deviations from the peak channel(center of peak). As a result, if the width of channel is DC, thenumber of channels per area is given as C = 6a/DC + 1. Whenthe background channel is determined to be somewhere out ofthe 3a range from the peak channel, the background channelrange (a) is determined to range from channel 3 at least, to 3a/DC.

As shown in Eq. (9), after coefficient values ß1 and ß2 of back-ground channel range (a) on the both sides of the peak are con-verted to average coefficients per channel, it is possible tocalculate the net peak area (N) by subtracting the average coeffi-cients from the entire peak area. In this case, the standard devia-tion of the net peak area (N) is provided as follows (KoreaElectric Power Corporation, 1992):

A� A0 ¼ ðN � SðNÞÞ�� R� t � V

Bqkg� dry

� �ð10Þ

where N ± S(N): net area and area standard deviation of the peak,e: peak efficiency (detection efficiency); R: gamma ray emissionratio; t: measurement time; V: amount of sample (kg).

The minimum detectable activity (MDA) of the detector, whichdemonstrates the quality of the spectrum, is provided as follows(Battist et al., 2000):

MDAðEÞ �ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiRðEÞBðEÞ

peðEÞ ð11Þ

R(E) represents the detector’s resolution as a function of energy,B(E) represents background according to energy, and e(E) repre-sents the absolute value of energy efficiency.

24 M.-H. Kim et al. / Annals of Nuclear Energy 47 (2012) 21–27

3. Results

3.1. Correlation with radioactivity concentration in soil by area

Relative to the correlation with measurement values of radioac-tivity concentration for K-40, Cs-137, Be-7, Tl-208, Pb-212, Bi-214,and Ra-226 by latitude, the correlation coefficient was 0.5 or less sothat no significant meaning could be found in the correlation withmeasurement values for K-40, Cs-137, Be-7, Tl-208, Pb-212, Bi-214,and Ra-226 by latitude (Table 2).

3.2. Measurement results of 40K concentrations in investigated soils

Concentrations of 40 K (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 7.437 mBq/kg.

The concentration of K-40 was highest in Incheon MetropolitanCity, followed by Seoul Metropolitan City, and lowest on Jeju Is-land; the differences between areas were statistically significant(p < 0.001).

3.3. Measurement results of 137Cs concentrations in investigated soils

Concentrations of Cs-137 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values below the minimumdetectable activity (MDA) of 0.725 mBq/kg.

3.4. Measurement results of 7Be concentrations in investigated soils

Concentrations of Be-7 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 3.135 mBq/kg.

The concentration of Be-7 was highest in Seoul MetropolitanCity, followed by the Gangwon Province, while the lowest concen-tration values were in Incheon Metropolitan City; the differenceswere statistically significant (p < 0.001).

3.5. Measurement results of 208Tl concentrations in investigated soils

Concentrations of Tl-208 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 2.832 mBq/kg.

The concentration of Tl-208 was highest in Incheon Metropoli-tan City, followed by the Gangwon Province, while the lowest wasin Busan Metropolitan City; the differences were statistical signif-icant (p < 0.001).

3.6. Measurement results of 212Pb concentrations in investigated soils

Concentrations of Pb-212 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 3.012 mBq/kg.

The concentration of Pb-212 was highest in Incheon Metropol-itan City, followed by the Gangwon Province, and lowest in BusanMetropolitan City; the differences were found to be statisticallysignificant (p < 0.001).

3.7. Measurement results of 214Bi concentrations in investigated soils

Concentrations of Bi-214 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 2.821 mBq/kg.

The concentration of Bi-214 was highest in Incheon Metropoli-tan City, followed by the Gangwon Province, while the lowest radi-

ation values were on Jeju Island, showing the difference withstatistical significance (p < 0.001).

3.8. Measurement results of 226Ra concentrations in investigated soils

Concentrations of Ra-226 (mBq/kg) in the investigated soils arepresented in Table 1 and showed values above the minimumdetectable activity (MDA) of 2.012 mBq/kg.

The concentration of Ra-226 was the highest in Incheon Metro-politan City, followed by Daegu Metropolitan City, and the lowestin Busan Metropolitan City, showing a statistically significancewith statistical significance (p < 0.001).

3.9. Measurement results of radioactivity concentrations ininvestigated soils

According to the measurement results of radioactivity concen-tration for all areas combined, the concentration value of K-40was measured to be the highest at 871.70 ± 167.33, concentrationvalue of Be-17 was measured to be high at 146.77 ± 53.28, and theconcentration value of Cs-137 was measured to be lowest at0.458 ± 0.162 (Fig. 2).

4. Discussion

Much concern and attention have been increasingly shown tothe exposure of the human body and biosphere to ionizing radia-tion originating from the surroundings due to effects of the radia-tion on the human body. All humans and living organisms havecontinued to be exposed to such environmental radiation sincethe beginning of Earth’s history. Therefore, dose rate of such natu-ral radiation has been used as a touchstone for a study on the bio-logical effects of radiation that is produced by humans. The naturalbackground radiation is formed by cosmic radiation, radiationemitted from radioactive isotopes that exist in nature, and radia-tion emitted from a small number of radioactive isotopes thatare combined within living organisms (Ghiassi-nejad et al.,2002). In the meantime, the United Nations Scientific Committeeon the Effect of Atomic Radiation (UNSCEAR) announced in 1988that the annual average value of exposure dose due to natural radi-ation was 2.4 mSv (240 mrem), which causes small damage to hu-mans. However, the issue has been raised recently in the US andCanada that people who are exposed to natural radiation, even atlow levels over a long period are highly likely to develop variousdiseases such as lung cancer, bone cancer, and immune systemdeterioration (UNSCEAR, 1998). Moreover, the annual average in-creased by 100% from the average value of 1 mSv that had beenrecognized until 1988. The main reason for this increase is the in-creased concern over radiation exposure as new study results havedemonstrated environmental accumulation of radon and by-prod-ucts generated by its decay, hence providing new knowledge onenvironmental contamination.

For children (aged 15 or less) unlike adults are sensitive to radi-ation exposure. According to reports in some studies, as livingorganisms are younger, they have more cells dividing and suchcells are more sensitive to radiation than cells in the resting stage(Deacon et al., 1984; Schiller et al., 1997). Against this background,this study measured radioactivity concentration in soil with a focuson elementary schools nationwide that were living space for chil-dren who were sensitive to radioactivity. According to the studyresults by area, the K-40 concentration value was measured to bethe highest in Incheon Metropolitan City and lowest on Jeju Island.The Cs-137 concentration value was measured to be highest in theNorth Jeolla Province and lowest in Ulsan Metropolitan City. TheBe-7 concentration value was measured to be highest in Seoul

ble 1easurement results of radioactivity concentrations in investigated soils.

Measurementpoint

Radioactivityconcentration

p Radioactivityconcentration

p Radioactivityconcentration

p Radioactivityconcentration

p Radioactivityconcentration

p adioactivityoncentration

p Radioactivityconcentration

p

Mean ± SD(K-40)

Mean ± SD(Cs-137)

Mean ± SD (Be-17)

Mean ± SD(Tl-208)

Mean ± SD(Pb-212)

ean ± SDBi-214)

Mean ± SD(Ra -226)

Gyeonggi Province 977.37 ± 261.38 0.439 ± 0.193 207.27 ± 78.96 62.76 ± 24.05 68.76 ± 24.63 9.25 ± 9.67 64.43 ± 24.72Gangwon Province 868.81 ± 151.33 0.535 ± 0.120 256.87 ± 57.29 76.89 ± 21.34 86.78 ± 28.41 5.11 ± 21.20 85.07 ± 24.42South Chungcheong

Province783.43 ± 135.47 0.146 ± 0.024 80.76 ± 11.50 35.49 ± 18.30 41.19 ± 20.38 1.00 ± 13.05 46.96 ± 24.87

North ChungcheongProvince

919.07 ± 181.61 0.624 ± 0.124 72.94 ± 14.46 53.44 ± 17.63 59.64 ± 18.89 8.01 ± 10.96 61.71 ± 29.80

South GyeongsangProvince

800.66 ± 133.41 0.263 ± 0.130 102.79 ± 27.37 37.95 ± 17.97 42.82 ± 20.65 8.09 ± 9.59 47.55 ± 24.27

North GyeongsangProvince

828.63 ± 218.36 0.556 ± 0.169 33.81 ± 14.88 40.73 ± 24.73 46.29 ± 27.14 0.80 ± 13.93 53.05 ± 36.16

South Jeolla Province 748.86 ± 174.97 0.464 ± 0.150 11.81 ± 3.29 37.36 ± 18.23 42.30 ± 19.92 7.97 ± 9.05 45.61 ± 25.46North Jeolla Province 913.48 ± 82.01 0.0002* 0.819 ± 0.164 0.0043* 202.49 ± 46.32 0.0003* 45.94 ± 14.08 0.0002* 52.23 ± 15.57 0.0002* 3.86 ± 7.71 0.0006* 55.22 ± 25.61 0.0003*

Jeju Island 654.49 ± 365.05 0.558 ± 0.194 33.01 ± 9.25 27.55 ± 11.08 31.40 ± 13.80 4.79 ± 10.30 40.85 ± 12.56Seoul Metropolitan City 1162.50 ± 194.45 0.432 ± 0.154 979.5 ± 123.22 53.32 ± 12.41 56.09 ± 13.25 5.13 ± 0.92 55.03 ± 14.82Ulsan Metropolitan City 971.02 ± 117.61 0.140 ± 0.080 19.47 ± 4.49 42.24 ± 23.54 40.01 ± 25.18 7.82 ± 16.09 63.33 ± 22.93Busan Metropolitan City 839.00 ± 131.25 0.324 ± 0.032 24.29 ± 5.25 24.03 ± 8.25 25.23 ± 18.11 5.41 ± 4.23 36.77 ± 9.30Daegu Metropolitan City 719.60 ± 127.23 0.196 ± 0.044 19.01 ± 6.38 62.53 ± 12.33 71.90 ± 11.45 2.92 ± 10.22 76.68 ± 22.36Incheon Metropolitan

City1287.00 ± 299.81 0.537 ± 0.254 10.82 ± 3.24 90.82 ± 14.66 91.99 ± 25.94 2.70 ± 16.79 96.63 ± 32.12

Total 871.70 ± 167.33 0.458 ± 0.162 146.77 ± 53.28 49.36 ± 18.77 54.04 ± 19.83 5.27 ± 7.94 59.20 ± 17.11

te: The interaction effect was determined using the one-way ANOVA model. A post-hoc test was performed using the Duncan method. Units are expressed as the numb r of Bq/kg dry.p < 0.001.

M.-H

.Kim

etal./A

nnalsof

Nuclear

Energy47

(2012)21–

2725

TaM

No*

Rc

M(

232

2

1

2

12122134

2

e

Table 2Correlation coefficient of measurement values by area.

Correlation coefficient p

K-40 0.202 0.012Cs-137 0.293 0.0003Be-7 0.128 0.011Tl-208 0.240 0.020Pb-212 0.324 0.041Bi-214 0.128 0.032Ra -226 0.229 0.045

Note: Interaction effect using the Pearson correlation coefficient.

26 M.-H. Kim et al. / Annals of Nuclear Energy 47 (2012) 21–27

Metropolitan City and lowest in Incheon Metropolitan City. The Tl-208 concentration value was measured to be highest in IncheonMetropolitan City and lowest in Busan Metropolitan City. The Pb-212 concentration value was measured to be highest in IncheonMetropolitan City and lowest in Busan Metropolitan City. The Bi-214 concentration value was measured to be highest in IncheonMetropolitan City and lowest on Jeju Island. Lastly, the Ra-226 con-centration value was measured to be highest in Incheon Metropol-itan City and lowest in Busan Metropolitan City. Analysis was madefor monitoring posts by 12 local measurement stations of the KINSand soil samples taken in emergency soil sampling points. Accord-ing to the analysis results, concentration of 40K, which was mea-sured in the 12 local stations of the KINS, was 835.66 ± 184.9 Bq/kg dry while the average of measurement values in the studywas 871.70 ± 167.33 Bq/kg dry. The measurement value by theKINS was relatively high in Seoul while the measurement valuein this study was high in Incheon. Both of the measurement valuesby the KINS and in this study were low in Jeju Island. 40K is a nat-ural radioactive nuclide and a gamma isotope that exists not onlyin soil but also in agricultural, livestock and marine products aswell as marine sample. The nuclide is very critical to evaluate theharm that environmental radioactivity causes to residents andevaluate environmental effects. And the nuclide does not changedepending on operation of nuclear facilities or depth of soil. Butit is believed that the nuclide is related to components of theEarth’s crust. Since 40K is often found in granite region, presenceof the nuclide is attributable to the fact that Korea consists mainly

Fig. 2. Measurement results of radioactivity con

of granite region. In particular, such presence is also attributable tothe fact that Jeju Island has many basalt areas (Korea Institute ofNuclear Safety, 2006).

Radioactivity concentration of 137Cs, which was measured inthe 12 local stations of the KINS, was 1.165 ± 0.155 Bq/kg dry onaverage while the measurement value in the study was 0.458 ±0.162 Bq/kg dry. Difference in measurement values was due to dif-ference in measurement points. The measurement values in the 12local stations were obtained in the place where covering of soil didnot take place, whereas the measurement values in this study wererelated to difference in concentration values of 137Cs that was be-lieved to be concentrated relatively on surface soil since samplewas taken from soil in the playground with many people comingand going and with its surface exposed. In addition, the values de-tected at the MDA or less were the measurement values of realradioactivity in extremely tiny quantity and had a close relationwith detection efficiency of equipment. HPGe detector shows anexcellent resolution for gamma ray but has the weak point oflow relative efficiency. Therefore, it is also required to take intoconsideration errors related to such weak point. In general, thereare various types of HPGe detectors. In a board sense, HPGe detec-tor is considered as reverse-biased diode. Germanium is divided ton type and p type, which is determined by concentration of accep-tor or donor within crystal (Pérez-Moreno et al., 2002). Since elec-tric field within crystal is very important, a useful shape is limitedto disk shape or cylindrical shape with a deep core. The cylindricalshape is called coaxial type since one of its ends is closed while thedisk shape is called plane type. In particular, the coaxial type tendsto have increasing capacitance according to the increase in size ofdetector. High capacitance results in low resolution (Jurado Vargaset al., 2003). The HPGe detector used in this study was the coaxial-type detector. And resolution and detection efficiency of the detec-tor were believed to be degraded unlike the case with the detectorused by the KINS. In regard to other nuclides, the KINS has not con-ducted measurement. If diverse nuclides are detected at the na-tional level, comparative study will be conducted again in thefuture.

In conclusion, radioactive contamination could be severe in thesurrounding area of elementary schools, compared to other areas,due to the penetration of numerous radioactive nuclides in the soil

centration in soil of all the areas combined.

M.-H. Kim et al. / Annals of Nuclear Energy 47 (2012) 21–27 27

of playgrounds and flower beds. Since school children are livingin places that are directly exposed to such environments and couldbe exposed to a higher natural radiation dose in the schoolenvironment than in other ordinary environments, it is necessaryto measure and manage radiation dose with a long-termperspective.

The limitations on this study were difficulties in securing objec-tivity of the study because the number of measurements was notthe same area by area. Other difficulties included quantifying themeasurement values of ambient gamma dose rate by area becausethe measurement places were not uniform even though the coun-try was divided up into 14 areas for the study.

5. Conclusions

This study was conducted to measure soil radioactivity concen-tration in elementary schools nationwide that were living space forchildren who were sensitive to radiation. According to the resultsof radioactivity concentration measurement in entire areas, theconcentration of K-40 was the highest at 871.70 ± 167.33, that ofBe-17 was high at 146.77 ± 53.28, and that of Cs-137 was thelowest at 0.458 ± 0.162.

It is required to measure and manage radiation dose in the long-term perspective since school environment is more likely to beexposed to natural radiation dose than other ordinary environ-ment. It is expected that this study will increase attention to soilpollution in school environment and at the same time, make agreat change in awareness of environmental radioactivity. In addi-tion, it is necessary to increase the type of samples and the numberof analysis nuclides in order to obtain more segmented data andmanage environmental radioactivity continuously. Furthermore,for precise measurement and long-term management of radiationdose, it is believed that system should be established to verifythe entire procedures from pre-processing to analysis of sampleas a way to not only evaluate analysis results but also reduce errorrange.

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