Measurement of Radioactivity for Radium226 Isotopes in some Soil Samples from Different Regions in Karbala Governorate using Gamma Ray Spectrometry Hasan Issa Dawood




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Measurement of Radioactivity for Radium226 Isotopes in some Soil Samples from Different Regions in Karbala Governorate using Gamma Ray Spectrometry

Hasan Issa Dawood

Physical Department-College of Education-Qadisiya University
Abstract

In this work the calculation of the concentration of radionuclide Ra226 in some samples of soil in governorate of Karbala have been done by gamma-ray spectroscopy NaI(TL) scintillation detector. The range of Ra226 activity was found from 11.41 ± 3.37 to 99.6 ±16.8 Bq/Kg. The concentrations of radon gas in the air was determined as well as the activity concentrations of Ra226 in vegetables. The doses resulting from the consumption of vegetables and those were coming from the inhalation of radon gas were estimated using some of mathematical equations , also the mean value of the activity concentrations of Ra226 inside the soil samples that measured in the present work were compared with the values of the other countries in the world and it is found that within the permitted limits.



الخلاصة

تم في هذا البحث حساب تركيز النشاط الإشعاعي لنويد الراديوم 226 في بعض نماذج التربة في محافظة كربلاء وذلك باستخدام كاشف طيف أشعة كاما ألوميضي NaI(TL) , ولوحظ أن النشاط الإشعاعي في هذه النماذج تتراوح من 11.41 ± 3.37 إلى 99.6 ± 16.8 (Bq/Kg) . تم حساب تراكيز الرادون في الهواء إضافة إلى تراكيز الراديوم في الخضراوات وباستخدام بعض المعادلات الرياضية تم حساب الجرع الناتجة للراديوم 226من استهلاك الخضراوات والجرع الناتجة من استنشاق غاز الرادون 222 , وقد تم مقارنة معدل القيمة للنشاط الإشعاعي للراديوم 226 المقاسة في نماذج التربة مع قيم بقية بلدان العالم ووجدت أنها ضمن الحدود المسموحة بها.



Introduction

Studies on radiation levels and radionuclide distribution in the environment provide vital radiological baseline information .Such information is essential in understanding human exposure from natural and man made sources of radiation and necessary in establishing rules and regulations relating to radiation protection [Quindos et al ,2004] and [Ibrahim et al ,2006]. Measurements of natural radioactivity in soil have been performed in many parts of the world, mostly assessment of the dose and risk resulting from them [Rudge et al ,1993] , [Clouvas et al ,2001] , [Copplestone et al , 2001] , [Dowdall et al , 2004] and [El-Bahi et al , 2005].

The naturally occurring radionuclides present in soil include Ra226 , Th232 and K40 [Khan et al , 1998] . Gamma radiation emitted from those naturally occurring radioisotopes, called terrestrial background radiation , represents the main source of irradiation of the human body and contribute to the total absorbed dose via ingestion , inhalation and external irradiation [Steinhausler , 1992] . Calculations by [Beck , 1972] suggested that 50-80% of the total gamma flux at the earth´s surface arises from K40 , U238 and Th232 series in topsoil.

Natural environmental radioactivity and the associated external exposure due to the gamma radiation depend primarily on the geological and geographical conditions and appear at different levels in the soils of each region in the world , Since the radionuclides are not uniformly distributed , the knowledge of their distribution in soils play an important role in radiation protection and measurement [Khan et al , 1994], also the radioactivity of soils is essential for understanding changes in the natural background [Sroor et al , 2001] and [Chiozzi et al , 2002] .



System of detection and analysis

In the present work using gamma spectrometer with a scintillation detector (3 x 3) inch NaI (TL) as shown in fig (1) that working at (750 )volt with the efficiency of 60% . The viability of discrimination detector of energy in the limits (6.5-8.56)% for the energy values (0.662-1.332)Mev. The detector surrounded by lead shield to prevent the background radiation. The radioactive sources (Cs137 , Na22 , Co60) were used to calibrate the system and calculate the efficiency of the detector.



Collection and preparation of samples

(A) Collected six soil samples from different regions of the government of Karbala with

a weight of two kilogram for each sample and set in bags , after then placed on each bag zone name for soil taken .Details of the soil samples examined are as follows.



1- Drying : All samples were dried by exposing them to sunlight for time period of (72) hour , in addition the dried samples exposing to air for a full day to ensure fully dry .

2- Grinding : The samples are grinding with using hand-mill and then used a sieve with a diameter of 2mm in order to obtain smooth samples.

(B) Create a system:

Account background radiation to subtracting from the value of the radioactivity for all preparation soil samples at the same period measured , after then the crushed soil were measured in Marinelli-type beakers with a production capacity of one kilogram with the time period of one hour.



Method of calculations

A – The magnitude of the concentration of Ra226 inside the soil was calculated by [Chung et al , 1989];

CRa(n)= C(En) – B(En)/ m.f.t.P(En) ……………………..(1)

Where

n : is the number of soil sample , 1,2,3…..etc



CRa(n) : is the radioactive concentration of Ra226 in soil sample (n) in (Bq/Kg) .

C(En) : is the net γ-counts above continuum at the characteristic energy (En) .

B(En) : is the background counts at (En) .

m : is the mass of the sample in (Kg) .

f : is the branching ratio of the γ-emission at the energy considered .

t : is the measuring live time in (sec) .

P(En) : is the absolute efficiency at energy (En) .

BThe formula that used to measuring the radioactive concentration of Rn222 in the air as follow (UNSCEAR,1988) ; Firstly must be estimate the radioactive concentration of Rn222 inside the soil samples by ;

Gs(n) = Fr . ρ . CRa(n) …………….…. (2)

Where

Gs(n) : concentration of radon gas inside the soil for sample(n) in (Bq/m3) .



Fr : the constant of emission of Rn222 from the soil that is equal to (o.1) .

ρ : is the soil density that is equal to (1800 Kg/m3) .

CRa(n) : is the radioactive concentration of Ra226 in soil sample (n) in (Bq/Kg).

Now we can calculate the concentration of Rn222 in the air by the below equation ;

Ca(n)=Gs(n) (dsoil / Dair)1/2 ……………. (3)

Where

Ca(n) : is the concentration of Rn222 in the air for sample (n) in (Bq/m3) .



Gs(n) : concentration of radon gas inside the soil for sample(n) in (Bq/m3) .

dsoil : is the diffusion rate constant of Rn222 in the soil (o.5 ×10-4 m2/sec) .

Dair : is the diffusion rate constant of Rn222 in the air (5 m2/sec) .

C - : Expense of radioactivity in vegetables was determined by using the

following equation (UNSCEAR ,1988 ; IAEA ,1996) ;

Cn = An . CRa(n) ………………….…….(4)

Where

Cn : is the concentration of Ra226 in vegetables in (Bq/Kg) .



An : is the transfer coefficient of Ra226 from soil to Vegetables that is equal to (o.o4) ;

(IAEA ,1990) .

CRa(n) : is the radioactive concentration of Ra226 in soil sample (n) in (Bq/Kg) .

DThe doses rates that coming from inhalation of radon gas and vegetables consumption was determined by using the below equation (IAEA , 1996)

Hp =Cp . Ip . DCF ……………….(5)

Where

Hp : is the dose rate resulting from inhalation of radon gas or vegetables consumption



in (sv/y) .

Cp : is the concentration of Ra226 in vegetables (Bq/Kg) or the concentration of Rn222 in

the air (Bq/m3) .

Ip : is the amount of consumption of vegetables in year (90Kg/y) and for air outside the home (600 m3/y) ;(IAEA ,1990) .

DCF : is the dose conversion coefficient: for Ra226 equal to (2.8×10-7 sv/Bq) and for

Rn222 equal to (1.3 ×10-9 sv/Bq);(UNSCEAR,1988) .



Results and Discussion

The Ra226 activity concentrations were measured for six soil samples that collected from different locations of Karbala governorate. Sampling locations are marked in Fig(2). The data of these study are given in table (1) . The activity concentrations of Ra226 in soil samples ranges from 11.41 ± 3.37 to 99.6 ± 16.8 with mean value of 55.3 Bq/Kg . From the results in table (1) appear the higher concentration of Ra226 in regions of Al-hur (1) and Al-Ibrahimia (1) , this is due to the natural state and creation of soil . The radioactive radon gas that arises from the disintegration of U238 and Th232 in the earth´s crust is considered the main source of exposure to ionizing radiation for humans that representing 40% of the annual accumulated dose (UNSCEAR,1993) , therefore the present study some of mathematical equations models are used to estimate the activity concentrations of Rn222 in the air with the activities of Ra226 that contents in vegetables , as well as the doses rates that results from the vegetables consumption and from inhalation of radon gas were considered, table (2) ,(3) and (4) consists of these estimated concentrations and doses values respectively . The data of the doses rates from the vegetables consumption and inhalation of radon gas that given in table (4) within the allowed limits that equal (1msv/y) [FAO.1977 , IAEA,1996] in all regions that selected in the present search .



Comparison of activity concentrations with other countries: The mean value of activity concentrations of Ra226 in soil samples from studied area was compared with those from similar investigations in other countries and a summary results were given in table (5).

Conclusions

1- The present work developed that all soil samples that taken from all regions from the Kabala governorate have the Ra226 element with different activity concentrations.

2- The obtained values of natural radioactivity and γ-absorbed dose rates due to the activity concentrations of soil samples and in the air show that none of the studied samples is considered a radiological hazard.

3- Soils can be safely used in construction of buildings and exploits for the agriculture without posing any significant radiological threat to population .

4- It is important to point out that these values were not the representative values for the countries mentioned , but for the regions from where the samples were collected .









Scintillation detector NaI(TL)

View Screen of Data




Multi-Channel Analyzer



View The System Fully




Table (1) the activity concentrations of Ra226 in soil samples( Bq/Kg).

Activity of Ra226

Zone name

Sequence

93.2 ± 10.5

Al-Ibrahimia (1)

1

16.16 ± 4.01

Al-Ibrahimia (2)

2

99.6 ± 16.8

Al-Hur (1)

3

55.9 ± 16

Al-Hur (2)

4

55.7 ± 24.6

Al-Hur (3)

5

11.41 ± 3.37

Aon

6

Table (2) the activity concentrations of Rn222 in soil and in air (Bq/m3).

Activity of Rn222 in air

Activity of Rn222 in soil

Zone name

Sequence

53

16776

Al-Ibrahimia (1)

1

9.198

2908.8

Al-Ibrahimia (2)

2

56.69

17928

Al-Hur (1)

3

31.818

10062

Al-Hur (2)

4

31.7

10026

Al-Hur (3)

5

6.494

2053.8

Aon

6

Table (3) the activity concentrations of Ra226 in vegetables (Bq/Kg).

Activity of Ra226

Zone name

Sequence

3.7

Al-Ibrahimia (1)

1

0.64

Al-Ibrahimia (2)

2

3.98

Al-Hur (1)

3

2.24

Al-Hur (2)

4

2.23

Al-Hur (3)

5

0.45

Aon

6

Table (4) the doses rates resulting from consumption of vegetables(Ra226)and

inhalation of Rn222 gas (msv/y).

Doses from inhalation

Doses from vegetables

Zone name

Sequence

0.041

0.093

Al-Ibrahimia (1)

1

0.0077

0.016

Al-Ibrahimia (2)

2

0.044

0.1

Al-Hur (1)

3

0.024

0.056

Al-Hur (2)

4

0.024

0.056

Al-Hur (3)

5

0.005

0.011

Aon

6


Table (5) : Comparison of radioactivity levels(mean values) of Ra226 in soil samples under investigation with those in other countries.

References

Mean values (Bq/Kg)

Countries

Present work

55.3

Iraq (Karbala)

[UNSCEAR,2000]

40

United states

[Al-Jundi et al ,2003]

63

Aqaba (Highway)

[UNSCEAR,2000]

40

Switzerland

[UNSCEAR,2000]

45

Bulgaria

[Chowdhury et al ,2006]

42

South districts

[Akhtar et al , 2005]

25.8

Pakistan (Lahore)

[UNSCEAR,2000]

59

Hong Kong SAR

[UNSCEAR,2000]

48

Thailand

[UNSCEAR,2000]

44

Portugal

[UNSCEAR,2000]

172

OAP data

[Quindos et al , 1994]

39

Spain

[Kiss et al , 1988]

19

Canada (Saskatchewan)

[Malanca et al , 1996]

29.2

Rio Grande do Norte

[Mireles et al , 2003]

23

Mexico (Zacatecas)

[Narayanq et al , 2001]

35

South India

[Huy et al , 2006]

19.6

Vietnam (South – east)

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