Soil Assessment for Contamination Experiment

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23rd Sep 2019 Environmental Sciences Reference this

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Investigate of background radiation in an industrial area

 

Contents

Abstract

Background & Introduction

Materials and Methodology

The objective

The apparatus used

Measurement procedure and setup

Results

Measurement results for uncontaminated area

Results

Discussion

Conclusion

References

Abstract

The field experiment was conducted to allow assessment of soil for contamination. The most common radionuclide materials include thorium, uranium and potassium. This study was conducted at Queensland University and Holt Street. According to construction standards, soil has to be compressed before any building can be set up. During these activities, the radionuclide materials can be absorbed in the soil and can enhance radiation concentration.

Now, the study used specific survey meters. The presumed uncontaminated soil sample was collected from botanic garden (QUT). This was to determine the background radiation. The mean dose rate was determined to be 0.14 +or – 3.97 % (µ Sv). Likewise, the contaminated soil dose rate was found to be 0.94 + or – 3.22 (µ Sv). The contaminated soil sample was collected at Holt Street near the industry gate. This dose rate was due to human pollution and industrial poisoning.

The activity and activity in a cubic meter of the radioactive elements in uncontaminated and contaminated was determined. In addition, the exercise involved mixing of top 10 cm of contaminated soil with uncontaminated soil at 290cm depth and determining the activity and activity per cubic meter. The activities were determined, and the results showed they are within the allowable limit as stipulated in Queensland Radiation Safety Act of 2010 (Queensland Government, 2016).

Keywords: Radiation, Background Radiation, Potassium, Dose Rate, Isotopes, Thorium, Uranium, and Isotope Concentration

Introduction

Radiation usually occurs when a certain source release energy which then travels through a medium until it is absorbed by matter. There are two basic types of radiations. Ionizing and non-ionizing are the main types of radiation (Ahmed, 2007). Concerning the non-ionizing radiation, individual can get exposed to radiation as they go on with daily requirements. Besides, non-ionizing doesn’t have sufficient energy and therefore, cannot ionize atoms and molecules. The other form of radiation is ionizing because it causes ionization of atoms and molecules. It is as a result of decay process and it releases sufficient energy that can cause DNA change and increase the risk of cancer development in human lifetime. (National Research Council, 2006)

Background radiation occurs when people get exposed to radiation from the environment as they go on with daily work. This can result from ionizing radiation from an array of sources. There are two broad clarifications of radiations sources, which are man-made and natural sources (Haygood, 2013; Symonds et al., 2013). The natural radiations entail terrestrial, cosmic, intakes of natural radon nuclides through ingestion and inhalation. According to Haygood (2012), the outer atmosphere of the earth is in constant attack by cosmic radiations which can expose humans to potential radioactive pollution.

The Canadian Nuclear Safety Commission clarifies that nuclear radiation that is intercepted by human bodies comes from different aspects. The plants, radioactive rocks and soil, radon, cosmic sources all surround human bodies in relation to radioactive contamination (CNSC, 2015). The natural decay process result to natural deposits of uranium, thorium, and potassium. Through this decay process, ionizing radiation may also be present. The above mentioned minerals can be present in building materials and therefore can cause indoor and outdoor radiations (Shahbazi-Gahrouei et al., 2013).

The natural decay of thorium and uranium can result to release of radon and Thoron respectively. These are radioactive gases that can travel in air and also accumulate in buildings (Chen et al., 2014). Once trapped in the buildings, these harmful radioactive gases will be absorbed by occupants through inhalation.  Moreover, food and drinking water can also contain the aforementioned radioactive elements. For instance, food crops grown on contaminated soils have higher probability of having contaminated yields. Groundwater with these contaminants is also potentially harmful once ingested by humans (National Academic Press, 2011). Some assumptions have been made in a way to investigate activity of isotopes and background radiation. These assumptions are clearly explained in the later details of this report.

Materials and Methodology

 The objective

The main goal of this research was to investigate the natural background radiations of various locations to and determine the concentrations and activity of three elements; thorium (232), uranium (238), and potassium (40). It was carried out by examining the dose rate from soil and industrial locality.

The apparatus used

During the operation, survey mater was applied to take the necessary measurements. This is a radiation detector that uses the principle of radiation gas filled detector.

Figure 1; Shows the survey meter used to take measurements

Measurement procedure and setup

In this particular scenario, the assumptions were that background radiation is made of 50 percent terrestrial and 50 percent cosmic radiations. Soil was compressed and left for six months to affirm its full compression. Another assumption is that the dose meter shows that the top 10 cm soil is polluted by radiation as a result of industrial activities. Moreover, it is assumed that the rest 2.9 meters is not contaminated. The specified soil sample also is assumed to have same amounts of the uranium, thorium and potassium isotopes as specified above. The dose factors used are 0.39996, 0.54373, and 0.03995 nGy h-1 Bq-1 kg) and are denoted as K factors. Soil density was also used as another constant and is equal to 1.6×10-3 kg m.-3 the procedure to check whether 10 cm soil is contaminated, the process involves mixing it with the 2.9 meters of uncontaminated soil and observation and recording of activity of the mixture is done. After doing the determination, the results are then compared against the standards. The standards for Queensland soil activity are used in this case (Queensland Government, 2016). Through this comparison, it gives indication whether mixing the top layer soil is enough to avert contamination according to legal limits.

There were stepwise activities during the whole exercise. Initially, students met at room 401 an were given the relevant radiation meters. The students visited different points measuring and denoting the measurements. The students started taking the readings at QUT. In total, three multiple measurements were taken to record the local areas background radiation.

Figure 2; shows location at QUT garden point

In addition to location 1 the students also visited Holt street area and multiple locations were measured just like in first location. Equally, the outcomes were recorded and average calculated. These figures are available at outcomes segment of the report. Moreover, there were mathematical calculations done in this exercise. These calculations were to determine the activities of various elements used. Formula 2 was used in the determination of each element’s activity for the contaminated and uncontaminated soil samples. To make everything count, the standard deviation and uncertainty have also been applied in the formulas. Due to the linear nature of the equation applied, the interpolation of standard deviation as sown in formula 1 was used in determination of uncertainty. The last step of the procedure involved determining and comparing the underneath soil activity with the (standard acceptable limit).

Results

 Three sections are used to display the radiation measurements. These results are for contaminated, uncontaminated and the mixed area as indicated by the illustrative picture below.

Measurement results for uncontaminated area

 As explained in the previous section, various locations were measured and five locations found to have no contamination. As seen it table 1, there are recordings of the radiation survey. The average of the radiations measurements from the used points seemed to be lowest and it can be applied as the background radiations in our calculations. This activity can therefore be mathematically calculated using the formula;

D=ΓAd2A=D*d2Γ.(1)

Symbols used in the formula

D; dose rate (nGy)

D2; distance to source (1m)

Γ; K factor (nGy h-1 Bq-1 kg)

A; source activity (Bq per kg)

Table 1 below demonstrates results for uncontaminated area:

Location

measurement(1)

( / )

measurement  (2)

( / )

measurement (3)

( / )

Average

( / )

Standard deviation

 

Percentage for uncertainty

1.Garden point

0.15

0.14

0.14

0.1433

0.0057

3.977

2.  Holt Street

0.21

0.18

0.17

0.1867

0.0208

11.14

3. Holt Street

0.19

0.17

0.15

0.17

0.02

11.76

4. Holt Street

0.14

0.16

0.15

0.15

0.01

6.66

5. Holt Street

0.71

0.77

0.68

0.72

0.0458

6.36

Table 1

To correctly determine the background radiation various calculations were done as follows.

In the situation where there are both cosmic and terrestrial radiation playing part as a source of radiation, the average is therefore divided by two.

So, 0.1433 / 2 = 0.0716 ± 3.97 % /

Based on the assumptions that the soil has same amounts Potassium, Uranium, and Thorium, activity   in uncontaminated area can be is calculated by determining the third of the background radiation. Therefore, average dose rate D) = 0.0716 / 3 = 0.0238 ± 3.97 % / and since Sv= Gv, units should be changed to nGy h-1. So, 0.0238×1000= 23.8± 3.97 % nGy h-1

Also, by using the conversion factor of each particular radionuclide elements in m3, the density of soil in 1600 Kg m-3 is multiplied to activity (Bq/Kg).

Table 2 below outlines the conversion factors for the three isotopes:

Radioactive element

238Uranium

232Thorium

40Potassium

Conversion factor K in (nGy h-1 Bq-1 kg)

 

0.39996

0.54373

0.03995

Uranium 238 =  23.8 nGy h-1 / 0.39996 (nGy h-1 Bq-1 kg) = 59.5 ± 3.97 % Bq/Kg  

Activity per M3 = 59.5 × 1600 Kg m-3 = 95200 Bq /m3

Thorium 232=  23.8 nGy h-1 / 0.54373 (nGy h-1 Bq-1 kg) = 43.77± 3.97% Bq/Kg.

Activity per M3 = 43.77 × 1600 Kg m-3 = 70032 Bq /m3

Potassium 40=  23.8 nGy h-1 / 0.03995 (nGy h-1 Bq-1 kg) = 595.745 ± 3.97 % Bq/Kg

   Activity per M3 = 595.745 × 1600 Kg m-3 = 953191.489 Bq /m3

 

 

 

 

Measurement results for the contaminated zone

contaminated area (footbath site)

 

                         Footpath site

 

Location

Reading (1)

( / )

Reading (2)

( / )

Reading (3)

( / )

Average

( / )

Standard deviation

Uncertainty %

6 Holt street

0.96

0.91

0.93

0.93

0.03

3.22

 

Table 4

As seen in the tabulation above, the highest level of radiation was recoded in Holt Street (0.96 / ). It shows that the soil from the footpath was contaminated. To affirm this, same calculations used in the previous section have been applied while maintaining the same assumptions. The cosmic radiation was determined to be 0.0716 / .  The dose rate of three radioisotopes = 0.858×103/ 3= 286 ± 3.22 %   nGy h-1. The dose rate has been divided by three since it was assumed that the amounts for the three elements were equal.

To get activity of each element, the following calculations are done;

Uranium 238=  286 nGy h-1 / 0.39996 (nGy h-1 Bq-1 kg) = 715.071 ± 3.22 %    Bq/Kg         

         Per cubic meter for (238U) = 715.071 × 1600 Kg m-3 =1144114.41± 3.22 % Bq/m3

Thorium 32=  286 nGy h-1 / 0.54373 (nGy h-1 Bq-1 kg) = 525.99 ±Bq/Kg         

         Per cubic meter for (232Th) = 525.99 × 1600 Kg m-3 = 841584 ± Bq /m3

Potassium 40=  286 nGy h-1 / 0.03995 (nGy h-1 Bq-1 kg) =7158.948± 3.22 % Bq/Kg

          Per cubic meter for (40K) = 7158.948 × 1600 Kg m-3 = 11454316.8 ±3.22 % Bq /m3

Results

Activity at contaminated area ( uncertainty± 3.22 %)

Radioactive element

238U

232Th

40K

Activity (Bq / m3)

1144114.41

841584

11454316.8

Activity (Bq/Kg)

715.07

525.99

7158.9

Table 5

Determination of activity soil underneath (mixing of soil underneath) to see if mixing of top 10 cm soil (contaminated) with uncontaminated soil -290 cm can lower radiation levels to acceptable levels, it is fist assumed that 1 cubic meter of sol contains contaminated and the remaining 2.9 cubic meter contains uncontaminated.

238U

232Th

40K

Queensland limit for soil activity  (Bq/g)

10

1

100

The measured activity (A)   (Bq/g)

0.059± 3.97 %

0.0437± 3.97 %

0.595± 3.97 %

The activity at 2.9m soil underneath [A(2.9m)]      A(2.9m) = A× 2.9m     (Bq/g)      

0.1711

0.135

1.73

The activity at 0.1m soil underneath [A(0.1m)]  (Bq/g)

0.715± 3.22

0.525± 3.22

7.158± 3.22

The total activities of each element at 3m

A(3m)mix = ( A(2.9m) + A0.1m) / 3   (Bq/g)

0.295

0.22

2.962

Table 6

 Discussion

A number of measurements of background radiation for industrial and local area have been carried out. The highest record was at Holt Street with dose rate 93± 3.22 % / . Holt Street is close to industrial gate explaining why radioactive element constituent in soil was the highest. The clear picture of this conclusion is explained by the graph below.

Table 3 shows thorium had the least 43.77± 3.97% Bq/Kg. in table 5, the same thing reveals. Potassium was found to be highest (7.158± 3.22 % Bq/g) and thorium the lowest activity (0.525± 3.22% Bq/g). In addition, total activity determination is realized by combining the activity an element e element at 0.1m with the reaction at 2.9 meters depth of soil. In application, the mixing of the two helps in lowering contamination level of the contaminated area. After the analysis, thorium the lowest at 0.22± 3.22% Bq/g and potassium had the highest levels at 2.962± 3.22 % Bq/g.

Activities for the three soil depth i.e. 0.1m, 2.9m and 3m are shown in the graph below

So, activities for the three elements were the highest at 0.1m and lowest at 2.9m. However, after mixing A0.1m+ A2.9m), the activity level reduced for the three elements 238U (0.295 Bq/g), 232Th (0.22 Bq/g), and 40K (2.962 Bq/g. after the mixing, the activity of all three come to the accepted levels according the Queensland  radiation safety act. so, mixing the two soil samples  brings total activity within the acceptable levels no matter the soil depth. 1×101(Bq/g), 1×100(Bq/g), and 1×102(Bq/g), for uranium, thorium and potassium respectively.

The increase in contamination is caused by pollution of soil by increased radioactive material use in nearby industries.

Conclusion

Thus, this dramatic increase is well explained, so at same scenario and time of measurement, the areas were found to be safe for public use. For the contaminated areas, public need 1057 hours to reach annual recommended dose1mSv/year. Most importantly, the radioactivity or emissions of these three isotopes can be changed or reduced and doing the determinations more regularly is highly encouraged.

References

  • Top of Form
  • Ahmed, S. N. (2007). Physics and engineering of radiation detection. Amsterdam: Academic Press.
  • Chen, J., Bergman, L., Falcomer, R., & Whyte, J. (2014). Results of simultaneous radon and thoron measurements in 33 metropolitan areas of Canada. Radiation protection dosimetry, 163(2), 210-216.
  • CNSC. (2015, May 20). Types and sources of radiation – Canadian Nuclear Safety Commission. Retrieved August 19, 2018, from http://nuclearsafety.gc.ca/eng/resources/radiation/introduction-to-radiation/types-and-sources-of-radiation.cfm
  • Haygood, J. R. (2013). Radiation safety procedures and training for the radiation safety officer: guidance for preparing a radiation safety program: iUniverse
  • National Research Council (U.S.). (2006). Health risks from exposure to low levels of ionizing radiation: BEIR VII, Phase 2. Washington, D.C: National Academies Press.
  • National Academic Press. (2011). 6. In Uranium Mining in Virginia: Scientific, Technical, Environmental, Human Health and Safety, and Regulatory Aspects of Uranium Mining and Processing in Virginia. Washington: National Academies Press.
  • Queensland Government. (2016, February 4). Radiation Safety Regulation 2010; Radiation Safety Act 1999. Retrieved from https://www.health.qld.gov.au/radiationhealth/legislation
  • Shahbazi-Gahrouei, D., Gholami, M., & Setayandeh, S. (2013). A review on natural background radiation. Advanced biomedical research, 2.
  • Symonds, R. P., Deehan, C., Meredith, C., & Mills, J. A. (2012). Walter and Miller’s Textbook of Radiotherapy E-book: Radiation Physics, Therapy and Oncology.

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