Papaer: Revised XFR Methods by Dr. Jalpan S. Oyay Awin

Abstract:-

Concentration of natural radioactive material (norm) were measured by using x-ray florescence (XRF) to find the activity concentrations in Bq/kg of ²³⁸U, ²³²Th, and ⁴⁰K in the environmental soil from Malakal Town and their averages concentation were calculated from the ppm weight that were converted to Bq/kg and found to be for K = 323.43 ±72.25 Bq/kg, U = 3.72± 2.25Bq/kg and Th = 1± 0.23 Bq/kg, which shows that its very less than the world averages, and the most contributors element was found to 40K as have the highest concentrations among the other elements. And in some site the concentration of K was found to be within the world average, while the concentrations of U and Th were found to be lower than the world average.

Keywords:- XRF, Norm, Activity Concentration, K, U, Th, Bq/kg, Malakal

1. Introduction

South Sudan as part of Sudan previously has been counted as one of the countries, that their background radiation is to high comparable to the world averages background, and as this area of the world is un covered in any previous study, it’s so difficult to conform this allegation except by contacting a research that may prove or disprove it. Otherwise those allegations would be suspected as baseless considerations, as there is no scientific research or evidences that can justify these ideas. So these ideas would be given place of confidence in the reality of life if they are supported by scientific evidence in parts of the country, this, because Sudan as a country is too large, and it is has many diversity in its environments base on the locations and geological formation of the land soils and grounds, even though South Sudan have been separated from Sudan. This work is conducted in Malakal Town, located in Upper Nile State, Republic of South Sudan.

The aim of this study is to find the concentration of natural occurring radioactive materials in the soil of Malakal Town, and it is done to form a base comparative analysis data, which can be used as reference indices, in any observed elevated activity concentration in future due to human activity in the event of occupational and residential settlement on the land ^[1].

In many developing countries soils are affected my mine waste disposal, acid depositions, sewage, sludge and other anthropogenic activities. Radioactive materials can enter water in several ways by being deposited in surface water from the air, by entering ground water or surface water from the ground through erosion, seepage, or human activities such as miming, farming, storm water, and industrial activities and by dissolving from underground minerals deposited as water flows through them. The environment contains in abundance on manmade and natural radionuclides as well as polluting heavy metals. Their accumulation and the inevitable impact on human health is a matter of serious international concern. There are several way in which human can come into contact with this radionuclide: inhalation from the passing clouds external exposure in contaminated soil surface and ingestion due to food chin transfer of radionuclide. The types of diseases that can occur include leukemia, thyroid, bone, breast, lung and others. The International Basic Safety Standards (BSS) for protection against ionizing radiations and safety of radiation source are specifying the basic requirement for the protection of health and environment from ionizing radiation. These are based on the latest recommendations of International Commission on Radiological Protection on the regulation of practice and interventions. The BSS is applied to both natural and artificial sources of radiation in environment and the consequences on living and non- living species.

Irradiation of human body from external sources is mainly by gamma radiation from radionuclides of the ²³⁸U, ²³²Th decay series and from ⁴⁰K. These radionuclides may be present in the body and irradiate various organs with alpha, beta particles as well as gamma rays. [2]

For the above aim, the concentration activity of the ²³⁸U, ²³²Th and ⁴⁰K are being measured using x-ray florescent techniques (XRF), to measure the concentrations of those elements in a soil samples collected from Malakal Town.

Baseline measurement activity of the concentration levels in the natural environment, offers the opportunity to document present conditions in order to scientifically assess the future effects due to the other external factors such as human activity ^[1].

From the viewpoint of radiation protection, determination of natural radionuclides such as U, Th, and K in soil samples are so important.

It has been observed that granitic rocks contain higher amounts of U, Th, and K comparable to other igneous rocks such as basalt and andesites ^[3].

The aim of this study is to characterize the background levels of U, Th, and K in the environmental soil samples from three sites in Malakal town. The activities of ²³⁸U, ²³²Th, and ⁴⁰K, have been measured by using XRF techniques with Si (Li) detector.

2. Materials and Methods

2.1 Sample collections and analysis

The soil samples were taken from Malakal Town in Makal County, the aim was to know the concentration of a certain radioactive elements such as uranium, thorium, and potassium, as the main core of the researcher work, and also to know the levels of other element concentrations as a minor work, due to the lack of such data as there have been no experimental work being conducted in the area. Soil core samples were taken from a depth of 30cm in length from the ground ^[4] and those sampling were from the main three sectors being as northern sector, median sector, and southern sector, at three sites in different locations.

3. XRF Method

XRF (x-ray florescent) technique from the University of Khartoum, faculty of science, department of Physics-Applied Nuclear Sciences Laboratory, has been used to measure the concentration of the main targeted three, radionuclides in soil, which are Uranium (U), Thorium (Th), and potassium (K) beside the other any existing trice elements.

3.1 Preparation

The soil samples were crashed into fine powder, at the mailing laboratory of geological research in the ministry of mining in the Republic of Sudan, after being dried and kept for a period more than a month. And then they were pressed into pellet form suing a 15 ton pressing machine. They diameter of each pellet was about 2.5cm and the mass about 1g. The pellets were presented to the XRF spectrometer system, where each of them was measured for 2000 sec. The spectra obtained as a result of x- ray excitation using Cd-109, x-rays source were transferred to a computer. The spectra were analyzed and concentrations of the elements present in the samples were obtained using AXIL, XRF software available in the computer.

A plant standard was used to ensure reliability of the results (soil standard, obtained from the IAEA (International Atomic Energy Agency), Vienna).

4. The Results and Statistical Analysis

4.1 The analysis and discussion

The results obtained by XRF, can be converted into (Bq/kg), assuming that the state of radioactive equilibrium makes it possible to employ the obtained uranium concentration, to estimate values of U and Th and K in ppm, and those were converted to activity concentration, (Bq/kg), using the convention factors given by the international Atomic Energy Agency, (IAEA 1989). The activity concentration of a sample containing 1 ppm by weight of ²³⁸U is 12.35 (Bq/kg), 1 ppm of ²³²Th is 4.06 (Bq/kg) and ⁴⁰K is 313 (Bq/kg) ^[5]. These are showed in table (4.1.) bellows:

Table (4.1): Shows the concentrations of radioactive elements averages in ppm given by XRF

Fig (4.1): The graph of elements concentrations in ppm as given by XRF method

Table (4.2): Shows the concentration of the radioactive elements in (Bq/kg) as given by XRF method

Fig (4.2): The graph of the concentration of radioactive elements in Bq/kg as given by XRF

Table (4.3): Trace elements concentrations in ppm as give by XRF

Fig (4.3): A graph shows the concentration of trace element

From these results obtained by XRF method (Technique), the concentrations of radioactive elements K, U, and Th in the table (4.1), shows that, the concentration of K is within the range of the world average that is 400 Bq/kg^[6], where this finding of (1.033) in (ppm) which gives activity of 406.9 Bq/kg.

And this can be attributed chemically to the fact that Malakal Town soil is too muddy and have high concentrations of Fe, from the other trace elements table (4.3), it is seemed that iron has the highest concentration which 1.73 in ppm as the mean concentration for all soil samples.

XRF method, pears that it is able to be effective in detecting the light elements as K with 40 atomic weight, rather than heavy ones such as U, with 238 atomic weight and Th with 232 atomic weight.

So this also can be attributed physically to the fact that the existence of high concentrated Fe(Atomic weight =56) in Malakal soil allows K ( Atomic weight = 40) photons to pass without being absorbed markedly by electotransitions; this is due to the fact that X-rays Photons of K have less energy than the difference in energy of Fe atoms. This is due to the fact that the atomic weight and atomic number of K are less than that of Fe. Thus the emitted photons from K atoms are in the order of magnitude of

hf(k) …(6.1)

While the difference of energy of energy levels of Fe, which is heavier than K, are in order of magnitude of

(Large difference) … (6.2)

Thus

… (6.3)

Hence the absorption of probability of K photons by Fe due to electronic transitions is small. However the situation is different for U and Th elements which have atomic weights 238 and 232 respectivly. The corresponding emitted photons from them is expected to be energetic compared to the energy difference between Fe energy levels, i.e

hf_x (U,Th)

thus by successive collisions and interactions of photons by atoms of the matrix, the photon energies can be lowered to be just equal to the In this case U and Th photons can be absorbed considerably.

As a result the number of U and Th photons reaching the detector are small, thus XRF spectrometer gives low U and Th concentrations.

Table (4.4) Activity concentration of K-40 in Bq/kg

Fig.(4.4) A graph shows the activity concentration in Bq/kg

- Activity Concentration of K-40

In table (4.4) and fig.(4.4) above, the average activity concentration of K-40 is 323.4372.28 Bq/kg which is blew the world averages that is 400 according to (UNSCEAR 2000 Report)^[8].

Table (4.5) shows the activity concentration of U- 238

Fig.(4.5) This graph shows the concentration of U-238 in Bq/kg

- Activity concentration of U-238

Average activity of U -238 in the soil is found to be 3.72 3.25 Bq/kg which is very low by a factor of 9 times than the world averages that is 30Bq/kg ^[7].

Table (4.6) shows the activity concentration of Th-232 in Bq/kg

Fig. (4.6): Shows the activity concentration of Th-232 in Bq/kg

- Activity concentration of Th-232

The average activity of Th-232 is found to 0.95 0.23 Bq/kg which is much lower to counted as it is existed, when its comparer with the world average.

5. Conclusion

The total average activity concentrations in Bq/kg of ⁴⁰K, ²³⁸U and ²³²Th were found to be 328.1 75.76 Bq/kg, and ⁴⁰K is found to be the most contributor to the background radiation more than U and Th as their contribution is much lower than world averages.

6. Acknowledgement

For this work to come out, it would be wise enough to pass my thanks giving to the University of Khartoum, Department of Physics, Nuclear techniques lab., for their kind assistant to carry out this work. And special thanks go also to the University of Sudan for Sciences and technology, faculty of sciences, department of Physics, and finally my great thank goes to Prof. Mubarak Darar for his values guidance.

References:-

[1] A.M Umber, M.Y. Onimisi and S.A. Jonah, Baseline Measurement of Natural Radioactive in Soil,Vegetation and Water in Industrial District of the Federial Capital Territory (FCT). Abuja, Nigeria. British Journal of Applied Science & Technology, ISSN: 2231-0843,Vol.: 2, Issue.: 3 (July-September) - See more at: http://www.sciencedomain.org/abstract.php?iid=133&id=5&aid=561#.VADRr1c6ml0

[2] Abdullahi, M.A., Mohammed, S.S. and Iheakanwa, I.A., Measurement of Natural Radioactivity in Soil Along the Bank of River Kaduua –Nigeria. American Jounal of Engernering research(AJER), Vol.- 02-,Issue – 09, pp 224-227 (2013).

www.ajer.org

[3] Sarata Kumar SAHOO, Masah HOSODA, Sadatoshi KAMAGATA, Atsuyuki SORIMACHI, Tetsuo ISHIKAWA, Shinji TOKONAMI, Shigeo UCHIDA, Thorium, Uranium and Rare Earth Elements Concentration in Weathered Japanese soil samples. Research Center for Radiation Protection, Nuclear science and Technology , Vol 1, p.416 – 419(2011)

[4] Ahmad Saat, Nurulhuda Kassim, Zain iHamzah, Ahmad Fariz, Determination of Surface Radition Dose and Concentrations of Uranium and Thorium in soil at Uitm Perhilitanb Research Station Kuala Keniam, Taman Negara, Pahang. International Education Center, Journal of Nuclear and Related Technologies, Vol. 7, No. 2,P 49-54- December (2010).

[5] W.R ALHARBI, J.H HLZARANI and ADEL G.E ABBADY,

Assessment of Radiation Hazard indices from Granite rocks of the southeastern Arabian shield, Kingdom of Saudi Arabia. Australian Journal of Basic and Applied Sciences, 5(6): 672-682, June ( 2011).

[6] Michal Tzortzis and Haralabos Tsertos & Stelios Christofides and George Christodoulides. Gamma – ray measurement of natural occurring radioactive Samples from Cyprus characteristic geological rocks. UCY- PHY- 02/02, Revised version (02/12/2002).

[7] Dr. Kenneth H. Rubin, Depelted Uranium, Natural Uranium and Othere Natural Occrring Radioactive Elements in Hawaiian Environment. University of Hawaii- Final Version (30 May 2008).

[8] Michalis Tzortzis and Haralabos Tsertos , Determination of Thorium, Uranium, and Potassium elemental concentrations in surface soils in Cyprus, Revised version (08/03/2004).