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Elemental Analysis of Arable Soil by Proton Induced Gamma Emission (pige) Technique

M. Kamrujjaman
Lecturer
Department of Mathematics and Physics, Hajee Mohammad Danesh Science and Technology University, Dinajpur-5200

M N Hossain
Scientific Officer
Institute of Nuclear Medicine & Ultrasound, BAEC, Savar, Dhaka

A. K. M. F. Hoque
Principle Engineer
VDG Accelerator Facilities division, Bangladesh Atomic Energy Centre, 4, Kazi Nazrul Islam Avenue , Dhaka -1000

A. H. M. Saadat
Assistan professor
Department of Environmental Sciences, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh

Abstract/ Executive Summary:

Proton Induced Gamma Emission (PIGE) technique was employed for analyzing low Z elements (Na, Mg and F etc.) in arable soil. The soil samples were collected from the arable fields of Norshindi, Sylhet and Chittagong districts. Proton beam from the horizontal type 3 MeV Van de Graff accelerator at the AECD was used for irradiating the soil samples. The proton beam of energy 2.5 MeV was used with a beam current of 20 nA. A HPGe detector along with the associated equipment, such as pre-amplifier, amplifier, PC, MCA was used for the detection of gamma rays from the PIGE reactions in the irradiate soil samples. The PIGE reactions ¹⁹F(p, p^-, γ)¹⁹F, ²⁵Mg(p, p^-, γ)²⁵Mg and ²³Na(p, p^-, γ) ²³ Na were used for the determination of the yields and hence the concentrations and sensitivities for the elements Na, Mg, and F. The concentrations were obtained at the ppm level by comparing with the certified values of the IAEA standard soil-7. The experimental results were compared with the optimum concentrations of the above elements in arable soil. Mg and Na were found at a slightly toxic level in some soil samples and F was found rather at a high concentration in some samples.

Keywords: Proton Induced Gamma Emission (PIGE), HPGe detector, MCA and ppm.

Location: Laboratory of Bangladesh Atomic Energy Centre, Dhaka -1000

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

Objective of the study was to apply PIGE method to study low Z elements such as Na, Mg and F etc. in arable soil samples

Methodology:

The arable soils were collected form different places in Bangladesh. A total of 33 samples were collected, 14 samples from Norshindi, 12 samples from Sylhet and the rest from Chittagong. Proton beam from the horizontal type 3 MeV Van de Graff accelerator at the Atomic Energy Commission, Dhaka, was used for irradiating the soil samples. Proton Induced Gamma Emission (PIGE) is a nuclear reaction based analytical technique has been developed at the Atomic Energy Commission, Dhaka. The purpose of the development of the technique is to apply it for analyzing the low Z elements in the range of 3 ≤ Z ≤ 21. In the present study the proton induced nuclear reaction based analytical technique (PIGE) has been used in analyzing soil samples. PIGE analytical technique involves means of exciting the nuclei of a sample to emit gamma rays and the means to detect and identify them so that their measured intensities can be converted to their elemental concentrations in the sample. The number of characteristic γ-rays produced per unit incident charge per unit solid angle at particular proton energy is directly proportional to the number of atoms in the target material. The number of characteristic γ-rays produced is also dependent on the reaction cross-section and the stopping power of the sample material. The concentration of the element (isotope), Cs can be calculated from the gamma ray yield Ys for a certain γ-ray energy peak in a sample and the yield from a standard Y_stusing the formula. PIGE technique has been developed utilizing the proton beam from the 3 MeV Van de Graaff accelerator, which is a horizontal type (KN3000) accelerator and proton beam of energy upto 3 MeV can be obtained from it. Two collimators of 2mm diameter each and a 4 mm cleanup aperture were used. The target sample was irradiated in air (i.e., external beam). Kapton foils of 1.12-mg/cm2 thickness were used to extract the proton beams from the beam port into the air. The kapton windows of such thickness were found to be sufficiently strong to withstand about 400 μC of charge collected at proton beam current of 10-20 nA at an energy of 3 MeV on an area of ~3mm² without any deterioration of the high vacuum in the beam port. The beam spot was about 2 mm in diameter at the exit window. In the case of external beam, the energy of the proton beam on the target was found to be about 2.3 MeV after losing its energy in the kapton foil and the air between the exit window and the sample. In order to obtain the total proton charges incident on the sample, the current on the target and the kapton window was monitored. The window frame was insulated from the beam port and the collimator. This arrangement is reproducible for the measurement of total charge on the target (Wahiduzzaman, et. al.1988). The setup was designed to hold 35 mm slide frames for solid samples at an angle of 450 with the beam direction. The characteristics γ-rays were detected at 900 with respect to the beam direction. A plastic absorber (44 mg/cm² thickness) was used to reduce the background due to the presence of argon in the air around the targets. A beam area of 0.106 cm² on the sample was used for external beam experiments. The irradiation current was maintained within 10-20 nA and each of the target was irradiated for a preset charge of 80 μC depending on the net counts. The count rate was kept below 2000 cps in order to avoid the occurrence of sum peaks. The HPGe detector having an efficiency 12.3% at 1332 keV energy and a resolution of 1.9 keV for 1332 keV peak (the manufacture’s value for the resolution is 1.75 keV), was used to detect the γ-rays. The high voltage power supply, which has an output voltage up to 5 kV (dc.), was used for reverse biasing the detector ( MacArthur, et al. 1983) Many computer codes such as GAMANAL, SAMPO, HYPERMET, APTEC, EGM, GAUSS VIII, etc. are available for analyzing the spectra. Software from APTEC (Ali, et al., 1997) was used for data acquisition, display, identification of the elements through energy calibration, analysis of the γ-ray peaks and report generation. APTEC software incorporates PCMCA/SUPER software version 6.31, the operation of which includes smoothing the spectra, location of the centroid, energy calibration, determination of FWHM and FWTM (full width at tenth maximum), polynomial background fit, integral/net counts, etc. Another OSQ/Professional option that automates the energy vs. channel, FWHM vs. channel and efficiency vs. energy calibration and provides detailed error analysis report. In the present experiment several point sources such as ²²Na, ⁶⁰Co and ¹³⁷Cs, have been used for the calibration of energy E. The PC based MCA with APTEC software is used to have an energy calibration function to provide a linear calibration scale for the energy axis.

Source of Information: J. Soil. Nature. 2 (1): 34-39, 2008

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The proton induced nuclear reaction based analytical technique is more suitable for analyzing light elements like lithium(Li), boron(B), fluorine(F), magnesium(Mg), scandium(Sc), chlorine(Cl), phosphorus(P), and sodium(Na), which are often difficult to determine by other analytical techniques. Multi elemental proton induced nuclear reaction based analytical technique (PIGE) is very suitable for the measurement of light elements. The results of concentration measurements of Mg, Na and F on arable soil samples using PIGE technique though reliable is not however comprehensive enough to draw any definite conclusion about the toxicity or deficiency of these elements. Comprehensive elemental analysis of the soil of these regions should be carried out so that maps of these regions can be constructed showing their concentrations.

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