Mohamed S. Badawi

An empirical formula to calculate the full energy peak efficiency of scintillation detectors

This work provides an empirical formula to calculate the FEPE for different detectors using the effective solid angle ratio derived from experimental measurements. The full energy peak efficiency (FEPE) curves of the (2″(*)2″) NaI(Tl) detector at different seven axial distances from the detector were depicted in a wide energy range from 59.53 to 1408keV using standard point sources. The distinction was based on the effects of the source energy and the source-to-detector distance. A good agreement was noticed between the measured and calculated efficiency values for the source-to-detector distances at 20, 25, 30, 35, 40, 45 and 50cm.

New analytical approach to calibrate the co-axial HPGe detectors including correction for source matrix self-attenuation

To calibrate the co-axial HPGe semiconductor detectors, we introduce a new theoretical approach based on the Direct Statistical method proposed by Selim and Abbas (1995, 1996) to calculate the full-energy peak efficiency for cylindrical detectors. The present method depends on the accurate analytical calculation of the average path length covered by the photon inside the detector active volume and the geometrical solid angle Ω, to obtain a simple formula for the efficiency. In addition, the self attenuation coefficient of the source matrix (with a radius greater than the detectors radius), the attenuation factors of the source container and the detector housing materials are also treated by calculating the average path length within these materials. (152)Eu aqueous radioactive sources covering the energy range from 121 to 1408 keV were used. Remarkable agreement between the measured and the calculated efficiencies was achieved with discrepancies less than 2%.

New analytical approach to calibrate the NaI (Tl) detectors using spherical radioactive sources

A new theoretical approach was used to calibrate and calculate the full-energy peak efficiency of the NaI (Tl) detectors based on the direct statistical method proposed by Selim and Abbas for cylindrical detectors. In addition, the self-attenuation of the source matrix, the attenuation by the source container and the detector housing materials were considered in the mathematical treatment. Results were compared with those measured by a cylindrical NaI (Tl) detector with resolution (FWHM) at 662 keV equal to 7.5 %. (152)Eu aqueous radioactive spherical sources covering the energy range from 121 to 1408 keV were used. In comparison, the calculated and the measured full-energy peak efficiency values were in good agreement.

A numerical approach to calculate the full-energy peak efficiency of HPGe well-type detectors using the effective solid angle ratio

In the field of gamma-ray spectroscopy with HPGe detectors, applied to measurements of activity when the sample to be measured is small and has low radioactivity, the well-type HPGe detectors are widely used. To determine the sample activity, the full-energy peak efficiency is needed. In this work, the efficiency transfer method (ET) in an integral form is proposed to calculate the full-energy peak efficiency and to correct the coincidence summing effect for the HPGe well-type detector. This approach is based on the calculation of the effective solid angles ratio for a well-type detector with a cylindrical source inside and an axial point source outside the detector cavity, taking into account the attenuation of the gamma-rays. The calculated values of the full-energy peak efficiency are found to be in a good agreement with the measured experimental data obtained by using a mixed radionuclide gamma-ray source containing 60Co and 88Y.

STUDY ON THE EFFECT OF THE SELF-ATTENUATION COEFFICIENT ON γ-RAY DETECTOR EFFICIENCY CALCULATED AT LOW AND HIGH ENERGY REGIONS

The present work used the efficiency transfer method used to calculate the full energy peak efficiency (FEPE) curves of the (2“*2” & 3“*3”) NaI (Tl) detectors based on the effective solid angle subtended between the source and the detector. The study covered the effect of the self attenuation coefficient of the source matrix (with a radius greater than the detectors radius) on the detector efficiency. 152 An Eu aqueous radioactive source covering the energy range from 121.78 keV up to 1408.01 keV was used. In this study an empirical formula was deduced to calculate the difference between the measured and the calculated efficiencies [without self attenuation] at low and high energy regions. A proper balance between the measured and calculated efficiencies [with self attenuation] was achieved with discrepancies less than 3%, while reaching 39% for calculating values [without self attenuation] due to working with large sources, or for low photon energies.

Calibration of the 4π γ-ray spectrometer using a new numerical simulation approach

The 4pi gamma-counting system is well suited for analysis of small environmental samples of low activity because it combines advantages of the low background and the high detection efficiency due to the 4pi solid angle. A new numerical simulation approach is proposed for the HPGe well-type detector geometry to calculate the full-energy peak and the total efficiencies, as well as to correct for the coincidence summing effect. This method depends on a calculation of the solid angle subtended by the source to the detector at the point of entrance, (Abbas, 2006a). The calculations are carried out for non-axial point and cylindrical sources inside the detector cavity. Attenuation of photons within the source itself (self-attenuation), the source container, the detectors end-cap and the detectors dead layer materials is also taken into account. In the Belgium Nuclear Research Center, low-activity aqueous solutions of (60)Co and (88)Y in small vials are routinely used to calibrate a gamma-ray p-type well HPGe detector in the 60-1836keV energy range. Efficiency values measured under such conditions are in good agreement with those obtained by the numerical simulation.

New numerical algorithm method to calibrate the HPGe cylindrical detectors using non-axial extended source geometries

The knowledge of the full-energy peak efficiency for a specific source-detector arrangement is often required in various fields of research and applications, such as the analysis of nuclear waste or environmental samples, where both require modeling because it is not practical to prepare a standard that matches the physical and nuclear properties of every waste or environmental item. Therefore, a new numerical algorithm method (NAM) is proposed in the present work to calibrate the co-axial HPGe cylindrical detectors. Cylindrical sources are used in the calibration process placed perpendicularly to the detectors axis. The self-attenuation and the coincidence summing effects at low source-detector distance are also included in the algorithm. A remarkable agreement between the measured and the calculated efficiencies is achieved with discrepancies less than 3%.

An approach to evaluate the efficiency of γ-ray detectors to determine the radioactivity in environmental samples

This work provides an approach to determine the efficiency of γ-ray detectors with a good accuracy in order to determine the concentrations of either naturally occurring or artificially prepared radionuclides. This approach is based on the efficiency transfer formula (ET), the effective solid angles, the self- absorptions of the source matrix, the attenuation by the source container and the detector housing materials on the detector efficiency. The experimental calibration process was done using radioactive (Cylindrical & Marinelli) sources, in different dimensions, that contain aqueous 152Eu radionuclide. The comparison point to a fine agreement between the experimental measured and calculated efficiencies for the (NaI & HPGe) detectors using volumetric radioactive sources.

Synthesis and Characterization of Cobalt Nanoparticles Prepared by Arc Discharge Method Using an Ultrasonic Nebulizer

Magnetic cobalt nanostructured was synthesized by a two-stage method. First, a solution of cobalt precursor droplets was prepared by an ultrasonic nebulizer. Second, the arc discharge method between two electrodes in an inert gas at atmospheric pressure is used to obtain the nanostructured cobalt powder. The sample obtained was characterized by X-ray diffraction (XRD). Scanning electron microscope (SEM), High Resolution Transmission Electron Microscope (HR-TEM), UV-Vis Spectrophotometry, zeta potential (ZP) and vibrating sample magnetometer (VSM). The dielectric constant, and AC conductivity of the prepared sample was determined in the frequency range of 4 Hz to 8 MHz. The investigations showed that the Co nanoparticles prepared in this way have smaller and homogeneous nanoparticles with spherical shape morphology with good stability and unique magnetic properties as compared with the bulky one. The dielectric properties analysis shows an enhancement in the dielectric constant and the AC conductivity of the Co nanoparticles.

New numerical simulation method to calibrate the regular hexagonal NaI(Tl) detector with radioactive point sources situated non-axial

Scintillation crystals are usually used for detection of energetic photons at room temperature in high energy and nuclear physics research, non-destructive analysis of materials testing, safeguards, nuclear treaty verification, geological exploration, and medical imaging. Therefore, new designs and construction of radioactive beam facilities are coming on-line with these science brunches. A good number of researchers are investigating the efficiency of the γ-ray detectors to improve the models and techniques used in order to deal with the most pressing problems in physics research today. In the present work, a new integrative and uncomplicated numerical simulation method (NSM) is used to compute the full-energy (photo) peak efficiency of a regular hexagonal prism NaI(Tl) gamma-ray detector using radioactive point sources situated non-axial within its front surface boundaries. This simulation method is based on the efficiency transfer method. Most of the mathematical formulas in this work are derived analytically and solved numerically. The main core of the NSM is the calculation of the effective solid angle for radioactive point sources, which are situated non-axially at different distances from the front surface of the detector. The attenuation of the γ-rays through the detectors material and any other materials in-between the source and the detector is taken into account. A remarkable agreement between the experimental and calculated by present formalism results has been observed.