Ahmed M. El-Khatib

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 numerical simulation approach to calibrate the NaI(Tl) detectors array using non-axial extended spherical sources

The aim of the current study was to utilize the efficiency transfer technique (ET) to obtain the full-energy peak efficiency (FEPE) applying a new numerical simulation approach. The approach was implemented on a detection system array composed of two [NaI (Tl)] detectors. The simulation approach included a derivative of the effective solid angles subtended by an arbitrarily located source and the active volume of the detectors. The attenuation of the source matrix, the source container and the end-caps of the detector materials were considered. Resulting outcomes have been compared with those measured by the NaI(Tl) detector array comprising different volumes as (3 × 3 & 2 × 2) and resolutions (FWHM) of 7.5% and 8.5% at 662 keV respectively. 152Eu aqueous radioactive spherical sources were employed during the measurements, covering the energy range from 121.78 keV up to 1408.03 keV. A remarkable agreement was observed between the measured and the calculated efficiencies employing the new numerical approach. These conclusions were consistent for a variety of source-to-detector lateral distances, providing solid evidence for the stability of the developing method.

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.

Calibration of well-type NaI(Tl) detector using a point sources measured out the detector well at different axial distances

The high efficiency of well-type detector is one of its important advantages, when it is used to determine the low level activity of radiation in many different fields. In the present work the full-energy peak efficiency of 3× 3 NaI(Tl) well-type scintillation detector was calculated. The calculations were based on the efficiency transfer principle and a new straightforward analytical definition to compute the effective solid angle between a point source and the detector surfaces Moreover, the effective solid angle ratio subtended by the well-type detector and a point source located out the detector cavity at various distances was calculated, the attenuation of the photon by the source-detector system [detectorendcap,deadlayer and holder material] was considered and determined. This method is easily useful in setting up the efficiency calibration curve for well-type detectors when the source is outside. The computed efficiency values are found to be in a good agreement with the experimental data obtained in the case of radiating γ -ray standard point sources.

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.

Study on ferroelastic characteristics of gamma irradiated lithium potassium sulfate crystal

Abstract A detailed study of the optical absorption vs. γ-irradiation dose for lithium potassium sulfate crystal, LiKSO 4 cut out perpendicular to x , y and z directions is presented. The optical density was measured within the wavelength range from 200 to 600 nm at different γ-doses up to 300 kGy. The investigated optical parameters, e.g., absorption coefficient, relative absorbance and optical energy gap, were found to be gamma dose dependent as well as crystal orientation. The results were discussed in the view of interaction of point imperfections, introduced by irradiation, with the ferroelastic behavior of LiKSO 4 crystal.

Changes in the electrical properties of pure and doped polymers under the influence of small doses of X-rays

Abstract A study has been made of the temperature dependence of the d.c. conductivity of pure and borated low density polyethylene LDPE (4% and 8% borax). The above calculations were carried out before and after X-ray irradiation. The irradiation dose was varied from 0 to 1000 rad. The d.c. electrical conductivity of Polyvinyl chloride (PVC) and perspex was measured as a function of temperature ranging from 20°C to 100°C. These samples were irradiated with X-rays of dose 200 rad. The variation of the d.c. conductivity of the treated samples versus temperature was investigated. The results reveal that the d.c. conductivity of LDPE is highly affected by radiation and/or dopant. In addition, the sensitivity of the explored polymers to X-ray irradiation is strongly dependent on its chemical nature.

Fast neutron irradiation induced changes in the optical and thermal properties of modified polyvinyl chloride

Abstract The effect of both dopant and neutron radiation on the optical and thermal properties of polyvinyl chloride (PVC) has been studied. The doped samples with Pb and Cd were irradiated with a 14 MeV-neutron fluence in the range 7–28.8 × 109 n/cm2. The optical energy gap Eop exhibits a significant dependence on the type of additive and the neutron irradiation fluence. The specific heat at constant pressure Cp showed a nonmonotonical change with radiation fluence. The results of this study show that PVC:Pb behaves as a crystalline structure which is only slightly affected by neutron irradiation, while PVC:Cd is highly affected.