Nafaa Reguigui

Phosphates, naturally containing trace amounts of uranium, were examined using direct γ-ray spectrometry. Both normal and Compton-suppressed counting modes were utilized. The 1001 keV photo peak of the second daughter of 238U was chosen because of its isolation from other, potentially interfering peaks. The findings suggest that with the aid of Compton suppression, it is possible to quantify low uranium levels in phosphates using samples sizes of order 10 grams within an accuracy of 5%. The uranium content was determined in several sample types and was found to range from 60±4 to 70±8 μg/g, depending on the sample composition. This investigation also considered the effects of sample size, counting time, and counting technique as sources of precision maximization. This work has shown that only a small amount of phosphate is needed to determine the constituent concentration, instead of the standard several hundred grams of material.

ABSTRACT In the phosphoric acid production process, the time a particle spends inside the chemical reactor (residence time) is of paramount importance to process engineers. Residence time distribution (RTD) gives information on the efficiency of the chemical reactor, on the efficiency of the process, and also the availabilities of the reactive volume for the reaction (active volume vs. dead volume). Traditionally, chemical engineers used chemical tracer to determine the RTD. However, first disadvantage is that the chemical tracer could not allow an online diagnosis: the samples containing chemical tracer have to go to a lab for analysis, second disadvantage is that the chemical tracer is less sensitive than radioactive ones because of its adsorption onto strata or its retention in rocks. Consequently, chemical tracer results are not always precise and cannot convincingly explain the multiple flow-path model. Radioactive tracers are the only tracers capable of measuring the active RTD with high degree of precision and give information on the internal recirculation rate. In this work, we will describe the application of radiotracer method for RTD measurement in the phosphoric acid production process and give results and discussion of each case encountered.

Recent developments in neutron generator technology suggest that compact instruments with high neutron yield can be used for NAA and PGNAA in combination with high count rate spectrometers. For laboratories far away from Research Reactors (RRs), such devices could serve as an alternative for training students in radioanalytical and nuclear Chemistry and certain specialized applications. As Neutron activation analysis is a well established technique with a long history of documented applications it could be made available to countries where no research reactors or other neutron irradiation facilities exist by using the proposed approach. Prompt gamma neutron activation analysis (PGNAA) is a versatile analytical tool with many applications unique to the technique. As PGNAA is generally performed at RRs external neutron guides with relatively low neutron flux, the proposed instrument has a potential to supplement existing PGNAA facilities far away from RRs. Neutron generators, particul...

• Radiotracer investigations were carried out in phosphate fertilizer production reactors. • RTD of process fluid was measured using Iodine-131 as radiotracer. • Mean residence time and dead volume were estimated. • A tank-in-series model with bypass was used to model the measured RTD. • Extent of bypassing was estimated, and flow patterns in the reactors were identified. Radiotracer investigations were carried out in two identical phosphoric acid production reactors and a triple super phosphate (TSP) production reactor in three different plants in Tunisia. The main objective of the study was to investigate and compare their flow behavior and identify flow abnormalities, if any. Residence time distribution (RTD) of the process material (ore pulp) was measured in the three reactors using Iodine-131. The measured RTDs were treated and analyzed to obtain flow parameters such as the mean residence time (MRT), dead volume, and extent of bypassing. The treated RTD curves were modeled using a suitable mathematical model, and the values of the parameters were obtained. The results of the investigations were used to evaluate and compare the flow performance of the reactors, quantify the degree of mixing, and visualize the prevailing flow patterns. The results of the investigations are expected to be used to make necessary modifications to enhance the efficiency and optimize the performance of the reactors or the production process.

To determine residence time distribution (RTD) in the phosphate treatment reactor we apply radiotracer method. However this method becomes effective and profitable only if the radiotracer is the suitable one. The problem to resolve in our study is "which phase of the phosphate slurry our injected radiotracer is following?". For that we add radiotracer to the phosphate slurry and we proceed to phase separation using a filtration system. We follow simultaneously -using appropriate detectors- the behavior and the quantity of the radiotracer in both phases during the separation stage. The same experiment is applied twice using successively (99m)Tc and (131)I radiotracers. The comparative study proves that (131)I is more suitable than (99m)Tc for solid phase labeling of phosphate slurry.

A new deuterium-deuterium (D-D) neutron generator has been developed by Adelphi Technology for prompt gamma neutron activation analysis (PGNAA), neutron activation analysis (NAA), and fast neutron radiography. The generator makes an excellent fast, intermediate, and thermal neutron source for laboratories and industrial applications that require the safe production of neutrons, a small footprint, low cost, and small regulatory burden. The generator has three major components: a Radio Frequency Induction Ion Source, a Secondary Electron Shroud, and a Diode Accelerator Structure and Target. Monoenergetic neutrons (2.5MeV) are produced with a yield of 10(10)n/s using 25-50mA of deuterium ion beam current and 125kV of acceleration voltage. The present study characterizes the performance of the neutron generator with respect to neutron yield, neutron production efficiency, and the ionic current as a function of the acceleration voltage at various RF powers. In addition the Monte Carlo N-Particle Transport (MCNP) simulation code was used to optimize the setup with respect to thermal flux and radiation protection.

An explosive detection system based on a Deuterium-Deuterium (D-D) neutron generator has been simulated using the Monte Carlo N-Particle Transport Code (MCNP5). Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma emission (10.82MeV) following radiative neutron capture by (14)N nuclei. The explosive detection system was built based on a fully high-voltage-shielded, axial D-D neutron generator with a radio frequency (RF) driven ion source and nominal yield of about 10(10) fast neutrons per second (E=2.5MeV). Polyethylene and paraffin were used as moderators with borated polyethylene and lead as neutron and gamma ray shielding, respectively. The shape and the thickness of the moderators and shields are optimized to produce the highest thermal neutron flux at the position of the explosive and the minimum total dose at the outer surfaces ...

In this study we investigate the radiological hazard of naturally occurring radioactive material in Tunisian and Algerian phosphorite deposits. Eight samples of phosphorite were collected from the phosphorite mines. The Tunisian and Algerian phosphorites occur in the Late Paleocene and Lower Eocene (Ypresian-Lutetian) in age (Béji Sassi 1984 and Zaïer 1999). Activity concentrations in all the samples were measured by alpha spectrometry and gamma spectrometry. Alpha spectrometry analyses show that the specific activity values of ...

In this study we investigate the radiological hazard of naturally occurring radioactive material in Tunisian and Algerian phosphorite deposits. Eight samples of phosphorite were collected from the phosphorite mines. The Tunisian and Algerian phosphorites occur in the Late Paleocene and Lower Eocene (Ypresian-Lutetian) in age (Béji Sassi 1984 and Zaïer 1999). Activity concentrations in all the samples were measured by alpha spectrometry and gamma spectrometry. Alpha spectrometry analyses show that the specific activity values of 238U, 234U and 235U in the samples of Tunisian phosphorite were 327±7 (321–327), 326±6 (325–331) and 14.50±0.72 (13.90–15.57) Bq kg−1, respectively. Specific activity measured by gamma spectrometry in the samples of the Tunisian and Algerian phosphorite shows a small difference. Specific activity levels of 40K, 226Ra, 232Th, 235U and 238U in the phosphorite samples from Tunisia were, respectively, 71.10± 3.80, 391.54±9.39, 60.38±3.74, 12.72±0.54 and 527.42± 49.57 Bq kg−1 and Algeria were 15.72±1.73, 989.65±12.52, 12.08±1.20, 47.50±1.52 and 1,148.78±7.30 Bq kg−1, respectively. The measured value of specific activity of 232Th and 40K in the Tunisian phosphorite samples is relatively higher than  that found in the samples of Algerian phosphorite. The measured  activity of uranium (238U) in the Tunisian phosphorite (527±49) Bq kg−1 is lower than in Algerian phosphorite. The measured activity of 238U in the Tunisian phosphorite samples was (527–1,315±65) 238U Bq kg−1 which is higher than its maximum background value of 110 Bq kg−1 in soils of the various countries of the world (Tufail et al. Radiat Meas 41:443–451, 2006). Different geological origins of phosphorites deposits are the main reason for the large spread in worldwide specific activities. The obtained results of uranium concentrations in phosphorites of different types (Algerian and Tunisian) demonstrate that the uranium concentrations are mainly governed by the phosphatic material. The present study reveals that phosphorite deposits contain natural radioactivity higher than background level