Comparison of three analytical techniques for determination of Th and U in environmental samples.

Alpha-particle spectrometry, gamma spectrometry and neutron activation analysis techniques for determination of Th and U in environmental samples have been compared. The analytical parameters studied include detection limit, accuracy, repeatability, reproducibility and surrogate recovery. The results show that neutron activation analysis technique has the best accuracy among the studied techniques; the other two techniques were assessed relative to it. The percentage difference between the three techniques results is about [-20, 20]. In addition, U and Th concentrations are generally overestimated by gamma spectrometry and alpha-particle spectrometry in all cases except Th concentration in the former technique, which is underestimated.

NEUTRON FLUX DISTRIBUTION IN THE RADIOISOTOPES TARGET ROOMS AND MAZE IN SYRIAN CYCLOTRON.

Gold activation foils were used in this work to measure thermal, epithermal and fast neutron fluxes in the 18F, 123I, (201Tl, 67Ga) production units in Syrian cyclotron. The neutron flux distribution around the targets were determined. It shows that, the maze thermalizes the fast neutrons and reduces the flux about four orders of magnitudes. The results can be adopted by medical centers to identify radioactive hot spots and develop radiation protection.

Neutron and high energy photon fluence estimation in CLINAC using gold activation foils.

AIM: The thermal neutron, epithermal neutron and high-energy photon fluence were measured in this work around the Varian 21EX 23 MV CLINAC, which is operated in Albairouni hospital in Damascus, Syria. BACKGROUND: Photoneutron measurements around medical CLINAC aim to protect both patients and staff from unwanted radiation. MATERIALS AND METHODS: Neutron and photon activation techniques were applied using gold foils. RESULTS: It was found that high-energy photons fluence has practically a constant value in the field size. The thermal and epithermal neutron fluence along ox and oy axes has the same order of magnitude. CONCLUSION: Gold foils have been used successfully to measure neutron flux and high-energy photons simultaneously using activation techniques.

MONITORING OF HIGH-ENERGY PHOTON FLUENCE IN CLINAC USING Zn AND Cr PHOTOACTIVATION.

Monitoring of high-energy photon dose in radiation therapy is crucial for radiation protection, as well as to estimate the radiation effects in the operating microelectronic devices. The aim of this work was to investigate the possibility of using the photoactivation technique to monitor the high-energy photon fluence in the Varian 21EX 23MV CLINAC. The 52Cr(γ,n)51Cr and 66Zn(γ,n)65Zn reactions were used. It was found that 51Cr and 65Zn can be used successfully to monitor the fluence for short term (80 days) and long term (110 days), respectively.

Determination of 226Ra Contamination Depth Around Phosphogypsum Pit Using In-Situ Gamma Spectrometer.

The feasibility of applying multiple photopeak method (MPM) and peak to valley ratio (PVRM) method to determine Radium-226 contamination depth (226Ra hc) has been investigated. Gamma spectra in eight positions around phosphogypsum disposal pit has been measured using portable NaI(Tl) gamma spectrometer. MPM was investigated by calculating the ratio [Formula: see text] of 609 keV gamma line net counts to the corresponding value of 352 keV. PVRM was investigated by calculating the ratio [Formula: see text] of net counts of 609 keV gamma line to the corresponding valley counts. 226Ra hc in the positions has been determined using traditional soil coring. It was found that, [Formula: see text] and [Formula: see text] have good linear correlations with 226Ra hcTherefore, 226Ra hc can be determined by MPM and PVRM. These methods save a lot of time, costs and efforts in comparison with the traditional one.

Fast self-attenuation determination of low energy gamma lines.

Linear correlation between self-attenuation factor of 46.5keV ((210)Pb) and the 1764keV, 46.5 counts ratio has been developed in this work using triple superphosphate fertilizer samples. Similar correlation has been also developed for 63.3keV ((238)U). This correlation offers simple, fast, and accurate technique for self-attenuation determination of low energy gamma lines. Utilization of 46.5keV in the ratio has remarkably improved the technique sensitivity in comparison with other work, which used similar concept. The obtained results were used to assess the validity of transmission technique.

Neutron activation analysis of thermal power plant ash and surrounding area soils.

Elemental concentrations of As, Cd, Co, Cr, Fe, Hg, Mo, Ni, Se, and Zn have been determined in fly and bottom ash collected from Syrian power plants fired by heavy oil and natural gas using instrumental neutron activation analysis. The results showed that all elements were more concentrated in fly ash than in the fly ash; there was a clear increasing trend of the elemental concentrations in the fly ash along the flue gas pathway. The annual emission of elements was estimated. Elemental concentrations were higher inside the campus area than in surrounding areas, and the lowest values were found in natural-gas-fired power plant. In addition, the levels have decreased as the distance from power plant campus increases. However, the levels in the surrounding villages were within the Syrian standard for agriculture soil.

Assessment of soil contamination by (210)Po and (210)Pb around heavy oil and natural gas fired power plants.

Soil contamination by (210)Pb and (210)Po around heavy oil and natural gas power plants has been investigated; fly and bottom ash containing enhanced levels of (210)Pb and (210)Po were found to be the main source of surface soil contamination. The results showed that (210)Pb and (210)Po in fly-ash (economizer, superheater) is highly enriched with (210)Pb and (210)Po, while bottom-ash (boiler) is depleted. The highest (210)Pb and (210)Po activity concentrations were found to be in economizer ash, whereas the lowest activity concentration was in the recirculator ash. On the other hand, (210)Pb and (210)Po activity concentrations in soil samples were found to be higher inside the plant site area than those samples collected from surrounding areas. The highest levels were found in the vicinity of Mhardeh and Tishreen power plants; both plants are operated by heavy oil and natural fuels, while the lowest values were found to be in those samples collected from Nasrieh power plant, which is only operated by one type of fuel, viz. natural gas. In addition, the levels of surface soil contamination have decreased as the distance from the power plant site center increased.

Determination of 226Ra contamination depth in soil using the multiple photopeaks method.

Radioactive contamination presents a diverse range of challenges in many industries. Determination of radioactive contamination depth plays a vital role in the assessment of contaminated sites, because it can be used to estimate the activity content. It is determined traditionally by measuring the activity distributions along the depth. This approach gives accurate results, but it is time consuming, lengthy and costly. The multiple photopeaks method was developed in this work for (226)Ra contamination depth determination in a NORM contaminated soil using in-situ gamma spectrometry. The developed method bases on linear correlation between the attenuation ratio of different gamma lines emitted by (214)Bi and the (226)Ra contamination depth. Although this method is approximate, but it is much simpler, faster and cheaper than the traditional one. This method can be applied for any case of multiple gamma emitter contaminant.

Study the effect of beryllium reflector poisoning on the Syrian MNSR.

Neutron interactions with beryllium lead to formation of (3)H and strong neutron absorbers (3)He and (6)Li in the reflector (so called beryllium poisoning). After the reactor shutdown, the concentration of (3)He increases in time due to tritium decay. This paper illustrates the impact of poisoning accumulation in the beryllium reflectors on reactivity for the Syrian MNSR research reactor. The prediction of (6)Li and (3)He poison concentrations, initiated by the 9Be(n,α) reaction, in the beryllium reflectors of the MNSR was also presented. The results were based on MCNP Monte Carlo calculations and solutions to the differential equations which describe the time dependent poison concentrations as a function of reactor operation time and shutdown periods. The whole reactor history was taken into account to predict reliable values of parasitic isotope concentrations. It was found that the (3)He and (6)Li accumulations in the beryllium reflectors during the actual working history decreased the excess reactivity by about 28%. While, the effect became more significant at the reactor life's end and the reactor became subcritical after 25,000 h operation. The results contained in this paper could be used in assess the safety analysis of the MNSR reactor.

NORM emissions from heavy oil and natural gas fired power plants in Syria.

Naturally occurring radioactive materials (NORM) have been determined in fly and bottom ash collected from four major Syrian power plants fired by heavy oil and natural gas. (210)Pb and (210)Po were the main NORM radionuclides detected in the fly and bottom ash. (210)Pb activity concentrations have reached 3393±10 Bq kg(-1) and 4023±7 Bq kg(-1) in fly ash and bottom ash, respectively; lower values of (210)Po were observed due to its high volatility. In addition, (210)Po and (210)Pb annual emissions in bottom ash from mixed (heavy oil and natural gas) fired power plants varied between 2.7×10(9)-7.95×10(9) Bq and 3.5×10(9)-10(10) Bq, respectively; higher emissions of (210)Po and (210)Pb from gas power plants being observed. However, the present study showed that (210)Po and (210)Pb emissions from thermal power plants fired by natural gas are much higher than the coal power plants operated in the World.

Measurement of 60Co high gamma dose using gamma activation of 115 In and 111 Cd foils.

Cobalt-60 gamma irradiation facilities are used in many industrial and medical applications. Gamma activation technique of (115)In and (111)Cd foils was used in this work to assess the performance of ethanol-chlorobenzene gamma dosimeter at high dose range of (60)Co irradiation facility. Dose mapping was also performed using (115)In foils. These measurements are required to control the irradiation quality and to validate dose calculations.

Monitoring of MNSR operation by measuring subcritical photoneutron flux.

Passive nondestructive assay methods are used to monitor the reactor's operation. It is required for nuclear regulatory, calculation validation and safeguards purposes. So, it plays a vital role in the safety and security of the nuclear plants. The possibility of MNSR operation monitoring by measuring the subcritical state photoneutron flux were investigated in this work. The photoneutron flux is induced by the fuels hard gamma radiation in the beryllium reflector. Theoretical formulation and experimental tests were performed. The results show that within a specified cooling time range, the photoneutron flux is induced by a single dominant hard gamma emitter such as (117)Cd (activation product) and (140)Ba ((140)La fission product). This phenomenon was utilized to monitor the cooling time and the operation neutron flux during the last campaign. Thus a passive nondestructive assay method is proposed with regard to the reactor operation's monitoring.

Passive nondestructive burnup monitoring of MNSR irradiated fuel by measuring photoneutrons produced within fission products.

A passive nondestructive method for monitoring of Syrian miniature neutron source reactor (MNSR) fuel burnup is introduced. The inner irradiation site design inside the Be reflector was exploited to measure the generated photoneutrons induced by fission products hard gamma radiation in the subcritical state. The photoneutron flux was measured using gold foils as a function of cooling time and operation power. For cooling time ranges between 10 and 25d, experiments show that (140)Ba is the extremely dominating inducer of photoneutrons and the measured flux is proportional to the accumulated (140)Ba. This result forms a new method base for MNSR fuel burnup monitoring. It might be used also as a safeguards technique to check the operator declared information.

Correction factors determination in large samples gamma assay using its own multi-gamma lines spectrum.

An easy and simple method for gamma assay of large multi-gamma lines samples was introduced in this work. This method performs the assay using point source calibration. The correction factors for volume and self-attenuation are experimentally deduced from the spectra of different thicknesses samples utilizing the following two simple well known facts: large and small samples of the same homogenous material have identical specific activities; the self-attenuation of gamma line decreases as its energy increases. The method was successfully applied to naturally occurring radioactive material (NORM) large samples. This method does not require complicated mathematical procedures. Neither sample matrix data nor detector unit composition is needed.