External radiation assessment in a wet phosphoric acid production plant

The factories dedicated to the production of phosphoric acid by the so-called wet acid method are usually considered typical NORM industries, because the phosphate rock used as raw material usually contains high concentrations of ²³⁸U-series radionuclides. The magnitude and behaviour of the radionuclides involved in the production process revealed the need to determine its dosimetric impact on workers. This work aims to partially compensate this lack of knowledge through the determination of external effective dose rates at different zones in the process at a typical plant located in the southwest of Spain. To this end, two dosimetric sampling campaigns have been carried out at this phosphoric acid production plant. The first sampling was carried out when phosphate rocks originating in Morocco were processed, and the second one when phosphate rock processed came from the Kola Peninsula (Russia Federation). This differentiation was necessary because the activity concentrations are almost one order of magnitude higher in Moroccan phosphate rock than in Kola phosphate rock.The results obtained have reflected external dose rate enhancements as high as 1.4 μSv h⁻¹ (i.e., up to thirty times the external exposition due to radionuclides in unperturbed soils) at several points in the facility, particularly where the digested rock (pulp) is filtered. However, the most problematic points are characterised by a small occupation factor. That means that the increment in the annual effective external gamma dose received by the most-exposed worker is clearly below 1 mSv (European Commission limit for the general population) under normal production. Nevertheless, special care in the design and schedule of cleaning and maintaining work in the areas with high doses should be taken in order to avoid any possibility of exceeding the previously mentioned general population limit.In addition, the results of the dosimetric campaign showed no clear correlation between ^226,228Ra activity concentrations in the material fluxing during the process (the most important radionuclides from the dosimetric point of view) and the external dose rates. Furthermore, any general dependence of the origin of the rock (i.e., on their radioactive contents) on the external effective dose rate measured has not been observed. These latter findings could be a consequence of three effects: (1) a variable radiation shielding at the different points along the process, (2) a changing geometry of irradiation (from a rock pile up to a thin-layered pulp passing through a solid mass inside pipes and deposits), and (3) the existence of a “memory effect”, or background contamination in the installation equipment due to the presence of radionuclide-enriched scales and sludges in pipes and deposits.     

三种含天然放射性布料使用所致成年男性参考人的辐射剂量评估

目的评估使用含天然放射性物质的3种布料所致人体的皮肤年当量剂量与年有效剂量。方法首先利用γ能谱仪测量3种布料样品中所含放射性核素的活度。然后利用蒙特卡罗软件建立理论照射模型,基于国际放射防护委员会(ICRP)男性参考体素模型计算器官剂量及有效剂量,从而对人体的皮肤年当量剂量和年有效剂量进行评估。结果在四周包裹和上覆盖的估算模型中,样品质量从135 g至7197 g变化范围内,这些布料所致成年男性参考人皮肤的年当量剂量范围为:155.41~9028.61μSv,一年中的有效剂量范围为:11.91~1234.44μSv。结论含放射性物质的消费品对人体会产生一些影响。     

Reproducibility of global three-dimensional motion during manual atlanto-axial rotation mobilization: an in vitro study

Abstract

The reproducibility of the three-dimensional (3D) kinematic aspects of motion coupling patterns during manual mobilizing techniques is still a debatable matter. The present in vitro study analysed segmental 3D motion of the atlanto-axial joint during manual axial rotation mobilization. Twenty fresh frozen human cervical specimens were studied in a test–retest situation with two examiners. The specimens were manually mobilized using three different techniques: (1) a regional mobilization technique of the cervical spine; (2) a segmental mobilization technique of the atlas with manual fixation of the axis; and (3) a segmental mobilization of the atlas on the axis applying a locking technique. Segmental atlanto-axial kinematics was registered with a Zebris CMS-20 ultrasound-based tracking system. The Euclidian norm was used as a representation of overall 3D motion. The results indicated good reproducibility (mean intraclass correlation coefficient, ICC: 0.87). Intraobserver reproducibility was slightly higher (mean ICC: 0.91; range: 0.76–0.99) than interobserver reproducibility (mean ICC: 0.85; range: 0.56–0.98) (P < 0.05). The total range of motion expressed as the Euclidean norm of 3D motion components was a parameter with good reproducibility in the study of segmental kinematics of manual atlanto-axial mobilization. Although previous studies have demonstrated poor inter-rater reliability of manual examination and mobilization of segmental motion components, the results of the present study shed a new and more positive light on the reproducibility of techniques for manual mobilization of the upper cervical spine.     

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.     

Implications for analysis of 226Ra in a low-level gamma spectrometry laboratory due to variations in radon background levels

The background spectrum of HPGe detectors is found to vary significantly as function of the radon concentration in the air surrounding it, especially with regard to the count rates of ²²²Rn daughter peaks. This effect is shown to potentially have a large impact on measured values of radon daughter activity concentration, as well as detection limits for low-level measurements. As these radionuclides are commonly used for estimating the activity of ²²⁶Ra, care needs to be taken to ensure that background levels are accurately determined.     

中国伴生放射性固体废物处理处置现状分析

我国伴生放射性固体废物累积贮存量大,迫切需要对其进行科学规范地处理处置。通过调研我国伴生放射性固体废物的处理处置现状及相关技术、辐射环境保护法规标准体系,提出需要进一步完善的法规标准、适合推广应用的处理处置技术,为我国矿产资源绿色和可持续发展提供重要参考。     

Preparation of in-house reference soil sample containing high levels of naturally occurring radioactive materials from the oil industry

An in-house reference soil sample containing high levels of naturally occurring radioactive materials collected from contaminated areas in the Syrian oilfields has been prepared as a part of the quality assurance program in AECS. Homogeneity of the sample has been examined using three methods, viz. particle size distribution of the sample matrix, total alpha/beta counting and gamma spectrometry. In conjunction with Dixon and Grubb tests as statistical tools, ten random samples from the original sample were used for this investigation. Reference values for the three radium isotopes (²²⁴Ra, ²²⁶Ra, ²²⁸Ra) were determined using gamma spectrometry equipped with HPGe detectors having high relative efficiencies of 80%, while the reference value of ²¹⁰Pb in the sample was determined using radiochemical separation and counting of its daughter ²¹⁰Po by alpha spectrometry. ANOVA analysis was used to estimate the uncertainties due to measurement and inhomogeneity of the sample; uncertainty due to inhomogeneity was found to be around 2.6 times the measurement uncertainty.