Assessment of plutonium exposures for an epidemiological study of US nuclear workers

An ongoing case-control study evaluating the association between workplace external radiation exposures and leukaemia mortality required an assessment of internal plutonium exposures as a potential confounder. Of the study participants, 1,092 were employed at four Department of Energy sites where plutonium-bearing materials were processed or stored. Exposures were assessed by first categorising exposure potentials based on available bioassay data, then estimating doses for workers in the highest categories using recent recommendations of the International Commission on Radiological Protection. Given the aetiology of leukaemia, equivalent dose to active bone marrow was chosen as the exposure variable. There were 556 workers each with at least one plutonium bioassay result, assigned to one of three evaluation categories. Dose estimates were made for 115 workers resulting in a collective equivalent dose of 2.1 person-Sv for 2,822 exposure-years, compared with 29.8 person-Sv estimated from photon exposures. Modelling uncertainties were examined by comparison of results from independent analyses and by Monte Carlo simulation.     

Capabilities of the Los Alamos National Laboratory in nuclear target technology

Targets are made at Los Alamos for experiments at the Ion Beam Facility (Van de Graaff), the Medium Energy Physics Facility (LAMPF), and for experiments conducted at many other accelerators in the US and Europe. Thin, isotopic targets are made by sputtering and evaporation. Versatile, large-scale facilities exists for ceramics and plastics fabrication, electroplating, powder metallurgy, fabrication by pressing, casting and rolling, chemical and physical vapor deposition, and sputtering. Special developments include ultra-precision machining, cryogenic targets, and shaped-foil targets.     

Comparison of carbon and corrugated diamond stripper foils under operational conditions at the Los Alamos PSR

To accumulate high-intensity proton pulses, the Los Alamos Proton Storage Ring (PSR) uses the charge-exchange injection method. H⁻ ions merge with already circulating protons in a bending magnet, and then are stripped off their two electrons in a carbon stripper foil. The circulating protons continue to interact with the foil. Despite efforts to minimize the number of these foil hits, like “painting” of the vertical phase space, they cannot totally be eliminated. As a result, foil heating and probably also radiation damage limit the lifetime of these foils. In recent years, LANL has collaborated with KEK to improve the carbon foils in use at PSR, and these foils now last typically for about 2 months. Recently, an alternative in the form of corrugated diamond foils has been proposed for use at SNS. These foils have now been tested in PSR production for a year, and have already shown to be at least as enduring as the LANL/KEK carbon foils. Advantages of the diamond foil concept, as well as some noteworthy differences that we observed with respect to the LANL carbon foils, will be discussed here.     

A preliminary study of dihydroxyurea application in plutonium purification cycle

The back extraction of Pu from 30% TBP/kerosene with dihydroxyurea (DHU) was studied in relation to the contact time, nitric acid concentration, phase ratio, etc. The back-extraction efficiency can reach 87% at phase ratio (o/a) ≤4: 1, contacting time ≥1 min, niitric acid concentration ≤0.4 M, and reductant concentration ≥0.4 M at 15°C and Pu concentration in the organic phase of 12 g l⁻¹. The back-extraction efficiency decreases with an increase in the Pu(IV) concentration in the organic phase or in the Pu(III) concentration in the aqueous phase. The application of DHU in Pu cycle was studied in a 12-step countercurrent cascade experiment. The results show that DHU can satisfy the technical requirements at 15°C and phase ratio (2BF: 2BX: 2BS) = 4: 1: 1. The Pu recovery efficiency is 99.96%.     

Workplace monitoring for exposures to radon and to other natural sources in Europe: integration of monitoring for internal and external exposures

Part of the action of the EURADOS working group (European Radiation Dosimetry Group) on "Harmonisation of Individual Monitoring in Europe" was to investigate how the results from personal dosemeters for external radiation, from monitoring for internal exposure and from workplace monitoring, can be combined into a complete and consistent system of individual monitoring. To facilitate this work, the "EURADOS questionnaire Q3" relating to radon and other natural sources of radiation in the workplace was distributed to relevant institutes across Europe. A total of 24 countries replied to the questionnaire. This study offers an important overview on actual regulations, national standards and reference levels for protection of employees from radon and other natural sources in different workplace scenarios. Information was also collected on individual monitoring and area monitoring to determine individual doses in workplaces with elevated levels of natural radiation. The article discusses in detail the results obtained showing by country the reference level in workplaces for radon gas and other natural sources. In both instances, exposures in mines, other underground workplaces, industry workplaces/waterworks, offices, schools and day-care homes were considered. The resultant data clearly indicate that there is a need for harmonisation among countries, not least in the areas of regulation and use of reference levels in the workplace.     

Improvement of precision spectrophotometric method with internal reference and its application to analysis of plutonium solutions

A spectrophotometric precision method with internal reference [1, 2] was applied to analysis of straight Pu solutions for certifying Pu reference materials and for studying the PuO₂ solubility in the framework of developing methods for accounting and control of nuclear materials. In the context of the activities mainly concerned with certification of reference materials, a two-channel spectrophotomer and the corresponding technique were further improved in order to decrease the error of the method. This allowed the random component of the relative error of the method to be decreased from 0.1 to 0.04% at the confidence level p = 0.95 and the number of degrees of freedom f = 25. The fixed component of the error of the method was studied in relation to impurities of U, Np and corrosion products of structural materials. Also, the extent of Pu oxidation during sample preparation was studied as influenced by the fluoride ion. The revealed lack of such influence within the limits of the study indicates that the method is suitable for analysis of Pu in mixed solutions.     

A method for calculating Bayesian uncertainties on internal doses resulting from complex occupational exposures

Estimating uncertainties on doses from bioassay data is of interest in epidemiology studies that estimate cancer risk from occupational exposures to radionuclides. Bayesian methods provide a logical framework to calculate these uncertainties. However, occupational exposures often consist of many intakes, and this can make the Bayesian calculation computationally intractable. This paper describes a novel strategy for increasing the computational speed of the calculation by simplifying the intake pattern to a single composite intake, termed as complex intake regime (CIR). In order to assess whether this approximation is accurate and fast enough for practical purposes, the method is implemented by the Weighted Likelihood Monte Carlo Sampling (WeLMoS) method and evaluated by comparing its performance with a Markov Chain Monte Carlo (MCMC) method. The MCMC method gives the full solution (all intakes are independent), but is very computationally intensive to apply routinely. Posterior distributions of model parameter values, intakes and doses are calculated for a representative sample of plutonium workers from the United Kingdom Atomic Energy cohort using the WeLMoS method with the CIR and the MCMC method. The distributions are in good agreement: posterior means and Q(0.025) and Q(0.975) quantiles are typically within 20 %. Furthermore, the WeLMoS method using the CIR converges quickly: a typical case history takes around 10-20 min on a fast workstation, whereas the MCMC method took around 12-72 hr. The advantages and disadvantages of the method are discussed.     

Characterisation of workplaces with risks of internal exposures: air sampling

The measurement of air samples may be used to assess risks of internal exposures, either by the use of workplace static air samplers (SAS) or personal air samplers (PAS). These measurements need to incorporate information on the physical and chemical nature of the aerosol, and the relationship between the sampled and potentially breathed aerosol. This paper provides an overview of methods, which are typically used in occupational dosimetry to determine these characteristics. A specific practical example is provided to illustrate how SAS are used to determine that potential personal doses are less than 1 mSv per year, and therefore do not require individual monitoring. The paper also discusses the nature and potential impact of the uncertainties associated with PAS monitoring, and how this is managed in practice.     

Individual monitoring for internal exposures in Europe: conclusions of an EURADOS action

Once the EC Directive 96/29 has been implemented into national regulation across Europe, the coordination of dosimetry laboratories for the monitoring of occupational exposures becomes the principal aim to achieve. Within this framework the European Radiation Dosimetry Group, EURADOS, carried out an Action on 'Harmonisation of Individual Monitoring' (2000-2004) to promote coordination in the field of individual monitoring of occupational exposures throughout Europe. With reference to internal exposures, the main aims were the completion of a catalogue of internal dosimetry services and an inventory of methods and techniques used for individual monitoring at European internal dosimetry facilities. At the end of this EURADOS Action, a report was published in Radiation Protection Dosimetry in 2004. The information collected related to various topics: the equipments used for the measurement of internal exposures, calibration and sensitivity data, the methods applied for the assessment of internal doses, Quality Control procedures, Quality Assurance Programmes in the facilities and legal requirements. The information to be presented here will give a general overview of the actual status of individual monitoring for internal exposures in Europe.     

State-of-the-art dosimetric methods for internal and external exposures: conclusions of a EURADOS action

In radiation protection dosimetry the quantity of interest is the effective dose (E); the dose limit to an adult worker applies to the sum of the relevant doses from external exposures and the relevant committed effective doses from intakes of radionuclides, during the same period of time. A EURADOS study was carried out to investigate how the results from personal dosemeters for external radiation, from workplace monitoring and from monitoring of internal exposures can be combined into a consistent system of individual monitoring. The integration of dosimetric methods and data for external and internal radiation require the complete characterisation of the occupational exposure present at the workplace, and the availability of adequate equipment and tools for the assessment of effective dose. To evaluate the capability of services to accomplish this approach, a European Dosimetry Network has been established among 28 European countries through the respective contact-persons and their dosimetric facilities which collaborated with EURADOS providing relevant data about performance and legal aspects. The information collected was presented as a monograph in Radiation Protection Dosimetry in 2004. The more relevant conclusions of this study are presented here.     

First-principles study of electronic structure and metal-insulator transition of plutonium dihydride and trihydride

The electronic structures of cubic PuH₂ and hexagonal PuH₃ have been calculated by combining the full potential linearized augmented plane wave method (FLAPW) with the local spin density and generalized gradient approximation plus a Hubbard parameter U (LSDA + U and GGA + U) for considering the strong Coulomb correlation between localized Pu 5f electrons. Our study indicates that PuH₂ is metallic, while PuH₃ is a semiconductor with a small band gap about 0.26 eV. The bonds in PuH₂ system have some covalent character. For PuH₃, besides the covalent bonds, particularly, the bonding between Pu and octahedral H atoms is of prominent ionicity. In addition, the conductivity and resistivity data is also worked out at 300 K and low temperature of 4 K. The conductivity decreases from a metallic behavior of PuH₂ to the semiconducting region of PuH₃. The experimentally undetermined metal-insulator transition has been firstly discovered in Pu-H system theoretically.     

Evaluation of patient doses due to fluoroscopic exposures

The present study measures entrance surface doses of radiation administered to patients during various fluoroscopic procedures using a dose-area product meter as well as the duration of each procedure. A conversion factor for entrance skin dose to patients was calculated. The average dose to patient during the insertion of intravenous hyperalimentation was 10.2 (maximum, 74.0) mGy, during a barium meal, 58.4 (maximum, 184.0) mGy, for endoscopic retrograde cholangio-pancreatography (ERCP), 97.3 (maximum, 376.0) mGy and for a barium enema, 86.1 (maximum, 271.0) mGy. Doses tended to increase in the abdominal domain and when patients undergo not only diagnostic evaluation but also treatment requiring procedures such as drainage. The management of radiation doses determined using a dose-area product meter is very important and that of individual patients is enabled using the Radiation Information System (RIS).     

Experimental study of internal cavitating flows

The parameters of a cavitating liquid are determined on the basis of measurements of the initial flow parameters and forces acting on the nozzle. The volume concentrations of a cavitating flow are also measured by a conductometric method simultaneously with a determination of their values from measurements of the forces acting on the nozzle.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 26, No. 2, pp. 309–313, February, 1974.     

阀门内漏识别及内漏速率量化技术研究

阀门作为天然气管线的关键部件,若发生内漏会带来经济损失及生产安全隐患。因此,阀门内漏的有效诊断及内漏速率的准确量化具有重大意义。针对复杂背景噪声下内漏诊断效率不高的问题,以内漏信号和非泄漏噪声信号的功率谱密度图作为输入,构建了阀门内漏卷积神经网络(convolutional neural network, CNN)识别模型;针对物理理论及浅层网络模型在多工况阀门内漏数据上存在量化误差大的问题,构建了阀门内漏速率深度信念网络(deep belief network, DBN)量化回归模型,并与支持向量回归机、BP神经网络等模型进行了对比研究。研究结果表明:所构建模型的内漏识别准确率及内漏速率量化平均绝对百分比误差分别为99%和9.101 2,证实了所构建模型的高效性,为阀门内漏诊断与评价开拓了新的研究方向。