Performance of a PADC personal neutron dosemeter at simulated and real workplace fields of the nuclear industry.

In the framework of the EVIDOS (Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields) project, funded by the EC, measurements with PADC personal neutron dosemeters were carried out at several workplace fields of the nuclear industry and at simulated workplace fields. The measured personal neutron dose equivalents of the PADC personal neutron dosemeter are compared with values that were assessed within the EVIDOS project by other partners. The detection limits for different spectra types are given. In cases were the neutron dose was too low to be measured by the PADC personal neutron dosemeter, the response is estimated by convoluting the responses to monoenergetic neutrons with the dose energy distribution measured within EVIDOS. The advantages and limitations of the PADC personal neutron dosemeter are discussed.

Performance of a personal neutron dosemeter based on direct ion storage at workplace fields in the nuclear industry.

In the framework of the EVIDOS project, funded by the EC, measurements were carried out using dosemeters, based on ionisation chambers with direct ion storage (DIS-N), at several workplace fields, namely, at a fuel processing plant, a boiling and a pressurised water reactor, and near transport and storage casks. The measurements and results obtained with the DIS-N in these workplaces, which are representative for the nuclear industry, are described in this study. Different dosemeter configurations of converter and shielding materials were considered. The results are compared with values for personal dose equivalent which were assessed within the EVIDOS project by other partners. The advantages and limitations of the DIS-N dosemeter are discussed.

Progress report of the CR-39 neutron personal monitoring service at PSI.

At the Paul Scherrer Institute a personal neutron dosimetry system based on chemically etched CR-39 detectors and automatic track counting is in routine use since the beginning of 1998. The quality of the CR-39 detectors has always been a crucial aspect to maintain a trustable personal neutron dosimetry system. This paper summarises the 7 y experience in routine use. The effect of detector material defects which could lead to false positive neutron doses is described. The potentiality of improving the background statistics by extending the pre-etch time is investigated and involves as a drawback a quite lower sensitivity to thermal neutrons. Furthermore, the impact of small changes in the production process of the detectors on the response to fast and thermal neutrons is shown. For the personal dosimetry at CERN, a new dosimetry concept was launched by combining a CR-39 neutron dosemeter with a Direct-Ion Storage (DIS) dosemeter for photon and beta radiation. The usage period of the CR-39 dosemeters is prolonged now from 3 months up to 12 months. In this context, the long-term behaviour over 1 y of the background track density and the response to Am-Be are described.

Achievements in workplace neutron dosimetry in the last decade: lessons learned from the EVIDOS project.

The availability of active neutron personal dosemeters has made real time monitoring of neutron doses possible. This has obvious benefits, but is only of any real assistance if the dose assessments made are of sufficient accuracy and reliability. Preliminary assessments of the performance of active neutron dosemeters can be made in calibration facilities, but these can never replicate the conditions under which the dosemeter is used in the workplace. Consequently, it is necessary to assess their performance in the workplace, which requires the field in the workplace to be fully characterised in terms of the energy and direction dependence of the fluence. This paper presents an overview of developments in workplace neutron dosimetry but concentrates on the outcomes of the EVIDOS project, which has made significant advances in the characterisation of workplace fields and the analysis of dosemeter responses in those fields.

Evaluation of individual dosimetry in mixed neutron and photon radiation fields (EVIDOS). Part I: Scope and methods of the project.

Supported by the European Commission, the EVIDOS project started in November 2001 with the broad goal of evaluating state of the art dosimetry techniques in representative workplaces of the nuclear industry. Seven European institutes joined efforts with end users at nuclear power plants, at fuel processing and reprocessing plants, and at transport and storage facilities. A comprehensive programme was devised to evaluate capabilities and limitations of standard and innovative personal dosemeters in relation to the mixed neutron-photon fields of concern to the nuclear industry. This paper describes the criteria behind the selection of dosimetry techniques and workplaces that were analysed, as well as the organisation of the measurement campaigns. Particular emphasis was placed on the evaluation of a variety of electronic personal dosemeters, either commercially available or previously developed by the partners. The estimates provided by these personal dosemeters were compared to reference values of dose equivalent quantities derived from spectrometry and fluence-to-dose equivalent conversion coefficients. Spectrometry was performed both with conventional multisphere and with some original instrumentation providing energy and direction resolution, based on silicon detectors and superheated drop detectors mounted on or in spherical moderators. The results were collected in a large, searchable database and are intended to be used in the harmonisation of dosimetric procedures for mixed radiation fields and for the approval of dosimetry services in Europe.

Direction distributions of neutrons and reference values of the personal dose equivalent in workplace fields.

Within the EC project EVIDOS, double-differential (energy and direction) fluence spectra were determined by means of novel direction spectrometers. By folding the spectra with fluence-to-dose equivalent conversion coefficients, contributions to H*(10) for 14 directions, and values of the personal dose equivalent Hp(10) and the effective dose E for 6 directions of a person's orientation in the field were determined. The results of the measurements and calculations obtained within the EVIDOS project in workplace fields in nuclear installations in Europe, i.e., at Krümmel (boiling water reactor and transport cask), at Mol (Venus research reactor and fuel facility Belgonucléaire) and at Ringhals (pressurised reactor and transport cask) are presented.

Evaluation of individual dosimetry in mixed neutron and photon radiation fields (EVIDOS). Part II: Conclusions and recommendations.

The paper presents the main conclusions and recommendations derived from the EVIDOS project, which is supported by the European Commission within the 5th Framework Programme. EVIDOS aims at evaluating state of the art neutron dosimetry techniques in representative workplaces of the nuclear industry with complex mixed neutron-photon radiation fields. This analysis complements a series of individual papers which present detailed results and it summarises the main findings from a practical point of view. Conclusions and recommendations are given concerning characterisation of radiation fields, methods to derive radiation protection quantities and dosemeter results.

Characterisation of mixed neutron photon workplace fields at nuclear facilities by spectrometry (energy and direction) within the EVIDOS project.

Within the EC project EVIDOS, 17 different mixed neutron-photon workplace fields at nuclear facilities (boiling water reactor, pressurised water reactor, research reactor, fuel processing, storage of spent fuel) were characterised using conventional Bonner sphere spectrometry and newly developed direction spectrometers. The results of the analysis, using Bayesian parameter estimation methods and different unfolding codes, some of them especially adapted to simultaneously unfold energy and direction distributions of the neutron fluence, showed that neutron spectra differed strongly at the different places, both in energy and direction distribution. The implication of the results for the determination of reference values for radiation protection quantities (ambient dose equivalent, personal dose equivalent and effective dose) and the related uncertainties are discussed.

Neutron area survey instrument measurements in the EVIDOS project.

Neutron survey instruments have been exposed at all the measurement locations used in the EVIDOS project. These results have an important impact in the interpretation of the results from the project, since operationally the survey instrument will be used for an initial assessment of and routine monitoring of the ambient dose equivalent dose rate. Additionally, since the response of these instruments is in some cases very well characterised, their systematic deviations from the reference quantities provide an important verification of the determination of those quantities.

Summary of personal neutron dosemeter results obtained within the EVIDOS project.

Within the EC project EVIDOS ('Evaluation of Individual Dosimetry in Mixed Neutron and Photon Radiation Fields'), different types of active neutron personal dosemeters (and some passive ones) were tested in workplace fields at nuclear installations in Europe. The results of the measurements which have been performed up to now are summarised and compared to our currently best estimates of the personal dose equivalent Hp(10). Under- and over-readings by more than a factor of two for the same dosemeter in different workplace fields indicate that in most cases the use of field-specific correction factors is required.

Application of workplace correction factors to dosemeter results for the assessment of personal doses at nuclear facilities.

Ratios of H(p)(10) and H*(10) were determined with reference instruments in a number of workplace fields within the nuclear industry and used to derive workplace-specific correction factors. When commercial survey meter results together with these factors were applied to the results of the locally used personal dosemeters their results improved and became within 0.7 and 1.7 of the reference values or better depending on the response of the survey meter. A similar result was obtained when a correction was determined with a prototype reference instrument for H(p)(10) after adjustment of its response. Commercially available survey instruments both for photon and neutron H*(10) measurements agreed with the reference instruments in most cases to within 0.5-1.5. Those conclusions are derived from results reported within the EC supported EVIDOS contract.

Evaluation of individual monitoring in mixed neutron/photon fields: mid-term results from the EVIDOS project.

EVIDOS is an EC sponsored project that aims at an evaluation and improvement of radiation protection dosimetry in mixed neutron/photon fields. This is performed through spectrometric and dosimetric investigations during different measurement campaigns in representative workplaces of the nuclear industry. The performance of routine and, in particular, novel personal dosemeters and survey instruments is tested in selected workplace fields. Reference values for the dose equivalent quantities, H(*)(10) and H(p)(10) and the effective dose E, are determined using different spectrometers that provide the energy distribution of the neutron fluence and using newly developed devices that determine the energy and directional distribution of the neutron fluence. The EVIDOS project has passed the mid-term, and three measurement campaigns have been performed. This paper will give an overview and some new results from the third campaign that was held in Mol (Belgium), around the research reactor VENUS and in the MOX producing plant of Belgonucléaire.

Electronic neutron personal dosemeters: their performance in mixed radiation fields in nuclear power plants.

This work describes spectral distributions of neutrons obtained as function of energy and direction at four workplace fields at the Krümmel reactor in Germany. Values of personal dose equivalent H(p)(10) and effective dose E are determined for different directions of a person's orientation in these fields and readings of personal neutron dosemeters--especially electronic dosemeters--are discussed with respect to H(p)(10) and E.

COMPARISON OF DIFFERENT PADC MATERIALS AND ETCHING CONDITIONS FOR FAST NEUTRON DOSIMETRY.

Etched-track polyallyl diglycol carbonate (PADC) dosemeters have been in use at the Paul Scherrer Institute since 1998 in neutron dosimetry for individual monitoring. In the last years, the availability of PADC materials from different manufacturers has grown, and different etching conditions were proposed, with the intention to improve the quality and overall performance of PADC in individual neutron monitoring. The goal of the present study was to compare the performance of different PADC materials and to investigate the influence of different etching conditions on sensitivity to fast neutrons and lower detection limit. The comparison covers six different PADC materials and eight different etching conditions.

Glycosyl inositolphospholipid-anchored structures in Herpetomonas davidi.

Glycosyl inositolphospholipid (GPI)-anchored structures in the monogenetic parasite Herpetomanas davidi, were labeled with [3H]glucosamine, and characterized by enzymatic and chemical treatments that are typical for the identification of GPI anchors. [3H]Myristate incorporated into two different pools of GPI-linked structures that could be separated by chromatography on octyl-Sepharose. One pool consisted of three GPI-anchored proteins with apparent molecular masses of 21,31 and 45 kDa, and the GPI lipid moieties were identified as alkyl-lysoglycerols. The label in the other pool associated with lipopeptidophosphoglycan (LPPG)-like structures of approximately 12-kDa molecular mass, containing ceramide-type GPI lipid anchors. While protein GPI anchors could also be labeled using [3H]glucosamine as radiolabeled GPI anchor precursor, hardly any radioactivity was incorporated into the LPPG-like structures. H. davidi is one of the few organisms identified to date that synthesizes two structurally different lipid moieties for GPI anchoring of membrane components.

Conditional expression of glycosylphosphatidylinositol phospholipase C in Trypanosoma brucei.

Trypanosoma brucei glycosylphosphatidylinositol phospholipase C (GPIPLC) is expressed in the bloodstream stage of the life cycle, but not in the procyclic form. It is capable of hydrolyzing GPI-anchored proteins and phosphatidylinositol (PI) in vitro. Several roles have been proposed for GPIPLC in vivo, in the release of variant surface glycoprotein during differentiation or in the regulation of GPI and PI levels, but none has been substantiated. To explore GPIPLC function in vivo, tetracycline-inducible GPIPLC gene (GPIPLC) conditional knock-out bloodstream form and tetracycline-inducible GPIPLC-expressing procyclic cell lines were constructed. We were unable to generate GPIPLC null mutants. Cleavage of GPI-anchored proteins was abolished in extracts from uninduced conditional knock-outs and was restored upon induction. Despite the barely detectable level of GPIPLC activity in uninduced conditional knock-out bloodstream forms, their growth was not affected. GPI-protein cleavage activity could be induced in procyclic cell extracts, up to wild-type bloodstream levels. Myo-[3H]inositol incorporation into [3H]inositol monophosphate was about 14-fold lower in GPIPLC conditional knock-out bloodstream forms than in the wild type. Procyclic cells expressing GPIPLC showed a 28-fold increase in myo-[3H]inositol incorporation into [3H]inositol monophosphate and a 1.5-fold increase in [3H]inositol trisphosphate levels, suggesting that GPIPLC may regulate levels of inositol phosphates, by cleavage of PI and phosphatidylinositol 4,5-bisphosphate.

The fission track detector revisited: application to individual neutron dosimetry.

A system based on fission fragment tracks had previously been developed for individual neutron dosimetry. The dosimeter detects both fast neutrons by means of the 232Th(n,f) reaction, and thermal and albedo neutrons by means of the 235U(n,f) reaction. The fission tracks produced in a plastic foil are chemically etched and counted by spark discharges. The response of the dosimeter has recently been re-investigated in 36 different neutron fields: monoenergetic beams, reference fields near isotopic sources, and radiation fields encountered in a variety of situations inside nuclear power plants. The results obtained have been compared to those computed by convolution of the neutron spectra with the energy response functions of the dosimeters. In practical situations, it is essential to know the shape of the neutron spectrum, approximately at least, in order to perform an acceptably accurate dose evaluation. For that purpose, the neutron fields encountered inside nuclear power plants have been grouped into four categories, for which algorithms for dose evaluation have been developed. Concerning the neutron equivalent dose, the error associated with this approach does not exceed a factor of 2, a performance which is comparable to other detection systems used in the field of individual neutron dosimetry.

Accreditation of a personal dosimetry service in Switzerland: practical experience and transition from EN 45004 to ISO 17025.

In compliance with the Swiss legislation on radiological protection, the Paul Scherrer Institute (PSI) operates a dosimetry service that is approved by the Swiss Federal Nuclear Safety Inspectorate. In 1997, the dosimetry service was also accredited by the Swiss Federal Office of Metrology and Accreditation as an inspection body for legal personal and environmental dosimetry, according to EN 45004. The accreditation covers determination of personal dose equivalent for photon, neutron and beta radiation, and ambient dose equivalent for photon and neutron radiation, by means of thermoluminescence and solid state track detection techniques. Within this formal accreditation it was confirmed that the relevant requirements of ISO 9002 are also fulfilled. The first re-accreditation will take place in 2001 and work is going on to achieve the transition from EN 45004 to ISO 17025. Accreditation is a feasible, practicable and acceptable way to achieve harmonisation in the field of dosimetry. However, before starting on the path to formal accreditation, a careful analysis should be made, taking into consideration not only cost-benefit aspects but also national legal requirements.

A legally approved personal dosemeter for photon and beta radiation based on direct ion storage.

The novel DIS-1 dosemeter developed by RADOS is based on ionisation chambers with so-called Direct Ion Storage (DIS). The dosemeter can measure Hp(10) and Hp(0.07) of photon and Hp(0.07) of beta irradiation. The characteristics of the commercially available DIS-1 dosemeter were studied at the Paul Scherrer Institute, particularly in respect to the requirements laid down in the Swiss Dosimetry Ordinance. Detailed tests were carried out in terms of linearity, photon and beta responses, angle dependence, long-term stability of the signal, reproducibility and environmental conditions. The DIS-1 dosemeter has been qualified by the authority to conform to the requirements of the Swiss Dosimetry Ordinance for personal photon and beta dosemeters. It is now used as a legally approved personal dosemeter system at PSI.

Present status of the personal neutron dosemeter based on direct ion storage.

In this paper the present status of the Direct Ion Storage Neutron (DIS-N) prototype dosemeter (RADOS) is described. The separation of neutron from photon dose equivalent has been improved by adding tin shieldings. The neutron energy response has been changed by additional plastic covers containing 40% B4C in order to reduce the over-response to thermal neutrons. The responses of the dosemeters were determined for standard photon and neutron fields (monoenergetic neutrons, neutron sources and simulated workplace fields). Irradiations in real workplaces were also performed. The dependence of the neutron response on the angle of incidence was measured for different neutron sources.