Comité de Rédaction

La contamination radioactive, qu’elle soit de nature surfacique ou atmosphérique, peut être la cause d’une exposition interne de l’individu. Les valeurs Limites pratiques de concentration dans l’air (LPCA) permettent aux médecins du travail ainsi qu’aux Personnes compétentes en Radioprotection (PCR) de pré-évaluer les risques résultant d’une contamination atmosphérique. Ces valeurs sont utilisées pour déterminer la conduite à tenir au poste de travail mais aussi comme outil d’optimisation de la protection des personnes dans le cadre de l’application du principe ALARA (As Low As Reasonably Achievable). Lors des analyses de poste, les PCR des laboratoires Pierre Fabre ont été confrontées à des valeurs de dose efficace engagée qui semblaient, de leur point de vue, anormalement élevées. Ces valeurs étaient en contradiction avec les résultats des examens de radiotoxicologie urinaire réalisés dans le cadre de la surveillance médicale renforcée des manipulateurs, qui se sont toujours avérés négatifs (que ces examens soient effectués périodiquement ou de façon ponctuelle à la fin d’une série de manipulations radioactives). C’est pourquoi il a été jugé pertinent de louer des systèmes de barboteurs, équipements utilisés pour la surveillance des faibles niveaux de concentration en tritium et carbone 14. Les mesures réalisées ont permis de mettre en évidence des niveaux de contamination atmosphérique en tritium négligeables, notamment lors des étapes de manipulation jugées a priori pénalisantes. Ce travail, mené dans le cadre des études de poste, nous a permis d’abaisser la valeur du facteur de volatilité des composés tritiés intervenant dans le calcul de dose efficace engagée.

Indoor radon surveys were carried out in some of the Arab countries through a Coordination Research Program (CRP) organized by the Arab Atomic Energy Agency (AAEA). The objectives of the program aim at establishing a database on indoor radon concentration levels in the region and investigating any anomalies, where they exist. The approach adopted by the survey teams to achieve public participation in accepting the radon detectors in dwellings is presented and discussed. Most of the participants in the CRP used the passive method (CR-39 plastic detectors) for long-term radon measurements, while others used charcoal detectors and E-Perm systems for short-term measurements. The results of the surveys showed that radon concentration levels in most of the dwellings were low, whilst in some old cities and in an area close to a phosphate mine the levels were found to be relatively high.

The knowledge of the absorbed radiation dose is essential in order to interpret the results of animal experiments with chronic ingestion of radionuclides by rodents. In order to evaluate this absorbed dose, we applied the dose conversion factors proposed by ICRP publication 108 to mouse chronic ingestion experiments with 20 kBq.L-1137Cs- or 90Sr-contaminated water. The results indicated that whole-body absorbed doses were 9 mGy and 10 mGy by the end of 20 weeks of 137Cs or 90Sr ingestion, respectively. These results of dose calculations were compared with results obtained with a more refined method using published organ-specific absorbed fractions of energy. There was good agreement between the two methods, indicating that, despite the simple hypotheses used to apply the ICRP 108 dose conversion factors to our mouse model, this method allows one to calculate in a simple and reliable way the absorbed radiation dose received by the rodents during long-term experiments on chronic ingestion of radionuclides.

The aim of our study was to distinguish the stress-related molecular response of the pulmonate mollusc Lymnaea stagnalis from the Chernobyl area in comparison with the consequences of other harmful effects, including the short-term effects of radiation and heating. Specimens inhabiting ponds near the Chernobyl nuclear power plant, the cooling channel of the electric power station and the soil-reclamation channel (groups R, T and C, correspondingly), and specimens adapted to laboratory conditions (a control group (CL), a disposable group exposed to 2 mGy X-ray radiation over the body (RL), and a group exposed to 25 °C for 4 days (TL)) were compared. Despite high variability of responses, Principle Component Analysis distinctly separated the laboratory and feral groups into two sets. In the feral groups, low levels of the stress-related and metal-binding protein metallothionein (MT), protein carbonyls and lactate dehydrogenase in the digestive gland were indicated. The main separating criteria selected by classification and regression tree analysis were the protein carbonyls, cholinesterase and MT. Molluscs from group R were clearly distinguished by the lowest levels of MT, Mn-superoxide dismutase and lactate dehydrogenase, and the highest level of glutathione, demonstrating that the oppression of the gene-determined stress-related response and its partially metabolic compensation can be possible markers for chronic environmental effects of irradiation.

The radioactivity concentrations of 226Ra, 232Th and 40K were measured using gamma-ray spectroscopy with NaI (Tl) detectors in four tantalite mining sites in the Oke-Ogun area, South-Western Nigeria. The measured values of the activities of 40K, 226Ra and 232Th in the soil samples were found to lie in the ranges 123.7 ± 3.8 – 1372.3 ± 8.6, 16.8 ± 1.6 – 71.1 ± 2.53 and 3.0 ± 0.7 – 31.9 ± 1.0 Bq kg–1, respectively. These samples were also found to have radium equivalent activity in the range 74.2–121.0 Bq kg-1. Values of 0.2–0.3 for the external and 0.3–0.4 for the internal hazard indices were estimated for the samples and the annual effective dose varied from 70.3 ± 13.5 to 100.8 ± 42.8 µSv with a mean of 87.5 ± 18.6 µSv y–1. The annual effective dose is higher than the world average.

Inhalation of indoor radon has been recognized as the largest contributor to the total effective dose received by human beings. Indoor radon data were collected from the dwellings lying on the sedimentary rocks (sandstones, siltstones and clays) of the Murree Formation, Nagri Formation, Dhok Pathan Formation, Mirpur conglomerate and surficial deposits of the Kotli area in Azad Jammu and Kashmir, Pakistan. Radon measurements were made using the passive time-integrated method using Kodak CN-85 Solid-State Nuclear Track Detectors. The radon concentration in dwellings varied from 13 ± 6 Bq.m-3 to 185 ± 23 B. qm-3, with an average of 73 ± 15 Bq.m-3.The radon concentration in the Murree Formation, Nagri Formation, river terrace and Dhok Pathan Formation were 89.7 ± 16.5, 72 ± 15, 68.5 and 69 Bq.m-3, respectively. The average value of all the measured concentrations (73 ± 15 Bq.m-3) within the framework of this study is more than the world average value of 40 Bq.m-3 given by UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation, report to the General Assembly, United Nations, New York, 2000) and is within the action level of 200-600 Bq.m-3 fixed by the ICRP(International Commission on Radiological Protection, ICRP publication65, Protection against radon at home and at work, 1993). The ambient gamma dose rates both indoors and outdoors in different parts of Kotli were also measured. The average value of gamma absorbed dose rates prevailing in the indoor environment was 131.2 ± 16.6 nGy/h. The gamma exposure rates recorded outdoors were 35% lower than in the indoor environment. The measured gamma dose rates have a weak positive correlation with indoor radon concentration. The annual effective dose for inhabitants in Kotli due to radon ranged from 0.32 to 4.7 mSv.y-1, with an average value of 1.8 mSv.y-1. This dose is relatively higher than the world mean dose of 1.15 mSv/y. That is explained by the particular geology of the state of Azad Jammu and Kashmir, and the method of construction of the dwellings.

Calculations are presented of the effective doses per unit neutron fluence according to the ICRP publications 60 and 103. Monte Carlo N-Particle (MCNPX) code was used for six geometrical conditions of irradiation (Anterior-Posterior, Posterior-Anterior, Left-Lateral, Right-Lateral, Rotation and Isotropic) on Oak Ridge National Laboratory (ORNL) modified mathematical adult phantoms for monoenergetic neutrons from 10-9 MeV to 20 MeV. The conversion coefficients were compared with the results of an analytical phantom (Medical Internal Radiation Dose (MIRD-5)) and some voxel model (ICRP/ICRU Reference Voxel Phantom (ICRP/ICRU RVP), HANAKO, TARO and Visible Human Project (VIPMAN)). From these comparisons, one can conclude that large discrepancies between data sets appear when wR and different sizes of the phantoms have been used for calculations. Furthermore, the differences in applied Monte Carlo codes or simulated body models could make some discrepancies less than 15%.

The assessment of the radiological impact of a decommissioned nuclear power plant is presented here through the results of an environmental monitoring survey carried out in the area surrounding the Garigliano Power Plant. The levels of radioactivity in soil, water, air and other environmental matrices are shown, in which α, β and γ activity and the γ equivalent dose rate are measured. Radioactivity levels of the samples from the Garigliano area are analyzed and then compared with those from a control zone situated more than 100 km away. Moreover, a comparison is made with a previous survey carried out in 2001. The analyses and comparisons show no significant alteration in the radiological characteristics of the area surrounding the plant, with the overall radioactivity depending mainly on the global fallout and natural sources.

En France, les effluents générés par des personnes traitées et hospitalisées en médecine nucléaire doivent être collectés dans des cuves de décroissance avant leur rejet dans le réseau d’assainissement, en accord avec les limites règlementaires définies. Un modèle utilisant une série d’exponentielle décroissante a été mis au point permettant de simuler l’évolution de l’activité volumique dans les cuves de décroissance. Ainsi son utilisation permet d’optimiser le nombre et la capacité des cuves par rapport à l’activité médicale actuelle ou future. En outre, ce modèle est très modulable puisqu’il intègre comme variables : la période physique du radioélément, le volume total de chaque cuve, l’activité excrétée par patient, le volume total d’effluents générés par patient durant son séjour en chambre blindée, le nombre de patients pris en charge lors de chaque semaine et le nombre de semaines avant la mise en décroissance de la cuve. Par ailleurs, les simulations avec ce modèle montrent qu’à activité médicale équivalente, il est possible de travailler soit avec 2 grandes cuves soit avec 3 cuves ayant une capacité réduite de 50 %. L’utilisation de plusieurs petites cuves permet en outre de maintenir la rotation des cuves de décroissance en cas de mise hors service d’une d’entre elles.