Showing papers in "Health Physics in 1998"

Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz)

Abstract: IN 1974, the International Radiation Protection Association (IRPA) formed a working group on non-ionizing radiation (NIR), which examined the problems arising in the field of protection against the various types of NIR. At the IRPA Congress in Paris in 1977, this working group became the International Non-Ionizing Radiation Committee (INIRC). In cooperation with the Environmental Health Division of the World Health Organization (WHO), the IRPA/INIRC developed a number of health criteria documents on NIR as part of WHO’s Environmental Health Criteria Programme, sponsored by the United Nations Environment Programme (UNEP). Each document includes an overview of the physical characteristics, measurement and instrumentation, sources, and applications of NIR, a thorough review of the literature on biological effects, and an evaluation of the health risks of exposure to NIR. These health criteria have provided the scientific database for the subsequent development of exposure limits and codes of practice relating to NIR. At the Eighth International Congress of the IRPA (Montreal, 18–22 May 1992), a new, independent scientific organization—the International Commission on Non-Ionizing Radiation Protection (ICNIRP)—was established as a successor to the IRPA/INIRC. The functions of the Commission are to investigate the hazards that may be associated with the different forms of NIR, develop international guidelines on NIR exposure limits, and deal with all aspects of NIR protection. Biological effects reported as resulting from exposure to static and extremely-low-frequency (ELF) electric and magnetic fields have been reviewed by UNEP/ WHO/IRPA (1984, 1987). Those publications and a number of others, including UNEP/WHO/IRPA (1993) and Allen et al. (1991), provided the scientific rationale for these guidelines. A glossary of terms appears in the Appendix.

Differences in energy absorption between heads of adults and children in the near field of sources.

Abstract: This paper was motivated by a recent article in which the levels of electromagnetic energy absorbed in the heads of mobile phone users were compared for children and adults at the frequencies of 835 MHz and 1,900 MHz. Significant differences were found, in particular substantially greater absorption in children's heads at 835 MHz. These findings contradict other studies in which no significant changes had been postulated. The clarification of this issue is crucial to the mobile communications industry since current SAR evaluations as required by the FCC are only performed with phantoms based on the heads of adults. In order to investigate the differences in absorption between adults and children due to their differing anatomies, simulations have been performed using head phantoms based on MRI scans of an adult (voxel size 2 x 2 x 1 mm3) and two children (voxel size 2 x 2 x 1.1 mm3) of the ages of 3 and 7 y. Ten different tissue types were distinguished. The differences in absorption were investigated for the frequencies of 900 MHz and 1,800 MHz using 0.45 lambda dipoles instead of actual mobile phones. These well-defined sources simplified the investigation and facilitated the comparison to previously published data obtained from several numerical and experimental studies on phantoms based on adults. All simulations were performed using a commercial code based on the finite integration technique. The results revealed no significant differences in the absorption of electromagnetic radiation in the near field of sources between adults and children. The same conclusion holds when children are approximated as scaled adults.

Deposition of charged particles on lung airways.

Abstract: The effect of a single electric charge on the efficiency with which ultrafine particles deposit in human airways has been investigated. When inhaled short-lived radon progeny are attached to electrically neutral particles their deposition efficiency is controlled by diffusion. But most ambient particles carry one, or a few, charges. We measured and compared the deposition (DE) of singly charged, charge-neutralized, and zero-charge 20-nm and 125-nm particles in hollow-cast models of human airways. These particle sizes were selected because they are about where modal peaks occur for the activity of the short-lived radon progeny in indoor air. For singly charged 20-nm particles deposition (+/- standard error) in the casts was 3.4 +/- 0.3 times that for charge neutralized aerosols and 5.3 +/- 0.3 times the amount deposited for zero-charged particles. Corresponding ratios for the 125-nm particles were 2.3 +/- 0.3 and 6.2 +/- 0.7. Since most ambient particles are charged this effect must be considered when models are used to predict dose from inhaled ultrafine particles.

Mapping radon-prone areas by lognormal modeling of house radon data.

Abstract: Results of radon measurements in houses are generally distributed approximately lognormally, whether large or small areas are considered. The properties of the lognormal distribution allow the proportion of houses above a threshold level to be estimated even when there are insufficient data to calculate the proportion directly. In this paper the properties of the data set of radon measurements made in UK houses with etched-track radon detectors are examined, with the purpose of using them to map radon-prone areas. Individual results are normalized depending on the average outdoor temperature during the measurement to estimate the annual average radon level. For certain types of maps, results may also be normalized to estimate the radon level in a standard house or mixture of house types on the same site. Methods to use the lognormal model to estimate the geometric mean radon concentration and geometric standard deviation for data grouped by area have been developed. These data are then used to map radon-prone areas of England and Wales.

Neutron fluence and energy spectra around the Varian Clinac 2100C/2300C medical accelerator.

Abstract: We have simulated the head geometry of a Varian Clinac 2100C/2300C medical accelerator in a Monte Carlo calculation to produce photoneutrons and transport them through the head shielding into a typical therapy room (modeled by a test cell at Varian Associates). The fast neutron leakage fluence and energy spectra have been calculated at 7 positions around the linac head for typical beam operation at 10, 15, 18 and 20 MV. The results of these calculations have been compared with limited measurements made using the same model accelerator operating in a Varian test cell. Calculations were also made for the fluence and energy spectra outside the head with no surrounding concrete walls, floor or ceiling to eliminate the effects of scattering from concrete. Comparisons were also made with calculations using a much simplified head geometry. The results indicate that the calculations using the complex head geometry compare, within the uncertainties, with the measurements. The simple head geometry leads to differences of a factor of 2 from the complex geometry. Results of these calculations can be used to calculate fast neutron transmission through various shielding configurations and through labyrinths.

Soil ingestion by humans: a review of history, data, and etiology with application to risk assessment of radioactively contaminated soil.

Abstract: Ingestion of soil by humans has been a documented phenomenon for centuries and still takes place today according to various literature. The literature reviewed here shows that there are two distinct soil ingestion phenomenon: inadvertent and purposeful (geophagia). Certain lifestyles, occupations, and living conditions will likely put different individuals or different groups at risk to these separate, but sometimes related, phenomenon. In particular, reports of geophagia are relatively common for the life stages of adolescence and periods of growth, and during pregnancy and lactation. Geophagia also appears to be relatively common among indigenous peoples on all continents, sometimes taking place to extreme degrees. Because of their high dependence on the land, indigenous peoples are also at highest risk for inadvertent ingestion. Inadvertent intake is more a function of either primitive living conditions or professions that may bring workers into close and continual contact with the soil. It is the purpose of this report to review and summarize literature related to ingestion of soil by humans with emphasis on the relevance of soil ingestion to radiological dose assessment, the etiology of geophagia and its relationship to risk assessment, qualitative observations and quantitative studies of direct soil ingestion by humans with interpretations useful for different lifestyle scenarios, the status of a number of current radiological assessment models in accounting for soil ingestion, and some unresolved issues in modeling the ingestion of soil.

Natural background radiation and cancer death in rocky mountain states and gulf coast states

Abstract: Calculations based on data from NCRP reports show that the average level of natural background radiation (NBR) in Rocky Mountain states is 3.2 times that in Gulf Coast states. However, data from the American Cancer Society show that age-adjusted overall cancer death in Gulf Coast states is actually 1.26 times higher than in Rocky Mountain states. The difference from proportionality is a factor of 4.0. This is a clear negative correlation of NBR with overall cancer death. It is also shown that, comparing 3 Rocky Mountain states and 3 Gulf Coast states, there is a strong negative correlation of estimated lung cancer mortality with natural radon levels (factors of 5.7 to 7.5).

Calculation of the effective dose and its variation from environmental gamma ray sources.

Abstract: Effective dose, an indicator of the stochastic effect of radiation, has been widely used in dose evaluation in the environment. Though conversion factors have been used to obtain E from the air kerma or air absorbed dose, the variation of the conversion factors due to the change of exposure conditions has not been sufficiently investigated. This report documents an investigation of the variation of the effective dose per air kerma for environmental gamma rays depending on the exposure conditions using anthropomorphic phantoms and Monte Carlo calculations, taking into account the precise angular and energy distributions of the environmental gamma rays incident on the human body. As causes of the variation, posture of human bodies, biases of environmental source distributions, and body size were considered. The variation of effective dose in a prone position compared with that in a standing position was found to be within 30%. The bias of environmental sources causes the effective dose per air kerma to vary by 20% at maximum, but in some cases for low-energy gamma rays the variation was found to be up to 40% due to the change in the energy spectrum. The effective dose for a new born infant was estimated to be higher than that for an adult by a maximum of 80-90% for low-energy gamma rays from anthropogenic sources because of a lower shielding effect of the smaller body. The variation of the effective dose equivalent shows a similar tendency to the effective dose. Consequently, this study made it possible to estimate the uncertainties of effective dose and effective dose equivalent evaluated from air kerma or absorbed dose in air using the standard available conversion factors.

The Characterization of a Commercial Mosfet Dosimeter System for Use in Diagnostic X-Ray

Abstract: A commercial patient dose verification system utilizing non-invasive metal oxide semiconductor field effect transistor (MOSFET) dosimeters originally designed for radiotherapy applications has been evaluated for use at diagnostic energy levels. The system features multiple dosimeters that ma

Radiation dosimetry for extremity radiographs.

Abstract: The energy imparted, epsilon, to a patient undergoing an extremity x-ray examination may be obtained from the dose-area product incident on the patient. Values of energy imparted can be subsequently converted into the corresponding effective dose, E, using an extremity specific E/epsilon ratio. In this study, an E/epsilon ratio of 3 mSv/J was used to convert values of energy imparted into the corresponding upper limit of adult effective doses for all types of extremity examinations. A modification factor, based on the patient mass, was employed to determine the corresponding extremity effective doses to pediatric patients undergoing extremity examinations. Representative clinical technique factors for six common extremity examinations (hand, forearm, elbow, ankle, tibia/fibula, knee) were used to determine the dose-area product and the corresponding values of energy imparted. For adult extremity x-ray examinations, values of energy imparted ranged from 55 microJ to 920 microJ, with the energy imparted to 1-y-old patients being a factor of about 20 lower. Upper limits of effective doses for adult extremity x-ray examinations ranged from 0.17 to 2.7 microSv, whereas the corresponding doses to 1-y-old patients were about a factor of three lower.

Secondary shielding barriers for diagnostic x-ray facilities: scatter and leakage revisited.

Abstract: Methods are presented for determining the thickness requirements for barriers against scatter and leakage radiation generated in a diagnostic x-ray facility. Equations are developed that express the shielded doses due to scatter and leakage with explicit dependence on the operating potential used in clinical settings. The 1972 scatter experiment of Trout and Kelley is revisited, with suggested values for the scatter fraction that are somewhat different from those used in Report Number 49 of the NCRP. The dose from leakage radiation due to operation at clinical kVp settings is seen to be orders of magnitude below that predicted by the model in NCRP49. The unshielded secondary radiation dose in air at unit distance and workload is presented as a function of operating potential and for clinical workload distributions. The net transmission of secondary radiations through common shielding materials is presented. Compared to that for the primary beam at the same potential, the transmission of secondary radiation is more penetrating due to the inclusion of leakage radiation that has been hardened by the tube housing. Sample shielding calculations illustrate the utility of this scheme.

On the discrepancy between epidemiologic studies in individuals of lung cancer and residential radon and Cohen's ecologic regression

Abstract: There is still substantial confusion in the radiation effects community about the inherent limitations of ecologic analysis. As a result, inordinate attention has been given to the discrepant results of Cohen, in which a negative estimate is observed for the regression of county mortality rates for lung cancer on estimated county radon levels. This paper demonstrates that Cohen's ecologic analysis cannot produce valid inference on the exposure-response relationship for individuals unless lung cancer risk factors (smoking, age, occupation, etc.) for individuals are statistically uncorrelated with indoor radon level within counties or unless risk effects for radon and other factors are additive. Both of these assumptions are contradicted in the literature. Thus, contrary to common assumption, when a linear no-threshold model is the true model for radon risk for individuals, higher average radon concentration for a county does not necessarily imply a higher lung cancer rate for the county. In addition, valid inference from county-level ecologic analysis and the elimination of the ecologic bias cannot be achieved with the addition of county-wide summary variables (including "stratification" variables) to the regression equation. Using hypothetical data for smoking and radon and assuming a true positive association for radon and lung cancer for individuals, the analysis demonstrates that a negative county-level ecologic regression can be induced when correlation coefficients for smoking and radon within county are in the range -0.05 to 0.05. Since adverse effects for radon at low exposures are supported by analysis of miner data (all data and data restricted only to low cumulative exposures), a meta-analysis of indoor radon studies, and molecular and cellular studies, and since ecologic regressions are burdened by severe limitations, the negative results from Cohen's analysis are most likely due to bias and should be rejected.

Monte Carlo Based Method for Conversion of In-Situ Gamma Ray Spectra Obtained with a Portable Ge Detector to an Incident Photon Flux Energy Distribution

Abstract: A Monte Carlo based method for the conversion of an in-situ gamma-ray spectrum obtained with a portable Ge detector to photon flux energy distribution is proposed. The spectrum is first stripped of the partial absorption and cosmic-ray events leaving only the events corresponding to the full absorption of a gamma ray. Applying to the resulting spectrum the full absorption efficiency curve of the detector determined by calibrated point sources and Monte Carlo simulations, the photon flux energy distribution is deduced. The events corresponding to partial absorption in the detector are determined by Monte Carlo simulations for different incident photon energies and angles using the CERN's GEANT library. Using the detector's characteristics given by the manufacturer as input it is impossible to reproduce experimental spectra obtained with point sources. A transition zone of increasing charge collection efficiency has to be introduced in the simulation geometry, after the inactive Ge layer, in order to obtain good agreement between the simulated and experimental spectra. The functional form of the charge collection efficiency is deduced from a diffusion model.

Modifiers of lung cancer risk in uranium miners from the Colorado Plateau.

Abstract: Given the scientific consensus that exposure to radon decay products causes lung cancer, most recent studies have focused on the nature of the exposure-response relationship. Since residential radon exposure is now a primary public health issue, a better understanding of the effects of low levels of radon as well as factors modifying risk estimates has become very important. Several factors are shown to affect risk estimates in the latest update of the vital status follow-up (through 1990) and smoking history for the cohort of underground uranium miners in the Colorado Plateau. This analysis confirms earlier results indicating a strong dependence of relative risk estimates upon attained age. Quantitative estimates of relative risk as a function of cumulative exposure to radon decay products (WLM) are provided for three age strata. The non-linearity often reported in the Colorado Plateau data is shown to be at least partially due to an inverse exposure-rate effect, i.e., low exposure rates for long periods are more hazardous than equivalent cumulative exposure received at higher rates for shorter periods of time. However, this effect is shown to diminish at lower exposure rates and cumulative exposures. In addition, use of the new smoking data indicates that the radon/smoking interaction is submultiplicative and may depend upon attained age.

Diagnosis of acute localized irradiation lesions: review of the French experimental experience.

Abstract: In the last 50 years several radiation accidents occurred in which industrial radiographers and others suffered severe radiation injuries from inadvertent contact with radiation sources. Such accidents involving acute localized injuries are characterized by a severe initial reaction progressing through erythema to skin necrosis with a spontaneous resolution of the lesion over a 2-mo period for the lower doses. However, the early symptoms observed on the skin give no indication as to the in-depth pathology, and cutaneous and muscular radionecrosis started generally from early epithelial, microvascular, and vascular lesions and from delayed muscular and connective tissue lesions. In a case of acute localized irradiation, different biophysical techniques are able to give real responses in biological dosimetry. More numerous are the methods, especially imaging methods, that make it possible for the clinician to evaluate the extent of the early injuries and to manage the medical intervention. We have developed animal experimental models of acute localized irradiation: overexposure to the gamma rays of a 192Ir industrial radiographic collimated source (in the pig and the rabbit) and overexposure to the beta rays of a 90Sr-90Y collimated source (in the pig). In these experimental models, most of the imaging techniques used in clinical practice, as infra-red thermography, microwave thermography, cutaneous and tissular vascular scintigraphy (beta or gamma emitters), cutaneous blood flow measurements by cutaneous laser Doppler, x ray computed tomography, nuclear magnetic resonance imaging, and skin topography, were correlated with clinical evaluation and histopathological observations, after high doses of gamma or beta irradiations ranging from 4 to 340 Gy at the skin surface. All these techniques are not for isolated use and the present review indicates that their combination is necessary to give an improved diagnostic and prognostic picture of early and late delayed radiation damage to the skin and subcutaneous tissues.

Radioactive Materials in Recycled Metals-An Update

Abstract: In April 1995, Health Physics published a review paper titled "Radioactive Materials in Recycled Metals." At that time, 35 accidental meltings of radioactive sources in metal mills were reported, including 22 in the U.S., along with 293 other events in the U.S. where radioactive material was found in metals for recycling. Since that date, there have been additional accidental meltings of radioactive sources in metal mills both in the U.S. and elsewhere. There also was an incident in Texas that involved stolen radioactive devices, which resulted in exposures of members of the general public. Also, the U.S. Nuclear Regulatory Commission took steps to address the underlying problem of inadequate control and accountability of radioactive materials licensed by the Nuclear Regulatory Commission. The Steel Manufacturers Association made available data collected by its members beginning in 1994 that expanded the database for radioactive materials found by the metal recycling industry in recycled metal scrap to over 2,300 reports as of 30 June 1997.

Threshold models in radiation carcinogenesis

Abstract: Cancer incidence and mortality data from the atomic bomb survivors cohort has been analyzed to allow for the possibility of a threshold dose response. The same dose-response models as used in the original papers were fit to the data. The estimated cancer incidence from the fitted models over-predicted the observed cancer incidence in the lowest exposure group. This is consistent with a threshold or non-linear dose-response at low-doses. Thresholds were added to the dose-response models and the range of possible thresholds is shown for both solid tumor cancers as well as the different leukemia types. This analysis suggests that the A-bomb cancer incidence data agree more with a threshold or non-linear dose-response model than a purely linear model although the linear model is statistically equivalent. This observation is not found with the mortality data. For both the incidence data and the mortality data the addition of a threshold term significantly improves the fit to the linear or linear-quadratic dose response for both total leukemias and also for the leukemia subtypes of ALL, AML, and CML.

Indoor radon prediction from soil gas measurements.

Abstract: This study of radon levels in southwest England investigates the correlation between indoor and soil gas radon concentrations and considers the influence of geology, meteorological variables, spatial and depth variations. This paper examines the value of soil gas measurements as an indicator of potential indoor radon concentrations and highlights a number of factors that need to be considered. Only a very weak correlation was obtained between the overall 222 Rn concentration in soil gas and inside the home. However, for high soil gas concentrations a stronger correlation with the indoor level was observed. Typically, the soil gas concentration was between a factor of 10 and 1,000 times greater than that indoors. Levels as low as 10 kBq m -3 in the soil could produce an indoor concentration above the UK action level of 200 Bq m -3 . The moisture content and the inhomogeneity of soil permeability were identified as chiefly responsible for any perturbation of a soil gas concentration associated with a particular geology. Alone, measured soil gas concentrations have only a limited use in the prediction of indoor 222 Rn concentrations.

Uranium in urine--normalization to creatinine.

Abstract: “Spot samples” of urine are routinely used to monitor occupational exposure to uranium and other toxic heavy metals, such as mercury, lead, and cadmium. In the present work, it was shown that diurnal variations in the uranium concentration in different urine samples from the same individual could be quite large. However, these variations were in correlation to the Creatinine level of the same samples, with values of R = 0.72–0.99, for the five subjects studied here. Thus, it is proposed here that uranium concentrations in “spot” urine samples be expressed in terms of ng uranium g−1 Creatinine rather than ng uranium L−1. Once the 24-h Creatinine level is estimated for the individual based on weight, height and age, the adjusted values can be used for determination of the internal dose of uranium.

Primary shielding barriers for diagnostic x-ray facilities: a new model.

Abstract: Traditional methods of diagnostic x-ray shielding design assume that the raw primary beam impinges directly on the structural barrier with attenuation by the patient and by the hardware in the x-ray beam (cassette, cassette holder, x-ray table) being ignored. Moreover, primary barrier calcul

Issues in the reconstruction of environmental doses on the basis of thermoluminescence measurements in the Techa riverside

Abstract: The potential of thermoluminescence measurements of bricks from the contaminated area of the Techa river valley, Southern Urals, Russia, for reconstructing external exposures of affected population groups has been studied. Thermoluminescence dating of background samples was used to evaluate the age of old buildings available on the river banks. The anthropogenic gamma dose accrued in exposed samples is determined by subtracting the natural radiation background dose for the corresponding age from the accumulated dose measured by thermoluminescence. For a site in the upper Techa river region, where the levels of external exposures were extremely high, the depth-dose distribution in bricks and the dependence of accidental dose on the height of the sampling position were determined. For the same site, Monte Carlo simulations of radiation transport were performed for different source configurations corresponding to the situation before and after the construction of a reservoir on the river and evacuation of the population in 1956. A comparison of the results provides an understanding of the features of the measured depth-dose distributions and height dependencies in terms of the source configurations and shows that bricks from the higher sampling positions are likely to have accrued a larger fraction of anthropogenic dose from the time before the construction of the reservoir. The applicability of the thermoluminescent dosimetry method to environmental dose reconstruction in the middle Techa region, where the external exposure was relatively low, was also investigated.

Measurement of 222Rn concentration in Kenyan groundwater.

Abstract: Groundwater samples from different parts of Kenya have been analyzed for their 222Rn concentrations. Samples were drawn from municipal supplies, springs, wells and bore holes in different geological terrains. In the analysis, conventional liquid scintillation counting, using the Packard prot

237Np: oxidation state in vivo and chelation by multidentate catecholate and hydroxypyridinonate ligands.

Abstract: Chemically, 237Np(V) is as toxic as U(VI), and radiologically, about as toxic as 239Pu. Depending on redox conditions in vivo, 237Np exists as weakly complexing Np(V) (NpO2+) or as Np(IV), which forms complexes as stable as those of Pu(IV). Ten multidentate catecholate (CAM) and hydroxypyridinonate (HOPO) ligands with great affinity for Pu(IV) were compared with CaNa3-DTPA for in vivo chelation of 237Np. Mice were injected intravenously with 237NpO2Cl: those in a kinetic study were killed 1 to 2880 min; in ligand studies, fed mice were injected intraperitoneally with a ligand 5, 60, or 1440 min after 237Np(V) (molar ratio 5.6 to 73), mice fasted for 16 h were gastrically intubated with a ligand 3 min after 237Np(V) (molar ratio 5.6 to 274), and all were killed 24 h after ligand administration; tissues and excreta were radioanalyzed. Rapid plasma clearance and urinary excretion of 237Np(V) resemble U(VI); deposition and early retention in skeleton and liver resemble Pu(IV). The x-ray absorption near edge structure spectroscopy (XANES) spectra of femora of 237Np(V)-injected mice, compared with spectra of Np(V) and Np(IV) from reference solids, showed predominantly Np(IV). Significant in vivo 237Np chelation was obtained with all of the HOPO and CAM ligands injected at molar ratio 22; the HOPO ligands reduced 237Np in skeleton, liver, and other soft tissue, on average, to 72, 25, and 25% of control, respectively, while CaNa3-DTPA was ineffective. Two HOPO ligands injected 60 min after 237Np (molar ratio 5.6) significantly reduced body and liver 237Np, and three HOPO ligands given orally (molar ratio > or = 73) significantly reduced body and liver 237Np, compared with controls. Combined with earlier work, these results indicate that: the dominant neptunium species circulating and excreted in urine is Np(V), while that in bone and liver deposits is Np(IV); Np(V) must be reduced to Np(IV) before it can be stably chelated; efficient decorporation of neptunium requires multidentate ligands that form exceptionally stable actinide(IV) chelates and facilitate Np(V) reduction.

NMR microscopy of trabecular bone and its role in skeletal dosimetry

Abstract: One of the more intractable problems in internal dosimetry is the assessment of energy deposition by alpha and beta particles within trabecular, or cancellous, bone. In the past few years, new technologies have emerged that allow for the direct and nondestructive 3D imaging of trabecular bone with sufficient spatial resolution to characterize trabecular bone structure in a manner needed for radiation dosimetry models. High-field proton nuclear magnetic resonance (NMR) imaging is one such technology. NMR is an ideal modality for imaging trabecular bone due to the sharp contrast in proton density between the bone matrix and bone marrow regions. In this study, images of the trabecular regions within the bodies of human thoracic vertebra have been obtained at a field strength of 14.1 T. These images were digitally processed to measure chord length distribution data through both the bone trabecular and marrow cavities. These distributions, which were found to be qualitatively consistent with those measured by F.W. Spiers and colleagues at the University of Leeds using physical sectioning and automated light microscopy, yielded a mean trabecular thickness of 201 {micro}m and a mean marrow cavity thickness of 998 {micro}m. The NMR techniques developed here for vertebral imaging may be extendedmore » to other skeletal sites, allowing for improved site-specific skeletal dosimetry.« less

Environmental contamination and assessment of doses from radiation releases in the Southern Urals.

Abstract: The Southern Urals in Russia was contaminated by radioactive discharges into the Techa River (1949-1956), the Kyshtym accident (1957), and the current releases and discharges from the Mayak Nuclear Materials Production Complex. In this paper, the consequences of radioactive contamination of the Ural region are analyzed. The current content of 90Sr in the components of food chains is as follows (Bq kg(-1) wet weight): potatoes, 0.2-6.7; grain, 0.5-12.6; milk, 0.2-6.3; beef, 0.2-1.7; lake water, 0.12-1.0; river water, 0.2-8.5; fish, 7-480; mushrooms, 400-1,100; and berries, 700-16,000. The content of 137Cs is as follows: potatoes, 0.5-3.8; grain, 0.3-2.9; milk, 0.2-4.5; beef, 0.3-2.6; lake and river water, 0.002-0.019; fish, 2-32; mushrooms, 110-1,600; and berries, 150. A major fraction of the dose to humans comes from the consumption of local food products, including natural ones, which have higher contamination levels than agricultural products. The average annual dose rates in contaminated areas are (0.5-4) x 10(-4) Sv y(-1), which is lower by a factor of 10(2)-10(4) than in the periods of "acute" exposure (1950-1951 and 1957-1958). Natural organisms received very high doses up to 200-800 Gy resulting from radioactive discharges into the Techa River and the radiation accident in 1957. In all cases, including the "acute" exposure followed by the chronic irradiation, the doses to biota were by a factor of 10-10(3) higher than those to humans.

Rejoinder : Cohen's response to "On the discrepancy between epidemiologic studies in individuals of lung cancer and residential radon and Cohen's ecologic regression"

Abstract: There is still substantial confusion in the radiation effects community about the inherent limitations of ecologic analysis. As a result, inordinate attention has been given to the discrepant results of Cohen, in which a negative estimate is observed for the regression of county mortality rates for lung cancer on estimated county radon levels. This paper demonstrates that Cohen's ecologic analysis cannot produce valid inference on the exposure-response relationship for individuals unless lung cancer risk factors (smoking, age, occupation, etc.) for individuals are statistically uncorrelated with indoor radon level within counties or unless risk effects for radon and other factors are additive. Both of these assumptions are contradicted in the literature. Thus, contrary to common assumption, when a linear no-threshold model is the true model for radon risk for individuals, higher average radon concentration for a county does not necessarily imply a higher lung cancer rate for the county. In addition, valid inference from county-level ecologic analysis and the elimination of the ecologic bias cannot be achieved with the addition of county-wide summary variables (including stratification variables) to the regression equation. Using hypothetical data for smoking and radon and assuming a true positive association for radon and lung cancer for individuals, the analysis demonstrates that a negative county-level ecologic regression can be induced when correlation coefficients for smoking and radon within county are in the range -0.05 to 0.05. Since adverse effects for radon at low exposures are supported by analysis of miner data (all data and data restricted only to low cumulative exposures), a meta-analysis of indoor radon studies, and molecular and cellular studies, and since ecologic regressions are burdened by severe limitations, the negative results from Cohen's analysis are most likely due to bias and should be rejected.

Radiation hazard of coal-slags as building material in Tatabánya town (Hungary).

Abstract: High concentrations of 226 Ra (865-2,383 Bq kg -1 ) were measured in the coal-slags, originated from the region of the settlement Tatabanya, Transdanubian Middle Mountains, Hungary. These slags are commonly used as building materials in this district. The external gamma dose rate was measured in 188 rooms at different heights above the floor. In 124 rooms with slags used for construction, the average absorbed dose rate was 296 nGy h -1 , In 10 apartments the average radon concentration was 502 Bq m -3 . In that case the estimated effective dose due to inhaled radon and its progeny and gamma radiation was 10.3 mSv y -1 .