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PubMed1999

Contribution of cosmic ray heavy ions to the radiation hazard in manned space flights.

Primary cosmic radiation arriving near the Earth may be classified into two general categories: the gamma component and the hadronic component. The hadronic component contains mainly protons, a small amount of alpha particles and a smaller amount of heavier charged nuclei (ions). Although the fluxes of these heavier ions are very small in comparison to those of protons, they are able to originate a huge linear energy transfer (LET). This work studies the contribution of heavy ions from cosmic rays to the radiation hazard to which the crew of a manned long duration space flight might be exposed. The geometry of the energy deposition by a heavy ion is studied, and it is found that energies of the order of up to 10(23) J kg-1 are deposited.

Cosmic Radiation↗

PubMed2006

Experimental techniques for studying bystander effects in vitro by high and low-LET ionising radiation.

Ionising radiation can induce responses within non-exposed neighbouring (bystander) cells which potentially have important implications on the estimates of risk from low dose or low dose rate exposures of ionising radiations. A range of strategies have been developed for investigating bystander effects in vitro for both high-LET alpha particles or low-LET ultrasoft X rays using either partial shielding (grids, half-shields and slits) or by using a co-culture system where two physically separated populations of cells can be cultured together, allowing one population of cells to be irradiated while the second population remains unirradiated. The techniques described provide a useful tool to study bystander effects and complement microbeam studies. Studies using these systems show significant increases in the unirradiated bystander cells for various end points including the induction of chromosomal instability in haemopoetic stem cells and transformation in CGL1 cells.

Bystander Effect↗

PubMed2006

A model for the induction of chromosome aberrations through direct and bystander mechanisms.

A state vector model (SVM) for chromosome aberrations and neoplastic transformation has been adapted to describe detrimental bystander effects. The model describes initiation (formation of translocations) and promotion (clonal expansion and loss of contact inhibition of initiated cells). Additional terms either in the initiation model or in the rate of clonal expansion of initiated cells, describe detrimental bystander effects for chromosome aberrations as reported in the scientific literature. In the present study, the SVM with bystander effects is tested on a suitable dataset. In addition to the simulation of non-linear effects, a classical dataset for neoplastic transformation in C3H 10T1/2 cells after alpha particle irradiation is used to show that the model without bystander features can also describe LNT-like dose responses. A published model for bystander induced neoplastic transformation was adapted for chromosome aberration induction and used to compare the results obtained with the different models.

Animals↗

PubMed2006

The PTB microbeam: a versatile instrument for radiobiological research.

The PTB microbeam is routinely used for the irradiation of living cells using protons (1-20 MeV) and alpha particles (1-28 MeV). The beam diameter is approximately 2 microm (fwhm), achieved by focussing, resulting in an excellent energy resolution and practically no scattered particles. Recently, an electrostatic beam scanner was added to the facility which allows targeting of each cell within 1 ms. This and other improvements led to an increase in the experimental speed of the system to a maximum of 50,000 cells per hour including all experimental steps. To improve the versatility of the facility further, a module for automatic quantification of immunocytochemical staining was implemented. This allows the analysis of protein activation, taking into account the positional information of the irradiation run.

Cell Culture Techniques↗

PubMed2006

Simulation of light ion induced DNA damage patterns.

The biophysical simulation code PARTRAC was extended by a module to handle ions heavier than alpha particles. Cross sections for ion-electron interactions were taken from He(++) ions of the same velocity and scaled by Z(eff(2))/4. Calculated linear energy transfer values, radial dose distributions and secondary electron spectra were found in agreement with experimental results. DNA damage due to irradiation of human fibroblast cells by several light ions from H to S was calculated for various energies complemented by 220 kV(p) X rays as reference radiation. With increasing linear energy transfer, the calculated total yield of double-strand breaks per dose showed saturation behaviour at about twice the value for reference radiation. When data analysis methods for experimental double-strand break yield determination were applied to the simulated DNA damage patterns, the two data sets were found in accord. The calculated patterns of DNA damage clusters were analysed on local and regional scale finding regional clusters in closer correlation to experimental cell inactivation data.

Chromatin↗

PubMed2007

Modeling lung cancer incidence in rats following exposure to radon progeny.

Lung cancer incidence in Sprague-Dawley rats was simulated by a biologically based carcinogenesis model, which is formulated mathematically in terms of a stochastic state-vector model. Doses to the sensitive target cells in the bronchial epithelium of the rat lung were calculated by a stochastic dosimetry model, considering the distinct monopodial branching structure and the crossfire of alpha particles from alveolar tissue to bronchial epithelium. Bronchial and alveolar cellular doses could reasonably be approximated by lognormal distributions, with geometric standard deviations (GSD) between 7 and 10, depending on exposure conditions. Based on a dose-exposure conversion factor of 8.5 mGy WLM(-1) and a GSD of 8, lung cancer incidences were calculated for each cumulative exposure category in the rat inhalation study, consisting of different exposure rates and exposure times. The fair agreement between theoretical predictions and experimental data over the whole exposure range emphasises the necessity to incorporate the full cellular dose distributions rather than their mean values.

Animals↗

PubMedDate not supplied

Environmental lead-210 and bismuth-210 accrue selectively in the brain proteins in Alzheimer disease and brain lipids in Parkinson disease.

We studied the occurrence of the environmental radon daughters, 210Po (alpha particles), and 210Bi (beta particles), in the protein and lipid fractions of cortical gray and subcortical white matter from the frontal and temporal lobes of human brains of persons with Alzheimer disease (AD), persons with Parkinson disease (PD), smokers, or persons with no previous evidence of clinical neurologic disease (controls). We found a 10-fold increase in 210Po and 210Pb radioactivity in the protein fraction from both the cortical gray and subcortical white matter in AD and smokers, and a similar increase in the lipid fraction in PD. The pathognomonic distribution of the radon daughters to the lipids in PD and to the proteins in AD was inferred to reflect the increase of local chlorine availability to which radon daughters bound selectively. Cigarette smoking strongly increases radon daughter retention in the central nervous system.

Aged↗

PubMed1982

Measurement of natural neutron background using electrochemically etched polycarbonate foils and boron-10 radiators.

Electrochemical etching of polycarbonate foils was performed using a KOH solution with various concentrations of ethyl alcohol under different conditions of field strength, frequency, temperature and etching time to register alpha-particles from a 10B radiator positioned in the center of a 25-cm diameter polyethylene sphere. These studies showed that the highest neutron sensitivity relative to the inherent background in the foil was obtained under the following etching conditions: 32 kV/cm, 1 kHz, 30 degrees C, 2 hr in a solution of 35 gm KOH + 25 cm3 C2H5OH + 75 cm3 H20. Under these conditions, 1 mrem of neutrons from a Ra-Be source gave 155 pits per cm2 while background was 1-3 pits per cm2. The pit diameters were about 75 microns. The dose can be measured to an uncertainty of +/- 100% at 0.1 mrem and +/- 10% at 1 mrem. This method was used to measure the natural neutron background and gave 17 pits per cm2 (0.1 mrem +/- 0.1 mrem) per month in a building.

Background Radiation↗

PubMed1983

Leukaemia incidence in the U.S. dial workers.

Late biological effects of radium deposited in the human skeleton have manifested themselves unequivocally as osteogenic sarcomas or carcinomas of the mastoid air cells or paranasal sinuses. On the basis of current estimated risk factors, it might be expected that an excess of certain other malignancies could occur in a population of the size of the group exposed to radium (some 3500 cases located, which more than 2000 have measured 226Ra and 228Ra burdens), compared with the incidence in the population at large. An increased incidence of breast cancer has already been reported in female dial workers and it was related to the initial radium intake. On the other hand, very little information is available on the induction of leukaemia by alpha-radiation in human bone marrow. This paper therefore reports an investigation of the incidence of leukaemia among the radium workers. This covers a very wide range of radium burdens and has been done in the light of reasonable estimates of the mean alpha-particle dose received by the skeletal haemopoietic marrow. The number of leukaemia cases is identified and compared with (a) the expected number in a comparable population of the same size and age distribution and (b) predictions based on the risk factor proposed for protection purposes by the ICRP and on the estimated bone marrow doses.

Adult↗

PubMed1983

Cells at risk for the production of bone tumors in radium exposed individuals: an electron microscope study.

The endosteal cells of bone from a 75-yr-old woman who had acquired radium internally, as a consequence of her previous employment as a radium dial painter, are documented here for the first time by electron microscopy. As a result of amputation for a fibrosarcoma in the region of the right knee joint, fresh samples of bone and tumor tissue from the femur were made available. A sample of bone, also obtained at amputation from an unirradiated control patient, age 65, was examined from the same site in the femur. A comparison of the bone-marrow interface from the two patients showed that, unlike the control bone where cells were seen close to bone mineral a fibrotic layer was interposed between the marrow cells and the bone mineral in the bone from the radium case. This layer varied in thickness up to 50 microns and was often acellular, although cell remnants and cells, which appeared viable, were sometimes seen within this layer. It is suggested that irradiation of those cells proliferating within, and at the edge of, this replacement fibrotic layer may be the most important in the induction of bone tumors rather than the original cells lying within the 0-10 microns range from bone mineral which has previously been supposed. The nuclear dimensions of the endosteal bone lining cells and their distance from bone mineral have been measured in the bones from the radium and control cases. These dimensions are important not only in understanding the mechanisms by which bone tumors arise but in developing models of carcinogenic risks of other alpha-particle emitting isotopes such as plutonium.

Aged↗

PubMed1985

The occurrence of radioactivity in public water supplies in the United States.

Examination of the collected data for radionuclide concentration measurements in public water supplies in the United States show more than 51,000 measurements for gross alpha-particle activity and/or Ra, 89,900 measurements for U, and 9,000 measurements for Rn. These measurements were made as part of national and state surveys of radionuclide concentrations in utility water supplies for Ra and Rn; and the National Uranium Resource Evolution (NURE) survey for U which included non-utility water supplies. Surface water has low values for Ra and Rn but levels comparable to ground water for U. Separate isotope measurements were not taken for much of the Ra and U data. Because 226Ra to 228Ra ratios and 238U to 234U ratios are not fixed in water, further measurements are needed to establish the specific isotopic concentrations by region. Analysis of the state average values in geological provinces shows the highest provincial areas for Ra are the Upper Coastal Plain, the glaciated Central Platform, and the Colorado plateau. For U, the highest areas are the Colorado plateau, the West Central Platform, and the Rocky Mountains. For Rn, the highest provinces are New England and the Appalachian Highlands-Piedmont. Regional hydrogeological and geochemical models are suggested for guiding the formulation of regional standards and monitoring strategies. Utility supplies serving small populations have the highest concentration for each radionuclide and have the lowest fraction of samples measured, which shows a need for further measurements of these small population water supplies. Risk estimates for the average concentration of Ra in utility ground water give about 941 fatal cancers per 70.7-yr lifetime in the United States. Risk estimates for the average concentration of U in utility surface and ground water give about 105 fatal cancers per 70.7-yr lifetime in the United States. Using 1 pCi/liter in air for 10,000 pCi/l in water, the Rn in utility water risk estimate is for 4,400-22,000 fatal cancers per 70.7-yr lifetime in the United States.

Air Pollutants, Radioactive↗

PubMed1985

Measurements of airborne 212Pb and 220Rn at varied indoor locations within the United States.

Measurements have been made at varied locations within the United States comparing the concentration of 212Pb in air with that of the progeny of 222Rn to see if 212Pb is typically a significant contributor to indoor radioactivity. Auxiliary measurements were made comparing 220Rn with 222Rn. In terms of potential alpha-particle energy, 212Pb is significant (the ratio of its contribution to the combined contribution of 218Po, 214Pb, and 214Bi averaged about 0.6) and may warrant greater consideration as a component of indoor radioactivity. Correlations were found between the concentration of 220Rn progeny and 222Rn progeny, and the concentration of 220Rn and 222Rn. Environmental factors such as transport pathways and ventilation rates which exert a common influence on the concentrations of airborne isotopes provide a possible explanation for these correlations.

Air Pollutants↗

PubMed1991

Surface to nuclear distances in human bronchial epithelium: relationships to penetration by Rn daughters.

Lung cancer in U miners is thought to be related to the inhalation of particulate Rn daughters. Since the depth of penetration by alpha particles is short, the thickness of the epithelium lining the bronchial tree may be a critical factor in the development of cancers at specific sites in the lung. The objectives of the study were to measure the thickness of the epithelium at all levels of the human bronchial tree, to determine the distances of epithelial nuclei from the mucociliary surface, and to compare these parameters in smokers and nonsmokers. Twenty-nine surgically removed specimens were examined; 26 were from smokers. No significant differences were found between smokers and nonsmokers, allowing us to treat the 29 cases as a homogeneous group. With progressive divisions of the bronchi, the epithelium decreases in thickness, and distances of nuclei from the surface are also less in the peripheral bronchi. Allowing for artefacts of tissue preparation, the mean distance from the mucociliary surface to the underlying nuclei varies between 17 and 38 microns.

Aged↗

PubMed1991

Radium-226 whole-body gamma counting and 222Rn breath analysis: report on a subject exposed to uranium mill tailings.

One of two boys born in September 1949 who played on U mill tailings between age 8 and 12 was diagnosed as having leukemia at age 15.5. The exposed and control subjects were well matched; they were approximately the same age and both were 1.85 m (6' 1") in height and weighed 75.2 kg (165 pounds). The result obtained by gamma spectrometric method for the exposed subject was 0 +/- 17 Bq (0 +/- 470 pCi), while that for the control subject was 4 +/- 15 Bq (100 +/- 400 pCi). The result obtained by the Rn breath method for the exposed subject was 4.4 +/- 0.7 Bq (120 +/- 20 pCi), while that for the control was 5.4 +/- 1.4 Bq (150 +/- 38 pCi). These results suggest that the 226Ra body burden of the exposed subject is within the range of those observed in subjects exposed only through normal food sources, which have a mean 226Ra content of 1.5 Bq (range: 0.4-4.4 Bq) so that no significant mill-tailing intake is indicated. The best estimate of alpha particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. This dose, when compared to that observed in the dial painters, suggests that the leukemia was not caused by uptake of Ra from the mill tailings.

Adult↗

PubMed1991

Radium-226 dose to a boy from playing on mill tailings.

Two boys born in September 1949 played on uranium mill tailings from about ages 8 to 12. One of these boys was diagnosed as having leukemia at age 15.5. The 226Ra body burden of the survivor was measured at age 38. The whole-body 226Ra content measured by counting in vivo was 0 +/- 17 Bq and independently by Rn breath analysis as 4.3 +/- 2.1 Bq. At the same time, a control subject with no known exposure to 226Ra, matched in age, height, and weight, was also measured. The whole-body content was estimated as 4 +/- 15 Bq and independently by Rn breath analysis as 5.5 +/- 3.7 Bq. The body burden of the control subject was not significantly different from that of the exposed person. The radiation dose to the marrow-free skeleton assuming a constant 226Ra:Ca ratio since birth was 0.49 and 1.33 mGy at ages 14 and 38, respectively. The radiation dose to the marrow-free skeleton assuming 226Ra intake only between ages 8 to 12 was 1.4 and 2.8 mGy at ages 14 and 38, respectively. The best estimate is the mean of these two estimates: 0.9 and 2.1 mGy at ages 14 and 38, respectively. The alpha-particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. Since no excess was found for the radium dial painters whose doses were much higher, the induction of leukemia by doses of this magnitude would seem quite unlikely.

Body Burden↗

PubMed1991

Radon exposure system for mammalian cells in culture: design, operation, and dosimetry.

A novel system for Rn gas exposure of mammalian cells in culture has been designed, constructed, and used to directly assess both the magnitude and the nature of chronic, low-dose Rn/Rn daughter toxicity of exposed vital lung cells isolated from normal pulmonary tissue, propagated and exposed in vitro. Direct correlations between atmospheric Rn concentrations, alpha-particle fluences, and macro- and microdoses of absorbed radiation doses by lung cells provide for a heretofore unavailable assessment of critical doses to vital cells.

Air Pollutants, Radioactive↗

PubMed1992

222Rn detection efficiency and sensitivity coefficient of the LR 115-II nuclear track detector.

Radon activity concentrations in air were measured by the Kodak-Pathé LR 115-II nuclear track detector. Using the calibrated sensitivity coefficient of the detector (k = 0.0285 Bq-1 m3 tr cm-2 d-1 = 0.33 cm), the critical detection angle was calculated. In the alpha-particle energy region of 1-3.7 MeV, the detector efficiency for 241Am was near 32% but the 222Rn detector efficiency was 23%. The permeability constant of the detector paper filter was measured in a standard radon atmosphere and a value of 9.08 x 10(-6) cm2 s-1 was obtained.

Air Pollution, Radioactive↗

PubMed1992

Portable 220Rn detector used to assess Thorotrast exposure.

Patients who are exposed by injection to the radiological contrast medium Thorotrast (232ThO2) had been considered by early researchers to be an unfortunate but important model of alpha-particle carcinogenesis in the lung as well as liver and bone marrow because they continuously exhale 220Rn, in the breath of Thorotrast patients and (as the first step to lung dosimetry) to investigate the relationship between exhaled 220Rn activity concentration (Bq L-1) and 232Th body burden. Results revealed that reliable estimation of 232Th burden by 220Rn measurement is possible because a fairly good correlation was obtained between 220Rn in the breath and the known quantity of 232Th in the body. Mean 220Rn activity concentration in the breath was 9.21 Bq L-1 g-1 of 232Th deposited in the liver and spleen. This value was very close to that published for German patients. Our data and those of other investigators indicate that apparent discrepancies in mean 220Rn activity concentration among previous studies was caused by using different 228Th:232Th activity ratios.

Body Burden↗