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At least 775 records · Page 43Linked to original sources
PubMed2000

Muonic helium atom as a classical three-body problem

We study the classical problem of the muonic helium atom, a helium atom with one of its electrons replaced by a muon. First, we establish the connection of the model with the one-dimensional frozen planetary approximation of the helium atom and find that there is classically stable motion for the configuration alpha-particle-electron-muon, and no stable motion for the alpha-particle-muon-electron configuration. After that, we introduce the restricted muonic helium problem, a model for the movement of an electron in the potential of the alpha particle/muon pair moving in a circular orbit. In this model, the equilibrium points, their associated Lyapunov families of periodic orbits, and their stability parameters were studied. The most interesting feature is the stability of the halo orbits, for a range of energy values. The vicinity of the alpha particle is also studied, examining Poincare sections for increasing energy values showing an increase of the chaotic motion.

Journal Article↗
PubMed2001

The bystander effect in radiation oncogenesis: II. A quantitative model.

There is strong evidence that biological response to ionizing radiation has a contribution from unirradiated "bystander" cells that respond to signals emitted by irradiated cells. We discuss here an approach incorporating a radiobiological bystander response, superimposed on a direct response due to direct energy deposition in cell nuclei. A quantitative model based on this approach is described for alpha-particle-induced in vitro oncogenic transformation. The model postulates that the oncogenic bystander response is a binary "all or nothing" phenomenon in a small sensitive subpopulation of cells, and that cells from this sensitive subpopulation are also very sensitive to direct hits from alpha particles, generally resulting in a directly hit sensitive cell being inactivated. The model is applied to recent data on in vitro oncogenic transformation produced by broad-beam or microbeam alpha-particle irradiation. Two parameters are used in analyzing the data for transformation frequency. The analysis suggests that, at least for alpha-particle-induced oncogenic transformation, bystander effects are important only at small doses-here below about 0.2 Gy. At still lower doses, bystander effects may dominate the overall response, possibly leading to an underestimation of low-dose risks extrapolated from intermediate doses, where direct effects dominate.

Apoptosis↗
PubMed1995

An intercomparison study of 237Np determination in artificial urine samples.

An intercomparison study of low-level 237Np determination in artificial urine samples has been carried out. The purpose of this study was to find the "optimal" method presently available for use in a routine in-vitro radiobioassay program for occupationally exposed workers. Four synthetic urine samples with differing 237Np concentrations were prepared: (1) 3 mBq kg-1 of 237Np; (2) 3 mBq kg-1 of 237Np with natural uranium, 239Pu and 241Am as interferences; (3) 50 mBq kg-1 of 237Np; and (4) a matrix blank. The solutions were submitted to 10 alpha-particle and 10 inductively coupled plasma-mass spectrometry (ICP-MS) laboratories of which six and four laboratories, respectively, returned results. Two laboratories performed assays using both techniques. The radiochemical method of choice used 239Np as the tracer, which utilized a combination of coprecipitation and anion-exchange separation. The best results obtained by ICP-MS were comparable with but not better than the most accurate results obtained by alpha-particle spectrometry. Alpha-particle spectrometry measurements overall gave consistently better agreement with known values.

Biological Assay↗
PubMed1998

1H NMR spectroscopy study of the dynamic properties of glycogen in solution by steady-state magnetisation measurement with off-resonance irradiation.

The dynamics of size-selected fractions of glycogen in solution have been investigated by proton NMR spectroscopy, using a recently described relaxation study method which relies on strong offresonance irradiation. The dependence of the steady-state magnetisation on angle and intensity of the effective radio-frequency field was measured and compared to theoretical curves derived from different models of motion. Absence or presence of contributions to relaxation from molecular motions on the microsecond time scale can be tested with this method, without having to resort to models. We found that glycogen dipolar relaxation did not result from isotropic Brownian rotation, and despite some contribution from slow motion (> 1 microsecond) to relaxation in glycogen alpha-particles extracted from rat liver, bulk movement of the molecules did not appear to participate in averaging the dipolar term to zero. Whereas hepatic glycogen rat beta-particles and commercial oyster glycogen displayed very similar relaxation properties, alpha-particles showed significantly different behaviour. However, all results were compatible with a diversity of movements within the molecule, ranging from freely rotating pyranoside rings through collective chain motion and possibly to bulk movement of the beta sub-units within the alpha-particle.

Animals↗
PubMed1998

The cytotoxicity and microdosimetry of astatine-211-labeled chimeric monoclonal antibodies in human glioma and melanoma cells in vitro.

The cytotoxicity of alpha-particle-emitting endoradiotherapeutic compounds is of increasing interest because clinical evaluation of these potential therapeutic agents is commencing. Astatine-211 is a radionuclide with a 7.2-h half-life that emits 5.87 and 7.45 MeV alpha particles. In the present work, we have investigated the in vitro cytotoxicity of 211At-labeled chimeric monoclonal antibodies (mAbs) in monolayers of D-247 MG human glioma cells and SK-MEL-28 human melanoma cells. The mAbs studied were 81C6, reactive with the extracellular matrix antigen tenascin, Mel-14, directed against the cell membrane antigen proteoglycan chondroitin sulfate, and a nonspecific control mAb, TPS3.2. Cell uptake increased as a function of activity concentration after a 1-h exposure to the 211At-labeled mAbs. The retention of activity was also measured to calculate cumulative activity associated with the cells and the medium. The clonogenic survival as a function of activity concentration was linear in all cases with no detectable shoulder. Microdosimetric analyses were performed based on measured cell geometry, cumulative activity and Monte Carlo transport of alpha particles. Using 18 kBq/ml activity concentration and 1 h of incubation, a two to five times higher activity bound to the microcolonies was found for the specific mAbs compared to the nonspecific mAb. These calculations indicated that a survival fraction of 0.37 was achieved with 0.24-0.28 Gy for D-247 MG cells and 0.27-0.29 Gy for SK-MEL-28 cells. The microdosimetric cell sensitivity, z0, for D-247 MG cells was significantly lower than for SK-MEL-28 cells (0.08 compared to 0.15 Gy). For both cell lines, reduction in survival to 0.37 required an average of only 1-2 alpha-particle hits to the cell nucleus.

Antibodies, Monoclonal↗
PubMed1998

The promoting effect of tumour necrosis factor alpha in radiation-induced cell transformation.

The ability of tumour necrosis factor alpha (TNF-alpha), a potent endogenous inflammatory agent, to promote malignant transformation of Syrian hamster embryo cells (SHE) initiated by a 0.5-Gy dose of alpha-particles was investigated. Opsonized zymosan particles, which were phagocytosed by a human macrophage-like cell line, triggered TNF-alpha production from U937 cells. This cell supernatant could significantly increase the transformation frequency (TF) of primary SHE cells previously irradiated by a 0.5-Gy dose of alpha-particles. The TF decreased significantly if monoclonal antibody against TNF-alpha was added to the supernatant. Similarly, recombinant human TNF-alpha (rhTNF-alpha) increased the TF of alpha-irradiated primary SHE cells to an even greater extent. Addition of TNF-alpha to subcultures of irradiated SHE cells permitted the continuous propagation of these primary cells. In contrast, both TNF-alpha-treated control and alpha-irradiated cells without subsequent TNF-alpha treatment senesced after 7-15 passages. Irradiated SHE cells treated continuously with TNF-alpha could be subcultured over 40 passages and produced fibrosarcomas upon inoculation into nude mice. Our results provide the first evidence that TNF-alpha released by activated macrophages may contribute to the process of malignant transformation initiated by low-dose alpha-particles.

Animals↗
PubMed1994

Radiation-induced systemic and local bone tumors: two types of late effects with possible different origins?

Bone sarcomas may be induced throughout the skeleton (systemic) in mice by relatively low internal alpha-particle doses that are distributed over the whole skeleton. The induction of local (periosteal) bone sarcomas after paratibial deposition of insoluble radiocolloids required much higher doses, and in addition high energies of emitted particles. Paratibial deposition of alpha-particle-emitting radiocolloids of 227Th and 228Th resulted in formation of both local and systemic bone sarcomas. The latter were most probably induced by the released radium daughters of the thorium isotopes and were distributed about the skeleton. Paratibial injections with beta-particle emitters 144Ce+ 144Pr (29 kBq per mouse) showed an incidence of local bone sarcomas of more than 80%. An estimation of the local effective doses led to values of more than 1000 Gy for the beta-particle emitter 144Ce and around 150 Gy for the thorium isotopes. Thus induction of local bone sarcomas required doses considerably greater than those needed for systemic bone sarcomas. The local induction of bone sarcomas has been reported for high-energy beta particles using similar high doses of 144Ce+ 144Pr in rats and for external 90Sr+ 90Y irradiation in mice. We conclude that the processes involved in the induction of local and systemic bone sarcomas by radiation may be quite different.

Animals↗
PubMed1994

Multicellular dosimetry for micrometastases: dependence of self-dose versus cross-dose to cell nuclei on type and energy of radiation and subcellular distribution of radionuclides.

UNLABELLED: In radioimmunotherapy, the treatment of bulk tumors by radionuclides that emit energetic beta particles is the preferred approach. However, for the eradication of small clusters of cancer cells, radionuclides that emit Auger electrons or alpha particles are considered to be advantageous because of their ability to deposit radiation energy locally. If such radionuclides are internalized by the cells, the total dose to the cell nuclei is thought to be primarily determined by the self-dose (dose to cell nucleus from activity within the cell) in comparison to the cross-dose (dose to the cell nucleus from activity in all other cells). METHODS AND RESULTS: The self-dose-to-cross-dose ratios to the cell nucleus were calculated for different cluster sizes (26-400 microns) with monoenergetic electron and alpha particle sources distributed uniformly in different cell compartments (cell surface, cytoplasm, nucleus). Model calculations were also performed for several radionuclides (Auger, beta and alpha emitters). Absorbed fractions for sources of monoenergetic electron and alpha particles, distributed uniformly in small spheres (26-5000 microns), were also calculated along with S-values for a number of radionuclides. CONCLUSIONS: When most of the cells in the cluster are labeled with beta or alpha emitters, the cross-dose component of the total dose is important irrespective of cluster size and subcellular source distribution and increases as the cluster size increases. The self-dose is always important for Auger emitters. When the self-dose is negligible, the mean absorbed dose to the cell nuclei is well represented by the mean dose to the micrometastasis.

Alpha Particles↗
PubMed1981

Biophysical investigations of the dose-effect relationship in chromosome aberrations of human lymphocytes caused by thorotrast deposits. I. Physical aspects.

Thorotrast is a X-ray contrast medium which has been used in the years 1930-1950. It is hardly ever eliminated from the body and is stored in the organs of the reticulohistiocytic system (RHS). Since Thorotrast contains all radionuclides of the thorium decay chain, the effect of internal irradiation by these radionuclides can be investigated in the so called "Thorotrast patients". It is the purpose of this study to determine the radiation dose absorbed by the lymphocytes of the peripheral blood of these persons, and to correlate it with their chromosome aberration rate. Part I of the paper describes the physical aspects of dose evaluation. The chromosome aberration rates of Thorotrast patients were subjected to a repeated statistical test. They show a logarithmic normal distribution at a mean value of about seven dicentric chromosomes per 100 cells. The corresponding dose has to be determined. The method for evaluating size and distribution of Thorotrast conglomerates in the examined tissue is demonstrated, and the function and resolution power of the applied "texture analysing system" (TAS) is described. Size-distributions of Thorotrast conglomerates of lymph nodes from the neck, the lung and from the lower aorta (bifurcatio) are given. In the lymphatic system more than 90% of the absorbed dose in tissue is due to alpha-particles. The computation method of calculating the self-absorption of alpha-particles in the conglomerates and of calculating the annual doses in the lymph nodes is described. The values lie between 135 and 1200 rad/year. The contribution to irradiation from outside the lymphatic system can be neglected. The method of dose determination is discussed and compared with microdosimetric methods. With these methods, the dose of a lymphocyte caused by one hit of an alpha-particle lies between 80 and 920 rad. An energy dissipation does not take place and the total energy emitted acts on the lymphocytes thus inducing chromosome aberrations.

Animals↗
PubMed1987

Surface radioactivity resulting from the deposition of 222Rn daughter products.

Studies of indoor radiation environments typically involve measurements of 222Rn, airborne 222Rn decay products, and the degree of radioactive equilibrium. This paper describes the relationship between the 222Rn in air, and the level of surface radioactivity that results from the build-up and decay of the daughter isotope, 210Pb. Samples of 222Rn were collected from Mystery Cave, which is located in southeastern Minnesota and from the basement of a house in Minneapolis, MN. Lead-210 was measured on surfaces within the cave, on a rock removed from the cave, and on a basement window. Surface alpha activities were measured on the rock sample and on the window. Radon-222 concentrations in the cave air ranged from 3 to 13 kBq m-3. In the basement, 222Rn levels were between 0.2 and 0.4 kBq m-3. Virtually all the surface radioactivity resulted from the deposition and decay of airborne 222Rn daughter products and was not produced by the decay of U in the rock. Radon-222 concentrations in the cave air were almost 30 times higher than in the basement air; however, the surface 210Pb activity in the cave was 100 times higher than that in the basement. This suggests that in the cave air, 222Rn daughter products are more likely to reach the walls and decay to 210Pb. The measurements of surface alpha activity did not show a similar trend primarily because 210Pb had diffused further into the coating of dirt on the rock than into the glass of the window. The resulting surface activity of the rock was lower than expected based on the 210Pb concentration, because many of the alpha-emitting nuclei were at depths beyond the range of emitted alpha particles. On surfaces where the penetration range of alpha particles is greater than the diffusion depth of 210Pb atoms, either the 210Pb concentration or surface alpha-activity measurements should provide estimates of average long-term 222Rn concentrations.

Air Pollutants↗
PubMed1990

[Effects of At-211 alpha irradiation on Ehrlich ascites tumor cells].

The biological effect of 211At alpha-particles has been investigated using the Chinese hamster fibroblasts and Ehrlich carcinoma cells growth in vitro. The mean energy of 211At alpha-particles is 6.8 MeV, LET in tissue is 70-160 keV/microns; the half-life period of decomposition of 211At is 7.2 h. The end-points used were a decrease in the mitotic activity, an elevation of the number of degenerating cells, cell with chromosome aberrations and the cell survival. The RBE of alpha-particles in comparison with 60Co gamma-rays is close to 3.

Alpha Particles↗
PubMed2004

Effects of irradiated medium on chromatid aberrations in mammalian cells using double mylar dishes.

We examined the potential contribution of irradiated medium on the bystander effect using custom made double-mylar stainless steel rings. Exponentially growing Human-hamster hybrid (AL) cells were plated on either one or both sides of double-mylar dishes 2-4 days before irradiation. One side (with or without cells) was irradiated with alpha particles using the track segment mode of a 4 MeV Van de Graaff accelerator at the Radiological Research Accelerator Facilities of Columbia University. Since alpha particles can only traverse a very limited distance, cells plated on the other side of a medium-filled mylar dish will not be irradiated by the alpha particles. The results of chromosomal aberrations on un-irradiated target cells that were attached to the top mylar layer indicate that the number of chromatid-type aberrations was higher when there was a bottom layer of cells in the medium filled chambers than just medium alone. Furthermore, when transferring the medium from these cell-irradiated dishes to fresh AL cultures, chromatid-type aberrations were produced in the un-irradiated fresh cells. In contrast, medium irradiated in the absence of cells had no effect on chromatid aberrations. These results suggest that certain modulating factors secreted from the irradiated cells on the bottom mylar layer into the medium, induce chromatin damage in the un-irradiated, bystander cells.

Alpha Particles↗
PubMed2000

Protection by DMSO against cell death caused by intracellularly localized iodine-125, iodine-131 and polonium-210.

The mechanisms by which DNA-incorporated radionuclides impart lethal damage to mammalian cells were investigated by examining the capacity of dimethyl sulfoxide (DMSO) to protect against lethal damage to Chinese hamster V79 cells caused by unbound tritium ((3)H(2)O), DNA-incorporated (125)I- and (131)I-iododeoxyuridine ((125)IdU, (131)IdU), and cytoplasmically localized (210)Po citrate. The radionuclides (3)H and (131)I emit low- and medium-energy beta particles, respectively, (125)I is a prolific Auger electron emitter, and (210)Po emits 5.3 MeV alpha particles. Cells were radiolabeled and maintained at 10.5 degrees C for 72 h in the presence of different concentrations of DMSO (5-12.5% v/v), and the surviving fraction compared to that of unlabeled controls was determined. DMSO afforded no protection against the lethal effects of the high-LET alpha particles emitted by (210)Po. Protection against lethal damage caused by unbound (3)H, (131)IdU and (125)IdU depended on the concentration of DMSO in the culture medium. Ten percent DMSO provided maximum protection in all cases. The dose modification factors obtained at 10% DMSO for (3)H(2)O, (131)IdU, (125)IdU and (210)Po citrate were 2.9 +/- 0.01, 2.3 +/- 0.5, 2.6 +/- 0.2 and 0.95 +/- 0.07, respectively. These results indicate that the toxicity of Auger electron and beta-particle emitters incorporated into the DNA of mammalian cells is largely radical-mediated and is therefore indirect in nature. This is also the case for the low-energy beta particles emitted by (3)H(2)O. In contrast, alpha particles impart lethal damage largely by direct effects. Finally, calculations of cellular absorbed doses indicate that beta-particle emitters are substantially more toxic when incorporated into the DNA of mammalian cells than when they are localized extracellularly.

Animals↗
PubMed2005

Organic-inorganic hybrid liquid crystals: thermotropic mesophases formed by hybridization of liquid-crystalline phosphates and monodispersed alpha-Fe2O3 particles.

A novel organic-inorganic hybrid thermotropic liquid crystal (LC) is developed by the hybridization of an organic phosphate having a mesogenic core and monodispersed alpha-Fe2O3 particles with different shapes through the specific adsorption of the phosphate group to the surfaces parallel to the c-axis of the alpha-Fe2O3. The hybrid LC shows thermotropic nematic or cubic liquid-crystallinity in wide ranges of temperatures. Variable-temperature small-angle X-ray measurements reveal that the spontaneous formation of periodic structure by the hybridization induces the thermotropic liquid crystallinity. This technique would lead development of novel types of dynamic functional materials with multi-responsiveness to magnetic and electric fields.

Crystallization↗
PubMed2002

A new method specifically designed to expose cells isolated in vitro to radon and its decay products.

A system was set up to provide direct exposure of cells cultured in vitro to radon and its decay products. Radon gas emanating from a uranium source was introduced at a measured concentration in a closed 10-m(3) exposure chamber. Cells were cultured on the microporous membrane of an insert that was floating over the culture medium in a six-well cluster plate. Plates with cells were placed in an open thermoregulated bath within the chamber. Under these conditions, cells were irradiated by direct deposition of radon and radon decay products. During exposure, all parameters, including radon gas concentrations, decay product activities, and potential alpha-particle energy concentrations, were determined by periodic air-grab samplings inside the chamber. The energy spectrum of deposited decay products was characterized. An estimation of alpha-particle flux density on the area containing cells was performed using CR-39 detector films that were exposed in cell-free wells during the cell exposure. The number of alpha-particle traversals per cell was deduced both from the mean number of CR-39 tracks per surface unit and from measurements of entire cells or nuclear surfaces. This paper describes the design of experiment, the dosimetry of radon and radon decay product, and the procedures for aerosol measurements. Our preliminary data show the usefulness of the in vitro cell culture approach to the study of the early cellular effects of radon and its decay products.

Alpha Particles↗
PubMed2006

AFM interaction study of alpha-alumina particle and c-sapphire surfaces at high-ionic-strength electrolyte solutions.

Ionic strength dependence of interaction and friction forces between hydrophilic alpha-alumina particles and c-sapphire surfaces (0001) were investigated under basic pH conditions using the colloidal probe method. The compression of the double layer could be seen from force-distance curves as the ionic strength of the solution increased. The forces were repulsive at all ionic strengths measured, even though the interaction distance changed drastically. No jump to contact occurred. The interaction distance decreased from about 20 nm in 10(-3) M KCl solution to about 7 nm in the 1 M KCl case. The lubricating effect of hydrated cations on the lateral friction force was demonstrated at high electrolyte concentrations. This was attributed to more hydrated cations being present in the solution. The friction behavior was closely related to the short-range repulsive forces between the alpha-alumina surfaces at pH 11.

Journal Article↗
PubMed2006

Analysis of gamma-rays induced chromosome aberrations: a fingerprint evaluation with a combination of pan-centromeric and pan-telomeric probes.

PURPOSE: To evaluate the types of induced chromosome aberrations after the exposure of peripheral blood to gamma-rays by the simultaneous detection of all centromeres and telomeres; and to analyse the suitability of different radiation fingerprints for the assessment of radiation quality in cases of recent exposures. MATERIAL AND METHODS: Peripheral blood samples were irradiated at 2, 4 and 6 Gy of gamma-rays. Cytogenetic analysis was carried out by fluorescence in situ hybridization (FISH) technique with pan-centromeric and peptide nucleic acid (PNA)-telomeric DNA probes. Cells were analysed using a Cytovision FISH workstation, chromosome aberrations and the length of the acentric fragments were recorded. RESULTS: The total number of the incomplete chromosome elements was 276. The ratio between incomplete elements and multicentrics was 0.38. The number of acentrics was 1096, 71% were complete acentrics, 15% incomplete acentrics, and 14% interstitial fragments. The relative length of complete, incomplete and interstitial acentrics fragments were 2.70 +/- 0.04, 1.91 +/- 0.07, and 1.42 +/- 0.04 respectively. The mean value of the F-ratio was 11.5 higher than the one, 5.5, previously obtained for alpha-particles. For the G-ratio there was no difference between gamma-rays and alpha-particles, 2.8 and 2.8 respectively. The mean value of the H-ratio for gamma-rays, 0.25, was lower than for alpha-particles 0.40. CONCLUSION: The results support that the percentage of incomplete chromosome aberrations depends on radiation type; low-linear energy transfer (LET) radiation would produces less incomplete aberrations than high-LET radiation. The F- and H-ratios seem to be good indicators of radiation quality, although a real estimation of the H-ratio is only possible using pan-telomeric probes.

Adult↗