Results 1 - 10 of 130
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[en] Purpose: This review examines the evidence for the hypothesis that epigenetics are involved in the initiation and perpetuation of radiation-induced genomic instability (RIGI). Conclusion: In addition to the extensively studied targeted effects of radiation, it is now apparent that non-targeted delayed effects such as RIGI are also important post-irradiation outcomes. In RIGI, unirradiated progeny cells display phenotypic changes at delayed times after radiation of the parental cell. RIGI is thought to be important in the process of carcinogenesis; however, the mechanism by which this occurs remains to be elucidated. In the genomically unstable clones developed by Morgan and colleagues, radiation-induced mutations, double-strand breaks, or changes in messenger RNA (mRNA) levels alone could not account for the initiation or perpetuation of RIGI. Since changes in the DNA sequence could not fully explain the mechanism of RIGI, inherited epigenetic changes may be involved. Epigenetics are known to play an important role in many cellular processes and epigenetic aberrations can lead to carcinogenesis. Recent studies in the field of radiation biology suggest that the changes in methylation patterns may be involved in RIGI. Together these clues have led us to hypothesise that epigenetics may be the missing link in understanding the mechanism behind RIGI. (author)
[en] Purpose: This study was designed to investigate the effect of a 900-MHz continuous-wave (CW) radiofrequency radiation (RFR) exposure on the hematopoietic system in the rat. Materials and methods: Rat long bones (femur and tibia) were divided into two groups: Sham-exposed and radiofrequency (RF)-exposed. The mean Specific energy Absorption Rate (SAR) at 900-MHz averaged over the bone marrow (calculated by the finite-difference-time-domain (fdtD) method) was 2 W/kg at 16.7 W root mean square (rms) forward power into a Transverse Electromagnetic (TEM) cell. The bones, placed in a Petri dish containing media, were kept in the TEM cell for 30 min duration of sham or RF exposure. After exposure, the bone marrow cells were extracted and the following end points were tested: (a) Proliferation rate of whole bone marrow cells, (b) maturation rate of erythrocytes, (c) proliferation rate of lymphocytes, and (d) DNA damage (strand breaks/alkali labile sites) of lymphocytes. Results: Our data did not indicate any significant change in the proliferation rate of bone marrow cells and lymphocytes, erythrocyte maturation rate and DNA damage of lymphocytes. Conclusion: Our findings revealed no effect on the hematopoietic system in rats for 900 MHz CW RF exposure at the 2 W/kg localised SAR limit value recommended by the International Commission for Non-Ionising Radiation Protection (ICNIRP) for public exposures. (authors)
[en] Purpose: Xerostomia is a common, disturbing side-effect among patients treated with radiotherapy for head-and-neck cancer. The aim of the present work was to investigate whether histamine could prevent salivary gland dysfunction and histological alterations exerted by ionising radiation. Materials and methods: Forty-eight rats were divided into four groups. Histamine and histamine-5 Gy groups received a daily subcutaneous histamine injection (0.1 mg/kg) starting 24 h before irradiation. Histamine-5 Gy and untreated-5 Gy groups were irradiated with a single dose of whole-body Cesium-137 irradiation. Control and untreated-5 Gy groups were given daily saline injections. Three days post irradiation metacholine-induced salivary secretion was measured or animals were sacrificed and submandibular gland (SMG) removed, stained and histological characteristics were evaluated. Proliferation and apoptosis markers were studied by immunohistochemistry. Results: Radiation decreased salivary secretion by 40% in comparison to untreated rats, which was associated with loss of SMG mass, alteration of epithelial architecture, partial loss of secretor granular material, diminished proliferation and a remarkable apoptotic response. In contrast, histamine completely reversed the reduced salivation induced by radiation, conserved glandular mass with normal appearance and preserved the structural organisation of secretor granules. Radiation-induced toxicity is prevented by histamine essentially by suppressing apoptosis of ductal and acinar cells, reducing the number of apoptotic cells per field (19.0 ± 3.8 vs. 106.0 ± 12.0 in untreated animals, P < 0.001), and also by preventing the radiation-induced decrease in cell proliferation. Conclusions: Histamine prevents morphological and functional radiation-induced damage on SMG, representing a potential radioprotector for treatment of patients undergoing radiotherapy for head and neck malignancies. (authors)
[en] Purpose: To quantitatively and qualitatively investigate the changes in chromosomal aberrations during early cleavage in mouse embryos derived from γ-irradiated spermatozoa. Materials and methods: Mature males were exposed to 2 Gy or 4 Gy of 137Cs γ-rays, and their spermatozoa were used to produce embryos via in vitro fertilisation (IVF). The metaphase chromosomes were prepared from one-cell, two-cell, and four-cell embryos. In the chromosome preparations from two-cell and four-cell embryos, the separation of the sister blastomeres was precluded by treatment of the embryos with concanavalin A. The incidence of embryos with structural chromosomal aberrations, aneuploidy, or mosaicism was estimated. The fates of the different types of γ-ray-induced structural chromosomal aberrations were also investigated in those embryos. Results: The exposure of spermatozoa to 2 Gy or 4 Gy γ-rays caused structural chromosomal aberrations in 25.9% and 35.7% of the resultant one-cell embryos, respectively. At two-cell embryonic stage, the incidence of structural chromosomal aberrations was 17.4% in the 2 Gy group and 27.1% in the 4 Gy group. At the four-cell embryonic stage, although the incidence of control embryos with structural chromosomal aberrations was considerably high, the net incidence of embryos with radiation-induced structural chromosomal aberrations was similar to that at the one-cell stage. The incidence of aneuploidy was high in two-cell and four-cell embryos after both doses of γ-rays. The incidence of mosaicism increased significantly in dose- and embryonic-stage-dependent manners. Anaphase lag, and the degeneration and non-disjunction of the aberrant chromosomes were frequently observed in aneuploid and mosaic embryos. Conclusions: Mouse sperm DNA is highly vulnerable to γ-rays. The structural chromosomal aberrations of sperm origin are unstable in their behaviour and structure during cleavage, and therefore cause secondary aneuploidy and mosaicism in the early cleavage embryos. (authors)
[en] Muon catalyzed dd fusion in D2 and HD gases in the temperature range from 28 to 350 K was investigated in a series of experiments based on a time-projection ionization chamber operating with pure hydrogen. All main observables in this reaction chain were measured with high absolute precision including the resonant and non-resonant ddμ formation rates, the rate for hyperfine transitions in dμ atoms, the branching ratio of the two charge symmetric fusion channels 3He + n and t + p and the muon sticking probability. The report presents the final analysis of the data together with a comprehensive comparison with calculations based on recent μCF theories. The energy of the loosely bound ddμ state with quantum numbers J = 1, ν = 1, which is central to the mechanism of resonant molecule formation, is extracted with precision ɛ11(fit) = −1.9651(7) eV. in impressive agreement with the latest theoretical results ɛ11(theory) = −1.9646 eV.
[en] A brief review of the status of neutrino oscillations is given. The phenomenology of neutrino mixing and the standard seesaw mechanism of neutrino mass generation is discussed. Different approaches to neutrino oscillations are considered and compared. The role of the Heisenberg space-momentum uncertainty relation and the Mandelstam-Tamm time-energy uncertainty relation in neutrino oscillations is discussed in some detail.
[en] Experiments carried out on the gas-filled separator of recoil nuclei at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, in the past several years have proved the hypothesis of the existence of a stability island of superheavy nuclei. The accelerator, beam diagnostics, and detector technologies underlay the success. It is the highly sensitive detecting system of the separator combined with the method of “active correlations” that allowed rare events of the decay of superheavy nuclei to be reliably detected under almost background-free conditions. In turn, to a large extent, this has been made possible owing to special algorithms and software developed for long-term experiments in the beam of 48Ca ions.
[en] An artificial reference material (RGMIX) has been constructed from three IAEA materials (RGU-1, RGTH-1, RGK1). The material is analogous of an environmental radioactive material. The material is systematically analysed on a NaI(Tl) detector using the method of spectrum decomposition. The spectrum of the sample is similar to that of a geological material. (author)
[en] The fundamental importance of searching for neutrinoless double-beta decay (0νββ-decay) is widely recognized. Observation of the decay would tell us that the total lepton number is not conserved and that, consequently, neutrinos are massive Majorana fermions. A brief history of the double-beta decay is presented. The 0νββ-decay is discussed in context of neutrino oscillation data. The perspectives of the experimental 0νββ-decay searches are analyzed. The importance of reliable determination of the 0νββ-decay nuclear matrix elements is pointed out. The problem of distinguishing of the light-neutrino exchange, heavy-neutrino exchange and the trilinear R-parity breaking supersymmetric ( SUSY) mechanisms of the 0νββ-decay is addressed. Further, the process of resonant neutrinoless double-electron capture (0νɛɛ) is revisited. Arguments are presented that an experimental search for the 0νɛɛ might be feasible.
[en] Automatic translation: This Federal Law defines the legal basis for ensuring the radiation safety of the population in order to protect its health. 1. The main principles of ensuring radiation safety are: the principle of rationing - not exceeding the permissible limits of individual exposure doses to citizens from all sources of ionizing radiation; the principle of justification - the prohibition of all types of activities involving the use of sources of ionizing radiation, in which the benefits received for a person and society do not exceed the risk of possible harm caused by radiation additional to the natural radiation background; the optimization principle is to maintain at the lowest possible and achievable level, taking into account economic and social factors, of individual doses of radiation and the number of exposed persons when using any source of ionizing radiation. 2. In a radiation accident, the radiation safety system of the population is based on the following principles: the proposed measures to eliminate the consequences of a radiation accident should bring more benefits than harm; the types and scope of activities to eliminate the consequences of a radiation accident should be implemented in such a way that the benefits of reducing the dose of ionizing radiation, with the exception of the harm caused by these activities, are maximized.
[ru]Настоящий Федеральный закон определяет правовые основы обеспечения радиационной безопасности населения в целях охраны его здоровья. 1. Основными принципами обеспечения радиационной безопасности являются: принцип нормирования - непревышение допустимых пределов индивидуальных доз облучения граждан от всех источников ионизирующего излучения; принцип обоснования - запрещение всех видов деятельности по использованию источников ионизирующего излучения, при которых полученная для человека и общества польза не превышает риск возможного вреда, причиненного дополнительным к естественному радиационному фону облучением; принцип оптимизации - поддержание на возможно низком и достижимом уровне с учетом экономических и социальных факторов индивидуальных доз облучения и числа облучаемых лиц при использовании любого источника ионизирующего излучения. 2. При радиационной аварии система радиационной безопасности населения основывается на следующих принципах: предполагаемые мероприятия по ликвидации последствий радиационной аварии должны приносить больше пользы, чем вреда; виды и масштаб деятельности по ликвидации последствий радиационной аварии должны быть реализованы таким образом, чтобы польза от снижения дозы ионизирующего излучения, за исключением вреда, причиненного указанной деятельностью, была максимальной.