Radiation quality dependence of DNA damage induction

Analysis of DNA fragmentation and repair in relation to radiation quality may give important information about the role of break complexity and correlated double strand breaks (DSBs). DNA fragment analysis was performed by pulsed-field gel electrophoresis after exposure to different radiation qualities. Normal human fibroblasts were irradiated with boron ions (40, 80 and 160 keV.micron-1), nitrogen ions (80, 125, 175 and 225 keV.micron-1) and neon ions (225 and 300 keV.micron-1). The amount of DNA less than 1.1 Mbp decreased with increasing linear energy transfer (LET) for all three ions. When theoretical random distributions were subtracted from the experimental data for 225 keV.micron-1 nitrogen ions in all size intervals (5-5700 kbp), there was a significant non-random distribution of DSBs for sizes up to 1-3 Mbp. This non-random distribution of breaks, probably produced by intra-track correlated DSBs, may constitute a substantial portion of the high-LET induced DSBs.     

氚气标准源的研制

氚是涉氚场所中辐射防护监测的重点核素,对涉氚场所中的气态氚浓度进行有效监测具有重要的意义。根据GB/T 7165.5-2008第5部分要求,氚活度监测校准应使用与被测对象成分一致的参考源,即标准氚气。解决该难题需要研究并建立标准氚气的制备方法和定值方法,确保氚气活度量值源头的有效性。基于稀释法研制了气载氚标准源,通过长度补偿法进行氚活度浓度定值,并进行了不确定度的分析和评定。氚气标准源的研制填补了国内该领域的空白,为氚监测仪的量值溯源提供了重要支撑。     

Radiation safety and quality control in the cyclotron laboratory

Radiation safety was determined to maintain quality control in the cyclotron laboratory. Based on the results of 438 runs in the Faraday cup (20 microA for 10 min), 20 runs on 18O-water target (40 microA for 2 h) and 10 runs on 18O-gas targets (30 microA for 45 min), we have established that occupationally exposed workers remain 10 +/- 5 times below federal regulatory limits (FRLs) in the cyclotron vault, 30 +/- 8 times below FRL in the radiochemistry laboratory and 200 +/- 10 times below the FRL outside the cyclotron laboratory during beam operation. (The FRL for unrestricted area are <20 microSv in 1 h.) The non-occupationally exposed workers serving in offices in the vicinity of the cyclotron vault within 100 m distance remained 200 times below the FRL irrespective of beam being on or off, suggesting that routine beam operation of 40 microA for 2 h once a day during office hours is safe provided quality control and system performance measures as discussed in this report are strictly maintained.     

Handling high specific activity tritium

The Chalk River Nuclear Laboratories' (CRNL) Tritium Laboratory was designed and built to develop techniques and methods for the safe handling and storage of pure tritium (T₂). The laboratory currently handles up to 20 000 Ci (0.74 PBq). The laboratory, its components and equipment selected for use with tritium, the monitoring system, and health and safety procedures are described. The design and operation of uranium and titanium beds, used for tritium transfer and storage, are also discussed.     

Synthesis of difluorobenzene double-labeled with tritium

A procedure based on nuclear-chemical generation of free nucleogenic reactive species was developed for the synthesis of difluorobenzene double-labeled with tritium as a precursor for the generation of previously unknown difluorophenyl cations.     

Radiation quality of photons in small and large receptors--a microdosimetric analysis

The quality of different photon radiations in small and largereceptors is assessed in terms of microdosimetry. Monte Carlosimulations are performed for the electrons released by photons.To represent the case of a small receptor, only electrons releasedby the non-degraded incident photons are tracked. For a largereceptor, all electrons released in the complete degradationprocess are followed. Dose averaged values, y_D, of the linealenergy are derived from the simulated tracks for monoenergeticphotons from 10 keV to 2 MeV. In microdosimetry, the dose meanlineal energy is the major parameter of radiation quality. Theresults demonstrate distinct differences in radiation qualitybetween high-energy gamma rays and conventional X rays thatare present not just in small cell samples but also in largereceptors, such as the human body. The values of y_D suggestthat, for both small and large receptors, conventional X raysshould be about twice as effective as gamma rays from ⁶⁰Co.     

Quick management of accidental tritium exposure cases

Removal half-life (RHL) of tritium is one of the best means for optimising medical treatment, reduction of committed effective dose (CED) and quick/easy handling of a large group of workers for medical treatment reference. The removal of tritium from the body depends on age, temperature, relative humidity and daily rainfall; so tritium removal rate, its follow-up and proper data analysis and recording are the best techniques for management of accidental acute tritium exposed cases. The decision of referring for medical treatment or medical intervention (MI) would be based on workers' tritium RHL history taken from their bodies at the facilities. The workers with tritium intake up to 1 ALI shall not be considered for medical treatment as it is a derived limit of annual total effective dose. The short-term MI may be considered for tritium intake of 1-10 ALI; however, if the results show intake ≥100 ALI, extended strong medical/therapeutic intervention may be recommended based on the severity of exposure for maximum CED reduction requirements and annual total effective dose limit. The methodology is very useful for pressurized heavy water reactors (PHWRs) which are mainly operated by Canada and India and future fusion reactor technologies. Proper management will optimise the cases for medical treatment and enhance public acceptance of nuclear fission and fusion reactor technologies.     

Isotope exchange reactions of trans-zeatin with tritium

Isotope exchange of trans-zeatin with high-activity tritium water and with gaseous tritium in solution, and also the solid-phase catalytic hydrogenation of this compound were studied. The isotope exchange of trans-zeatin with gaseous tritium, both in solution and without a solvent at 160°C and higher temperatures, is accompanied by virtually complete hydrogenation of the starting compound with the formation of tritium-labeled dihydrozeatin. The isotope exchange of trans-zeatin with high-activity tritium water allows preparation of tritium-labeled zeatin in 67% yield and molar activity of 0.68 PBq mol^?1. When the solid-phase isotope exchange is performed at 150–155°C, the reaction products contain tritium-labeled trans-zeatin along with the hydrogenation product, dihydrozeatin. At 170°C, the only reaction product is dihydrozeatin. Thus, the selectivity of tritium labeling varies with the temperature of solid-phase catalytic hydrogenation. Below 160°C, the solid-phase reaction can be performed selectively, i.e., with the preservation of the double bond in the starting trans-zeatin. Above 170°C, the selectivity is lost, and the compound is virtually fully hydrogenated to dihydrozeatin.     

Model of tritium dispersion by ground water

A three-dimensional model of ground-water contamination in the zone of a steady source of tritium is presented. The model is oriented toward long-term modeling of contamination (for up to several decades) on a large area (of up to several hundred square kilometers) where the contaminant arrives through the roof of the aquiferous stratum by infiltration. The three-dimensional equation of convective diffusion is solved numerically by the method of splitting. The convective component is calculated by the method of particles. The dispersion component of the transfer is calculated using the finite-difference method. A transformation of the vertical coordinate is introduced. A solution of the model problem is presented and an interpretation of the results is given. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 673–679, July–August, 2000.     

阻氚乳胶材料的阻隔性与成膜性研究

高分子材料可以应用到国际热核实验反应堆(ITER)中国实验包层(TBM)涉氚系统的非初级包容系统作为阻氚迁移扩散的材料之一。以几种高分子材料胶乳为原料采用涂布工艺制备了一定厚度的高分子片材,使用氢气作为介质通过渗透实验获得了氢气在几种材料中的渗透率,这些数据可作为氚防护手套和氚防护服的材料选择依据之一。以丁基胶乳为例进一步研究了胶乳的成膜性能和吸水性能,结果表明烘干脱水温度和硫化温度对成膜质量有重要影响,缓慢的升温烘干脱水和低温快速硫化可以获得较少内部缺陷的橡胶材料。由于胶乳中含有亲水物质而导致成型后橡胶材料的吸水性增强,而沥滤处理可以减少橡胶内的亲水物质从而降低材料的吸水性。     

NMR lineshapes in solid tritium and deuterium-tritium

We report on the NMR free induction decays (FID) from solid tritium (T₂), deuterium-tritium (D-T), and H₂, HD and D₂ containing 2% tritium. The FID in pure components is typically a beat decay for spin concentrations >30%, an exponential for spin concentrations <10%, and a Gaussian or Gaussian-exponential for spin concentrations in between. In mixtures of DT or HD, the deuteron FID is a Gaussian-exponential while the T or H FID is typically a beat decay or Gaussian depending on temperature. The linewidth is shown to consist mostly of intermolecular and intramolecular contributions, with a small component resulting from unpaired hydrogen atoms created by the tritium radioactivity.     

The high-pressure equation of state of solid molecular tritium

We have calculated the equation of state for solid molecular tritium using a semiempirical approach, closely guided by experimental results for H₂ and D₂. TheT=0 K isotherm is calculated from a self-consistent phonon model of the free energy. Temperature effects are treated by the Mie-Grüneisen model. A tabulation of pressure, bulk modulus, and thermal expansion is given for a dense set of molar volumes, as a function of temperature up toP=22 kbar.     

The thermal behaviour of the tritium source in KATRIN

The tritium source in the Karlsruhe Tritium Neutrino Experiment (KATRIN) will deliver 10¹¹ β decay electrons per second, in order to determine the mass of the electron antineutrino through analysing the tritium β spectrum. The source is built of a 10 m long beam tube of 90 mm inner diameter, which is operated at 30 K. Gaseous tritium is injected through a central injection chamber and diffuses towards the tube ends, where it is pumped by large turbomolecular pumps and further processed in a closed tritium loop. In order to achieve the KATRIN sensitivity of 0.2 eV/c², the decay rate in the source (and hence the tritium density profile) must be stable to a level of ±0.1%. As the density profile is influenced by the beam tube conductance, both the temperature stability and the temperature homogeneity must be within a range of ±0.03 K at 30 K. A thermosiphon with saturated neon was developed for this purpose, with horizontal evaporator tubes connected all along the 10 m beam tube. The system behaviour was tested in a 12 m long test cryostat, containing the original beam tube with the adjacent pumping chambers, as well as the cooling circuits and the thermal shields. The so-called “Demonstrator” was operated in the Tritium Laboratory Karlsruhe (TLK) being connected to the cryogenic infrastructure of KATRIN. The temperature stability was found a factor 20 better than specified, achieving a standard deviation of only 1.5 mK/h, which corresponds to ΔT/T = 5 × 10⁻⁵ h⁻¹ relative stability at 30 K. The ±0.03 K temperature homogeneity along the 10 m beam tube was not yet reached, because of an increased heat load through the pump ports. The repeatability of the temperature measurement with vapour pressure sensors was within ± 0.004 K.     

Polymeric matrices promising for immobilization of tritium radioactive wastes

The resistance of polymeric matrices to leaching of tritium water incorporated in oil microcapsules or in chemisorbent particles was studied. The phenol-formaldehyde matrix with tritium and cesium in oil microcapsules ensures highly reliable radionuclide immobilization: The half-decile leaching rate, g cm^?2 day^?1, is 9 × 10^?5 for ³H and 2 × 10^?5 for ¹³⁷Cs. A borate chemisorbent in combination with a polyurethane matrix was suggested for immobilization of highly radioactive tritium water vapor.     

Reassessment of tritium dose coefficients for the general public

Concerns of increased risk from tritium intake by humans have been claimed in the past. The arguments concerning the radiobiological effectiveness of tritium, its longer retention in the human body and the presence of tritium in the DNA hydration shell are analysed in this paper. A biokinetic model for tritiated water and organically bound tritium retention in the human body is used, based on a common approach for mammals using energy and hydrogen metabolism and tested separately with animal experiments. Extension to this model to humans considers the increased role of the brain, food quality and unique growth patterns of humans. Various ages and genders for Caucasians are considered. For an intake of tritium in organic forms in the diet, the retention for the female is of about a factor 2 compared with ICRP recommendations. Effective dose coefficients are estimated to be about a factor of 2 to 3 higher than those of the ICRP.     

辐射发射与辐射法测温—如何接近表面真实温度

从辐射测法中辐射率变化对温度的影响，讨论了多色辐射测量法的发展与应用实践，比较了不同处理方法的优缺点。     

Specific features of deuterium and tritium labeling of SB258585

Samples of SB258 585 labeled with hydrogen isotopes were synthesized. [²H]SB258 585 containing one ²H atom per molecule and [³H]SB258585 with the molar radioactivity of 15 Ci mmol^?1 were obtained in preparative amounts. From 0.18 to 1.5 ²H atoms were incorporated, on the average, into an SB 258 585 molecule depending on the reaction conditions. The isotope exchange efficiency strongly depends not only on the catalyst-substrate ratio and on the reaction temperature, but also on processes occurring on the support surface. The isotope effects strongly influence the degree of deuterium or tritium incorporation into the samples in cases when the organic compound largely decomposes in the course of the reaction.     

Solid-phase catalytic reactions of tritium with carbohydrates: 3. Mechanism of isomerization of epimeric pentoses in the course of solid-phase catalytic hydrogenation with tritium

The mechanism of isomerization of ribose into arabinose in the solid phase under the action of spillover hydrogen in the course of solid-phase catalytic hydrogenation was studied. Isomerization of ribose was shown to occur by a complex mechanism similar to acid-catalyzed keto-enol tautomerization of epimeric sugars in solution; the active species in SCH of D-ribose with tritium is spillover hydrogen in the proton form.     

Sample preparation for quantitation of tritium by accelerator mass spectrometry

The capability to prepare samples accurately and reproducibly for analysis of tritium (3H) content by accelerator mass spectrometry (AMS) greatly facilitates isotopic tracer studies in which attomole levels of 3H can be measured in milligram-sized samples. A method has been developed to convert the hydrogen of organic samples to a solid, titanium hydride, which can be analyzed by AMS. Using a two-step process, the sample is first oxidized to carbon dioxide and water. In the second step, the water is transferred within a heated manifold into a quartz tube, reduced to hydrogen gas using zinc, and reacted with titanium powder. The 3H/1H ratio of the titanium hydride is measured by AMS and normalized to standards whose ratios were determined by decay counting to calculate the amount of 3H in the original sample. Water, organic compounds, and biological samples with 3H activities measured by liquid scintillation counting were utilized to develop and validate the method. The 3H/1H ratios were quantified in samples that spanned 5 orders of magnitude, from 10(-10) to 10(-15), with a detection limit of 3.0 x 10(-15), which is equivalent to 0.02 dpm tritium/mg of material. Samples smaller than 2 mg were analyzed following addition of 2 mg of a tritium-free-hydrogen carrier. Preparation of organic standards containing both 14C and 3H in 2-mg organic samples demonstrated that this sample preparation methodology can also be applied to quantify both of these isotopes from a single sample.