Measurement of Dead Zone Characteristics of Gas Counter with Gamma-Ray

An evaluation method with uncollimated γ-rays has been proposed for the dead zone of gas counters without entrance windows. The obtained dead zone characteristics for the proportional, SQS and GM modes are almost consistent with those obtained with β-rays. Some difference in the dead zones obtained with γ-rays and β-rays has been discussed. This new method is effective to confirm and improve the operation mode of counters.     

8米长μ子SQS计数管电荷分配定位实验

本工作是因北京正负电子对撞机上通用谱仪的需要而作的一个模型实验。谱仪要求μ子计数管平行束流安放,而且对穿过它的带电粒子位置灵敏。要做到这一点,用电荷分配空位子最简单。因为当粒子射入计数管后,只要收集时间长,电荷在阳极丝两端的分配,只依赖于从入射点到丝两端的丝电阻比值,而与丝电阻的大小、丝上的电感电容分布以及信号的传输机制都无关系。因此,只要阳极丝足够均匀就应该得到好的结果。     

Significance of Ionization-Track Contribution to Self-Quenching Streamer (SQS) Formation Induced by Alpha-Rays

Positive-parity collective band structures of low-lying levels in even-even actinide nuclei were analyzed based on an extension of the Davydov-Chaban soft rotator model, which accounts for the rotation and β- and γ-vibrations of even-even nuclei with non-axial quadrupole deformation. The parameters to reproduce the 4-bands, i.e., the ground-state rotational band, the K≈2 band, and the n _β=1 and n _γ=l bands, were obtained, and their systematic trends were deduced. Based on this result the unassigned band having a sequence of 0⁺, 2⁺, 4⁺,…, which is observed in many actinide nuclei, was assigned likely to be the n _β=1 band. The systematic trends of the parameters found in this work could be a guide to estimate the collective band structure of nuclei for which such data are poorly known. The correct assignment of collective levels was found to be important for the calculation of neutron inelastic scattering cross sections.     

北京谱仪端盖簇射计数器工作气体的研究

为使北京谱仪端盖族射计数器更好地工作在自猝灭流光ＳＱＳ模式下，提高其能量分辨以及线性等指标，用Ａｒ，ＣＯ２，Ｌｓｏｂｕｔａｎｅ三元工作气体对探测器的工作性能进行了仔细研究，找出了一适合于主雇地数器的工作气体，此外，还研究了异丁的纯度对探测器性能的影响。     

INFORMATION FOR OVERSEAS CONTRIBUTORS

Experiments on the separation of H₂-HD isotopic gas mixture were performed with a 1,020 mm-height “Cryogenic-Wall” thermal diffusion column with a heated tube of 9.63 mm-outer-radius and a cooled tube of 14.21 mm-inner-radius which was cooled by liquid nitrogen. Abandance ratios of HD to H₂ in the feed, product and waste flow were measured by stable isotope mass spectrometer Finnigan MAT252.

Our rigorous numerical code has predicted dependence of separation factors obtained experimentally upon the operating pressure fairly well.     

Failure Propensities of Pressurized Zircaloy Tube Containing Iodine and Other Chemical Species

Abstract

Failure propensities of Zircaloy-4 cladding tube internally pressurized with Ar gas containing iodine and iodine plus each of other chemical species were examined at 360°C, to study the effect of corrosive fission products (FPs) on the integrity of spent nuclear fuel rods during dry storage, and also to assess the capability of preventing the spent fuel rod degradation.

The iodine stress corrosion cracking (SCC) of Zircaloy tube occurred in the long time/low stress exposure tests at stresses much lower than the conventional “threshold stress”, with considerably large strains at failure. The addition of cesium to iodine perfectly suppressed the SCC. It is inferred from these results that the degradation of spent fuel rods induced by corrosive fission products is unlikely during dry storage. Even if iodine alone should take effect, a proper strain limit could prevent spent fuel rods from incurring iodine induced effects because of considerably large strains necessary for iodine SCC of Zircaloy tube at low stresses.     

Measurement of heat transfer coefficients for steam condensation on a vertical 21.5-mm-O.D. tube in the presence of air

ABSTRACT

Governing the rate of heat transport by condenser tubes in the passive containment cooling system (PCCS), the steam condensation over a vertical cylinder in the presence of air was investigated experimentally. The main objective of this study was to explore if the condensation heat transfer coefficient relies on the tube dimension, which has been a variable missed in most condensation models or has been embraced without experimental demonstration under phase change environments. The mean heat transfer coefficient was measured in the condensation test facility named JERICHO (JNU Experimental Rig for Investigation of Condensation Heat transfer On tube). The outer diameter of the condenser tube used in this study was set to 21.5 mm. The measured heat transfer coefficients were compared to those obtained from the 40-mm-O.D. tube, and a multiplier to correct the variation of the heat transfer coefficient with the tube diameter was proposed for its application to Lee correlation. The proposed correlation was further validated against another set of experimental data obtained from a separate test facility housing the 31.8-mm-O.D. tube.     

Temperature rising characteristics of ammonium diurante in microwave fields

The temperature rising characteristics of ammonium diurante, triuranium octaoxide (U₃O₈), and their mixture were investigated under microwave irradiation, aiming at exploring newly theoretical foundation for advanced metallurgical methods. The temperature rising curves showed that ammonium diurante had weak capability to absorb microwave energy, while triuranium octaoxide had the very strong absorption capability. The temperature of mixture containing 20% of U₃O₈ could rise from room temperature to 1171 K within 280 s. The ability to absorb microwave energy for the mixture with different ratios increased with the increase in the amount of U₃O₈. These are in good agreement with the results of Maxwell-Garnett effective medium theory. It is feasible to calcine ammonium diurante by adding of small amounts of U₃O₈ in microwave fields.     

Development of Soft X-Ray Sources with Electron Guns of Field Emission- and Thermal Cathode-Types and Their Application to Counter Experiments

Soft X-ray sources have been developed with electron guns of field emission- and thermal cathode-types. Those sources are used mainly to investigate the electron drift and avalanche properties in a gas counter. Thin films of aluminum, titanium, iron, copper and nickel are used as the X-ray targets. Beams of quasi-monochromatic X-rays are obtained with these targets. The emitted X-rays consist of characteristic and bremsstrahlung radiations, which are checked by using a high purity germanium detector. Generation of pulsed X-rays is also tried. As an example of the application of the X-ray source, results of measurements of the SQS (Self Quenching Streamer) phenomenon in a gas counter have been shown.     

Vacuum plasma etching of 1 wt% La2O3 dispersed tungsten

Vacuum plasma etching of 1 wt% La₂O₃ doped tungsten alloy surfaces were carried out to refine the surface morphology for enhancing its bonding characteristics with copper for fusion reactor components. Three different gas compositions containing argon with zero, 14.3 and 25 vol% hydrogen were used to carry out the plasma etching from 30 to 120 s on the given samples. Mitutoyo surface roughness (R_a) measurement, FORM TALYSURF and scanning electron microscopy (SEM) were employed to measure the changes in the surface roughness. Plasma etching with 14.3 vol% hydrogen mixture was found to be the best in micro-roughening the alloy surface. The maximum increase of 44% in R_a value was obtained with this gas mixture, when etched for 90 s.     

Nuclear Characteristics of Molten-Salt-Cooled D-D Fusion Reactor Blankets

To consecutively decompose ¹⁴CO₂ into carbon (¹⁴C) through its reaction with Hz, an apparatus using microwave discharge and its conditioning were investigated. The reaction produces CO as an intermediate, and proceeds in the two steps of (1) “CO₂+H₂ → CO+H₂O” and (2) “CO+H₂+C_n → C_n+1+H₂O”, where C_n denotes the carbon already deposited on the wall of the discharge tube. Preliminary dispersion of carbon to the wall of the discharge tube by sputtering of a graphite particle was effective to promote the reaction. Two silica discharge tubes (6 mm O.D., 4 mm I.D., and 150 mm length each) were connected in series to proceed the former reaction in the first discharge tube and the latter one in the second one. When a 1:3 mixture of CO₂ and H₂ (total pressure 0.67kPa) was passed through the discharge tubes at a linear gas velocity of approximately 30mm/s and discharged for 60 h under microwave of 30–40 W supplied from two 2,450MHz power generators (200 W each), more than 90% of CO₂ was converted into CO in the 1st tube and about 23% of the CO was then decomposed into carbon in the 2nd tube. However, about 50% of the CO escaped from the tube without being decomposed, and about 0.5% and 1% of the carbon fed were hydrogenated into CH₄ and C₂H₂, respectively. The rest about 25% which was not confirmed was probably evacuated from the 2nd tube as microparticles of carbon. To completely decompose CO₂ into carbon, additional discharge tubes are necessary downstream of the 2nd tube.     

Radiolysis of Dyes in Aqueous Solutions, (V)(1)–(4)

Abstract

Fission gas behavior of UO₂ fuel pellets with controlled microstructure irradiated to 23 GWd/t in a test reactor has been studied by using a postirradiation annealing experiment. Four types of fuel pellets with or without additives were examined : (1) un-doped standard (grain size: 16/μm), (2) un-doped large grained (43μm), (3) 0.7 wt% Nb₂O₅-doped large grained (110/μm), (4) 0.2wt% TiO₂-doped large grained (85μm) fuels. The annealing was conducted at 1,600 or 1,800°C for 5 h in reducing or oxidizing atmospheres.

Fission gas release and bubble swelling caused by the high temperature annealing for the two un-doped fuels were reduced to about 1/3–1/2 by increasing the grain size from 16 to 43 μm, which roughly corresponded to the ratio of their grain sizes. By contrast, the performance of the two large grained fuels doped with Nb₂O₅ or TiO₂ was roughly equivalent to, or rather inferior to that of the standard fuel, despite their large grain sizes of 110 and 85 μm. The fission gas behavior of un-doped fuels was aggravated by increasing the oxygen potential in the annealing atmosphere, while that of additive doped fuels did not depend on it. The effects of grain size, additive doping and oxygen potential on fission gas release and bubble swelling were discussed in connection with the diffusivities of fission gas atoms and cation vacancies.     

An interpretation of the mechanism of the self quenching streamer

In this paper, the experiments on self quenching streamer (SQS) discharge in single wire and multi-wire chambers are performed, and a possible Interpretation of the SQS mechanism is proposed on the basis of analyzing the previous experimental results. According to this model, the excited atoms or molecules created in the latent track and subsequent avalanches play an important role. They form the main photo electron source. The interaction between them is also possibly a source of ionizing photons. Thus, a formula that describes the streamer transition and streamer charge is deduced. A comparison between theory and experiments is made. It is indicated that whether the streamer transition occurs or not, the absorption and radiation characteristics of the atoms or molecules of gases in the mixture is the decisive factor, and as a result of the difference in those characteristics, the different operating modes appear     

Application of Neutron Radiography to Visualization and Void Fraction Measurement of Air-Water Two-Phase Flow in a Small Diameter Tube

Abstract

The purpose of this study is to investigate the feasibility of visualization and void fraction measurement of air-water two-phase flow in a small diameter tube (I.D.: 4.08mm) by using the real-time neutron radiography and image processing techniques. Video images of two-phase flow were taken by using the real-time neutron radiography system (thermal neutron radiography facility No. 2) installed at the Japan Research Reactor 3 M of the Japan Atomic Energy Research Institute. The shape of bubbles and its moving behavior were clearly observed from the video images. The image corrections for dark current, shading, field intensity fluctuation and electrical system drift were examined in order to measure the void fraction from the video images. Though, generally speaking, the effect of the scattered neutron could not be ignored for quantification of the images taken by the neutron radiography, the scattered neutron could not affect the final results of void fraction in the case of a small diameter tube. The void fraction calculated from the corrected images was correlated well with the drift flux equation, indicating that the existing drift flux equation could be applied to predict the void fraction of two-phase flow in a small diameter tube. It was demonstrated that the real-time neutron radiography technique could be useful for measuring the void fraction of two-phase flow in a small diameter tube.     

Investigation and application of hollow anode glow discharge ion source

In the present work, a new shape of a glow discharge ion source has been designed, fabricated and constructed at Accelerators and Ion Sources Department, Nuclear Research Center, Egyptian Atomic Energy Authority, Egypt. The discharge and output beam characteristics of the ion source at different operating gas pressures have been measured at the optimum distance between the anode and the cathode (3.5 mm) using hydrogen and nitrogen gases. Furthermore, mixture of different gases was studied, e.g., addition of H₂ gas to N₂ gas with different ratios has been investigated. Finally, as an application of this new ion source, ion beam modification of insulators (glass) which depends on glass structure has been achieved. It has been found that, the transmission of light is decreased by coating the glass surface with Ar ion beam more than coating with plasma of Ar gas at the same pressure and the same exposure time. So we could use this ion source as a coating tool for borate glass surface. The parameters affected the glow discharge ion source efficiency have been examined carefully using a mixture of gases. Using helium gas, the glow discharge is in a turbulent state due to instabilities. An investigated H₂-N₂ mixture has been used in order to obtain an optimum percentage of the mixture of the two gases to increase the electric field necessary for ionization balance.     

A direct current glow discharge plasma source for inner surface modification of metallic tube

A dc glow discharge plasma source was developed for inner surface modification of metallic tubes with an inner diameter of 10 mm. A tungsten wire of 30 μm thick was stretched inside the tube to form coaxial electrodes. DC glow discharge plasma was generated inside the tube by applying a negative high dc voltage to the tube. It was found that the length of the cylindrical plasma bulk depends linearly on the applied voltage. The electron excitation temperature of Ar plasma was measured as 12830 ± 550 K by optical emission spectroscopy method. As a preliminary application, diamond-like carbon (DLC) films were deposited onto the inner surface of stainless steel tube of 100 mm in length and 10 mm in inner diameter by using CH₄/Ar mixture with 40% CH₄ at 40 Pa pressure. The chemical structure of the DLC film deposited on the substrate was analyzed by Raman spectroscopy. The integrated intensity ratio (I_D:I_G) was obtained as 1.62 from the Raman spectra. The thickness of the DLC film deposited on the substrate was estimated as 1.5 μm by scanning electron microscopy (SEM) observation.     

Radiation Treatment of Exhaust Gases, (VIII)

The NO₂ decomposition by electron beam irradiation was studied in the NO₂-N₂ and NO₂-rare gas mixtures. The NO₂ decomposition yields, G (-NO₂), at low doses in the case of the 500 ppm NO₂ initial concentration were 2.9, 10.4 and 5.9 for the NO₂-N₂, NO₂-He and NO₂-Ar mixtures respectively. A large amount of NO was formed by irradiation of these mixtures. The G (NO) was almost equal to the G (-NO₂). The N₂O was also formed in the NO₂-N₂ mixture. The NO₂ decomposition is mainly attributable to the attack of N, formed by the radiolysis of N₂, on NO₂ in the NO₂-N₂ mixture, and to the attacks of R⁺ and R*, formed by the radiolysis of a rare gas (R), on NO₂ in the NO₂-rare gas mixture. The NO₂ decomposition in the NO₂-N₂ mixture was depressed markedly by the addition of a small amount of O₂. This may be mainly attributable to the regeneration of NO₂ by the reaction of NO with O.     

Radiation Treatment of Exhaust Gases, (VII)

The NO decomposition by electron beam irradiation was studied in the NO-N₂ and NO-rare gas mixtures. The NO decomposition yields, G (?NO) at low doses in the case of the 500 ppm NO initial concentration were 4.04.4 and 1.2 for the NO-N₂, NO-He and NO-Ar mixtures respectively. A small amount of NO₂ was formed by irradiation of these mixtures. The NO decomposition is mainly attributable to the attacks of N and N₄ ⁺ (or N₂ ⁺), formed by the radiolysis of N₂on NO in the NO-N₂ mixtureand to the attacks of R⁺ and R^*, formed by the radiolysis of a rare gas (R)on NO in the NO-rare gas mixture. The NO decomposition in the NO-N₂ mixture was depressed markedly by the addition of a small amount of O₂. This may be mainly attributable to scavenging of N and N₄ ⁺ (or N₂ ⁺) by O₂.     

Local Gamma-Ray Counting Efficiency of Halogen Counter with Thick Anode

A substance for solidifying waste containing ¹²⁹I is sought that effectively sorbs iodine to inhibit its release from repository into the environment. Three candidate media—commercial alumina cement mixed with calcium sulfate and/or calcium hydroxide—were investigated. The criterion applied for evaluating iodine sorption performance was the distribution coefficient Kd of iodine between solid and solution in an emulsion of sodium iodide solution and powder prepared from the alumina cement/calcium compound mixture, which was molded, cured and ground. Batch sorption experiments were performed on different combinations of the above-mentioned calcium compounds added to alumina cement. The solidified substance was also examined for mechanical strength. The highest iodine sorption performance was obtained with calcium sulfate added to alumina cement to a SC₄/Ca mole ratio of 0.16, which ensured a Kd value raised to a level of not lower than 0.2 m³/kg from the (1.8–3.2)x10^-3 m³/kg obtainable with alumina cement before calcium compound addition. The enhancement of iodine sorption with addition of calcium sulfate is attributed to formation in the substance of monosulfate (3CaO·Al₂O₃·CaSO₄12H₂O) or tetracalcium aluminate hydrate (4CaO·Al₂O3·XH₂O (X=13 to 19)).