Radiochemical characteristics of tritium to be considered in fusion reactor facility design

The results of research and development related to radiochemical characteristics of tritium to be considered in a fusion reactor facility design are summarized. Reactions induced by tritium beta-decay under presence of high purity tritium, which might give an impact to tritium inventory control and safety, have been identified and investigated. Results of researches of radiolysis of tritiated water implied necessity of some measures to prevent hydrogen explosion and avoid a corrosive condition. A calorimetric method to measure tritium decay heat has been applied successfully to accountancy of the ITER fuel storage system with satisfaction of the required specification.     

Acoustic emission in solid-liquid decomposition reactions

The chemical acoustic emission method was used to study solid-liquid decomposition reactions for the example of the interaction of potassium carbonate pellets with solutions of hydrochloric acid (HCl). The reaction was shown to follow different mechanisms at different hydrochloric acid concentrations (the concentration was varied from 0.12 to 12 M). An increase in the concentration of HCl not always caused an increase in the rate of generation of acoustic emission signals and, therefore, the reaction rate. The generation of acoustic emission was studied at various reaction stages. The advantages of the chemical acoustic emission method include measurements in real time (this is of importance for fast reactions, the reaction studied took no more than 5 min) and the possibility of determining rates at separate reaction stages. An automated acoustic emission unit was tested. The unit showed high reproducibility of measurement results, reliability, and rich possibilities for studying chemical acoustic emission in solids.     

几种高聚物拉伸过程中的声发射现象

研究了４种塑料ＰＳ、ＰＯＭ、ＡＢＳ和ＰＣ拉伸过程中的声发射现象，发现声发射信号主要产生在屈服前和断裂时，说明高聚物的声发射信号主查由于分子链的解缠结，晶体的滑移裂纹的亚临界扩展和分子链的断裂等诸因素产生的，ＡＢＳ拉伸时大面积银纹的生成也可能是信号源，拉伸应变速率，材料的结构和不同的屈服过程等对塑料的拉伸声发射规律有较大影响。     

Acoustic emission monitoring of damaging of fiberglass

The results of studies on determining the nucleation moment of microcracks in fiberglass are presented on the basis of a full-strength glassfiber mat and vinyl ether binder by the acoustic emission method in uniaxial tension. The research was carried out by continuous monotonic loading of samples under uniaxial tension until failure with simultaneous recording of the parameters of acoustic emission signal. Qualitative dependences of the parameters of acoustic emission signals on the stress value in the sample are revealed. It is found that, at a stress value of about 40% of the ultimate strength of material (about 420 MPa), microfracture processes—cracking of the polymer matrix—begin.     

Hydrogen isotope exchange reaction rate in tritium and methane mixed gas

Hydrogen isotope exchange reaction rate in tritium and methane mixed gas, as induced by tritium decay and beta radiation, has been experimentally measured. Initially T₂ gas was filled to 40 kPa and 20 kPa of CH₄ gas was added. The mixed gas spectrum was analyzed periodically by laser Raman spectrometry. The first order HT and H₂ formation rates and T₂ and CH₄ decay rates by hydrogen isotope exchange reaction were observed between 2.9·10^–3 h^–1 and 4.8·10^–3 h^–1. Although the estimated hydrogen isotope exchange reaction rate was 1/20–1/10 slower than the rate of H₂+T₂ mixed gases, it was nearly equivalent to the ion formation rate by tritium beta radiation. This suggested that isotopic hydrogen radicals formed via ionization would disappear in the presence of methane.     

Factors affecting broadband acoustic emission measurements of a heterogeneous reaction

Broadband acoustic emission signals were obtained by attaching a piezoelectric transducer, sensitive up to 750 kHz, to the external wall of a 1 L jacketed glass reactor. Measurements were acquired of itaconic acid particles mixing in toluene; the total area of the acoustic emission signal from 55-500 kHz increased when the particle concentration, particle size or stir rate were increased. Signals at frequencies above 200 kHz were less sensitive to changes in particle size than those at lower frequencies. From calculation of the area of the signal in the range 55-200 kHz as a percentage of the signal area over the range 55-500 kHz, for mixtures of different size ranges of itaconic acid, it was possible to obtain an estimate of the mean particle size of a mixture. The heterogeneous esterification reaction of itaconic acid and 1-butanol was monitored non-invasively. A decrease in the overall acoustic signal area between 60 and 500 kHz was observed as the reaction progressed. Particle size and concentration information were contained in the amplitude of the acoustic emission signal, while the emission frequency yielded information on changes in the mean particle size.     

Fast heavy ion induced photon emission from organic solids and plasma desorption mass spectrometry

Fission fragments from a ²⁵²Cf source have been used to study fast heavy ion induced desorption of ions and luminescence in the wavelength region 200–680 nm from samples of Csl, the amino acids valine, isoleucine and tyrosine, and of the peptide substance P. All samples emit photons under fast heavy ion bombardment. Most of the emission is confined to the near-UV region and within narrow time profiles. Analysis of the fast decay regions of the time profiles show that all the compounds have at least a fast and a slow decay component, both in the nanosecond region. The use of such narrow photon signals as start time markers for time-of-flight measurements (TOF) has been demonstrated. As the photon signal is derived directly from the desorption event it gives the true number of starts for a secondary ion TOF spectrum. Characteristics of the photon emission from a CsI target together with correlation studies between the desorbed secondary ions and the photon signal indicate that the light emission is from the bulk of the material and not correlated with the secondary ions.     

Monitoring of a heterogeneous reaction by acoustic emission

The feasibility of monitoring the reaction of itaconic acid and 1-butanol by non-invasive acoustic emission measurements has been assessed. A piezoelectric transducer with a resonant mode at 90 kHz was attached to the external wall of a 1 L jacketed glass reactor. Acoustic emission from the oil jacket, stirrer and toluene was insignificant in comparison to that produced by the itaconic acid particles, which was transmitted through the glass walls and heating oil to the transducer. The transducer responded to acoustic emission from itaconic acid up to approximately 300 kHz, with the region around 90 kHz having the highest sensitivity. The effect of particle concentration and size on the acoustic emission generated has also been investigated, with higher concentrations and larger particles giving the greater signals. The detection limit for itaconic acid particles was 14 g dm(-3) of toluene. The effect of 1-butanol concentration and temperature on the progression of reactions was monitored using acoustic emission. It was possible to detect differences in the rate and extent of the reaction under different conditions, and also to identify when a combination of the concentration and/or size of itaconic acid particles had reached a steady state. However, it was not possible to differentiate between changes in particle size and concentration using the resonant transducer.     

Ultraweak and Induced Photon Emission After Wounding of Plants

The ultraweak and induced photon emission were measured by a single photon counting equipment (Photomultiplier Hamamatsu R562) on Cucurbita pepo variaca styriacae after wounding. Wounding significantly changes the emission from a stationary to a nonstationary state and the shape of the decay curve obtained after light illumination. The rise in the ultraweak photon emission depends on the kind of wounding and its localization on the plant. The decay curves obtained after wounding could be better fit by an exponential function than by a hyperbolic one. So the biophoton emission correlates with physiological and bioelectrical changes like membrane depolarizations as they also depend on the kind of injury.     

Radiochemical determination of nuclear data for theory and applications

A vast knowledge of nuclear data is available and is grouped under three headings, namely, nuclear structure, nuclear decay and nuclear reaction data. Still newer aspects are under continuous investigation. Data measurements are done using a large number of techniques, including the radiochemical method, which has been extensively worked out at Jülich. This method entails preparation of high-quality sample for irradiation, isolation of the desired radioactive product from the strong matrix activity, and preparation of thin source suitable for accurate measurement of the radioactivity. It is especially useful for fundamental studies on light complex particle emission reactions and formation of low-lying isomeric states, both of which are rather difficult to describe by nuclear model calculations. The neutron induced reaction cross section data are of practical application in fusion reactor technology, particularly for calculations on tritium breeding, gas production in structural materials and activation of reactor components. The charged particle induced reaction cross section data, on the other hand, are of significance in medicine, especially for developing new production routes of novel positron emitters and therapeutic radionuclides at a cyclotron. Both neutron and charged particle data also find application in radiation therapy. A brief overview of advances made in all those areas is given, with major emphasis on nuclear reaction cross section data.     

Detection of tritium and alpha decaying radionuclides in L/ILW by measurements of helium isotopes

As decay products, helium isotopes can clearly indicate the presence of tritium and alpha decaying isotopes in a closed system. This study presents the helium and neon measurements and their interpretation of long-term headspace gas investigations in L/ILW waste drums from Paks Nuclear Power Plant and closed vaults of the Radioactive Waste Treatment and Disposal Facility, Püspökszilágy, Hungary. Development of special sampling methods and preparation lines as well as isotope-analytical measurements of the headspace gas samples were done in the Hertelendi Laboratory of Environmental Studies in the ATOMKI. In the gas samples helium isotopes as well as neon isotopes have been determined mass spectrometrically. While neon content can be of atmospheric origin only, helium can be produced either by alpha decay (⁴He) or decay of tritium (³He). ³H/⁴He and He/Ne ratios have been used to determine the different origin of the helium isotopes. Helium isotope ratios always represented ³He enrichment in the headspace gases produced by the decay of the tritium in the waste. Using the recent ³He concentration in headspace gas the total amount of ³H restored in L/ILW vaults was estimated. The investigated seven different vaults were closed between 1979 and 1995 when they had been full with L/ILW. The calculated tritium activities based on the He measurements showed good agreement with the documented isotope inventory of the vaults. Typical tritium activity concentrations were between 0.1 and 10 Bq/L gas in the drums and between 10 and 1000 Bq/L gas in the vaults. Additionally, one drum showed a higher He/Ne ratio compared to air, which clearly indicates ⁴He excess, thus the presence an alpha source in the waste.     

<Emphasis Type="Italic">New Ideas and Hypotheses:</Emphasis> Acoustic emission on phase transformations in aqueous medium

Acoustic emission on phase transitions in aqueous medium, including ice melting, was experimentally studied. It was shown that the frequency, time, and other parameters of induced acoustic pulses depend on the nature of the substance and on outer conditions. Acoustic emission in melt water (homogeneous liquid) was reliably detected. This finding shows that acoustic emission can be used to control the technological processes involving metastable substances, and it can prove to be the only suitable technique for such processes.     

Photoinduced multimode coherent acoustic phonons of metallic nanoprisms and the effects of shape-induced anisotropic electronic stresses

In this work we reported experimental measurements of ultrafast structural dynamics in metallic nanoprisms induced by a femtosecond laser pulse. The main focus of this study of anisotropic heating in nanoprisms is about laser fluence effects on photoexcitation of two planar coherent acoustic phonon modes, namely, the breathing mode and the totally symmetric mode. We presented a combined two-temperature model and 2-D Fermi-Pasta-Ulam model to explain both the dependence of the initial phases and the mode weight on the excitation power. Our transient optical absorption data for both the initial fast monotonic decay and the subsequent coherent acoustic oscillations clearly indicate the presence of anisotropic thermal expansion in nanoprisms.     

Effect of chemical quenching on background counting rate in tritium channel of a large volume liquid scintillation counter

Background counting rate in tritium channel of a large volume liquid scintillation counter increased with water content ranged 0 to 50% of liquid scintillator. This phenomenon can be explained as follows: The height of scintillation pulses of Compton electrons induced by background gamma radiation is lowered by chemical quenching and shifts to tritium channel. The background counting rate in tritium channel showed a linear relationship with external standard channel ratio of background samples. This relationship is applicable to determine the correct background counting rate for quenching samples and to achieve higher precision of tritium measurement.     

Development of an environmental atmospheric tritium monitoring system at the Toki site

n this study, the application for monitoring atmospheric tritium at the site of nuclear fusion facility is presented. Construction and examination of the tritium sampler and its arrangement at the site are mainly discussed. Atmospheric tritium concentrations at Toki site were determined in the sampling period from September 2000 to June 2001. Although the data for HTO were low because of their low specific activity (0.62 Bq/l), our average HT and CH₃T data were 9.1 and 3.3 mBq/m³, respectively, and systematically lower than the previously reported values at the same site, even if the considerable decay correction was carried out. Suitable monitoring points are discussed by considering the local meteorological features at the Toki site. Since the wind conditions at this site were governed by diurnal and nocturnal wind blowing to the contrary directions, it is concluded that the monitoring points should be placed at the site boundary of downwind direction of these winds. Considering that the expected levels of effluent tritium in the D-D experiment at the National Institute for Fusion Science are competitive with those in the environment, the detailed variations of the environmental tritium should be comprehended to detect minute amounts of the artificial tritium.     

Self contained enrichment cell for tritium

Tritiated water is probably the most mobile manmade nuclide found in the environment. The low-energy beta decay produces few health concerns except at extremely high concentrations of tritium. However, because of the ubiquitous nature of tritiated water, when identified in the bionetwork, it can be viewed as a precursor of nuclides with greater health risks. For this reason alone it becomes desirable to determine tritium concentrations many orders of magnitude below that considered a health concern. A devise is described that eliminates the need for large water-filled chest freezers used as coolers. The enrichment cells can be employed individually or in series.     

RESOLUTION OF TWO EMISSION SPECTRA FOR TRYPTOPHAN USING FREQUENCY-DOMAIN PHASE-MODULATION SPECTRA

We describe a novel application of frequency-domain fluorometry which allows resolution of the decay times and emission spectra of samples which display multi-exponential decay kinetics. This method does not require any previous knowledge about the decay times or any assumptions about the shape of the emission spectra. We record the wavelength-dependent phase angles and modulations (phase angle and modulation spectra) using a number of light modulation frequencies. The data is analyzed by non-linear least-squares to recover the emission spectra and their associated decay times. Phase and modulation spectra (PM Spec) were used to recover the emission spectra associated with the two decay times of tryptophan at pH = 7 (0.54 and 3.44 ns). The emission spectra of these components are centered at 340 and 355 nm, respectively, with the amplitude of the 0.54 ns component contributing 6% to the total emission. These results are in agreement with previous time-resolved studies by Szabo and Rayner [J. Am. Chem. Soc. 102, 554-563 (1980)]. Control experiments were performed on mixtures of N-acetyl-L-tryptophanamide (NATA) and PPD, which demonstrate our ability to recover the spectra and decay times from two component mixtures. NATA itself displayed a single decay time and only one emission spectrum.     

2',7'-Difluorofluorescein excited-state proton reactions: correlation between time-resolved emission and steady-state fluorescence intensity

The presence of excited-state buffer-mediated proton exchange reactions influences the steady-state fluorescence signals from dyes in solution. Since biomolecules in general have some chemical groups that can act as proton acceptors/donors and are usually dissolved in buffer solutions which can also behave as appropriate proton acceptors/donors, the excited-state proton exchange reactions may result in distorted steady-state fluorescence signals. In a previous paper (J. Phys. Chem. A 2005, 109, 734-747), we evaluated kinetic and other pertinent parameters for the excited-state proton reactions of the prototropic forms of 2',7'-difluorofluorescein (Oregon Green 488, OG488), recording a fluorescence decay surface at different pH values and acetate buffer concentrations, analyzed by means of global compartmental analysis. In this article we use the rate constants and the corrected pre-exponential factors from the previously recorded fluorescence decay traces to simulate the decay times and associated pre-exponentials at different acetate buffer concentrations and constant pH and compare these theoretically calculated values with new experimental data. We also calculate the steady-state fluorescence intensity vs pH and vs acetate buffer concentration (at constant pH) and compare these calculated emission values with the experimental data previously published. The agreement between the experimental and simulated data is excellent.     

Analysis of the debonding process in polypropylene model composites

Polypropylene (PP) model composites were prepared using cross-linked PMMA particles with a very narrow particle size distribution as filler in order to study the micromechanical processes, which take place during deformation. Composites containing a commercial CaCO₃ filler with a broad particle size distribution were also prepared and studied for comparison. The filler loading of the composites was changed from 0 to 0.3 volume fraction in 0.05 volume fraction steps. Measurements of acoustic emission signals during the elongation of PP/PMMA model composites allowed us to assign the debonding process, including its initiation, unambiguously to a well-defined section of the stress vs. strain curve. The number and intensity of the acoustic signals detected during the deformation of the matrix polymer and the composite, respectively, differed considerably, which made possible the separation of the various micromechanical deformation processes occurring in them. At low extensions the composite is deformed elastically, then debonding takes place in a very narrow deformation range, followed by the plastic deformation of the matrix. At small particle content debonding occurs at relatively low stresses, which differ significantly from the yield stress. Considerable plastic deformation of the matrix begins at the yield point. At larger filler content debonding and shear yielding occur simultaneously. Micromechanical deformation processes cannot be separated as clearly in composites prepared from the commercial CaCO₃ filler with a broad particle size distribution. The debonding of particles with different size occurs in a wide deformation range because of the particle size dependence of debonding stress. The analysis of characteristic values derived from acoustic emission experiments proved that the interacting stress fields of neighboring particles influence the deformation process and that even large particles may aggregate or at least associate at large filler content.     

Ar atom emission as a probe of craze formation and craze growth in polystyrene

A report of measurements of Ar emission during the loading of polystyrene and high impact polystyrene in vacuum is presented. Argon was introduced into the material prior to the experiment by storing the samples in an Ar atmosphere. The development of crazes during loading was monitored by videotaped visual observations and scattered light measurements. Increased Ar emission is observed at the onset of crazing, provided that the crazes intersect the surface. The strength of the Ar signal depends upon the extent of crazing; especially intense signals are observed from samples which display significant crazing prior to fracture. High-impact polystyrene shows intense emissions at yield which soon decay due to the depletion of Ar from the near surface material. The emission intensity rises again prior to fracture, when surface crazes become connected to crazes in the bulk. Thus the emission of volatile species during deformation reflects the growth of crazes intersecting the surface, as well as changes in the “connectivity” of the craze network. © 1993 John Wiley & Sons, Inc.