The initial atmospheric behavior of radon decay products

The chemical and physical properties of²¹⁸Po immediately following its formation from²²²Rn decay are important in determining its behavior in indoor atmospheres and play a major part in determining its potential health effects. In 88% of the decays, a singly charged, positive ion of²¹⁸Po is obtained at the end of its recoil path. These ions can interact with water vapor or other volatile organic compounds (VOCs) that may exist in indoor air. The ions can be neutralized by 3 different mechanisms, small-ion recombination, electron transfer, and electron scavenging. In typical indoor air, the ion will be rapidly neutralized by transfer of electrons from lower ionization potential gases such as NO₂. The neutral molecule can then become incorporated in ultrafine particles formed by the radiolytic processes in the recoil path. These particles will typically be formed by the presence of the air ions produced by the passage of the emitted -particle through ion-induced nucleation. In addition these energetic ions can react with water molecules to produce hydroxyl radicals. Thus, the decay of the radon nucleus produces a variety of effects and can result in changes in the size of the radioactive species that includes the radon progeny.     

Mitigation effects of radon decay products by air cleaner

One of the most effective methods for reducing exposure is the use of air cleaners. In this study, a dose mitigation of a commonly-used Japanese air cleaner under conditions in which aerosols are continuously supplied was investigated. Although the values of the EERC during an operation of air cleaner decreased, values of the f _p increased with the use of air cleaner. An effective dose was calculated on the basis of our experimental results, resulting in the dose mitigation of about 40 % by the air cleaner. Air cleaners can be regarded as an effective tool for the dose mitigation under with conditions in which aerosols are continuously supplied.     

Development of a new fluorescence decay measurement system using two-dimensional single-photon counting

A new fluorescence decay measurement system has been developed. The system consists of a spectrograph and a new two-dimensional photon counter. The combination enables measurements to be made of the fluorescence decay as a function of time and wavelength simultaneously. The time resolution is better than 5 ps with deconvolution processing, and the wavelength resolution is approximately 0.15 nm with 1200 grooves mm⁻¹ gratings. The dynamic range is 10⁵. The instrument response function (IRF) of the system is nearly gaussian, and has no tail or “after pulses” which are commonly observed using a photomultiplier in a time-correlated photon counting (TCPC) system. Therefore fast fluorescence decay of several tens of picoseconds can be measured accurately. In addition, the two-dimensional single-photon counting can be performed without wavelength scanning, so that the wavelength-dependent fluorescence decay can be easily and direcly observed with a fast throughput and a high signal-to-noise ratio. The principle of two-dimensional photon counting is discussed together with characteristics including linearity and statistical behavior.     

Electrostatic deposition of thoron decay products used for labeling of surface layers

Alpha spectroscopy was used to study the mechanism of electrostatic collection of thoron daughters from the air. The results indicate that ThA atoms are primarily collected on negatively charged surfaces. Atoms of ThB produced by decay of ThA already attached to the collecting surface are injected by recoil into the surface layers of solids and are suitable for use in radiotracer experiments.     

Water-vapor adsorption and surface area measurement of poorly crystalline boehmite

Water-vapor adsorption on poorly crystalline boehmite (PCB) was studied using a gravimetric FTIR apparatus that measured FTIR spectra and water adsorption isotherms simultaneously. The intensity of the delta(HOH) band of adsorbed water changed linearly with water content and this linear relationship was used to determine the dry mass of the sample. Adsorption and desorption isotherms of PCB showed a Type IV isotherm. The BET(H2O) surface area of PCB was 514+/-36 m2/g. The mean crystallite dimensions of PCB were estimated to be 4.5 x 2.2 x 10.0 nm (dimensions along the a, b, and c axes, respectively) based on application of the Scherrer equation to powder diffraction data of PCB. A surface area value of 504+/-45 m2/g calculated using the mean crystallite dimensions was in good agreement with the BET(H2O) surface area. This work also demonstrated a method to determine surface areas for materials with minimal perturbation of their surface structure. In addition, the FTIR spectra of PCB were influenced by changes in water content. The delta(AlOH) band at 835 cm(-1) observed under dry conditions was assigned to the non-H-bonded surface OH groups. As the amount of adsorbed water increased, the intensity at 835 cm(-1) decreased and that at 890 and 965 cm(-1) increased. The 890- and 965-cm(-1) bands are assigned to surface OH groups H-bonded with adsorbed water.     

Development of a mobile radon calibration system at KRISS

Journal of Radioanalytical and Nuclear Chemistry - A mobile radon calibration system was developed with a high-sensitivity radon detector, a movable calibration chamber, and a 226Ra solid source at...     

A simple technique for surface labeling of solids with222Rn and its short-lived decay products

A simple radioactive labeling technique is described which is based on a recoil injection of atoms of²²²Rn and its decay products from a²²⁶Ra source into thin surface layers of solids.     

Consideration of measurement error when using commercial indoor radon determinations for selecting radon action levels

An examination of year-long, in-home radon measurement in Colorado from commercial companies applying typical methods indicates that considerable variation in precision exsts. This variation can have a substantial impact on any mitigation decisions, either voluntary or mandated by law, especially regarding property sale or exchange. Both long-term exposure (nuclear track greater than 90 days), and short-term (charcoal adsorption 4–7 days) exposure methods were used. In addition, periods of continuous monitoring with a highly calibrated alpha-scintillometer took place for accuracy calibration. The results of duplicate commercial analysis show that typical results are no better than ±25 percent with occasional outliers (up to 5 percent of all analyses) well beyond that limit. Differential seasonal measurements (winter/summer) by short-term methods provide equivalent information to single long-term measurements. Action levels in the U.S. for possible mitigation decisions should be selected so that they consider the measurement variability; specifically, they should reflect a concentration range similar to that adopted by the European Community.     

Measurement of the radon exhalation rate from the medium surface by tracing the radon concentration

The paper will present a method based on the accumulation chamber technique for measuring of radon exhalation from the medium surface. A radon monitor traces the change of radon concentration in the accumulation chamber, and then the radon exhalation can be obtained accurately through linear fit. Based on our recent experiments, the radon exhalation rate from the medium surface obtained from this method is in good agreement with the actual exhalation rate of our simulation facility. This method is superior to the competition method which obtains the radon exhalation through the exponential fit by an external PC-system. The calculation for the exponential fit is very easy by computer and related software. However, for portable instruments, the single chip microcomputer can’t calculate the exponential fit rapidly. Thus, this method is usable for developing the new portable instrument to classify building materials, etc.     

Development of a reference measurement procedure for the determination of methylmercury in fish products

The development of an analytical procedure for speciation analysis of methylmercury in fish products is presented. The method is based on high-performance liquid chromatography hyphenated to inductively coupled plasma-mass spectrometry. The metrological approach is stressed out in this paper, in order to provide reliable and comparable results. A complete uncertainty budget has been evaluated and the method has been validated by the use of a certified reference material. Moreover, the detection could rely on the isotope dilution mass spectrometry, a powerful strategy capable of highly accurate results traceable to the “Système International d’Unités” and recognised by the “Comité Consultatif pour la Quantité de Matière” as a primary method of measurement. Presented at MEFNM 2008, September 2008, Budapest, Hungary.     

定容-氧气循环燃烧法测定捕收剂吸附量的方法研究

研究了一种定容-氧气循环燃烧法测定捕收剂吸附量的方法,并与传统的溶剂萃取-分光光度法进行了比较。实验表明,定容-氧气循环燃烧法较溶剂萃取-分光光度法测定油酸钠在磷矿石表面的吸附量更简便,也更准确。     

An automated system for track measurement for the employment of CR-39 as alpha spectrometer in radon and its daughters monitoring

In this work we studied an automated analysis of alpha particle tracks in CR-39, by employing a MITAKA photo-microdensitometer with a C1522 HAMAMATSU Image Analysis System. This system can be used to measure track diameters (with a nominal precision of 0.8 m), superficial track density, and track darkness. This information can be used to determine the alpha particle energies and also their incidence angles (azimuthal and zenithal). The performance of such an automated system, to analyze CR-39 samples which were exposed to alpha particles of known energies, was studied, comparing its response with measurements performed manually by experienced microscopists. The experimental results indicate that the MITAKA/HAMAMATSU system is very reliable for alpha track analysis in CR-39, making possible its use to perform time-consuming measurements in microscopy, as in the case of radon and its daughters surveys.     

Interaction model for the adsorption of organic molecules on the silver surface

Adsorption of organics on a silver surface is simulated. An Embedded Atom Model is used for the metal, a standard force field for the organics, and a combination of the charge equilibration model and the Morse potential for their electrostatic and nonbonding interactions. The only adjustable parameters of this approach appear in the Morse potential. They are tuned to reproduce experimental and high level quantum chemical data. The adsorption energies of 13 molecules on the Ag(111) surface are obtained with an average error of less than 1 kcal mol(-1). The model should be transferable to molecules with the same chemical groups used in regressing the potential parameters when physisorption or weak chemisorption, i.e., no bond breaking, occur, and also to other Ag surfaces. When used to simulate perylene tetracarboxylic acid dianhydride (PTCDA) on Ag(111), correct geometry of mono- and multilayers are observed in molecular dynamics simulations at room temperature.     

Protein adsorption on microporous membranes for plasma separation and its effects on flux decay

The present study elucidates the adsorption characteristics of bovine serum albumin (BSA) on microporous membranes for plasma separation. Based on adso in hydraulic permeability after contact with BSA solutions, the effects of the material and structure of the microporous membranes on adsorption charac resistance increases as BSA solutions are filtered through the microporous membranes. This may result from protein adsorption on the pore walls of the decreases with an increase in BSA concentration and cumulative perfusate volume. The adsorbed amount of BSA and the decreases in filtrate flux are stro and internal structure of the microporous membranes for plasma separation.     

A transportable gamma spectroscopy system applied to the measurement of fission products

Normally, gamma-ray spectroscopy is performed by equipment positioned in the SLOWPOKE-2 Facility at the Royal Military College; however, there have occasionally been requirements for analyses externally. A transportable gamma spectroscopy system was thus assembled by acquiring a commercially available multichannel analyzer, analysis program and detector, and by designing and constructing a transportable shielding castle. It was then used to take measurements of fission product concentrations at several research reactors.     

Screening of silver nanoparticles containing carbonized yeast cells for adsorption of few long-lived active radionuclides

The present study involves the screening of silver nanoparticles containing carbonized yeast cells isolated from coconut cell sap for efficient adsorption of few long lived radionuclides like ¹³⁷Cs₅₅, ⁶⁰Co₂₇, ¹⁰⁶Ru₄₄, ²³⁹Pu₉₄ and ²⁴¹Am₉₅. Yeast cells containing silver nanoparticles produced through biological reduction were subjected to carbonization (400 °C for 1 h) at atmospheric conditions and their properties were analyzed using fourier transform infra-red spectroscopy, X-ray diffraction, scanning electron microscope attached with energy dispersive spectroscopy and transmission electron microscope. The average size of the silver nanoparticles present on the surface of the carbonized silver containing yeast cells (CSY) was 19 ± 9 nm. The carbonized control yeast cells without silver exposure (CCY) did not contain any particles on its surface. The efficiency of CSY and CCY towards the radionuclide adsorption was studied in batch mode at fixed contact time, concentration, and at its native pH. CSY was efficient in removal of ²³⁹Pu₉₄ (76.75%) and ¹⁰⁶Ru₄₄ (54.73%) whereas CCY showed efficient removal only for ²⁴¹Am₉₅ (62.89%). Both the adsorbents did not show any retention with respect to ⁶⁰Co₂₇ and ¹³⁷Cs₅₅. Based on the experimental data, decontamination factor and distribution coefficient (K _d) were calculated and, from the values, it was observed that these adsorbents have greater potential to adsorb radionuclides.     

Bismuth microelectrode system with in situ renewable surface for electroanalysis and adsorption studies

A modified scrape method for preparation of nearly single crystalline bismuth microelectrode with the in situ renewable surface and the corresponding measurement system has been worked out, being a promising replacement of the toxic dropping mercury electrode. The cleaved bismuth capillary electrode (BiCCE) surface is renewed in situ by breaking 320 μm long cylinders onto a top of a capillary. This process can be repeated 150 times for the 5 cm long electrode. The AFM data and electrochemical measurements of pyridine adsorption indicate that the cleaved surface consists mainly of the Bi(1 1 1) single crystal plane areas. The very pure in situ renewable surface enables to measure the zero charge potential at the moment of the electrode cleavage. Some examples of electrochemical detection with the BiCCE are shown like trace metal stripping and flow-injection analysis of some ions and organic compounds.     

The effect of humidity on the accuracy of measurement of an electret radon dosimeter

Test has been conducted for the response of electret radon dosimeters with varying levels of humidity. At a constant value of radon concentration, measured values have been found to increase linearly with increasing humidity, from 30% RH up to a value of 85% RH. On this basis we argue for the establishment of a humidity-dependent calibration factor.     

A simple passive collector for direct measurement of radon flux from soil

A simple technique for measurement of the soil-atmosphere radon flux has been developed by fastening a charcoal canister inside a PVC cylindrical container. This device, which is deployed at the ground surface for approximately 16 hours, captures radon emanating from the soil by adsorption onto the charcoal surface. After recovery of the canister and measurement of the radon daughter activity on a NaI detector, the radon flux may be calculated if the adsorption efficiency of radon onto the charcoal is known. This parameter was determined by exposure of charcoal canisters to²²⁶Ra-spiked barium palmitate filter sources for timed intervals. Since this compound is known to emanate 100% of the²²²Rn generated during radium decay, it forms a useful flux standard. The accuracy of our flux measurements was assessed by comparison to a more established technique, the enclosed-chamber or accumulator method. Concentration measurements were made for the chamber over a less than 2-hour period while the canister flux measurements were based on single overnight deployments. The experiment was repeated 5 times at two different sites and the two techniques generally agreed within a 95% confidence interval.