Fraction of the positive 218Po and 214Pb clusters in indoor air.

The fraction of the positively charged unattached radon decay products, 218Po and 214Pb in indoor air was determined by model calculations. The results of the calculations were confirmed by measurements in a test chamber (volume: 8 m3). The fraction of both radionuclides depends on the attachment parameter (S(1)) and the neutralisation rate (nu) in room air. The total removal parameter S1 = lambda1 + v + q(f) + X = lambda1 C1f/C0 considers the attachment rate to aerosol particles (X), plate-out rate to room surfaces (q(f)) and the ventilation rate (nu) (lambda1: decay constant of 218Po). The S1-value of room can be determined by measurement of the concentration of the unattached 218Po clusters (C1f) and radon (C0). The neutralisation rate (nu) in environmental air depends mainly on the ion production rate. The influence of the relative humidity in the range 30-95% (temperature: 20 degrees C) is negligible. In addition, equal neutralisation rates for 218Po and 214Pb could be derived. In room air with ion production rates between 5 and 500 nC kg(-1) h(-1) mainly generated by the alpha emitters of radon, thoron and their short-lived decay products, the fractions for positive 218Po clusters vary between 55 and 17% and for 214Pb clusters between 53 and 14%. For a typical average concentration of radon (50 Bq m(-3)) and thoron (10 Bq m(-3)) in homes, 48% of 218Po clusters and 45% of 214Pb clusters are positively charged.

Determination of neutralisation rates of 218Po ions in air.

The electric charge of the radon decay product, 218Po, has an influence on its mobility characterised by the diffusion coefficient, which chiefly controls the formation of the radioactive aerosol by attachment and the plateout processes on surfaces. These processes strongly affect the dose relevant quantities like concentration and particle size distribution of the short-lived radon decay products. The neutralisation rate of the positive 218Po ions in environmental air was determined quantitatively in chamber experiments. The experimental results show the great influence of the ionisation rate and the humidity concentration on the neutralisation rate of the 218Po ions in air. The obtained neutralisation rates were described by equations, taking into account the neutralisation processes like ion recombination, charge transfer and electron scavenging. In 'normal' environmental air with an ionisation rate of 45 muR.h(-1) = 1.16 x 10(-8) C/(kg.h) and a relative humidity of 50% (T = 20 degrees C), a neutralisation rate of the 218Po ions of 1.54 x 10(-2) s(-1) was obtained. Taking into account this neutralisation rate leads to a fraction of about 51% of the Po cluster that are neutral in air.

Physical parameters and dose factors of the radon and thoron decay products.

The dose per exposure unit of the short-lived radon and thoron decay products was calculated using a dosimetric approach. The calculations are based on a lung dose model with the structure that is related to the ICRP 66 respiratory tract model. The dose relevant parameters, unattached fraction of the decay product clusters (fp) and size distribution of the unattached and aerosol-attached decay products for different living and working places are reported. Taking into account these characteristics the dose conversion factors (DCF) of the radon and thoron decay products were estimated. In addition, the living and working places were divided concerning their aerosol parameters like particle number concentration and activity size distribution.

Observation of hot-electron pressure in the vibration dynamics of metal nanoparticles

We investigate the vibration dynamics of ellipsoidal silver nanoparticles, using time-resolved optical pump-probe spectroscopy. When excited with femtosecond laser pulses, the particles execute anisotropic shape oscillations. We show that these vibrations are triggered by the thermal expansion of the optically heated particles. The time dependence of the vibrations indicates that this expansion is caused by two mechanisms: The lattice anharmonicity and the extremely large pressure of the hot conduction electrons.

Radon: characteristics in air and dose conversion factors.

The dose conversion factor (DCF) which gives the relationship between effective dose and potential alpha energy concentration of inhaled short-lived radon decay products is calculated with a dosimetric approach. The calculations are based on a lung dose model with a structure that is related to the new recommended ICRP respiratory tract model. The characteristics of the radon decay products concerning the unattached fraction and the activity size distribution of the radon decay products are important input quantities for the calculation of DCF. Experimental data about these parameters obtained from measurements in homes, at working places, and in the free atmosphere at ground level in the last past years are summarized. Taking into account the measured aerosol characteristics the DCF fractions of the unattached (DCFu) and aerosol-attached (DCFae) radon decay products for different places were calculated. Variation of DCF for different places were caused dominantly by the variation of DCFu of the unattached radon clusters (0.3-32 mSv WLM(-1)). Nose inhalation drastically reduced (about a factor 4) the dose contribution by the unattached cluster. The dose fraction by the radon decay product aerosol (DCFae) varies between 4-10 mSv WLM(-1). Taking into account a relative sensitivity distribution between bronchial, bronchiolar and alveolar regions of the thoracic lung with 0.80:0.15:0.05 and nose breathing the DCF of most of the working places (inhalation rate: 1.2 m3 h(-1)) vary between 5.7-6.7 mSv WLM(-1) depending on the number concentration of the aerosol particles. The DCF-value of 4.2 mSv WLM(-1) for the general public in dwellings with higher aerosol concentration (>4 x 10(4) particles cm(-3)) has about the same value as recommended by ICRP 65 (1994b). Significantly higher are the DCF-values for "normal" aerosol conditions indoors (5 x 10(3)-4 x 10(4) particles cm(-3)) and in the open air (7.3 mSv WLM(-1) and 9.7 mSv WLM(-1)).

Radiation risk estimation based on activity measurements of zirconium oxide implants.

Implants made form zirconium dioxide exhibit higher specific radionuclide activities of the uranium-radium and thorium series than metallic and aluminum implants. This study presents data on activity measurements performed on different samples of ZrO2 raw material (powder) and on the ceramic joint heads belonging to it to formulate a correlation between the specific radionuclide activities of the uranium-radium and thorium series in the raw material, the flux density of the alpha particle leaving the implant surface, and the annual dose of the tissue surrounding the implant. Based on this experimental study, an equation for defining the limits of the specific activities in raw material is proposed, taking into account the long-lived radionuclides (key nuclides) of the uranium-radium and thorium series weighted with their relative dose contributions from alpha emitters.

Daily variation of the radon concentration indoors and outdoors and the influence of meteorological parameters.

Series of continuous radon measurements in the open atmosphere and in a dwelling, including the parallel measurement of meteorological parameters, were performed over a period of several weeks. The radon concentration in indoor and outdoor air depends on meteorological conditions. In the open atmosphere the radon concentration varies between 1 and 100 Bq m-3, depending on weather conditions and time of day. During time periods of low turbulent air exchange (high pressure weather with clear night sky), especially in the night and early morning hours (night inversion layer), the diurnal variation of the radon concentration showed a pronounced maximum. Cloudy and windy weather conditions yield a small diurnal variation of the radon concentration. Indoors, the average level and the diurnal variation of the indoor radon concentration is also influenced by meteorological conditions. The measurements are consistent with a dependence of indoor radon concentrations on indoor-outdoor pressure differences.

"Unattached" fraction of short-lived Rn decay products in indoor and outdoor environments: an improved single-screen method and results.

The unattached fraction fp of potential alpha energy of short-lived Rn decay products was measured under realistic, natural conditions in different dwellings and in the open atmosphere by a single-screen technique. An improved data evaluation method was developed where the measured activities of 218Po (RaA) and 214Pb (RaB) were corrected by the screen-attached activities of 214Bi (214Po) [RaC (RaC')]. This method is based on the experimental observation that the 214Bi (214Po) unattached activities are negligible under realistic living conditions and that the size distributions of the aerosol-attached activities of all short-lived Rn daughters are identical. In closed rooms without additional aerosol sources, a mean unattached fraction fp of the potential alpha energy of 0.096 was obtained at a mean aerosol particle concentration of 6100 cm-3 and at a mean equilibrium factor F of 0.30. This mean fp value is about three times higher than the value used in the literature for the radiation exposure calculation of the human public. In closed rooms with additional aerosol sources (cigarette smoke, heating systems, aerosols from a burning candle), the aerosol particle concentrations ranged up to 10(6) cm-3 and the attachment rates, X, increased up to 1000 h-1. The fp values sometimes decreased below the detection limit of 0.005, and the F values increased to as high as 0.77. In the ambient atmosphere in the vicinity of Göttingen, a mean unattached fraction fp of 0.02 and a mean aerosol particle concentration of 3.4 x 10(4) cm-3 were measured at 1 m above the ground. The mean equilibrium factor F was determined to be 0.7.

Measurements of the unattached fractions of radon daughters in houses.

Results are presented of the influence of the particle concentration on the activity concentrations of the attached and unattached shortlived radon daughters. The measurements were carried out in rooms of houses in Southern Germany with radon activity concentrations in the range of 150-900 Bqm-3. Consideration of the F factor and the fraction of the unattached daughters fp and comparison with theoretical predictions is one part of the data evaluation. In low (v less than 0.3 h-1) and moderate (0.3 h-1 less than v less than 1 h-1) ventilated rooms the particle concentrations (3*10(-3) - 4*10(4) cm-3), F values (0.2 - (0.2 - 0.3) and the unattached fraction fp (0.05-0.15) were measured. Only rooms with higher particle concentrations or with larger particle sizes due to special aerosol sources (cigarette smoke, cooking, stove heating) showed fp-values less than 0.05. In a second part the attachment rate, the plateout rates and the average attachment diameters of the room aerosols were derived from the measured data by model calculations.

[Investigations on the stability of droplets from medical jet and ultrasound aerosol atomizers (author's transl)]. / Untersuchungen zur Beständigkeit von Tröpfchen medizinischer Düsen- und Ultraschal-Vernebler.

The droplet size distribution of aerosols is not only determined by the process of aerosol production. After generation of an aerosol its spectrum undergoes very rapid changes due to vaporization and condensation process, that result in a spectrum depending on type and concentration of the used medicament and the partial pressure of water vapour in the vicinity of the droplets. The resulting spectrum is measured and calculated.

The cytotoxic action of leucocidan from Pseudomonas aeruginosa on human polymorphonuclear leucocytes.

Human polymorphonuclear leucocytes treated in vitro with leucocidin from Pseudomonas aeruginosa underwent characteristic morphological alterations as shown by phase-contrast and scanning electron microscopy. Within a few minutes of exposure to leucocidin the granulocytes became round, and protoplasmic extrusions appeared on the cell membrane, were withdrawn again and put out at another point of the cell. The final stage of the leucocidin-treated leucocyte was an enlarged, rounded vesicle with apparently intact plasma membrane. Omission of calcium ions from the diluting buffer caused certain differences in the morphologic appearance of the damaged leucocytes.

[Collimators for whole body counter enabling localization]. / Kollimatoren für einen Ganzkörperzähler zur Lösung von Lokalisationsproblemen

For the four 6 inches times 4 inches NaJ/Tl-crystals of a whole-body-counter several collimators were developed to perform not only counting but also localization. In respect of their good response, a 19-hole-collimator and several slit-collimators were designed. The geometrical dimensions were chosen in such a way that in a profile-scan one can distinguish between the right and the left side of the body. The physical characteristics, such as plane-source-response, spatial resolution, especially at high gamma-ray-energies, were obtained by analysing line-source-functions [4]. The results show that the advantages of using larger crystals are an increase of focal distance, higher sensitivity and adaptibility to high-energy-gamma-ray emitters. In consequence it is possible to decrease body burden of the patients and to use radionuclides normally not applicated in clinical routine scintigraphy.

Experiments on the formation of particles by chemical reactions in the dark and under influence of light.

Some experiments concerning the photochemical production of condensation nuclei are described. Preliminary measurements of filtered atomospheric air, initially free of particles yielded high concentrations of particles by reactions in the dark when the air was previously irradiated by sunlight. In further investigations a definite composition of pure gases was used. The formation of nitric acid particles from NO2 in pure nitrogen of different relative humidities in the dark and under influence of light was investigated. No particle formation was found which could be correlated to any production of nitric acid nuclei. Even within a spectral region in which photolysis of NO2 takes place no HNO3-nucleation could be found. The particles detected under certain conditions of irradiation originate from impurities in the walls of the reaction chamber. Particle growth in an irradiated mixture of N2 and NO2 with benzene is demonstrated and the mean radius of particles is calculated from measurement with a diffusion battery.