A search for new massive particles

We have searched for an almost stable, charged particle produced in 400 GeV proton-nucleus collisions. A total of 5 × 10¹⁰ light secondary particles were sampled in a secondary beam of 70 GeV/c momentum. If a 4.5 to 6.0 GeV mass particle is produced with a cross section comparable with the production cross section of the upsilon then this experiment places an upper limit on the lifetime of such a particle of about 5 × 10^?8 s.     

Measurement of filtration efficiency of Nuclepore filters challenged with polystyrene latex nanoparticles: experiments and modeling

Membrane filtration has been demonstrated to be effective for the removal of liquid-borne nanoparticles (NPs). Such technique can be applied to purify and disinfect drinking water as well as remove NPs in highly pure chemicals used in the industries. This study aims to study the filtration process of a model membrane filter, the Nuclepore filter. Experiments were carried out using standard filtration tools and the nanoparticle tracking analysis (NTA) technique was used to measure particle (50–500 nm) concentration upstream and downstream of the filter to determine the filtration efficiency. The NTA technique has been calibrated using 150-nm polystyrene latex particles to determine its accuracy of particle concentration measurement. Measurements were found reliable within a certain concentration limit (about 10⁸–10¹⁰ particles/cm³), which is dependent on the camera settings during the measurement. Experimental results are comparable with previously published data obtained using the aerosolization method, validating the capability of the NTA technique. The capillary tube model modified from that developed for aerosol filtration was found to be useful to represent the experimental results, when a sticking coefficient of 0.15 is incorporated. This suggests that only 15% of the particle collisions with the filter results in successful attachment. The small sticking coefficient found can be explained by the unfavorable surface interactions between the particles and the filter medium.     

Multiple light scattering from a moving layer of Brownian particles: comparison with a rigid phase screen

Abstract

The temporal fluctuations in the intensity of light scattered by a moving layer of emulsions and suspensions containing Brownian particles are investigated experimentally, and a comparison is made with light scattered by a translating phase screen. The intensity fluctuations of the scattered light are detected through an imaging system, which collects the light emanating only from a limited volume in the medium. The effect of translational motion of the particle layer on the decay rate of the autocorrelation function of intensity fluctuations depends on the illuminating form of a laser beam and on the point spread function of the imaging system. The Brownian motion of the particles causes the scattered light to fluctuate more rapidly than that arising from the translating phase screen. In the multiple-scattering regime, the influence of this diffusional motion increases with an increase of the particle concentration in the layer.     

Aerosol Charge Neutralization by a Radioactive Alpha Source

The performance of a Po-210 radioactive ionizer for aerosol charge neutralization and bipolar charging has been evaluated. Monodisperse neutral and singly charged aerosols have been passed through the ionizer and their approach to the steady-state Boltzmann charge measured by measuring the fraction of particles that are electrically charged. The result shows that an Nt of approximately 2.5 × 10⁵ cm^?3 s is needed for the development of a steady-state charge fraction equal to that given by the Boltzmann' s law where N is the ion concentration and t is the residence time of the aerosol in the neutralizer. In addition, the performance of the ionizer for particle charge neutralization in a vibrating-orifice aerosol generator has been evaluated and the result shows that the source is less effective for this application and the residual charge on the particles is considerably higher than that given by the Boltzmann's law.     

Dynamic Light Scattering Measurement of Nanometer Particles in Liquids

Dynamic light scattering (DLS) techniques for studying sizes and shapes of nanoparticles in liquids are reviewed. In photon correlation spectroscopy (PCS), the time fluctuations in the intensity of light scattered by the particle dispersion are monitored. For dilute dispersions of spherical nanoparticles, the decay rate of the time autocorrelation function of these intensity fluctuations is used to directly measure the particle translational diffusion coefficient, which is in turn related to the particle hydrodynamic radius. For a spherical particle, the hydrodynamic radius is essentially the same as the geometric particle radius (including any possible solvation layers). PCS is one of the most commonly used methods for measuring radii of submicron size particles in liquid dispersions. Depolarized Fabry-Perot interferometry (FPI) is a less common dynamic light scattering technique that is applicable to optically anisotropic nanoparticles. In FPI the frequency broadening of laser light scattered by the particles is analyzed. This broadening is proportional to the particle rotational diffusion coefficient, which is in turn related to the particle dimensions. The translational diffusion coefficient measured by PCS and the rotational diffusion coefficient measured by depolarized FPI may be combined to obtain the dimensions of non-spherical particles. DLS studies of liquid dispersions of nanometer-sized oligonucleotides in a water-based buffer are used as examples.     

高浓度超细颗粒的后向光子相关光谱测量技术研究

针对光子相关光谱颗粒粒径测量法不能在线测量高浓度超细颗粒的问题,通过分析溶液浓度对光子相关光谱测量法的影响,设计了一种后向散射光路,提出了后向光子相关光谱测量法.实验采用50 nm、100 nm以及500 nm三种标准乳胶球颗粒,在不同的浓度下分别用两种方法进行了测试.结果证明,后向光子相关光谱测量法能有效抑制多重散射的影响,适用于高浓度超细颗粒粒径的在线测量.     

Die Anlagerung von radioaktiven Atomen und Ionen an Aerosolteilchen

The attachment of radioactive atoms and ions to spherical aerosol particles has been studied theoretically. For uncharged atoms the deposition is considered to be solely governed by thermal diffusion. With calculations based on the “limiting-sphere”-method ofArendt-Kallman it is found, that the attached activity is proportional toΦ ² for aerosol particle diametersΦ smaller than 0.1 μm, and proportional toΦ forΦ greater than 1 μm. For charged ions the diffusion process is modified by the influence of electrostatic forces between the diffusing ions and the aerosol particles. In the frequently occurring case of a symmetrically bipolar charged aerosol this influence can be expressed by a functionG _p(Φ), which depends on the diameterΦ and the effective numberp of elementary charges on the aerosol particle. For an aerosol particle diameterΦ greater than 0.1 μm the attached activity is proportional toΦ ^1.1, and forΦ smaller than 0.01 μm it is proportional toΦ ^1.55. The effects of neglecting various terms in the calculation are considered. The distribution of natural radioactivity on atmospheric aerosols has been calculated for various particle size distributions according toJunge. The calculation shows that about 90% of the total natural activity should be attached to particles smaller thanΦ=0.5 μm, and about 35% to particles smaller thanΦ=0.1 μm. The time T_1/2, in which the concentration of the radioactive particles decreases to half the initial value, depends on the concentration of the aerosol particles and on their size distribution. For 10⁴ aerosol particles per cm³ and the size distributions mentioned,T _1/2 varies between 15 and 30 seconds for radioactive ions. For radioactive atomsT _1/2 is greater than it is for ions in the range of aerosol particle diameters belowΦ=0.25 μm, and smaller ifΦ greater than 0.25 μm.     

Signal processing system in cavity enhanced spectroscopy

The paper presents a signal processing system used for nitrogen dioxide detection employing cavity enhanced absorption spectroscopy. In this system, the absorbing gas concentration is determined by the measurement of a decay time of a light pulse trapped in a cavity. The setup includes a resonance optical cavity, which was equipped with spherical and high reflectance mirrors, the pulsed diode laser (414 nm) and electronic signal processing system. In order to ensure registration of low-level signals and accurate decay time measurements, special preamplifier and digital signal processing circuit were developed. Theoretical analyses of main parameters of optical cavity and signal processing system were presented and especially signal-to-noise ratio was taken into consideration. Furthermore, investigation of S/N signal processing system and influence of preamplifier feedback resistance on the useful signal distortion were described. The aim of the experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO₂ sensor which could replace, e.g., commonly used chemical detectors. Thanks to the developed signal processing system, detection limit of NO₂ sensor reaches the value of 0.2 ppb (absorption coefficient equivalent = 2.8 × 10⁻⁹ cm⁻¹).     

Search for highly charged particles in cosmic rays

The recently obtained results on e⁺e^? → hadrons and multigamma production in pp collisions provide some support for a previously made argument that heavy, highly charged subnucleons may exist, and a search for such particles in cosmic rays has been made. In 620 hours no candidates were detected, and an upper limit for the unaccompanied particle flux of 7 · 10^?10 cm^?2 sec^?1 sr^?1 at sea level under 600 g/cm² concrete is obtained with 90% confidence.     

Fractal Character of Dynamic Light Scattering of Particles

Dynamic light scattering signals from particles, exhibit fractal characteristics. This feature can be used to determine the particle size. The use of the fractal dimension, as a quantitative method to analyze the properties of dynamic light scattering signals from submicron particles, is presented. The analysis is performed directly on the time‐resolved scattered intensity, and the Box Dimensions of light scattering signals of particles with diameters 100, 200, 500 and 1000 nm. The experimental results show that the fractal dimensions of light scattering signals correlate well with particle size. In the submicron size range, the smaller the particles, the larger their fractal dimensions. Compared with the PCS technique, only several hundreds of samples are required in the fractal method. Therefore, the data processing is easily accomplished. However, this method only provides the mean particle size, but not the particle size distribution.     

A Theoretical and Experimental Study of the Total Light Scattering Technique for particle size analysis

The total light scattering method for particle size measurement has a series of outstanding features, e.g. very simple instrumental arrangement, no serious requirements for its optical, photodetecting and electronic systems and its ease of use. Nevertheless, some problems still remain unsolved which should be dealt with to improve its further applications. An improvement has been made in this work. Comprehensive theoretical studies showed that this method is applicable to particle size analysis in the range 0.1–10 μm, i.e. for those particles whose diameter lies between the lower limit of the diffraction method and the upper limit of photon correlation spectroscopic (PCS) technique. Experimental studies with different monodisperse polystyrene latex spheres as standard reference material give good agreement with their nominal values.     

Screening of excitonic states by low-density 2D charge carriers in GaAs/AlGaAs quantum wells

Screening of excitonic states by a system of 2D electrons (or holes) in GaAs/AlGaAs single quantum wells is studied. With increasing concentration of 2D charge carriers, a threshold-type disappearance of excitonic states is observed in both luminescence and reflectance spectra. The higher the quality of the 2D system, the lower the corresponding threshold concentration. In the best systems, the collapse of excitonic states occurs at unexpectedly low electron densities n _e =5×10⁹ cm^?2, which correspond to the mean dimensionless distance between the particles r _s =8. This value far exceeds the threshold values observed for 3D systems (r _s ≈2), as well as the values obtained for quantum wells in previous studies. The problem of measuring the concentration of low-density 2D charge carriers in photoexcitation conditions is solved by applying the method of optical detection of the dimensional magnetoplasma resonance. This method provides reliable measurements of the density of a 2D system to the values about 10⁹ cm^?2.     

Influence of annealing on the concentration profiles of boron implantations in silicon

The influence of annealing on the concentration profiles of boron implanted into silicon with does of 10¹⁴ ions/cm² up to 10¹⁶ ions/cm² and an energy of 70 keV was studied. The concentration profiles were measured with Secondary Ion Mass Spectrometry (SIMS). The broadening of the concentration profiles during annealing can be described as a superposition of effects resulting from a relatively immobile and a mobile boron fraction. The properties of the immobile boron fraction were studied by measuring the influence of a boron implantation on the distribution of a homogeneous boron background dope. From these experiments it was concluded that the immobile boron fraction consists of boron precipitates. The properties of the mobile fraction were studied from concentration profiles that were obtained after annealing during different periods at the same temperature. It was found that during the initial stage of the annealing process a fast broadening of the profile occurs; this was assumed to be due to an interstitial type boron diffusion. After prolonged annealing the much slower substitutional type diffusion prevails, due to trapping of the interstitial boron atoms by vacancies. The reliability of the SIMS method, as applied to profile measurements, was checked for the high boron doses used in this investigation. Excessive boron precipitates, obtained after annealing of a high dose, such as 10¹⁶ ions/cm² at about 1000°C, appear to give some increase of the ion yield.     

Die Anlagerung radioaktiver Atome an Aerosole (Schwebstoffe)

The attachment of the decay products of thorium emanation to aerosol particles has been studied. The dependence of the attached activity on the particle size was determined for spherical particles with radiiR ranging from 0·04 to 0·6 microns. The particles used were homogeneous dioctylphthalate droplets and polystyrene micro-spheres. It is found that the attached activity is proportional toR ²/(1+hR). This dependence can be derived theoretically by considering the deposition to be solely governed by the diffusion process (not by electrostatic forces) and assuming a quasi-stationary density distribution for the diffusing atoms. The constanth is uniquely determined by the average gaskinetic velocity and the diffusion constant of the diffusing atoms. For the decay products of thorium and radium emanation (atomic weight ≈210)h ≈ 7 · 10⁴ cm^?1. The derived equation holds for a wide range of particle sizes: For the particles with radii larger than about 10^?4 cm this means that the attachment is proportional to the radius; for particle radii below about 10^?6 cm it is proportional to the surface (R²) of the particles. It is also possible to derive an expression for the time-dependence of the attachment process from the theoretical considerations. The rate at which the average concentration of the radioactive atoms decreases is proportional to exp ?t/τ where τ=1+hR/πR² N¯ v (¯ v=average gaskinetic velocity of the diffusing atoms;N=aerosol concentration).     

Measurements on Particle Size Distribution and Concentration by Transmission Fluctuation Spectrometry with Temporal Correlation

Transmission fluctuation spectrometry with temporal correlation (TFS‐TC) is a new method for particle analysis. When a narrow light beam irradiates on a particle dispersion flow, the variation of the number of particles in the small measuring zone will cause the transmitted light to fluctuate, which includes the complete information on both particle size distribution (PSD) and particle concentration. The method may be used for real‐time, inline/online applications due to its simplicity of measuring principle and experimental setup. Until recently, the theory has been limited to low particle concentrations. In this work, an experimental study of the TFS‐TC measurement is presented for a very wide range of the particle concentrations. By introducing an empirical correction including the high concentration effects and considering the effect from rheological conditions in the inversion algorithm, the particle size distribution and particle concentration are reconstructed, resulting in the coverage of a broad range of particle size and concentration.     

The Physical Nature of Mesoscopic Inhomogeneities in Highly Diluted Aqueous Suspensions of Protein Particles

The dispersed composition of water samples prepared by the multiple-dilution technique has been investigated opto-physically using two laser diagnostics methods: dynamic light scattering and laser phase microscopy. We studied suspensions of antibodies (Ab) to the human interferon-gamma (IFNγ) in water with an initial concentration of 0.125 mg ml^?1 (5×10¹⁴ mol cm^?3), which were subjected to 12 successive 100-multiple volume dilutions (C12) in water. Individual antibodies and particles of about 300 nm in size, which can be considered as aggregates of individual antibodies, have been found in the initial suspensions. It turned out that some mesoparticles with a concentration on the order of 10³ cm^?3 exist also in suspensions subjected to C12 dilution. These particles have a refractive index close to typical values of protein refractive indices. A possible explanation of the origin of particles with sizes on the order of several hundreds of nanometers, revealed in highly diluted suspensions, is proposed. On the one hand, some of these particles may be aggregates of antibodies from the initial suspension, which remained (due to the flotation effect) in the bulk of the liquid after dilutions. On the other hand, the appearance of solid contaminant particles at the same mesoscopic scale (i.e., on the order of several hundreds of nanometers) cannot be excluded in the dilution process.

     

Determination of Particle Size Distribution by the analysis of intensity-constrained multi-angle photon correlation spectroscopic data

Laser light scattering (LLS), especially dynamic laser light scattering (DLS), also known as photon correlation spectroscopy (PCS), is a well established method for particle size distribution analysis. It usually involves a Laplace inversion of the field autocorrelation function. However, the resolution is limited because of the ill-conditioned nature of this Laplace inversion. No unique solution exists when noise is present on the data. In contrast with this ill-conditioned nature, the angular dependence of scattered (static) intensities is precisely not ill-conditioned, which allows the resolution of the ill-conditioned inversion of DLS data to be improved. In order to characterize samples with more complicated size distributions, an intensityconstrained multi-angle PCS data analysis program has been developed, which is an alternative way of normalizing the field correlation function to that reported by Cummins and Staples [12]. In this program, the field autocorrelation function is normalized to the scattering intensity by using a predetermined coherent factor at each angle, which provides an additional constraint on the Laplace inversion of multi-angle PCS data analysis. The alternative analysis improves the resolution of PCS and provides a more reliable particle size distribution than single-angle data analysis. Both simulated and measured LLS data are used to illustrate its application, resolution and limitations.     

Determination of aerosol extinction coefficient and mass extinction efficiency by DOAS with a flashlight source

With the method of differential optical absorption spectroscopy （DOAS）, average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter （SPM）. Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency （MEE） to be possible in the lower troposphere. The average MEE value is about 7.6m^2.g^-1 , and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.     

First dark matter search results from the PandaX-I experiment

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China JinPing Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, 3.7 × 10^?44 cm², for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49GeV/c² at 90% confidence level.     

Untersuchung von Raumladungsschichten an Zinkoxid-Oberflächen mit Hilfe der Elektroreflexion

Using the electroreflectance method space charge layers on crystals of different conductivities have been identified. The space charge layers were formed by adsorption of oxygen or atomic hydrogen. The limit of sensitivity required the irradiation with 5×10¹³ photons/cm²×sec of band gap energy. After exposure to atomic hydrogen all samples showed accumulation layers. With a partial pressure of oxygen above 350 mm Hg crystals of high conductivity (σ=47 ohm^?1 cm^?1) exhibit depletion layers, which change into accumulation layers, if the partial pressure is reduced below the limit. Crystals of a lower conductivity (σ=10^?3–10^?1 ohm^?1 cm^?1) show accumulation layers up to the highest applied oxygen pressure of 760 mm Hg. The phenomena are attributed to a dynamical equilibrium between adsorption and photo-desorption of oxygen. This equilibrium depends on oxygen pressure and free carrier concentration. By comparing a calculated curve with the experimental results the value of 3.31 ev is obtained for the energy gap, light polarized perpendicular to thec-acis.