Positrons annihilation method

The values of Df and dh for studied compositions HDPE+Z in table 1 are cited. The value dh can be compared with corresponding experimental data obtained by positrons annihilation method. For HDPE at 7=323 K experimental value is (4 6,8 A [14], This value dh corresponds well enough with corresponding calculated values dh cited in table 1. 

Despite all simplifications the model of particle in the rectangular potential well, extended to include the population of excited le els. describes quite well the dependence of ortho-positronium lifetime on the pore radius. In this model the o-Ps lifetime is ruled entirely by geometrical factors, however, maybe the chemical composition of the medium should be taken into account. The lifetime vs. average radius dependence is particularly steep below 5 nm. and in this range the positron annihilation method can be useful for determination of average pore radii. The specific surface determines the distribution of o-Ps between small voids in the bulk and pores. 

The positron annihilation method like the small angle scattering techniques is suitable in characterization of closed pores which are inaccessible for adsorbate molecules in classic experiments, like adsorption, mercury intrusion or thermoporometry. 

Let us consider, which processes result to necessary for yielding realization fluctuation free volume increasing. Theoretically (within the frameworks of polymers plasticity fractal concept [35] and experimentally (by positrons annihilation method [22]) it has been shown, that the yielding pro-... 

Positron annihilation methods have been used extensively in studies of the microstructure and physical and chemical properties of polymers [113-119], polymer blends [9-62], and recently polymer-based nanocomposites [120,121]. 

The other method for quality assurance inspection of pellet wt in the primer eliminates the need for a comparator oxygen-containing standard. Here, the Cu in the cup-anvil combination in the primer is used as an internal standard by comparing the 0.511 MeV positron annihilation radiation from 62Cu produced by the 63Cu(n,2n)62Cu reaction to the 6.1 MeV 7 from l6N produced by oxygen activation. In this case the actual determination of pellet wt is not required the ratio of Cu to O, which should be fixed for a pro-... 

In this work positron annihilation lifetime spectroscopy (PALS) was used to investigate structural diversity inside zeolite precursor matrix caused by the presence of alkali cations Na, K, Rb and Cs. PALS is an established and well-proven method for structural investigations of various materials, extensively used for metals and alloys, semiconductors and porous materials [3, 4]. In the investigations of zeolites PALS has been mostly used for their void structure and size study [5, 6, 7, 8], also in correlation to... 

Improvements in current, established technologies and the introduction of new ways to test materials, nondestmctively are expected to continue apac. One promising method is positron annihilation. The positron is the antiparticle of the electron thus apositron/electron pair is unstable and will annihilate. In this process, two gamma rays at approximately 180 to one another are emitted from the center of the mass of the pair. A very slight departure from 180° is directly proportional to the transverse component of the momentum, of the pair. The momenta of the electrons involved in such collisions can be calculated from the geometry and intensity of the gamma rays. The dynamics of the clcctron/positron system underlie the use of the technique for the study of defects in materials,... 

Positron annihilation lifetime spectroscopy (PALS) provides a method for studying changes in free volume and defect concentration in polymers and other materials [1,2]. A positron can either annihilate as a free positron with an electron in the material or capture an electron from the material and form a bound state, called a positronium atom. Pnra-positroniums (p-Ps), in which the spins of the positron and the electron are anti-parallel, have a mean lifetime of 0.125 ns. Ortho-positroniums (o-Ps), in which the spins of the two particles are parallel, have a mean lifteime of 142 ns in vacuum. In polymers find other condensed matter, the lifetime of o-Ps is shortened to 1-5 ns because of pick-off of the positron by electrons of antiparallel spin in the surrounding medium. 

Since the mid-1980s a new and radically different method of studying positron annihilation in gases has been developed by Surko and coworkers. 

K. Saarinen, P. Hautojdrvi, and C. Corbel, Positron Annihilation Spectroscopy of Defects in Semiconductors R. Jones and P. R. Briddon, The Ab Initio Cluster Method and the Dynamics of Defects in Semiconductors... 

The areas of inorganic and organic positron chemistry deal mainly with material characterization and industrial applications using PAS. Both chemical and electronic industries have found PAS to be a powerful method. In addition to the traditional solution chemistry of the positron and Ps [11], PAS has been developed to determine the free volume Bom-Oppenheimer approximation, such as molecular solids [14] and polymers [15]. The unique localization property of Ps in free volumes and holes has opened new hope in polymer scientific research that determination of atomic-level free volumes at the nanosecond scale of motion is possible. During the last ten years, most positron annihilation research has involved a certain amount of polymer chemistry, polymers and coatings, which will be discussed in Chapters 12 and 13. For inorganic systems, oxides are mostly studied using the positron and Ps. Silicon oxides and zeolites are the most important systems in positron and Ps chemistry. The developments in this area have on the cavity structure and chemical states of inner surfaces. Chapters 8 and 14 will discuss this subject. 

The data and methods discussed in the previous sections show the power of positron and positronium annihilation methods for the characterization of porous materials and low-k dielectrics in particular. The obvious question is, whether this power can be harnessed for an online diagnostic tool in a semiconductor production line. Such a tool should be reliable, compatible with existing processes, rapid, and not more complex than any other system. 

Gregory, R.B. and Zhu, Y. (1990) Analysis of positron annihilation lifetime data by numerical laplace inversion with the program CONTIN , Nucl. Instrum. Methods Phys. Res., Sect. A 290,1172. 

The calculation of PAES intensities largely reduces to the calculation core annihilation probabilities for positrons in the surface state [11]. This follows from the fact that almost all of the core hole excitations of the outer cores relax via Auger emission and that almost all of the positrons incident at low energies become trapped in a surface state before annihilation. First-principles calculations of the positron states and positron annihilation characteristics at metal and semiconductor surfaces are based on a treatment of a positron as a single charged particle trapped in a "correlation well" in the proximity of surface atoms. The calculations were performed within a modified superimposed-atom method using the corrugated-mirror model of Nieminen and Puska [12]. 

The objectives of this research are basically two firstly, to analyze the use of positron annihilation lifetime spectroscopy to the study of carbon materials with high surface area and, secondly, to get a correlation between the parameters observed in PALS experiments and the results obtained in the characterization of porous materials by well-known methods like gas adsorption and Small Angle X-Ray Scattering (SAXS). 

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