• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.367-373
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• 2011

It is described that the proton beam induces micro defects and electronic deep levels in Cz single crystal silicon. Enhance signal-to-noise ratio, Coincidence Doppler Broadening Positron Annihilation Spectroscopy has been applied to study of characteristics of p type and n type silicon samples. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S, defined as the ratio between the amount of counts in a central portion of the spectrum and the total counts of whole spectrum. The samples were exposed by 4.0 MeV proton beams ranging from 0 to ${\sim}10^{14}$ ptls. The S-parameter values were increased as increasing the irradiated proton beam, that indicated the defects generate more.

• Korean Journal of Materials Research
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• v.16 no.7
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• pp.455-459
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• 2006

Coincidence Doppler Broadening (CDB) of positron annihilation spectroscopy was applied to analyze defects in the chemical state of Department of Physics, $Gd_2O_2S$:Tb intensifying screens. The screen samples were irradiated by 80 MV X-rays in hospital and were used for 0, 2, 4, and 6 years respectively. There was a positive relationship between the S-parameter values and time of exposure to X-rays. Most of the defects were indicated to have been generated by X-rays. A 1D CDB was developed in order to reduce the background noise, and the S-parameter values of the $Gd_2O_2S$:Tb intensifying screens, using the 1D CDB, varied between 0.4974 and 0.4991.

• Journal of the Korean Vacuum Society
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• v.17 no.4
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• pp.311-316
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• 2008

Since the presence of the chemical impurities and defect at surfaces and interfaces greatly influence the properties of various semiconductor devices, an unambiguous chemical characterization of the metal and semiconductor surfaces become more important in the view of the miniaturization of the devices toward nano scale. Among the various conventional surface characterization tools, Electron-induced Auger Electron Spectroscopy (EAES), X-ray Photoelectron Spectroscopy (XPS) and Secondary Electron Ion Mass Spectroscopy (SIMS) are being used for the identification of the surface chemical impurities. Recently, a novel surface characterizaion technique, Positron-annihilation induced Auger Electron Spectroscopy (PAES) is introduced to provide a unique method for the analysis of the elemental composition of the top-most atomic layer. In PAES, monoenergetic positron of a few eV are implanted to the surface under study and these positrons become thermalized near the surface. A fraction of the thermalized positron trapped at the surface state annihilate with the neighboring core-level electrons, creating core-hole excitations, which initiate the Auger process with the emission of Auger electrons almost simultaneously with the emission of annihilating gamma-rays. The energy of electrons is generally determined by employing ExB energy selector, which shows a poor resolution of $6{\sim}10eV$. In this paper, time-of-flight system is employed to measure the electrons energy with an enhanced energy resolution. The experimental result is compared with simulation results in the case of both linear (with retarding tube) and reflected TOF systems.

• Korean Membrane Journal
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• v.1 no.1
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• pp.25-37
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• 1999

positron annihilation Lifetime Spectroscopy has been extensively applied in recent years to investigate the free volume in polymers owing to the capability of the electron-positron bound system (positronium) to probe the typical size of sub-nanometric cavities among the macromolecular chains. In this paper we show recent results obtained through this technique in some amorphous polymeric mem-branes(olyurethanes. PUs and polytrimethilsylilpropine PTMSP) after a brief survey of the general features of the annihilation process as well as of the experimental apparatus. Lifetime of o-ps decay({{{{ tau _3}}}}) in PUs increases going from sub {{{{ TAU _g}}}} to over {{{{ TAU _g}}}} temperatures following a sigmoid curve. The coefficient of dilatation of the free volume fraction is shown to be the sum of two contributes due to the variation with T of the number of holes and of their mean volume. PAL spectrum of PTMSP freshly prepared shows four lifetime components: {{{{ tau _3}}}} and {{{{ tau _4}}}}: only are useful for free volume study. Two kinds of holes of different equivalent radius are reported ({{{{ gamma _s}}}} 4.60 nm and {{{{ gamma _1}}}} 0.754) The equivalent volume does not change in a range of 100 K. however the physical aging increases density and decreases oxygen permeability while {{{{ gamma _s}}}} goes down to 0.374 and r1 to 0.735 The number of holes obtained from the intensities{{{{ IOTA _3}}}} and {{{{ IOTA _4}}}} of PAL spectra decreases with aging 21.7% and 3.5% for large and small holes respectively.

• Polymer Science and Technology
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• v.16 no.2
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• pp.246-254
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• 2005

• Korean Journal of Materials Research
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• v.18 no.8
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• pp.427-431
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• 2008

The mechanical property of a phosphore layer was investigated by measuring the resolution (LP/mm) and by positron annihilation spectroscopy and SEM. Image plate samples containing the phosphore layer were irradiated by X-rays in a hospital numerous times over a course of several years. The LP/mm values of a (Ba,Sr)FBr : Eu image plate irradiated by X-rays varied between 2.2 and 2.0 over a period of four years. Coincidence Doppler Broadening (CDB) positron annihilation spectroscopy was used to analyze defect structures. The S parameters of the samples from hospital use varied from 0.6219 to 0.6232. There was a positive relationship between the time of exposure to the X-rays and the S parameters. Most of the defects were found to have been generated by X-rays.

• Journal of Astronomy and Space Sciences
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• v.36 no.1
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• pp.21-33
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• 2019

This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the non-central part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted ${\gamma}-quantum$ and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of ${\gamma}-quanta$ formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The single-photon annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the ${\gamma}-ray$ spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of ${\gamma}-quanta$ emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in single-photon annihilation.

• Journal of the Korean Vacuum Society
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• v.19 no.6
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• pp.489-494
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• 2010

Enhance signal-to-noise ratio, slow positron coincidence Doppler Broadening method has been applied to study of characteristics of $Nb_3Ge$ superconductor film, which were performed from 20 K to 300 K sample temperature near Tc of it. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S, defined as the ratio between the amount of counts in a central portion of the spectrum and the total counts of whole spectrum. The S-parameter values between 0.598 and 0.594 were decreased while the temperature were decreasing, that indicated the voids into the samples. The temperature dependence came from specific positron trapping rate into the vacancy-type defects. It is believed that the positrons annihilate with normal-electrons instead of super-electrons in the Nb3Ge superconductor.

• Journal of the Korean Vacuum Society
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• v.22 no.5
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• pp.250-256
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• 2013

It is described that the proton beam induces micro-size defects and electronic deep levels in luminescence Thin Film. Coincidence Doppler Broadening Positron Annihilation Spectroscopy (CDBPAS) and Positron lifetime Spectroscopy were applied to study of characteristics of a poly crystal samples. In this investigation the numerical analysis of the Doppler spectra was employed to the determination of the shape parameter, S-parameter value. The samples were exposed by 3.0 MeV proton beams with the intensities ranging between 0 to ${\sim}10^{14}$ particles. The S-parameter values decreased as increased the proton beam, that indicates the protons trapped in vacancies. Lifetime ${\tau}_1$ shows that positrons are trapped in mono vacancies. Lifetime ${\tau}_2$ is not changed according to proton irradiation that indicate the cluster vacancies of the grain structure.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.3
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• pp.133-138
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• 2002

The growth of Au films grown on a Si(100)-2x1 surface and Si films on a Ge(100)-2x1 substrate is studied using Positron-annihilation induced Auger Electron Spectroscopy(PAES), Electron induced Auger Electron Spectroscopy(EAES), and Low Energy Electron Diffraction(LEED). Previous work has shown that PAES is almost exclusively sensitive to the top-most atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. This surface specificity is exploited to profile the surface atomic concentrations during the growth of Au on Si(100) and Si on Ge(100) and EAES provides concentrations averaged over the top 3-10 atomic layers simultaneously. The difference in the probe-depth makes us possible to use PAES and EAES in a complementary fashion to estimate the surface and near surface concentration profiles. The results show that (i) the intermixing of Au and Si atoms occurs during the room temperature deposition, (ii) the segregated Ge layer is observed onto the Si layers deposited at 300k. In addition, the prior adsorption of hydrogen prevents the segregation of Ge on top of the deposited Si and that the hydrogen adsorption is useful in growing a thermally stable structure.