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1
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Detection of Positron Implantation Profile in Different Materials

100%
Dryzek J.
Acta Physica Polonica A
|
2005
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vol. 107
|
issue 4
598-607
EN
The objective of this paper is experimental studies of the linear absorption coefficient, or mean penetration depth of positrons emitted from ^{22}Na isotope in different materials. For this purpose we constructed a new experimental setup which allows us to scan the depth implantation profile of positrons. For the studied metals: Mg, Al, the obtained values of mean penetration depth coincide well with those which can be calculated using the mathematical formula commonly used but for Si and S the discrepancy has been observed similarly like for polymers.
2
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New Experimental Approach to the Detection of Positron Annihilation in Flight Process

100%
Dryzek J.
Acta Physica Polonica A
|
2008
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vol. 113
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issue 5
1339-1346
EN
Positron annihilation in flight, when mainly positron contributes to the energy and momentum of the annihilating pair, is rarely observed in condensed matter due to its small probability. Additionally, this process does not manifest itself by any characteristic features, which would help in observation. Hence, our knowledge about that process is poor. In the paper we propose the new experimental method which allows us to detect this process. We applied the conventional positron lifetime spectrometer, which after changing photon energy ranges and layout of detectors was suitable for that detection. The first measurements allow us to estimate that in pure aluminum almost 4.76% of all implanted positrons from isotope source ^{22}Na annihilate in flight.
3
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Remarks on Reconstruction of Defects' Distribution by Positron Lifetime Measurements

100%
Dryzek J.
Acta Physica Polonica A
|
1995
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vol. 88
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issue 1
125-128
EN
It is well known that the positron trapping rate obtained from positron lifetime measurements depends upon defect concentrations and trapping efficiency. If a distribution of open volume defects exists, a distribution of trapping efficiency also could be present. As an example, the calculation of trapping efficiency as a function of radius of defects in Al is presented. The correct explanation of defect size distribution obtained by positron lifetime measurements needs to introduce some additional assumptions about trapping efficiency.
4
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Resonance Trapping of Positrons in Solids

100%
Dryzek J.
Acta Physica Polonica A
|
1993
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vol. 83
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issue 3
293-296
EN
Basing on a new approach to the calculations of the positron trapping rate, an attempt ',was made to explain the prevacancy effects observed in positron annihilation measurements in metals. The defect in the calculation is represented by a complex potential: the real part of it is responsible for the scattering and the imaginary part - for the trapping of incoming positrons. It is shown that the resonance trapping of the positron s-wave and p-wave at low temperature and d-wave and f-wave in prethermal regions provide substantial contributions to the trapping rate of positrons. The calculations were done for the point defect and for the dislocation, taking into account the thermal distribution of the positron energy and the thermal expansion of the crystal lattice. The resonance trapping of positrons could be responsible for prevacancy effects in metals and could help to solve some problems in the study of positron annihilation.
5
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Positron Trapping Model in Fine Grained Sample

100%
Dryzek J.
Acta Physica Polonica A
|
1999
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vol. 95
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issue 4
539-545
EN
In the paper we consider the positron trapping model in the sample where the spherical particles were immersed in the medium. The radius of the particles was small enough to take into account the diffusion of positrons. We present the exact solutions of the model for two cases, when transition of the positrons from the particle to the medium was neglected and when it was taken into consideration. The theoretical calculations were applied to description of the positron annihilation in the copper sample where the recrystallization process took place.
6
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Calculations of Annihilation Rate of o-Ps in Pick-Off Process

100%
Dryzek J.
Acta Physica Polonica A
|
1999
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vol. 95
|
issue 4
527-532
EN
In the paper we suggest the procedure of calculation of the o -Ps lifetime in the pick-off process. The procedure follows the scheme proposed by Tao but we employed the correct positron wave function. We extended our calculations for the case when the o-Ps is overlapping the core region of hydrogen and carbon atoms. The obtained dependence between the lifetime and the radius of the o-Ps fits much better to the experimental one observed in silica gel than the original Tao relation.
7
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The Computer Code for Calculations of the Positron Distribution in a Layered Stack Systems

64%
Siemek K., Dryzek J.
Acta Physica Polonica A
|
2014
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vol. 125
|
issue 3
833-836
EN
In this paper we present experimental and theoretical studies of the implantation profile of positrons emitted from ^{22}Na radionuclide into layered sample. The measured profile for the nonsymmetrical, around the positron emitter, stack of aluminium and silver foils was measured using the depth scanning of implantation profile technique. For the description of the obtained results two theoretical approaches were applied. The first one was the Monte Carlo simulation using the GEANT4 tool kit. The generated profile does not reproduce accurately the experimental profile. We proposed the multiple scattering model based on the fact that a positron due to backscattering can travel as an energetic particle several times through the whole sample before it annihilates. In this model absorption is also taken into account. The multiple scattering model algorithm was implemented in the LYS-1 program. The calculated profile using the LYS-1 program reproduces the experimental profile with much better accuracy.
8
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Positron Annihilation Studies of the Subsurface Zone in Aluminium Alloys

64%
Dryzek E., Dryzek J.
Acta Physica Polonica A
|
2006
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vol. 110
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issue 5
569-575
EN
The paper presents positron lifetime studies of the subsurface region of the aluminium cast AK64 alloy containing silicon as a main alloying element after sliding against stainless steel in the pin-on-disc tester. The subsurface zone of the depth exceeding 150μm has been detected. The scanning electron microscopy revealed only the plastically deformed region occurring at the depth up to ca. 50μm and cracks at the depth less than 30μm. The comparison with the results obtained for the AK12 alloy containing almost a twice higher amount of silicon demonstrates the influence of the hard silicon rich particles on the total depth of the subsurface zone. A higher amount of hard particle prevents to some extend the propagation of defects inside the material.
9
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Positron Implantation Profile in Kapton

64%
Dryzek J., Dryzek E.
Acta Physica Polonica A
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2006
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vol. 110
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issue 5
577-582
EN
The discussion presented in the paper focuses on processes accompanying positron implantation in condensed matter. They finally constitute the positron implantation profile which generally does not exhibit the exponential behavior as it is concluded from the Monte Carlo simulation made using the EGSnrc 4.0 code. The simulation was performed for the kapton and two commonly used positron sources ^{22}Na and ^{68}Ge/g^{68}Ga. New formula for the implantation profile was proposed.
10
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Algorithm for Shifting Positron Annihilation Spectra

64%
Dryzek J., Polak A.
Acta Physica Polonica A
|
2001
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vol. 99
|
issue 3-4
355-361
EN
We present a simple procedure which allows us to shift the positron annihilation spectra, e.g., the Doppler broadening spectrum of the annihilation line. That is especially required when we wish to compare different spectra obtained with a spectrometer with the reduction of background. As an application of the obtained algorithm we present the studies of positron annihilation in carbon material samples.
11
Publication available in full text mode
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Positron Lifetime Studies of the Subsurface Zones Created under Dry and Lubrication Conditions

64%
Dryzek J., Dryzek E.
Acta Physica Polonica A
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2001
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vol. 99
|
issue 3-4
351-354
EN
We present the measurement of the positron lifetime spectra in the subsurface zones in copper samples with surfaces damaged in dry and lubrication conditions. We observe that close to the damaged surface the single vacancies were present, but deeper in the sample treated in the dry condition the vacancy clusters were detected. A zone with dislocations was located deeper than the zone with the vacancies and their clusters.
12
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Defect Profile Induced by Friction and Wear Processes Detected by Positron Annihilation Method

51%
Dryzek J., Dryzek E., Cleff B.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
129-133
EN
The positron annihilation studies of defect profile in Cu samples whose surfaces were exposed to the friction and wear processes are presented. The values of the S-parameter and its dependences on the depth from the Cu surface are the functions of the value of the load applied in the sliding contact between two metals. It indicates possibilities of applying the presented measurement method in the industry.
13
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Calorimetric and Positron Lifetime Measurements οf Hydrogenated Carbon Nanocones

51%
Budziak A., Dryzek J., Krawczyk J., Zieliński P.
Acta Physica Polonica A
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2010
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vol. 117
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issue 4
574-577
EN
Two carbon nano-structured samples containing 5 and 20% of carbon nanocones in their volume were investigated. Using the Sieverts apparatus the hydrogen was loaded into the samples. The measurements of heat capacity in the temperature range from 100 K to 320 K and the positron lifetime measurements at the room temperature were performed for hydrogenated and non-hydrogenated carbon nanocones. The desorption of hydrogen at the temperature of 230 K is deduced from the heat capacity measurements. The detection of the positronium, the bound state of positron and electron, in the measured samples reveals the presence of open volume defects of ca. 0.198 ± 0.002 nm.
14
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Preferential Positron Annihilation in Binary Alloys

51%
Kuriplach J., Dryzek E., Dryzek J., Šob M.
Acta Physica Polonica A
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1999
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vol. 95
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issue 4
605-611
EN
The effect of preferential positron annihilation at individual constituent atoms in binary alloys is examined theoretically and experimentally. In particular, the results of recently studied alloys Fe-Al and Mg-Cd together with new preliminary results for the Sn-In system are discussed and summarised. In the case of the Sn-In system, the concentration dependencies of positron annihilation rates and Doppler broadening spectra are analysed.
15
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Defect Range and Evolution in Swift Xe-Ion Irradiated Pure Silver Studied by Positron Annihilation Technique

51%
Dryzek J., Horodek P., Skuratov V.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 5
1585-1589
EN
Variable energy positron beam and positron lifetime spectroscopy were used to study pure silver samples exposed to irradiation with swift Xe²⁶⁺ ions of energy 167 MeV with different dose: of 10¹³, 5×10¹³ and 10¹⁴ ions/cm². The positron lifetime spectroscopy revealed the presence of dislocations or vacancies associated with dislocations. They are distributed at the depth of about 6 μm, and this correlates with the ion implantation range, i.e. 9 μm. However, some defects are observed also to a depth of about 18 μm. At the depth less than 1 μm from the entrance surface strong dependence of positron diffusion length on the dose is observed. It indicates the presence of interstitial atoms and/or dislocation loops as a result of Xe²⁶⁺ ions implantation.
16
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Slow Positron Beam Studies of the Stainless Steel Surface Exposed to Sandblasting

27%
Horodek P., Dryzek J., Kobets A., Kulik M., Lokhmatov V., Meshkov I., Orlov O., Pavlov V., Rudakov A., Sidorin A., Siemek K.
Acta Physica Polonica A
|
2014
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vol. 125
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issue 3
714-717
EN
The paper presents slow positron beam studies of the stainless steel grade 304 AISI samples annealed in the flow N_2 atmosphere and sandblasted under different pressure from 1 to 7 bar. Heating of specimens caused formation of an additional layer on the surface which can be identified as oxides. Sandblasting reduces the thickness of the oxide layer and also defects concentration (vacancies as we suppose) decreases in dependence on pressure applied during blasting. Additionally, the atomic concentrations of oxygen have been obtained using nuclear methods (Rutherford backscattering and nuclear reactions) in the near surface layers of the studied samples.
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