The slowing down times of positrons emitted from selected β+ isotopes into metals

Dryzek, Jerzy; Horodek, P.; Siemek, Krzysztof

doi:10.1016/j.nimb.2012.09.009

Cited by 6 publications

(3 citation statements)

References 18 publications

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“…The best agreement with experiment [15] can be found for GC, LG and DB approaches, the DG values being too long. However, it should be mentioned that these experiments were carried out about 45 years ago and the results might not be very precise considering that no source correction was done, and other effects like the presence of vacancies [16] and impurities and thermalization issues [17] could influence measured lifetimes. Therefore, it would be very desirable to perform new lifetime measurements for alkalies addressing these possible problems.…”

Section: Resultsmentioning

confidence: 99%

Gradient correction scheme for bulk and defect positron states in materials: New developments

Kuriplach

Barbiellini

2014

J. Phys.: Conf. Ser.

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As local density approximation positron calculations systematically underestimate positron lifetimes when they are compared with their experimental counterparts, the generalized gradient approximation (GGA) for positrons was introduced in the 1990s, in analogy with the GGA for electrons. New developments in the GGA for positrons are summarized and presented here and it is also discussed how they affect and possibly improve calculated positron lifetimes. In particular, these new GGA approaches are based on the recent perturbed hypernetted-chain and quantum Monte Carlo results.

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Section: Resultsmentioning

confidence: 99%

Gradient correction scheme for bulk and defect positron states in materials: New developments

Kuriplach

Barbiellini

2014

J. Phys.: Conf. Ser.

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“…Nevertheless, lifetime experiments in the alkali metals are rather old and new measurements are needed in order to confirm these discrepancies. Another problem is the long positron thermalization time [72] which complicates the lifetime analysis in the alkali metals. In order to evaluate the deviation of calculations and experiment, we give in columns GC and DG a measure expressed by characters A, B, and C. This measure is based on the root-mean-square deviations determined using available experimental data where we considered rather newer than older data removing also unrealistic results.…”

Section: A Bulk Positron Lifetime and Affinitymentioning

confidence: 99%

Improved generalized gradient approximation for positron states in solids

Kuriplach

Barbiellini

2014

Phys. Rev. B

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Several first-principles calculations of positron-annihilation characteristics in solids have added gradient corrections to the local-density approximation within the theory by Arponen and Pajanne [Ann. Phys. (NY) 121, 343 (1979)] since this theory systematically overestimates the annihilation rates. As a further remedy, we propose to use gradient corrections for other local-density approximation schemes based on perturbed hypernetted chain and on quantum Monte Carlo results. Our calculations for various metals and semiconductors show that the proposed schemes generally improve the positron lifetimes when they are confronted with experiment. We also compare the resulting positron affinities in solids with data from slow-positron measurements.

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“…Further, as per the model, normally incident monoenergetic positrons slow down to the thermal energy firstly through elastic and inelastic scattering in materials and subsequent diffusion and annihilation with random electrons [8,9]. It is noteworthy that only thermalization processes were simulated in our study due to the lowenergy threshold of Geant4 [18,21]. However, the positron depth was not influenced because the depth during diffusion (in the nanometer scale) can be ignored relative to the depth during thermalization (about several millimeters in H 2 O) [22].…”

Section: Methods and Modelmentioning

confidence: 97%

Implantation profiles and depth distribution of slow positron beam simulated by Geant4 toolkit

Cao

Ning

et al. 2019

Phys. Scr.

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The positron implantation profiles and depth distribution in metal, semiconductor, and polymer surfaces are simulated using the Monte-Carlo-method-based Geant4 toolkit. As per the slow positron beam technique, the monoenergetic positron beams (in the range from 1 to 35 keV) with 1.5 mm radius is injected into semi-infinite samples in the present work. The implantation profile of 3.1 keV positrons in Fe is in good agreement with the Makhovian profile. The mean depth and depth resolution exhibit a general negative correlation with the material densities and incident position energy, respectively, while the fixed peak energy of backscattered positrons exhibits a net correlation with atomic number Z. Furthermore, the implantation profiles present better z-axis resolution with increasing incident angle, and this effect is more prominent for low-density materials. The results can provide theoretical support for new measurement methods based on the slow positron beam technique, such as segment measurements and micro-beam scanning measurements.

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The slowing down times of positrons emitted from selected β+ isotopes into metals

Cited by 6 publications

References 18 publications

Gradient correction scheme for bulk and defect positron states in materials: New developments

Gradient correction scheme for bulk and defect positron states in materials: New developments

Improved generalized gradient approximation for positron states in solids

Implantation profiles and depth distribution of slow positron beam simulated by Geant4 toolkit

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