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Title: Implantation profile of {sup 22}Na continuous energy spectrum positrons in silicon

Abstract

The implantation profile of positrons emitted from a continuous energy spectrum source of {sup 22}Na in close proximity to a silicon target is modeled. The primary motivation is the use of positron lifetime spectroscopy to characterize layers of defects such as those created by ion irradiation, usually deemed accessible only to techniques which utilize slow positrons. The model combines the Makhov profile, used with considerable success to describe the profile of low energy (<30 keV) monoenergetic positrons, with the well-established, universal {beta}-decay energy spectrum. The success of this approach is verified by measuring the fractions of positrons absorbed in thinned silicon samples. This verification utilizes lifetime measurements performed on silicon in a bilayer sandwich configuration with copper as a backing. The model accounts for the uncertainty in the positron backscattering at the silicon/copper interface. An optimal fit of the model to the experimental data requires that the parameter defining the mean depth of the Makhov profile (usually denoted r) is energy dependent. An example of application is provided in the form of a positron lifetime measurement of defects in silicon introduced by 1.5 MeV proton irradiation. Excellent agreement is found between the lifetime data and those obtained using a slowmore » positron technique.« less

Authors:
; ; ;  [1];  [2]
  1. Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4L7 (Canada)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
20982704
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 4; Other Information: DOI: 10.1063/1.2472645; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; BACKSCATTERING; BETA DECAY; COPPER; CRYSTAL DEFECTS; ENERGY DEPENDENCE; ENERGY SPECTRA; ION IMPLANTATION; IRRADIATION; KEV RANGE 10-100; LIFETIME; MEV RANGE 01-10; POSITRONS; PROTONS; SILICON; SODIUM 22; SPECTROSCOPY

Citation Formats

Foster, P. J., Mascher, P., Knights, A. P., Coleman, P. G., and Department of Physics, University of Bath, Bath, BA2 7AY. Implantation profile of {sup 22}Na continuous energy spectrum positrons in silicon. United States: N. p., 2007. Web. doi:10.1063/1.2472645.
Foster, P. J., Mascher, P., Knights, A. P., Coleman, P. G., & Department of Physics, University of Bath, Bath, BA2 7AY. Implantation profile of {sup 22}Na continuous energy spectrum positrons in silicon. United States. doi:10.1063/1.2472645.
Foster, P. J., Mascher, P., Knights, A. P., Coleman, P. G., and Department of Physics, University of Bath, Bath, BA2 7AY. Thu . "Implantation profile of {sup 22}Na continuous energy spectrum positrons in silicon". United States. doi:10.1063/1.2472645.
@article{osti_20982704,
title = {Implantation profile of {sup 22}Na continuous energy spectrum positrons in silicon},
author = {Foster, P. J. and Mascher, P. and Knights, A. P. and Coleman, P. G. and Department of Physics, University of Bath, Bath, BA2 7AY},
abstractNote = {The implantation profile of positrons emitted from a continuous energy spectrum source of {sup 22}Na in close proximity to a silicon target is modeled. The primary motivation is the use of positron lifetime spectroscopy to characterize layers of defects such as those created by ion irradiation, usually deemed accessible only to techniques which utilize slow positrons. The model combines the Makhov profile, used with considerable success to describe the profile of low energy (<30 keV) monoenergetic positrons, with the well-established, universal {beta}-decay energy spectrum. The success of this approach is verified by measuring the fractions of positrons absorbed in thinned silicon samples. This verification utilizes lifetime measurements performed on silicon in a bilayer sandwich configuration with copper as a backing. The model accounts for the uncertainty in the positron backscattering at the silicon/copper interface. An optimal fit of the model to the experimental data requires that the parameter defining the mean depth of the Makhov profile (usually denoted r) is energy dependent. An example of application is provided in the form of a positron lifetime measurement of defects in silicon introduced by 1.5 MeV proton irradiation. Excellent agreement is found between the lifetime data and those obtained using a slow positron technique.},
doi = {10.1063/1.2472645},
journal = {Journal of Applied Physics},
number = 4,
volume = 101,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • Energy levels of Na/sup 22/ were observed with the Mg/sup 24/ (d, alpha )Na/sup 22/ and Mg/sup 25/(p, alpha )Na/sup 22/ reactions. Bombarding energies in the range of 5.0 to 7.5 Mev were used, and the alpha particles were recorded with a broad-range spectrograph. Ground state Q-values are 1.954 plus or minus 0.007 Mev for the first and -3.153 Mev for the second reaction. Excited states, presumably with isobaric spin zero, were found at 0.585, 0.893, 1.533, 1.944, 1.990, 4.323 plus or minus 0.008, and 4.472 plus or minus 0.008 Mev (all plus or minus 0.005 except where shown otherwise)more » using the (d, alpha ) reaction. The first and second of these were also seen through the (p, alpha ) reaction and, in addition, a T = 1 state at 0.661 plus or minus 0.008 Mev. The ground state Q-value for the N/sup 14/(p, alpha ) C/sup 11/ reaction was found to be - 2.928 Mev. (auth)« less
  • Asymmetries and polarizations in the positron emission in beta decay of B/sup 8/, Na/sup 22/, and mu /sup +/ mesons are measured. (T.F.H.)
  • A simple form for an implantation profile of monoenergetic, low-energy (1--10 keV) positrons in solids is presented. Materials studied include aluminum, copper, molybdenum, palladium, and gold with atomic number ranging from 13 to 79. A simple set of parameters can describe the currently used Makhov profile in slow positron studies of solids. We provide curves and tables for the parameters that can be used to describe the implantation profiles of positrons in any material with atomic number in between 13 and 79.
  • Data from the annihilation of positrons (from a 22-Na source) in neon isotopes is presented. Experimental procedures are discussed.
  • Detailed descriptions are given of previously reported measurements of the longitudinal polarization (P/sub L/) of positrons in the allowed and unique second forbidden weak decays of /sup 22/Na. The measurements were performed relative to the allowed decay of /sup 68/Ga by application of time-resolved spectroscopy of the n = 1 hyperfine states of positronium formed in powder media. Assuming the theoretical value P/sub L/( /sup 68/Ga) = ..beta..(0.999 +- 0.001), the results are P/sub L/( /sup 22/Na, 3/sup +/..-->..2/sup +/) = ..beta..(+1.003 +- 0.011) and P/sub L/( /sup 22/Na, 3/sup +/..-->..0/sup +/) = ..beta..(+1.00 +- 0.05). The allowed decay resultmore » (combined with other /sup 22/Na experimental data on the decay rate, the capture ratio, the spectral shape, the ..beta gamma.. directional correlation, and the weak magnetic form factor) yields a determination of the full weak form factor structure of the transition through second order in recoil. The experimental value for the capture ratio is currently considered to be anomalously low compared to theoretical estimates. Our polarization result is not, however, sufficiently accurate to definitively favor one or the other value. The forbidden decay result, together with model-dependent nuclear structure calculations, restricts the contribution of previously neglected higher-order corrections to the allowed decay to be less than 10/sup -8/.« less