The Experts below are selected from a list of 150 Experts worldwide ranked by ideXlab platform
T.s. Stein - One of the best experts on this subject based on the ideXlab platform.
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Investigations of positronium formation and destruction using 3γ/2γannihilation-ratio measurements
Physical review letters, 2004Co-Authors: W.e. Kauppila, T.s. Stein, E. G. Miller, H. F. M. Mohamed, K. Pipinos, Eugene SurdutovichAbstract:Positronium (Ps) produced by 4 to 40 eV positrons colliding with Ne, Ar, Kr, CO2, and O2 is investigated by measuring the ratio of signals of two gamma rays in coincidence resulting from (a) three gamma annihilation of ortho-Ps and (b) two annihilation gamma rays due to para-Ps decay and destruction of ortho-Ps at an aluminum Scattering Cell surface. These ratios provide evidence that relates to the kinetic energy dependence of ortho-Ps interactions with an aluminum surface, the Ps formation potential at this surface, and the fact that Ps is being formed with inner orbital electrons for CO2 and O2.
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Measurements of cross-sections for positrons and electrons scattered by Cs atoms
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: Eugene Surdutovich, W.e. Kauppila, C. K. Kwan, E. G. Miller, S. P. Parikh, K. A. Price, T.s. SteinAbstract:Abstract Total Scattering cross-sections have been measured for 1–60 eV positrons and 6–200 eV electrons scattered by Cs atoms using a beam-transmission technique with a heated Scattering Cell. For 0.5–25 eV positron Scattering we have measured both upper and lower limits on positronium formation cross-sections.
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Experimental investigation of ortho-positronium-surface interactions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: T.s. Stein, W.e. Kauppila, E. G. Miller, Eugene SurdutovichAbstract:Abstract In an effort to measure absolute positronium formation cross-sections for positrons scattered by various target atoms and molecules, we detect coincidences of the two 511 keV γ rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of our Scattering Cell, and also coincidences of 2 of the 3 γ rays with energies between 300 and 460 keV produced by ortho-Ps decay. The ratio of the coincidence signals (3γ/2γ) plotted as a function of positron energy has a number of interesting features that we believe may provide useful information on ortho-positronium–surface interactions.
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Measurements of total and positronium formation cross sections for positrons and electrons scattered by hydrogen atoms and molecules
Physical Review A, 1997Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:We have measured total (${\mathrm{Q}}_{\mathrm{T}}$ ) and positronium formation (${\mathrm{Q}}_{\mathrm{Ps}}$ ) cross sections for 1--302-eV positrons (${\mathrm{e}}^{+}$ 's) and ${\mathrm{Q}}_{\mathrm{T}}$ 's for electrons (${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ 's) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure ${\mathrm{Q}}_{\mathrm{T}}$ 's where the projectile beam passes through a low-temperature Scattering Cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. ${\mathrm{Q}}_{\mathrm{Ps}}$ 's are measured using the same Scattering Cell by detecting coincidences of 511-keV annihilation \ensuremath{\gamma} rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The present ${\mathrm{e}}^{+}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's and ${\mathrm{Q}}_{\mathrm{Ps}}$ 's agree very well with theoretical calculations. Comparisons of the present ${\mathrm{e}}^{+}$ and ${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's show a merging to within 20% for energies above 12 eV.
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Measurements of positronium formation cross sections for positron-H Scattering
Bulletin of the American Physical Society, 1996Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:The authors have made preliminary measurements of positronium (Ps) formation cross sections for positron-H Scattering. As in their original system, the atomic hydrogen is obtained from an rf discharge source, and recombination in their aluminum Scattering Cell is minimized by maintaining the Cell at about 150 K. Their experimental approach involves setting lower limits on Ps formation cross sections using the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interactions of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The authors also plan to measure the upper limits of Ps formation cross sections by the determination of Scattering cross sections associated with the measured transmissions of the positron beam through the gas in their Scattering Cell.
S. Zhou - One of the best experts on this subject based on the ideXlab platform.
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Measurements of total and positronium formation cross sections for positrons and electrons scattered by hydrogen atoms and molecules
Physical Review A, 1997Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:We have measured total (${\mathrm{Q}}_{\mathrm{T}}$ ) and positronium formation (${\mathrm{Q}}_{\mathrm{Ps}}$ ) cross sections for 1--302-eV positrons (${\mathrm{e}}^{+}$ 's) and ${\mathrm{Q}}_{\mathrm{T}}$ 's for electrons (${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ 's) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure ${\mathrm{Q}}_{\mathrm{T}}$ 's where the projectile beam passes through a low-temperature Scattering Cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. ${\mathrm{Q}}_{\mathrm{Ps}}$ 's are measured using the same Scattering Cell by detecting coincidences of 511-keV annihilation \ensuremath{\gamma} rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The present ${\mathrm{e}}^{+}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's and ${\mathrm{Q}}_{\mathrm{Ps}}$ 's agree very well with theoretical calculations. Comparisons of the present ${\mathrm{e}}^{+}$ and ${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's show a merging to within 20% for energies above 12 eV.
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Measurements of positronium formation cross sections for positron-H Scattering
Bulletin of the American Physical Society, 1996Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:The authors have made preliminary measurements of positronium (Ps) formation cross sections for positron-H Scattering. As in their original system, the atomic hydrogen is obtained from an rf discharge source, and recombination in their aluminum Scattering Cell is minimized by maintaining the Cell at about 150 K. Their experimental approach involves setting lower limits on Ps formation cross sections using the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interactions of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The authors also plan to measure the upper limits of Ps formation cross sections by the determination of Scattering cross sections associated with the measured transmissions of the positron beam through the gas in their Scattering Cell.
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Measurements of total and positronium formation cross sections for positron-Mg Scattering
Bulletin of the American Physical Society, 1996Co-Authors: J. Jiang, W.e. Kauppila, C. K. Kwan, T.s. Stein, M. Harte, A. Surdutovich, S. ZhouAbstract:The authors are measuring total and positronium (Ps) formation cross sections for positron-Mg Scattering. Their experimental approach involves using a beam transmission technique to measure the total cross sections and setting lower and upper limits on Ps formation cross sections using a combination of (1) the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed, and (2) the determination of Scattering cross sections associated with the measured transmission of the positron beam through the vapor in their Scattering Cell with the angular discrimination of their apparatus deliberately made as poor as possible. Comparing with the theoretical results of Gribakin and King, their measured total cross sections differ in shape and their Ps formation lower limits are lower than the theoretical predictions.
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Measurements of total and positronium-formation cross sections for the Scattering of positrons by alkali atoms
Hyperfine Interactions, 1994Co-Authors: C. K. Kwan, W.e. Kauppila, T.s. Stein, S. P. Parikh, S. ZhouAbstract:We present a review of our recent measurements of total cross sections ( Q _T's) for the Scattering of positrons by Na, K, and Rb, and positronium-formation cross sections ( Q _Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For our Q _Ps measurements, our approach involves setting upper and lower limits on Q _Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the Scattering Cell. Comparison with theoretical calculations shows that our measured Q _T's and Q _Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in the n =1 and n =2 states. In the 3–10 eV energy range, this calculation predicts a peak in the Q _T's and Q _Ps's for K which also appears in our measurements. The absence of such a peak in our measured Q _T's and Q _Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations of Q _T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and Rb Q _T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb.
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Measurements of positronium formation cross sections for positron-ar and-K Scattering
Hyperfine Interactions, 1992Co-Authors: T.s. Stein, C. K. Kwan, W.e. Kauppila, S. P. Parikh, S. ZhouAbstract:We have made preliminary measurements of positronium (Ps) formation cross sections for 9 to 452 eV positrons scattered from Ar atoms and for 1 to 20 eV positrons scattered from K atoms. Our experimental approach involves setting lower and upper limits on Ps formation cross sections using a combination of (1) the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the wall of the Scattering Cell in which the Ps is formed, and (2) the determination of Scattering cross sections associated with the measured transmission of the positron beam through the gas in our Scattering Cell with the angular discrimination of our apparatus deliberately made as poor as possible. The constraints placed by these lower and upper limits are used to check for consistency with prior experimental and theoretical results for Ar and to provide the first measurements of Ps formation cross sections for K, which are compared with available theoretical results.
W.e. Kauppila - One of the best experts on this subject based on the ideXlab platform.
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Investigations of positronium formation and destruction using 3γ/2γannihilation-ratio measurements
Physical review letters, 2004Co-Authors: W.e. Kauppila, T.s. Stein, E. G. Miller, H. F. M. Mohamed, K. Pipinos, Eugene SurdutovichAbstract:Positronium (Ps) produced by 4 to 40 eV positrons colliding with Ne, Ar, Kr, CO2, and O2 is investigated by measuring the ratio of signals of two gamma rays in coincidence resulting from (a) three gamma annihilation of ortho-Ps and (b) two annihilation gamma rays due to para-Ps decay and destruction of ortho-Ps at an aluminum Scattering Cell surface. These ratios provide evidence that relates to the kinetic energy dependence of ortho-Ps interactions with an aluminum surface, the Ps formation potential at this surface, and the fact that Ps is being formed with inner orbital electrons for CO2 and O2.
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Measurements of cross-sections for positrons and electrons scattered by Cs atoms
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: Eugene Surdutovich, W.e. Kauppila, C. K. Kwan, E. G. Miller, S. P. Parikh, K. A. Price, T.s. SteinAbstract:Abstract Total Scattering cross-sections have been measured for 1–60 eV positrons and 6–200 eV electrons scattered by Cs atoms using a beam-transmission technique with a heated Scattering Cell. For 0.5–25 eV positron Scattering we have measured both upper and lower limits on positronium formation cross-sections.
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Experimental investigation of ortho-positronium-surface interactions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: T.s. Stein, W.e. Kauppila, E. G. Miller, Eugene SurdutovichAbstract:Abstract In an effort to measure absolute positronium formation cross-sections for positrons scattered by various target atoms and molecules, we detect coincidences of the two 511 keV γ rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of our Scattering Cell, and also coincidences of 2 of the 3 γ rays with energies between 300 and 460 keV produced by ortho-Ps decay. The ratio of the coincidence signals (3γ/2γ) plotted as a function of positron energy has a number of interesting features that we believe may provide useful information on ortho-positronium–surface interactions.
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Measurements of total and positronium formation cross sections for positrons and electrons scattered by hydrogen atoms and molecules
Physical Review A, 1997Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:We have measured total (${\mathrm{Q}}_{\mathrm{T}}$ ) and positronium formation (${\mathrm{Q}}_{\mathrm{Ps}}$ ) cross sections for 1--302-eV positrons (${\mathrm{e}}^{+}$ 's) and ${\mathrm{Q}}_{\mathrm{T}}$ 's for electrons (${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ 's) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure ${\mathrm{Q}}_{\mathrm{T}}$ 's where the projectile beam passes through a low-temperature Scattering Cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. ${\mathrm{Q}}_{\mathrm{Ps}}$ 's are measured using the same Scattering Cell by detecting coincidences of 511-keV annihilation \ensuremath{\gamma} rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The present ${\mathrm{e}}^{+}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's and ${\mathrm{Q}}_{\mathrm{Ps}}$ 's agree very well with theoretical calculations. Comparisons of the present ${\mathrm{e}}^{+}$ and ${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's show a merging to within 20% for energies above 12 eV.
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Measurements of positronium formation cross sections for positron-H Scattering
Bulletin of the American Physical Society, 1996Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:The authors have made preliminary measurements of positronium (Ps) formation cross sections for positron-H Scattering. As in their original system, the atomic hydrogen is obtained from an rf discharge source, and recombination in their aluminum Scattering Cell is minimized by maintaining the Cell at about 150 K. Their experimental approach involves setting lower limits on Ps formation cross sections using the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interactions of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The authors also plan to measure the upper limits of Ps formation cross sections by the determination of Scattering cross sections associated with the measured transmissions of the positron beam through the gas in their Scattering Cell.
C. K. Kwan - One of the best experts on this subject based on the ideXlab platform.
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Measurements of cross-sections for positrons and electrons scattered by Cs atoms
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004Co-Authors: Eugene Surdutovich, W.e. Kauppila, C. K. Kwan, E. G. Miller, S. P. Parikh, K. A. Price, T.s. SteinAbstract:Abstract Total Scattering cross-sections have been measured for 1–60 eV positrons and 6–200 eV electrons scattered by Cs atoms using a beam-transmission technique with a heated Scattering Cell. For 0.5–25 eV positron Scattering we have measured both upper and lower limits on positronium formation cross-sections.
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Measurements of total and positronium formation cross sections for positrons and electrons scattered by hydrogen atoms and molecules
Physical Review A, 1997Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:We have measured total (${\mathrm{Q}}_{\mathrm{T}}$ ) and positronium formation (${\mathrm{Q}}_{\mathrm{Ps}}$ ) cross sections for 1--302-eV positrons (${\mathrm{e}}^{+}$ 's) and ${\mathrm{Q}}_{\mathrm{T}}$ 's for electrons (${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ 's) scattered by hydrogen atoms and molecules. A beam transmission technique is used to measure ${\mathrm{Q}}_{\mathrm{T}}$ 's where the projectile beam passes through a low-temperature Scattering Cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. ${\mathrm{Q}}_{\mathrm{Ps}}$ 's are measured using the same Scattering Cell by detecting coincidences of 511-keV annihilation \ensuremath{\gamma} rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The present ${\mathrm{e}}^{+}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's and ${\mathrm{Q}}_{\mathrm{Ps}}$ 's agree very well with theoretical calculations. Comparisons of the present ${\mathrm{e}}^{+}$ and ${\mathrm{e}}^{\mathrm{\ensuremath{-}}}$ -H ${\mathrm{Q}}_{\mathrm{T}}$ 's show a merging to within 20% for energies above 12 eV.
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Measurements of positronium formation cross sections for positron-H Scattering
Bulletin of the American Physical Society, 1996Co-Authors: S. Zhou, W.e. Kauppila, C. K. Kwan, T.s. SteinAbstract:The authors have made preliminary measurements of positronium (Ps) formation cross sections for positron-H Scattering. As in their original system, the atomic hydrogen is obtained from an rf discharge source, and recombination in their aluminum Scattering Cell is minimized by maintaining the Cell at about 150 K. Their experimental approach involves setting lower limits on Ps formation cross sections using the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interactions of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed. The authors also plan to measure the upper limits of Ps formation cross sections by the determination of Scattering cross sections associated with the measured transmissions of the positron beam through the gas in their Scattering Cell.
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Measurements of total and positronium formation cross sections for positron-Mg Scattering
Bulletin of the American Physical Society, 1996Co-Authors: J. Jiang, W.e. Kauppila, C. K. Kwan, T.s. Stein, M. Harte, A. Surdutovich, S. ZhouAbstract:The authors are measuring total and positronium (Ps) formation cross sections for positron-Mg Scattering. Their experimental approach involves using a beam transmission technique to measure the total cross sections and setting lower and upper limits on Ps formation cross sections using a combination of (1) the detection of the coincidences of 511 keV annihilation gamma rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of the Scattering Cell in which the Ps is formed, and (2) the determination of Scattering cross sections associated with the measured transmission of the positron beam through the vapor in their Scattering Cell with the angular discrimination of their apparatus deliberately made as poor as possible. Comparing with the theoretical results of Gribakin and King, their measured total cross sections differ in shape and their Ps formation lower limits are lower than the theoretical predictions.
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Measurements of total and positronium-formation cross sections for the Scattering of positrons by alkali atoms
Hyperfine Interactions, 1994Co-Authors: C. K. Kwan, W.e. Kauppila, T.s. Stein, S. P. Parikh, S. ZhouAbstract:We present a review of our recent measurements of total cross sections ( Q _T's) for the Scattering of positrons by Na, K, and Rb, and positronium-formation cross sections ( Q _Ps's) for Na and K. For our total cross section measurements, a beam transmission technique has been used. For our Q _Ps measurements, our approach involves setting upper and lower limits on Q _Ps using a combination of (1) measuring the transmission of the positron beam with the angular discrimination of the apparatus made as poor as possible, and (2) measuring the 511 keV annihilation gamma rays in coincidence produced by the decay of para-Ps formed in the Scattering Cell. Comparison with theoretical calculations shows that our measured Q _T's and Q _Ps's for Na and K agree reasonably well with a close coupling approximation (CCA) calculation which takes into account the formation of Ps in the n =1 and n =2 states. In the 3–10 eV energy range, this calculation predicts a peak in the Q _T's and Q _Ps's for K which also appears in our measurements. The absence of such a peak in our measured Q _T's and Q _Ps's (preliminary) for Na in this energy range is also consistent with the same theory. Comparisons with five-state CCA calculations of Q _T which do not take Ps-formation into account also show good agreement with our positron-Na, K, and Rb Q _T measurements for energies above 20 eV, but show dramatic departures from our measurements below 10 eV for K and Rb.
N. Kugler - One of the best experts on this subject based on the ideXlab platform.
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Nd:YAG 200-W average-power oscillator-amplifier system with stimulated-Brillouin-Scattering phase conjugation and depolarization compensation
Journal of the Optical Society of America B, 1997Co-Authors: S. Seidel, N. KuglerAbstract:A flash-lamp-pumped, Q-switched Nd:YAG oscillator-amplifier system with an average output power of 215 W and a beam–parameter product of less than 1 mm mrad is developed. The system operates with a 100-Hz repetition rate and emits a burst of 20 Q-switched pulses during each flash-lamp pulse with pulse durations of 100 ns. The high beam quality of the amplified beam is realized by a double-pass configuration of the amplifiers with a phase conjugating stimulated-Brillouin-Scattering Cell. Additionally, the thermally induced birefringence of the amplifiers is compensated by a 90° rotator and an optical image-relay system between two identical amplifier rods.
