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Saito, Haruo; Hyodo, Toshio

doi:10.1103/physrevlett.90.193401

Cited by 109 publications

(137 citation statements)

References 23 publications

(38 reference statements)

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“…It clearly shows the existence of the quadrupole interaction of Ps in α-quartz. The quadrupole coupling constant has been determined to be d = (3.0 ± 0.9) × 10 −5 eV, yielding the ratio d/ω 0 ≈ 0.038 (for κ ≈ 0.34 [17]) in agreement with the theoretical predictions of Ref. [15].…”

Section: Ps Effective Quadrupole Interactions In Non-cubic Crystalssupporting

confidence: 68%

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Sensitivity of Positronium Momentum Distribution to Phase Transitions in Crystalline Dielectrics

Bondarev

Hyodo

2005

Acta Phys. Pol. A

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Section: Ps Effective Quadrupole Interactions In Non-cubic Crystalssupporting

confidence: 68%

“…The anisotropy measured yields the ratio d/ω 0 ≈ 0.16 for κ ≈ 0.34 reported recently in Ref. [17]. This is too large compared with the theoretical estimate d/ω 0 ≈ 0.03 [15].…”

Section: Ps Effective Quadrupole Interactions In Non-cubic Crystalsmentioning

confidence: 56%

Sensitivity of Positronium Momentum Distribution to Phase Transitions in Crystalline Dielectrics

Bondarev

Hyodo

2005

Acta Phys. Pol. A

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“…It is believed that much better timing resolution power can be obtained with the available BaF 2 crystals and PMTs if these are carefully selected according to their performance, specifically according to the UV light yield, the QE at 190-220 nm and the time jitter. In this context it is to be noted that performance of PMTs differs from piece to piece [12]: various pairs of Hamamatsu PMTs H3378-50 yield the timing resolution power in PLT measurements that changes within the range of 133-161 ps. Regarding the data on PMT time jitter, a novel, relatively cheap technique based on the use of sonoluminescence pulsed light sources may be employed [13].…”

Section: Discussionmentioning

confidence: 99%

Digital positron lifetime spectroscopy: present status and outlook

Bečvář

2007

Phys. Status Solidi (c)

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PACS 07.85.Fv, 78.70.Bj, 84.30.Sk This contribution summarizes achievements in instrumentation for positron lifetime measurements with emphasis on digital spectrometric systems. A significant part of the data presented are based on a longterm exploitation of a conventional positron lifetime spectrometer developed at Charles University in early 90s, on bench-mark testing measurements with this spectrometer working temporarily in conjunction with a pair of 8-bit, 4 GS/s digitizers and on analogous measurements with a recently assembled digital positron lifetime spectrometer. In addition, results from testing experiments with microchannel plate photomultipliers are briefly reported. Further development of positron lifetime technique is discussed.1 Introduction The positron-lifetime (PLT) spectroscopy turned out to be a well-proven and in many cases irreplaceable tool for studying microstructure of a broad class of condensed-matter systems. However, in spite of numerous efforts to improve quality of PLT measurements, these still suffer from a limited timing resolution and with hardly controllable distortions of the PLT spectra that may have a negative impact on correctness of the deduced positron lifetimes.In 1953, Bell and Graham, while studying behavior of positronium, observed that decay curves displayed components with positron lifetime of about 100 ps [1]. It is somewhat surprising that after five decades the threshold for observation of short positron lifetime components has been reduced only by a factor of three. Indeed, even now, only a few PLT spectrometers are able to reveal presence of components in the PLT spectra with a lifetime below 30 ps. This clearly demonstrates that the development of the PLT instrumentation stagnates.This contribution is focused on the latest improvements in PLT instrumentation and suggests ways how to enhance its performance.

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“…A long standing disagreement between experimental and theoretical values for the triplet rate has recently been laid to rest [8][9][10]. In the 1950's and 60's, this prediction was checked experimentally using 64 Cu and…”

Section: Introductionmentioning

confidence: 95%

Ratio of positron annihilation into three photons versus two

Pevovar

Weber

Lynn

2007

Phys. Status Solidi (c)

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.+z, 78.70.BjRare and exotic annihilations of free positrons have been investigated extensively since the first discovery of positrons. The annihilation into three photons, however, has been neglected following theoretical work by Øre and Powell and several experimental studies using radioactive sources. Øre and Powell predicted that only one in 372 annihilations would result in the emission of three photons due to the parallel spin alignment of the electron-positron pair. A number of approximations were made to make the calculation tractable most notably the assumption of low momentum. No material dependence was expected. Subsequent experiments showed some dependence on material properties, notably on Z and density. We have set up an experiment to measure the annihilation into two and three photons with a five detector coincidence technique. Our results for low Z targets of Kapton, silicon and carbon, indicate no material dependence. The simplicity of the experiment and the high sensitivity for three photon annihilations render this method suitable for the characterization of porosity particularly when the concentration of pores is small. 1 Introduction The most common mode of annihilation of free unbound positrons is the emission of two gamma rays. Energy and momentum conservation require annihilations into at least 2 photons, and in the case of opposite spin alignment of electrons and positrons, the number has to be even. This is the basis for positron annihilation as a tool for the study of electron momentum distributions in materials as initially demonstrated by deBenedetti et al. [1]. Since then the field of Doppler broadening has become a powerful tool for materials studies of Fermi surfaces and defects.In the case of spin alignment the number of photons has to be odd (in the absence of angular momentum) to accommodate the total spin of 1 for the pair. As a higher order process, this rarely occurs when a vast number of electrons with all spin orientations are present, such as in metals. Shortly after the prediction and discovery of the positrons, Øre and Powell predicted the ratio of three photon annihilations over two photon events in the case of nearly free electrons and low energy positrons [2,3]. Earlier work by Lifshitz [4] and Ivanenko and Sokolov [5] is now considered wrong. Øre and Powell obtained the ratio of three photon annihilation vs. two photon annihilation rates ( i λ) the spin averaged inverse ratio R of the lifetimes ( i τ) of triplet positronium (ortho-Ps, spins parallel, i = 3) to that of singlet positronium (para-Ps, spins antiparallel, i = 1). Using current theoretical lifetime values by Adkins, et al. [6,7]. the ratio is

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Direct Measurement of the Parapositronium Lifetime inα−SiO2

Cited by 109 publications

References 23 publications

Sensitivity of Positronium Momentum Distribution to Phase Transitions in Crystalline Dielectrics

Sensitivity of Positronium Momentum Distribution to Phase Transitions in Crystalline Dielectrics

Digital positron lifetime spectroscopy: present status and outlook

Ratio of positron annihilation into three photons versus two

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