Showing papers on "Positronium published in 1971"
TL;DR: Positron-hydrogen scattering below positronium pickup threshold by Hylleraas bound technique, discussing phase shifts and linear parameters as discussed by the authors, discussed phase shift and linear parameter.
Abstract: Positron-hydrogen scattering below positronium pickup threshold by Hylleraas bound technique, discussing phase shifts and linear parameters
98 citations
50 citations
TL;DR: In this paper, the authors reported the observation of free positronium emitted into a vacuum from the surface of a thin film of MgO powder, and they measured the kinetic energy of the positronsium.
26 citations
TL;DR: In this article, the influence of magnetic field on the longer living component in the time spectra of positrons annihilated in LiF and NaCl was studied and the resulting quenching effect was interpreted as evidence for the formation of positronium-like system.
Abstract: The influence of a magnetic field on the longer living component in the time spectra of positrons annihilated in LiF and NaCl was studied. The resulting quenching effect is interpreted as evidence for the formation of positronium-like system.
21 citations
TL;DR: In this article, the influence of a static magnetic field on the long-lived component in the time spectra of positrons annihilated in additively coloured kcl was studied.
Abstract: The influence of a static magnetic field on the long-lived component in the time spectra of positrons annihilated in additively coloured kcl was studied. The resulting quenching effect is interpreted as evidence for the formation of a relaxed positronium in an ion vacant site.
20 citations
19 citations
TL;DR: Positron annihilation lifetime spectra and two-gamma angular distributions have been measured for DL-leucine before and after γ-irradiation as discussed by the authors, showing that free radicals produced inhibit the formation of positronium rather than effect its ortho-to-para conversion.
18 citations
16 citations
14 citations
TL;DR: The time annihilation spectra of positrons in quartz single crystals was shown to be of complex structure and the τ 2 -component was quenched by a magnetic field to an extent which strongly suggests positronium formation as discussed by the authors.
11 citations
Journal Article•
TL;DR: In this article, a superposition of single center static and nonspherical polarization potentials is used to approximate the elastic positron-hydrogen collision in Legendre polynomials.
Abstract: Elastic positron–hydrogen molecule collisions are considered below the first electronic excitation threshold. The interaction of the incoming positron with the hydrogen molecule is represented by a superposition of single center static and nonspherical polarization potentials. The static potential is expanded to second degree in Legendre polynomials. The Chebyshev polynomials are used to improve the truncated Legendre series approximation and the effect of including the fourth degree contribution is shown to be slight. Positronium formation effects are neglected. Two semiphenomenological polarization potentials are used, and it is shown that the parameters can be suitably adjusted to reproduce the results obtained if the Henry and Lane polarization potential is used. It is shown that the partial Ramsauer–Townsend effect is useful in determining the values of polarization potential parameters. Total elastic scattering cross sections are given for incoming positron energies between about 0.4 and 14 eV while...
TL;DR: In this paper, the angular correlation of photons from the two-gamma decay of positrons in some substances (paraffin wax, nylon, teflon, fused quartz, liquid and solid water) has been measured in the presence of an external magnetic field up to 21 kG.
Abstract: The angular correlation of photons from the two-gamma decay of positrons in some substances (paraffin wax, nylon, teflon, fused quartz, liquid and solid water) has been measured in the presence of an external magnetic field up to 21 kG. The narrow-component intensity of the angular spectrum, due to the rate of positronium (Ps) which self-annihilates from the singlet state, results enhanced by theH field. The effect, produced by the magnetic mixing of two spin states of Ps, is shown to be in agreement with theory. Measurements in powdered air-saturated aluminium oxide reveal a different behaviour of Ps which can be explained by the ortho-Ps quenching property of the O2 molecules absorbed.
TL;DR: In this paper, the branching ratio of the forbidden decay, 1 3 S 1 → 4λ, to the allowed decay has been found to be F T 4λ = 1.2×10 -5 λ 2.
Abstract: If the electromagnetic interactions are invariant under charge conjugation, C, then singlet positronium (Ps) can only decay into an even number of photons, while triplet Ps can only decay into an odd number of photons. In this paper we consider a model Hamiltonian which violates C invariance but conserves parity. If λ is the coupling constant in the proposed C-noninvariant interaction, then the branching ratio of the forbidden decay, 1 3 S 1 →4λ, to the allowed decay, 1 3 S 1 →3λ, has been found to be F T 4λ =1.2×10 -5 λ 2 . An experimental upper limit on F T 4λ would provide a novel check of C invariance in electromagnetic interactions, and would also yield new information on the e - eγγγγ interaction. At present, indirect limits on F T 4λ show it to be less than about 10 -2 . We are now working on an experiment which is designed to reduce this upper limit to 10 -5 -10 -6 . If successful, it will subject the proposed interaction, or any similar interaction leading to 1 3 S 1 →4γ, to a stringent test. An outline of the experiment is included in this paper.
TL;DR: In this paper, the positron lifetimes in liquid argon confirm earlier results of Paul and of Liu and Roberts, in particular the orthopositronium intensity is anomalously low in this liquid, only 7%.
Abstract: New results for positron lifetimes in liquid argon confirm earlier results of Paul and of Liu and Roberts. In particular the orthopositronium intensity is anomalously low in this liquid, only 7%. I...
TL;DR: Positron lifetime spectra in γ-irradiated 10 M NaOH glass at 85°K show no significant effect due to the presence of 1.7 to 7.0 × 1018 trapped electrons cm−3 as mentioned in this paper.
TL;DR: Using a pseudopotential approach, an approximate wave function for positron-alkali atom bound state was constructed and a number of physical quantities calculated in this paper, including the electronic densities at the positron and the annihilation rates.
TL;DR: Positronium was found to be highly sensitive to the presence of carbonium ions in the structures of diamagnetic organic molecules as mentioned in this paper, due to strong positronium quenching by the carbonium ion.
Journal Article•
TL;DR: In this article, the optical potential of Bell and Squires was used to formulate the problem of elastic scattering of positrons from atoms, and the single-particle states of the electron were chosen to be the hydrogenic solutions, while the positron states were obtained by using a singleparticle potential which includes the Hartree potential plus a model polarization potential.
Abstract: The optical potential of Bell and Squires is used to formulate the problem of the elastic scattering of positrons from atoms. An application is made to the scattering of $S$-wave positrons from hydrogen below the threshold for positronium formation. The single-particle states of the electron are chosen to be the hydrogenic solutions, while the positron states are obtained by using a single-particle potential which includes the Hartree potential plus a model polarization potential. Various models are investigated and a choice is made which effectively maximizes the calculated phase shifts through second order in the perturbation expansion of the optical potential. Phase shifts thus obtained yield approximately 67-80% of the difference between the static Hartree results and the variational results of Schwartz. Higher-order effects are evaluated using the techniques of Kelly. Intermediate states of multipole $l\ensuremath{\le}3$ are included.
TL;DR: The physicochemical interaction of hydrogen-like positronium and muonium atomic systems, in which the proton is replaced by a positron or a μ+-meson, and mesonic atoms containing a μ− − or a π− −meson instead of an electron have been examined.
Abstract: The physicochemical interaction of hydrogen-like positronium and muonium atomic systems, in which the proton is replaced by a positron or a μ+-meson, and mesonic atoms containing a μ−- or a π−-meson instead of an electron have been examined. The nuclear-physical methods for the investigation of processes involving the new atoms have yielded information which significantly supplements that available from the usual research techniques. The bibliography includes 123 references.
01 Feb 1971
TL;DR: In this paper, the life-times of positrons inn-octane and n-hexadecane were measured at different temperatures and the viscosities and densities were correlated with the life times on the basis of the free volume model.
Abstract: The life-times of positrons inn-octane andn-hexadecane are measured at different temperatures. The viscosities and densities are shown to be correlated with the life-times on the basis of the free volume model. Similar data forn-alkanes and chemical isomers are interpreted in terms of this model.
TL;DR: In this article, the halfwidth of the narrow component of the correlation curves depends on the state of aggregation (whether the substance is a single crystal, a powder, or a glass).
Abstract: The angular distribution of annihilation γ's in quartz shows that the half-width of the narrow component of the correlation curves depends on the state of aggregation (whether the substance is a single crystal, a powder, or a glass). Before annihilation, the positronium atoms may be captured by defects (vacancies, pores, or regions of reduced electron density); if this is true, the half-width of the narrow component and the long positron lifetime depend on the characteristics of the defects or traps. The sizes of the defects in certain solids (quartz glass; powdered beryllium, magnesium, and aluminum oxides; and polytetrafluoroethylene) are evaluated from the experimental half-width of the narrow component and the long positron lifetime.