Measurement of positronium formation in positron collisions with hydrogen atoms

Sperber, Wolfgang; Becker, D.; Lynn, K. G.; Raith, Wilhelm; Schwab, A.; Sinapius, Günther; Spicher, Gottfried; Weber, Marc H.

doi:10.1103/physrevlett.68.3690

Cited by 67 publications

(24 citation statements)

References 33 publications

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“…In Figure 2 we show the cross section measured by Zhou et al (1997) from threshold to greater than 100 eV, where it becomes negligible. Near the peak, this cross section is significantly less than that measured by Sperber et al (1992) (used by Wallyn et al 1994 andGuessoum et al 1997), but the Sperber measurement was later superseded by a new measurement by the same group (Weber et al 1994), which is consistent with the Zhou et al (1997) result.…”

Section: Positronium Formation Processessupporting

confidence: 79%

The Physics of Positron Annihilation in the Solar Atmosphere

Murphy

Skibo

et al. 2005

ASTROPHYS J SUPPL S

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We compile the most recently measured and calculated cross sections for processes relevant to annihilation of positrons in solar flares and present the final evaluated cross sections. We calculate the 511 keV annihilation line spectrum, the number of 2 line photons produced per positron, and the relative strength of the 3 continuum for each of the annihilation processes, using a Monte Carlo code that simulates the thermalization of and positronium production by $MeV positrons. We calculate the thermally averaged annihilation and positronium production rates and the positronium quenching rates. We apply the results to four specific environments (fully ionized, neutral, partially ionized, and a non-local thermodynamic equilibrium model of the quiet solar atmosphere), calculating the relative strengths of each process and the combined total annihilation line spectrum. The results are compared with data obtained recently from the high spectral resolution detectors of RHESSI. We find that positron annihilation in solar flares can occur in a wide variety of environments. The cross sections presented here are also useful for evaluation of positron annihilation in other environments such as the interstellar medium.

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Section: Positronium Formation Processessupporting

confidence: 79%

The Physics of Positron Annihilation in the Solar Atmosphere

Murphy

Skibo

et al. 2005

ASTROPHYS J SUPPL S

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“…This means that from at least 31 eV up to 302 eV, although the integrated elastic cross section is appreciably larger for electrons than for positrons, the sum of the integrated inelastic cross sections, including all excitations, ionization, and (for e+'s) positronium formation must be just the right amount larger for e+'s than it is for e 's to nearly exactly compensate for the differences in their integrated elastic cross sections. It is~~~~~~I also intriguing that the e+ and e QT's have merged to within 5% at an energy of 31 eV where the measured [20] positronium formation cross section comprises about 70% of QT for e+-H scattering. Noise problems for e energies below 30 eV prevented us from investigating whether our observed merging of Qr's extends to even lower energies.…”

mentioning

confidence: 98%

Measurements of total cross sections for positrons and electrons colliding with atomic hydrogen

et al. 1994

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We have made the first measurements of total cross sections (gr) for 5 to 302 eV positrons (e+) and 31 to 302 eV electrons (e ) scattered by atomic hydrogen. A beam transmission technique is used where the e+ or e beam passes through a low temperature scattering cell containing a mixture of hydrogen atoms and molecules generated in an adjacent radio-frequency discharge region. We obtain absolute gr's by using the factor required to normalize our present relative e+-Hq Qr measurements to our prior absolute results. The present e+and e -H gr's are found to be merged within about 5% between 31 and 302 eV.

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“…This equation was obtained from the experimental data of Sperber et al (1992) with the approximation of Fatuzzo et al (2001). The corresponding time of positron annihilation at different energies an ¼ (nv an ) À1 is shown in Figure 1 by a dotted line.…”

Section: Numerical Calculations Of Thermal Positron Numbers For the Cmentioning

confidence: 99%

Annihilation Emission from the Galactic Black Hole

Cheng

Chernyshov

Dogiel

2006

ApJ

112

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Both diffuse high-energy gamma rays and an extended electron-positron annihilation line emission have been observed in the Galactic Center (GC) region. Although X-ray observations indicate that the Galactic black hole Sgr A Ã is inactive now, we suggest that Sgr A Ã can become active when a captured star is tidally disrupted and matter is accreted into the black hole. As a consequence the Galactic black hole could be a powerful source of relativistic protons. We are able to explain the current observed diffuse gamma rays and the very detailed 511 keV annihilation line of secondary positrons by p-p collisions of such protons, with appropriate injection times and energy. Relativistic protons could have been injected into the ambient material if the black hole captured a 50 M star at several tens times 10 6 yr ago. An alternative possibility is that the black hole continues to capture stars with $1 M every 10 5 yr. Secondary positrons produced by p-p collisions at energies k30 MeV are cooled down to thermal energies by Coulomb collisions and are annihilated in the warm neutral and ionized phases of the interstellar medium with temperatures about several eV, because the annihilation cross section reaches its maximum at these temperatures. It takes about 10 million years for the positrons to cool down to thermal temperatures so that they can diffuse into a very large extended region around the GC. A much more recent star capture may also be able to account for recent TeVobservations within 10 pc of the GC, as well as for the unidentified GeV gamma-ray sources found by EGRET at GC. The spectral difference between the GeV and TeV flux could be explained naturally in this model as well.

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Measurement of positronium formation in positron collisions with hydrogen atoms

Cited by 67 publications

References 33 publications

The Physics of Positron Annihilation in the Solar Atmosphere

The Physics of Positron Annihilation in the Solar Atmosphere

Measurements of total cross sections for positrons and electrons colliding with atomic hydrogen

Annihilation Emission from the Galactic Black Hole

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