Alternative interpretation of the double atomic-field bremsstrahlung experiment

Lehtihet, H.E.; Quarles, C.A.

doi:10.1103/physreva.39.4274

Cited by 12 publications

(3 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…10. Second, following the reasoning put forward by Lehtihet and Quarles, 14 we have calculated the (effective) cross section of the predicted alternative process as shown by the dashed lines in Figs. 1 and 2.…”

Section: Nyi Dkidilimentioning

confidence: 99%

Two-photon bremsstrahlung of free atoms

Hippler

1991

Phys. Rev. Lett.

View full text Add to dashboard Cite

The two-photon bremsstrahlung emitted in collisions of 7-15-keV electrons with free (gaseous) argon, krypton, and xenon atoms was observed. The agreement with recent theoretical calculations is poor.PACS numbers: 34.80.-iThe acceleration of electrons in the nuclear field of target atoms may give rise to the emission of a continuous spectrum of electromagnetic radiation. Since its first discovery by Rontgen in 1895, ! this "bremsstrahlung" has been recognized as one of the most fundamental physical processes; besides, it has been proven to be of considerably practical relevance to various disciplines. In following decades, the production and the properties of bremsstrahlung radiation were explored quite thoroughly; 2 " 4 today, it is believed that the bremsstrahlung process is well understood and that the corresponding continuous spectrum can be calculated with fair accuracy. This is certainly true for the one-photon process; in contrast, little is known about two-photon or multiphoton bremsstrahlung processes. While other multiphoton processes are well known, for example, in atomic photoionization processes 5 and in free-free transitions, 6 the corresponding bremsstrahlung processes have attracted comparatively little interest over the years. A main reason for this may be found in the relatively small probability for emitting two or more bremsstrahlung photons in a single collision. To our knowledge, the only experimental attempt to investigate the two-photon bremsstrahlung process was performed by Altman and Quarles, 7 who investigated the two-photon process during 75-keV electron impact on solid gold. These authors observed an appreciable fraction of two-photon bremsstrahlung processes, more than 2 orders of magnitude larger than predicted by calculations based on different theoretical approaches. 8,9

show abstract

Section: Nyi Dkidilimentioning

confidence: 99%

Two-photon bremsstrahlung of free atoms

Hippler

1991

Phys. Rev. Lett.

View full text Add to dashboard Cite

show abstract

“…This was undertaken by Lehtihet and Quarles [7][8][9]. A wide variety of background processes were identified and considered; finally, it was suggested that the large experimental cross section could have arisen from a rather complicated process.…”

mentioning

confidence: 99%

Double bremsstrahlung

Kahler¹,

Liu²,

Quarles³

1992

Phys. Rev. Lett.

Self Cite

View full text Add to dashboard Cite

The cross section for double bremsstrahlung differential in the radiated photon energies and angles has been measured for 70-keV electrons on targets of Al, Cu, Ag, Tb, and U for photons radiated at ±45° to the incident beam for photon energies in windows from 10 to 30 keV. In contrast with previous experiments at ±90°, the results are in reasonable agreement with the relativistic first Born approximation at lower Z. However, the results exhibit a Z dependence which disagrees with the first Born Z^ dependence, suggesting the need for consideration of a second Born approximation.PACS numbers: 34.80.-i Double bremsstrahlung is a quantum electrodynamic process in which two photons are radiated simultaneously in the scattering of an electron by an atom. This process was first mentioned by Heitler and Nordheim [I] who estimated that the cross section would be about 137 times smaller than that of single bremsstrahlung, or essentially smaller by a factor of the fine-structure constant due to the emission of the second photon. While the two-photon process is too small to make much contribution to the production of radiation, it is nevertheless especially interesting as an example of a quantum radiative process for which, unlike single bremsstrahlung, there seems to be no prescription for a classical calculation of the cross section. Although recently there has been much interest in two-photon and multiphoton processes, the radiative two-photon process has been studied in only two experiments [2,3], both in a ±90° geometry. In both experiments, a significant discrepancy, as large as 2 orders of magnitude, with theories has been observed.The first measurement of the cross section was made in 1985 by Altman and Quarles [2]. They measured the cross section for two-photon emission for 75-keV electrons on thin targets of silver, terbium, gold, and uranium. The electron was not observed, so a differential cross section integrated over the unobserved electron was measured. Altman and Quarles also evaluated the theoretical cross section by numerical integration of the very complicated formula for the cross-section differential in the two photon energies and angles and the electron angles worked out by Smirnov [4] in the relativistic first Born approximation. The experimental result for gold was about 300 times the computed theoretical value. It was not clear whether the discrepancy was due to an error in the theoretical formula, the numerical integration of the formula, or the experimental data. An independent evaluation of the theory in the nonrelativistic Coulomb approximation was then provided by Veniard, Gavrila, and Maquet [5] and also by Florescu and Djamo [6]. The result for the particular geometry of Ref. [2] was larger by about a factor of 3 than the relativistic Born approximation but was still about a factor of 100 smaller than the observed cross section. These nonrelativistic calculations when evaluated in the Born rather than the Coulomb approximation were close to the relativistic result computed in Ref. [2], sug...

show abstract

“…Theoretical activity was stimulated by a series of experiments [26][27][28][29][30][31][32][33] in which the data on the 2BrS cross section and angular distribution were obtained for relatively high energies of the incident electron and emitted photon (up to 70 keV). Apart from the early work of Smirnov [34], where the 2BrS process was treated in terms of the relativistic first Born approximation (see also [35]), theoretical investigations were based on second order non-relativistic perturbation theory.…”

Section: Introductionmentioning

confidence: 99%