Delbruck scattering
Encyclopedia
Delbrück
scattering, the deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization has been observed. However, the process of scattering of light by light, has not been observed. In both cases, it is a process described by Quantum Electrodynamics
(QED).
worked in Berlin as an assistant to Lise Meitner
, who was collaborating with Otto Hahn
on the results of irradiating uranium with neutrons. During this period he wrote a few papers, one of which turned out to be an important contribution on the scattering of gamma rays by a Coulomb field due to polarization of the vacuum produced by that field (1933). His conclusion proved to be theoretically sound but inapplicable to the case in point, but 20 years later Hans Bethe
confirmed the phenomenon and named it "Delbrück scattering".
In 1953, Robert Wilson
observed Delbrück scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei.
Addendum:
Delbrück scattering is the coherent elastic scattering of photons in the Coulomb field of heavy nuclei. It is one of the two nonlinear effects of quantum electrodynamics (QED) in the Coulomb field investigated experimentally. The other is the splitting of a photon into two photons. Delbrück scattering was introduced by Max Delbrück in order to explain discrepancies between experimental and predicted data in a Compton scattering experiment on heavy atoms carried out by Meitner and Köster [3]. Delbrück’s arguments were based on the relativistic quantum mechanics of Dirac according to which the QED vacuum is filled with electrons of negative energy or - in modern terms – with electron-positron pairs. These electrons of negative energy should be capable of producing coherent-elastic photon scattering because the recoil momentum during absorption and emission of the photon is transferred to the total atom while the electrons remain in their state of negative energy. This process is the analog of atomic Rayleigh scattering with the only difference that in the latter case the electrons are bound in the electron cloud of the atom. The experiment of Meitner and Köster [3] was the first in a series of experiments where the discrepancy between experimental and predicted differential cross sections for elastic scattering by heavy atoms were interpreted in terms of Delbrück scattering. From the present point of view these early results are not trustworthy. Reliable investigations were possible only after modern QED techniques based on Feynman diagrams were available for quantitative predictions, and on the experimental side photon detectors with high energy resolution and high detection efficiency had been developed. This was the case at the beginning of the 1970th when also Computers with high computing capacity were in operation which delivered numerical results for Delbrück scattering amplitudes with sufficient precision. After a first observation of Delbrück scattering in a high-energy, small-angle photon scattering experiment carried out at DESY (Germany) in 1973 [4], the essential breakthrough came with the Göttingen (Germany) experiment in 1975 carried out at an energy of 2.754 MeV [5]. The DESY experiment
corresponds to the case of extreme forward scattering where only the imaginary part of the scattering amplitude
is of importance. For the calculation approximations are possible which exist is two versions (i) the approximation of Cheng and Wu and (ii) the approximation of Milstein and Strakhovenko. Though differing substantially, the two calculations lead to the same result numerically. In the Göttingen experiment Delbrück scattering was observed as the dominant contribution to the coherent-elastic scattering process, in addition to minor contributions stemming from atomic Rayleigh scattering and nuclear Rayleigh scattering. This experiment [5] was the first where exact predictions based on Feynman diagrams were confirmed with high precision and, therefore, has to be considered as the first definite observation of Delbrück scattering. For a comprehensive description of the present status of Delbrück scattering
see [6,7].
Nowadays, the most accurate measurements of high-enegy Delbrück scattering are performed at the Budger Institute of Nuclear Physics in Novosibirsk (Russia) [8]. The experiment where photon splitting was really observed for the first time was also performed at the Budger Institute of Nuclear Physics [9,10].
Max Delbrück
Max Ludwig Henning Delbrück was a German-American biophysicist and Nobel laureate.-Biography:Delbrück was born in Berlin, German Empire...
scattering, the deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization has been observed. However, the process of scattering of light by light, has not been observed. In both cases, it is a process described by Quantum Electrodynamics
Quantum electrodynamics
Quantum electrodynamics is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and special relativity is achieved...
(QED).
Discovery
From 1932 to 1937, Max DelbrückMax Delbrück
Max Ludwig Henning Delbrück was a German-American biophysicist and Nobel laureate.-Biography:Delbrück was born in Berlin, German Empire...
worked in Berlin as an assistant to Lise Meitner
Lise Meitner
Lise Meitner FRS was an Austrian-born, later Swedish, physicist who worked on radioactivity and nuclear physics. Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded the Nobel Prize...
, who was collaborating with Otto Hahn
Otto Hahn
Otto Hahn FRS was a German chemist and Nobel laureate, a pioneer in the fields of radioactivity and radiochemistry. He is regarded as "the father of nuclear chemistry". Hahn was a courageous opposer of Jewish persecution by the Nazis and after World War II he became a passionate campaigner...
on the results of irradiating uranium with neutrons. During this period he wrote a few papers, one of which turned out to be an important contribution on the scattering of gamma rays by a Coulomb field due to polarization of the vacuum produced by that field (1933). His conclusion proved to be theoretically sound but inapplicable to the case in point, but 20 years later Hans Bethe
Hans Bethe
Hans Albrecht Bethe was a German-American nuclear physicist, and Nobel laureate in physics for his work on the theory of stellar nucleosynthesis. A versatile theoretical physicist, Bethe also made important contributions to quantum electrodynamics, nuclear physics, solid-state physics and...
confirmed the phenomenon and named it "Delbrück scattering".
In 1953, Robert Wilson
Robert R. Wilson
Robert Rathbun Wilson was an American physicist who was a group leader of the Manhattan Project, a sculptor, and an architect of Fermi National Laboratory , where he was also the director from 1967–1978....
observed Delbrück scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei.
Addendum:
Delbrück scattering is the coherent elastic scattering of photons in the Coulomb field of heavy nuclei. It is one of the two nonlinear effects of quantum electrodynamics (QED) in the Coulomb field investigated experimentally. The other is the splitting of a photon into two photons. Delbrück scattering was introduced by Max Delbrück in order to explain discrepancies between experimental and predicted data in a Compton scattering experiment on heavy atoms carried out by Meitner and Köster [3]. Delbrück’s arguments were based on the relativistic quantum mechanics of Dirac according to which the QED vacuum is filled with electrons of negative energy or - in modern terms – with electron-positron pairs. These electrons of negative energy should be capable of producing coherent-elastic photon scattering because the recoil momentum during absorption and emission of the photon is transferred to the total atom while the electrons remain in their state of negative energy. This process is the analog of atomic Rayleigh scattering with the only difference that in the latter case the electrons are bound in the electron cloud of the atom. The experiment of Meitner and Köster [3] was the first in a series of experiments where the discrepancy between experimental and predicted differential cross sections for elastic scattering by heavy atoms were interpreted in terms of Delbrück scattering. From the present point of view these early results are not trustworthy. Reliable investigations were possible only after modern QED techniques based on Feynman diagrams were available for quantitative predictions, and on the experimental side photon detectors with high energy resolution and high detection efficiency had been developed. This was the case at the beginning of the 1970th when also Computers with high computing capacity were in operation which delivered numerical results for Delbrück scattering amplitudes with sufficient precision. After a first observation of Delbrück scattering in a high-energy, small-angle photon scattering experiment carried out at DESY (Germany) in 1973 [4], the essential breakthrough came with the Göttingen (Germany) experiment in 1975 carried out at an energy of 2.754 MeV [5]. The DESY experiment
corresponds to the case of extreme forward scattering where only the imaginary part of the scattering amplitude
is of importance. For the calculation approximations are possible which exist is two versions (i) the approximation of Cheng and Wu and (ii) the approximation of Milstein and Strakhovenko. Though differing substantially, the two calculations lead to the same result numerically. In the Göttingen experiment Delbrück scattering was observed as the dominant contribution to the coherent-elastic scattering process, in addition to minor contributions stemming from atomic Rayleigh scattering and nuclear Rayleigh scattering. This experiment [5] was the first where exact predictions based on Feynman diagrams were confirmed with high precision and, therefore, has to be considered as the first definite observation of Delbrück scattering. For a comprehensive description of the present status of Delbrück scattering
see [6,7].
Nowadays, the most accurate measurements of high-enegy Delbrück scattering are performed at the Budger Institute of Nuclear Physics in Novosibirsk (Russia) [8]. The experiment where photon splitting was really observed for the first time was also performed at the Budger Institute of Nuclear Physics [9,10].