G. Breit

Bio: G. Breit is an academic researcher from Yale University. The author has contributed to research in topics: Scattering & Nucleon. The author has an hindex of 30, co-authored 115 publications receiving 7141 citations. Previous affiliations of G. Breit include New York University & University of Wisconsin-Madison.

Capture of Slow Neutrons

Abstract: Current theories of the large cross sections of slow neutrons are contradicted by frequent absence of strong scattering in good absorbers as well as the existence of resonance bands. These facts can be accounted for by supposing that in addition to the usual effect there exist transitions to virtual excitation states of the nucleus in which not only the captured neutron but, in addition to this, one of the particles of the original nucleus is in an excited state. Radiation damping due to the emission of $\ensuremath{\gamma}$-rays broadens the resonance and reduces scattering in comparison with absorption by a large factor. Interaction with the nucleus is most probable through the $s$ part of the incident wave. The higher the resonance region, the smaller will be the absorption. For a resonance region at 50 volts the cross section at resonance may be as high as ${10}^{\ensuremath{-}19}$ ${\mathrm{cm}}^{2}$ and 0.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}20}$ ${\mathrm{cm}}^{2}$ at thermal energy. The estimated probability of having a nuclear level in the low energy region is sufficiently high to make the explanation reasonable. Temperature effects and absorption of filtered radiation point to the existence of bands which fit in with the present theory.

The Effect of Retardation on the Interaction of two Electrons

Abstract: An approximate wave-equation (6) is set up which takes into account terms of the order ${(\frac{v}{c})}^{2}$ in the interaction of two electrons. This equation (6) is reduced to a form (48) which can be interpreted in terms of electronic spins. Disregarding the effect of retardation the two electrons are described by formula (10). This is reduced to a form (36) which can also be described in terms of spins. It is shown that the retarded equation (48) differs from the non-retarded (36) by terms which affect the fine structur of orthohelium and which have not been known so far.The derivation of the wave-equation (6) is made first in configuration space and later by the Heisenberg-Pauli theory of wave-fields. The latter method is used only to terms of the first order in the Coulomb interaction. It is shown from the consideration of (36) that it cannot be the correct equation and that the modifications due to retardation introduced in (6) and (48) are necessary. These modifications are appreciable only for spectra of elements with low atomic number.

Collision of two light quanta

Abstract: The recombination of free electrons and free positrons and its connection with the Compton effect have been treated by Dirac before the experimental discovery of the positron. In the present note are given analogous calculations for the production of positron electron pairs as a result of the collision of two light quanta. The angular distribution of the ejected pairs is calculated for different polarizations, and formulas are given for the angular distribution of photons due to recombination. The results are applied to the collision of high energy photons of cosmic radiation with the temperature radiation of interstellar space. The effect on the absorption of such quanta is found to be negligibly small.

CODATA Recommended Values of the Fundamental Physical Constants: 2006

Abstract: This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

Die gegenwärtige Situation in der Quantenmechanik

Abstract: § 71. Die Au]hebung der ,,Verschrdinkung". Das Ergebnis abhdingig vom Willen des Experimentators. W i r kehren wieder zum al lgemeinen Fal l der ,Ve r sch r~nkung" znrfick, ohne gerade den besonderen Fa i l eines ~{eBvorgangs im Ange zu haben, wie soeben. Die Erwar tungska ta loge zweier 1{6> per A und B sollen sich durch vorf ibergehende Wechse lwi rkung verschr~nkt haben. J e t z t sollen die K6rper wieder ge t renn t seth. ] )ann kann ich einen davon, e twa B, hernehmen und meine unter m a x i m a l gewordene Kenntn is yon ihm du tch ?¢Iessungen sukzessive zu einer max ima len erggnzen. Ich behaup te : sobald mi r das z u m erstenmal gelingt, und nicht eher, wird erstens die Verschrgnkung gerade gel6st sein und werde ich zweitens durch die Messungen an B u n t e r Ausnf i tzung der Kondi t ionalsa tze , die bestanden, max ima le Kermtnis such yon A erworben haben. D e n n erstens Meibt die Kem~tnis yore Gesarntsys tem framer maximal , well sie du t ch gu ie und genaue Messungen keinesfalls ve rdorben wird. Zwei tens: Kondi t ionalsgtze yon der F o r m ,,wenn an A . . . . . . dann an B . . . . . " , kann es n icht mehr geben, sobald wi t yon B einen Maximalka ta log erlangt haben. Denn der ist nieht bedingt und zu ibm kann f iberhaupt nichts auf B Bezfigliches mehr h inzut re ten . Dr i t t ens : Kond i t i ona l s i t z e in umgekehr t e r R ich tung (,,wenn an B . . . . . . dann an A . . . . . ") lassen sich in S~itze fiber A allein umwandeln , well j a alle Wahrsche in l ichke i ten ffir B schon bedingungslos bekann t sind. Die Ver sch r in kung ist a lso rest los beseit igt , und da die Kenntn is v o m Gesamtsys t em max ima l gebl ieben ist, kann sie nur dar in bestehen, dab zum Maximalka ta tog ffir B ein ebensolcher ffir A h inzut r i t t . Es kann abe t such nicht e twa vorkommen, dab A indirekt , durch die Messungen an B, schon max ima l bekann t wird, bevor B es noch ist. Denn dann funkt ionieren alle Schlfisse in umgekehr t e r Richtung, d. h. B ist es au th . Die Sys teme werden gleichzeit ig max ima l bekannt , wie behaupte t . Nebenbei bemerkt , wfirde das such geiten, wenn man das Messen nicht gerade auf eines der beiden Sys teme beschrltnkt. Abe t das In teressante ist gerade, dab m a n es auf eines der beiden beschrgnken lcann; dab mari dami t ans ZieI kommt . Welche 5{essungen an B und in welcher iReihenfolge sie vo rgenommen werden, fat ganz der ~Nill-

Feshbach resonances in ultracold gases

Abstract: Feshbach resonances are the essential tool to control the interaction between atoms in ultracold quantum gases. They have found numerous experimental applications, opening up the way to important breakthroughs. This review broadly covers the phenomenon of Feshbach resonances in ultracold gases and their main applications. This includes the theoretical background and models for the description of Feshbach resonances, the experimental methods to find and characterize the resonances, a discussion of the main properties of resonances in various atomic species and mixed atomic species systems, and an overview of key experiments with atomic Bose-Einstein condensates, degenerate Fermi gases, and ultracold molecules.