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Nobel prize to R. Hofstadter awarded in 1961 "for his pioneering studies of electron scattering in atomic nuclei and for his thereby achieved discoveries concerning the structure of the nucleons''. Co-winner R. Mössbauer "for his researches concerning the resonance absorption of gamma radiation and his discovery in this connection of the effect which bears his name''

MCALLISTER 1956

McAllister, R.W.; Hofstadter, R.;
Elastic Scattering of 188 MeV Electrons from Proton and the Alpha Particle
Phys. Rev. 102 (1956) 851;

Reprinted in
R. N. Cahn and G. Goldhaber, The Experimental Foundations of Particle Physics, Cambridge Univ. Press (1991) 234.

Abstracts
The elastic scattering of 188 MeV electrons from gaseous targets of hydrogen and helium has been studied. Elastic profiles has been obtained at laboratory angles between 35^° and 138^°. The areas under such curves, within energy limits of ±1.5 MeV of the peak, have been measured and the results plotted against angle. In the case of hydrogen, a comparison has been made with the theoretical predictions of the Mott formula for elastic scattering and also with a modified Mott formula (due to Rosenbluth) taking into account both the anomalous magnetic moment of the proton and a finite size effect. The comparison shows that a finite size of the proton will account for the results and the present experiment fixes this size. The root-mean-square radii of charge and magnetic moment are each (0.74 ± 0.24)´ 10^-13 cm. In obtaining these results it is assumed that the usual laws of electromagnetic interaction and the Coulomb law are valid at distances less than 10^-13 cm and the charge and moment radii are equal. In helium, large effects of the finite size of the alpha-particle are observed and the rms radius of the alpha particle is found to be (1.6 ± 0.1) ´ 10^-13 cm.

Accelerator STAN Detectors SPEC

Related references
More (earlier) information appears in
R. Hofstadter and R. W. McAllister, Phys. Rev. 98 (1955) 217;
R. Hofstadter, B. Hahn, A. W. Knudsen, and J. A. McIntyre, Phys. Rev. 95 (1954) 512;
R. Hofstadter, H. R. Fetcher, and J. A. McIntyre, Phys. Rev. 92 (1953) 978;
R. Hofstadter, H. R. Fetcher, and J. A. McIntyre, Phys. Rev. 91 (1953) 422;
See also
G. W. Tautfest and H. R. Fechter, Rev. Sci. Inst. 26 (1955) 229;
G. W. Tautfest and H. R. Fechter, Phys. Rev. 96 (1954) 35;
J. A. McIntyre and R. Hofstadter, Phys. Rev. 98 (1955) 158;
M. N. Rosenbluth, Phys. Rev. 79 (1950) 615;
Yennie, Wilson, and D. G. Ravenhall, Phys. Rev. 92 (1953) 1325;

Reactions

	e– p p e–	0.188 GeV (Elab)	angp
	e– He He e–	0.188 GeV (Elab)	angp

Particles studied

	p	mom
	He	mom

Record comments
First measurement of the proton electromagnetic radius.

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