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Title: Structure in the proton and the neutron

Abstract

A survey of the recent work on the structares of the proton and the neutron carried out by high-energy electron-scattering methods is presented. Early work established finite size effects in the proton and led to information about the charge and magnetic density distributions in the proton. The rms size was established to be close to (0.77 plus or minus 0.10) x 10/sup -13/ cm, and the density distributions of charge and anomalous magnetic moment were shown to be approximately of the same shape. The form factors could be described in terms of several alternative models given, for example, by an exponential, gaussian, hollow exponential, hollow gaussian, etc., distribution of densities. Many other shapes were excluded by the experimental data. Recent work by Bumiller and Hofstadter now fixes one among these models that is appropriate to the proton and provides an extremely good fit at all angles between energies of 200 and 650 Mev. The new evidence clearly favors the exponential model with rms radius (0.80 plus or minus 0.04) 10/sup -13/ cm. Recent studies of the proton have attempted to answer the question: how closely similar are the charge and magnetic form factors? This work now shows that the distributionsmore » have the same sizes and shapes to within 10 per cent, and each distribution is given very closely by the exponential model described above with radius (0.80 plus or minus 0.04) x 10/sup -13/. Certain other similar models will be discussed. Early work on the inelastic continuum in the deuteron established that the neutron's magnetic stracture was extended and not a point. It was further shown that the neutron's size was approximately the same as that of the proton. This work has recently been extended by Yearian and Hofstadter to a determination of the variation of the neutron's magnetic form factor over the range where the proton's form factor is known. The new results show: (1) the neutron is not a point, (2) the neutron's magnetic structure has a size lying between the limits 0.61 x 10/sup -13/ cm and 0.80 x 10/sup -13/ cm. The first value (0.61 x 10/sup -13/ cm) is determined by examing the total deuteron electro-disintegration cross section at a given angle and incident energy and comparing this cross section with that of the free proton under the same conditions. The second value (0.80 x 10/sup -13/ cm) is found by examining the peak of the deuteron electro-disintegration cross section. Because of possible contributions to the total cross section by mesonic exchange effects, the second method is believed to be slightly more accurate. The neutron size is, therefore, approximately (0.70 plus or minus 0.10) x 10/sup -13/ cm and probably the larger size 0.90 x 10/sup -13/ cm is correct. Thus the magnetic clouds of the neutron and proton are closely the same. The bearing of these results on the validity of electrodynamics is discussed. Because of the small radius implied by the neutron-electron experiments, there is an anomaly between the neutron and the proton. This is represented by the small charge radius for the neutron and the much larger radius of the proton. Additional information of the structure of the deuteron and on the production of pions by electrons is also furnished by the same experiments and will be discussed at the meeting. (auth)« less

Authors:
Publication Date:
Research Org.:
Stanford Univ., CA (United States)
OSTI Identifier:
4305780
Report Number(s):
A/CONF.15/P/1427
NSA Number:
NSA-12-014962
Resource Type:
Conference
Resource Relation:
Conference: 2. United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva (Switzerland), Jun 1958
Country of Publication:
United States
Language:
English
Subject:
PHYSICS; ANGULAR DISTRIBUTION; CONFIGURATION; CROSS SECTIONS; DECOMPOSITION; DENSITY; DEUTERONS; DISTRIBUTION; ELECTRIC CHARGES; ELECTRODYNAMICS; ELECTRON BEAMS; ELEMENTARY PARTICLES; ENERGY; ENERGY RANGE; FORM FACTOR; INELASTIC SCATTERING; MAGNETIC MOMENTS; MEASURED VALUES; NEUTRONS; NUCLEAR THEORY; PARTICLE MODELS; PIONS; PRODUCTION; PROTONS; SCATTERING; VARIATIONS

Citation Formats

Hofstadter, R. Structure in the proton and the neutron. United States: N. p., 1958. Web.
Hofstadter, R. Structure in the proton and the neutron. United States.
Hofstadter, R. Sun . "Structure in the proton and the neutron". United States. doi:. https://www.osti.gov/servlets/purl/4305780.
@article{osti_4305780,
title = {Structure in the proton and the neutron},
author = {Hofstadter, R.},
abstractNote = {A survey of the recent work on the structares of the proton and the neutron carried out by high-energy electron-scattering methods is presented. Early work established finite size effects in the proton and led to information about the charge and magnetic density distributions in the proton. The rms size was established to be close to (0.77 plus or minus 0.10) x 10/sup -13/ cm, and the density distributions of charge and anomalous magnetic moment were shown to be approximately of the same shape. The form factors could be described in terms of several alternative models given, for example, by an exponential, gaussian, hollow exponential, hollow gaussian, etc., distribution of densities. Many other shapes were excluded by the experimental data. Recent work by Bumiller and Hofstadter now fixes one among these models that is appropriate to the proton and provides an extremely good fit at all angles between energies of 200 and 650 Mev. The new evidence clearly favors the exponential model with rms radius (0.80 plus or minus 0.04) 10/sup -13/ cm. Recent studies of the proton have attempted to answer the question: how closely similar are the charge and magnetic form factors? This work now shows that the distributions have the same sizes and shapes to within 10 per cent, and each distribution is given very closely by the exponential model described above with radius (0.80 plus or minus 0.04) x 10/sup -13/. Certain other similar models will be discussed. Early work on the inelastic continuum in the deuteron established that the neutron's magnetic stracture was extended and not a point. It was further shown that the neutron's size was approximately the same as that of the proton. This work has recently been extended by Yearian and Hofstadter to a determination of the variation of the neutron's magnetic form factor over the range where the proton's form factor is known. The new results show: (1) the neutron is not a point, (2) the neutron's magnetic structure has a size lying between the limits 0.61 x 10/sup -13/ cm and 0.80 x 10/sup -13/ cm. The first value (0.61 x 10/sup -13/ cm) is determined by examing the total deuteron electro-disintegration cross section at a given angle and incident energy and comparing this cross section with that of the free proton under the same conditions. The second value (0.80 x 10/sup -13/ cm) is found by examining the peak of the deuteron electro-disintegration cross section. Because of possible contributions to the total cross section by mesonic exchange effects, the second method is believed to be slightly more accurate. The neutron size is, therefore, approximately (0.70 plus or minus 0.10) x 10/sup -13/ cm and probably the larger size 0.90 x 10/sup -13/ cm is correct. Thus the magnetic clouds of the neutron and proton are closely the same. The bearing of these results on the validity of electrodynamics is discussed. Because of the small radius implied by the neutron-electron experiments, there is an anomaly between the neutron and the proton. This is represented by the small charge radius for the neutron and the much larger radius of the proton. Additional information of the structure of the deuteron and on the production of pions by electrons is also furnished by the same experiments and will be discussed at the meeting. (auth)},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Jun 15 00:00:00 EDT 1958},
month = {Sun Jun 15 00:00:00 EDT 1958}
}

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