20th century physics: 1900–1933

Bruzzaniti, Giuseppe

doi:10.1007/978-1-4939-3533-8_2

Giuseppe Bruzzaniti²

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Abstract

The evening allocution of the Royal Institution of Great Britain on Friday April 27th, 1900, was entrusted to one of the most outstanding international scientific figures: Lord Kelvin. His speech was entitled “19th-century clouds over the dynamical theory of heat and light.”

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Notes

1.
W. Thomson (Lord Kelvin), Nineteenth Century Clouds over the Dynamical Theory of Heat and Light, Philosophical Magazine 2 (1901), p. 1.
2.
J. C. Maxwell, “Ether,” Enciclopedia Britannica, 9th ed., VIII (1878). Reprinted in The Scientific Papers of James Clerk Maxwell, 2 vols., Dover, New York 1965, II, p. 763.
3.
Ibid.
4.
Cf. T. Hiroshige, The ether problem, the mechanistic worldview and the origin of the theory of relativity, Historical Studies in the Physical Science 8 (1976), p. 3.
5.
R. P. Feynman, R. B. Leighton and M. Sands, The Feynman Lectures on Physics, Addison Wesley, California Institute of Technology 1963. Ch. 18, p. 3.
6.
J. C. Maxwell, op. cit.
7.
Drake translates the Italian “vaso di angusta bocca” into “wide vessel” instead of “vessel with a narrow opening,” probably confusing “angusta” with “augusta.”
8.
G. Galilei, Dialogo sopra i due massimi sistemi del mondo. Translated by S. Drake, Dialogue Concerning the Two Chief World Systems, University of California Press, Berkeley, 1953. p. 187.
9.
An inertial frame is a reference frame where any small body which is far away from any other matter — and is thus free from interactions — moves in a uniform rectilinear motion. The relative motion of two inertial frames is a uniform rectilinear motion.
10.
H. A. Lorentz, A. Einstein, H. Minkowski and H. Weyl, with notes by A. Sommerfeld, The principle of relativity; a collection of original memoirs on the special and general theory of relativity, Dover Publications, New York 1923, p. 37
11.
A. Pais, Subtle is the Lord, Clarendon Press — Oxford University Press, Oxford–New York 1982.
12.
There are two sources for this anecdote. The first is an unpublished paper written in 1921, known as the “Morgan Manuscript,” which is at the Pierpont Morgan Library in New York. The second is a talk given by Einstein at the University of Kyoto in 1922. The two sentences as reported here are from A. Pais, op. cit., p. 179.
13.
A. Einstein, L. Infeld, The Evolution of Physics, Cambridge University Press, London 1938, pp. 226–227.
14.
A. Pais, op. cit., p. 305.
15.
A. Pais, op. cit., p. 307.
16.
A. Einstein, Die Grundlagen der allgemeine Relativitätstheorie, Annalen der Physik 49 (1916), pp. 769–822. English translation: The Foundation of the General Theory of Relativity, in H. A. Lorentz, A. Einstein, H. Minkowski and H. Weyl, The Principle of Relativity; a Collection of Original Memoirs on the Special and General Theory of Relativity, Dover, New York 1952, p. 109.
17.
In B. Greene, The Elegant Universe, W. W. Norton & Company, New York–London 1999, p. 85.
18.
Translated from the French original, V. Weisskopf, La révolution des quanta, Hachette, Paris 1989. p. 20.
19.
J. C. Maxwell, A Discourse on Molecules, Philosophical Magazine, 46 (1873), p. 468.
20.
W. Röntgen, Über eine neue Art von Strahlen, Sitzungberichte der physikalische-medikalische Gesellschaft Würzburg, December 1895, p. 132. This was followed by a second communication, published in 1896 in the same journal. The two papers were partially translated in English in Nature 53 (1896). The original text with a translation into English was also published in E. C. Watson, The discovery of X-rays, American Journal of Sciences 13 (1945), No. 5, pp. 281–291.
21.
L. Olivier, La photographie de l’invisible, Revue général de sciences pures et appliquées 7 (1896), No. 49, p. 2.
22.
H. Becquerel, Sur quelques propriétés nouvelles des radiations invisibles émises par divers corps phosphorescents, Comptes Rendus de l’Académie des Sciences 11 (1896), p. 559; Sur les radiations invisibles émises par les corps phosphorescents, ibid., p. 501; Sur les propriétés différentes des radiations invisibles émises par les sels d’uranium, et du rayonnement de la paroi anticathodique d’un tube de Crookes, ibid., p. 762.
23.
This historical period has been analyzed in detail in G. Bruzzaniti, Dal segno al nucleo [From sign to nucleus], Bollati Boringhieri, Torino 1993.
24.
J. J. Thomson, Cathode Rays, Philosophical Magazine, 44 (1897), p. 310.
25.
M. Slodowska Curie, Rayons émis par les composés de l’uranium et du thorium, Comptes Rendus de l’Académie des Sciences 126 (1896), p. 1101.
26.
P. Curie and M. Curie, Sur un substance nouvelle radio-active contenue dans la pechblende, Comptes Rendus de l’Académie des Sciences 128 (1898), p. 175; E. Demarçay, Sur le spectre d’une substance radio-active, ibid., p. 128.
27.
E. Rutherford, Uranium radiation and the electrical conduction produced by it, Philosophical Magazine 47 (1899), p. 109. Reprinted in J. Chadwick (ed.), The Collected Papers of Lord Rutherford of Nelson, 3 vols., Allen & Unwin, London 1962–1965, vol. 1, p. 1169 (henceforth we shall refer to this work as CPR). Rutherford had the merit of detecting the α and β components of the uranium radiation, and discovering in 1903 the particle nature of the α rays (The magnetic and electric deviation of the easily absorbed rays from radium, Philosophical Magazine 5 (1903), p. 177). Henri Becquerel on the other hand was the first to identify the β rays with electrons (Influence d’un champ magnétique sur le rayonnement des corps radio-actifs, Comptes Rendus de l’Académie des Sciences 129 (1899), p. 996; Sur le rayonnement des corps radio-actifs, ibid., p. 1205). Paul Villard, finally, detected in the radiation emitted by radioactive bodies a component that is not deflected by the electromagnetic fields: the γ rays (Sur le rayonnement du radium, ibid., 130 (1900), p. 1178).
28.
E. Rutherford and F. Soddy, Radioactive change, Philosophical Magazine 5 (1903), p. 576.
29.
E. Rutherford, Some properties of the α rays from radium, ibid., 11 (1906), p. 166; Retardation of the α particle from radium in passing through matter, ibid., 12 (1906), p. 134.
30.
H. Geiger, On the scattering of the α particles by matter, Proceedings of the Royal Society A 81 (1908), p. 174.
31.
H. Geiger and E. Marsden, On a diffuse reflection of the α particles, ibid., 82 (1909), p. 495.
32.
J. J. Thomson, On the structure of the atom: an investigation of the stability and periods of oscillation of a number of corpuscles arranged at equal intervals around the circumference of a circle; with application of the results to the theory of the atomic structure, Philosophical Magazine 7 (1904), p. 237.
33.
E. Rutherford, The scattering of the α and β rays and the structure of the atom, Memoirs of the Literary and Philosophical Society of Manchester, 55 (1911) (CPF II, p. 212); The scattering of α and β particles and the structure of the atom, Philosophical Magazine, 21 (1911) p. 669 (CPR II, p. 238).
34.
For a detailed analysis of this issue see G. Bruzzaniti, op. cit.
35.
A. L. Debierne, Sur les transformations radioactives, in Les idées modernes sur la constitution de la matière, Gauthier-Villars, Paris 1913.
36.
Ibid., p. 331.
37.
Cf. G. Bruzzaniti, op. cit.
38.
N. Bohr, The constitution of atom and molecules, Philosophical Magazine 26 (1913), p. 1.
39.
Bohr stressed that, by dimensional reasons, to give account of the existence of electronic orbits whose radii have the same order of magnitude as the atom, it was necessary to introduce a new constant: “By the introduction of this quantity the question of the stable configuration of the electrons in the atoms is essentially changed, as this constant is of such dimensions and magnitude that it, together with the mass and charge of the particles, can determine a length of the order of magnitude required.” Ibid.
40.
G. Gamow, Thirty Years that Shook Physics, Dover, New York 1966. pp. 22–23.
41.
A. H. Compton, The spectrum of scattered X-rays, Physical Review 22 (1923), p. 409.
42.
E. Fermi [22], CPF I, p. 138.
43.
From an idea of A. Pais, op. cit., p. 385.
44.
E. Fermi [22], CPF I, p. 139.
45.
Cf. A. Pais, Niels Bohr’s Times, in Physics, Philosophy, and Polity, Clarendon Press, Oxford 1991.
46.
N. Bohr, The constitution of atom and molecules, op. cit.
47.
P. Ehrenfest, Adiabatic invariants and the theory of quanta, Philosophical Magazine 33 (1917), p. 500.
48.
A. Pais, Subtle is the Lord, op. cit., p. 405.
49.
A. Einstein, Zur Quantentheorie der Strahlung, Physikalische Zeitschrift 18 (1917), pp. 121–128. English translation On the quantum theory of radiation, in B. L. van der Waerden, Sources of Quantum Mechanics, North-Holland Publ. Co., Amsterdam 1967. p. 63.
50.
To understand Einstein’s idea, let us consider a gas in thermal equilibrium in an electromagnetic radiation field. Einstein conjectured that the probability that a molecule of the gas absorbs energy to pass between two energy levels is proportional to the energy of the electromagnetic field, while the probability to release energy to move between two energy levels is the sum of two terms, one independent of the radiation density (spontaneous emission) and one proportional to it. From this hypothesis Einstein obtained an important result, namely, that a necessary condition for Planck’s law to hold is that during the transitions between the energy levels a single quantum of energy is absorbed or emitted, with energy given by (and frequency proportional to) the difference between the two energy levels — exactly Bohr’s hypothesis.
51.
A. Pais, Niels Bohr’s Times, op. cit., p. 146.
52.
Ibid., p. 142.
53.
A. Sommerfeld, Atombau und Spektrallinien, English translation Atomic structure and spectral lines, Methuen & Co., London 1934.
54.
This idea is due Antonius van den Broek, a Dutch lawyer who studied the periodic system as a hobby. Between 1907 and 1914 he published, in some authoritative English and German journals, a number of papers about new interpretations of the periodic system. His most important papers are Das Mendelejeffsche “kubische” periodische System der Elemente und die Ernondnung der Radioelemente in diesem System, Physikalische Zeitschrift 12 (1911), p. 490; The number of possible elements and Mendeléeff’s “cubic” periodic system, Nature 92 (1911), p. 78; Die Radioelemente, das periodische System und die Konstitution der Atome, Physikalische Zeitschrift 14 (1913), p. 32; Intra-atomic charge, Nature 92 (1913), p. 372. For a more detailed study of van den Broek’s contribution see G. Bruzzaniti, op. cit.
55.
H. G. J. Moseley, The high-frequency spectra of the elements. Part I, Philosophical Magazine 26 (1913), p. 1024; The high-frequency spectra of the elements. Part II, Philosophical Magazine 27 (1913), p. 403.
56.
A. Sommerfeld, Die Feinstruktur der Wasserstoff und der Wasserstoff-ähnlichen Linien, Sitzungsberichte der mathematisch-physikalischen Klasse der K. B. Akademie der Wissenschaften zu München (1915), p. 459; Zur Quantentheorie der Spektrallinien, Annalen der Physik 51 (1916), pp. 1–94, 125–67.
57.
In 1914 Franck and Hertz made an experiment which proved the existence of quantized atomic energy levels. Franck and Hertz bombarded the vapors of different elements with electrons having a known kinetic energy, and observed that the atoms in the vapor were excited only for specific values of the energy of the incident electrons. J. Franck and G. Hertz, Über Zusammenstöße zwischen Elektronen und den Molekülen des Quecksilberdampfes und die Ionisierungsspannung desselben, Verhandlungen der Deutsches Phykalische Gesellschaft 16 (1914), p. 457.
58.
P. A. Schilpp, Albert Einstein, Philosopher-Scientist, MJF Books, New York, 1949, pp. 46–47.
59.
W. Pauli, Über den Einfluß der Geschwindigkeitsabhängigkeit der Elektronenmasse auf den Zeemaneffekt, Zeitschrift für Physik 31 (1925), p. 373; Über den Zusammenhang des Abschlusses der Elektronengruppen im Atom mit der Komplexstruktur der Spektren, ibid., p. 765. The first paper claims the existence of a fourth quantum number than cannot be described classically; the second contains the formulation of Pauli’s principle: “There can never be two or more equivalent electrons in an atom for which in strong fields the values of all quantum numbers […] are the same. If an electron is present in the atom for which these quantum numbers (in an external field) have definite values, this state is ‘occupied’.” (From the English translation On the connexion between the completion of electron groups in an atom with the complex structure of spectra, in D. ter Haar, The Old Quantum Theory, Pergamon Press, Oxford-London-Edinburgh 1924. pp1̇84–203.)
60.
G. E. Uhlenbeck and S. Goudsmit, Ersetzung der Hypothese vom unmechanischen Zwang durch eine Forderung bezüglich des inneren Verhaltens jedes einzelnen Elektrons, Naturwissenschaften 13 (1925), p. 953.
61.
N. Bohr, H. A. Kramers and J. C. Slater, Über die Quantentheorie der Strahlung, Zeitschrift für Physik 24 (1924), p. 69.
62.
W. Heisenberg, Die Entwicklung der Quantentheorie 1918–1928, Naturwissenschaften 17 (1929), p. 490.
63.
From a letter by Slater to his family, reported by A. Pais, Niels Bohr’s Times, op. cit., p. 235.
64.
N. Bohr, H. A. Kramers and J. C. Slater, op. cit.
65.
A. H. Compton and A. W. Simon, Directed quanta of scattered X-rays, Physical Review 26 (1925), p. 289.
66.
Ibid., p. 299. Italics in original.
67.
Letter by N. Bohr to Ch. G. Darwin, cited in A. Pais, Niels Bohr’s Times, op. cit., p. 238.
68.
Ibid., p. 239.
69.
P. Duhem, op. cit., p. 357.
70.
F. Soddy, Intra-atomic charge, Nature 92 (913), p. 399.
71.
F. W. Aston, A positive ray spectrograph, Philosophical Magazine 38 (1919), p. 707; The constitution of atmospheric neon, Philosophical Magazine 39 (1920), p. 449; The mass-spectra of chemical elements, Philosophical Magazine 40 (1920), p. 628. A more detailed historical reconstruction can be found in G. Bruzzaniti, op. cit.
72.
Discussion on isotopes opened by Sir J. J. Thomson, Proceedings of the Royal Society A 99 (1921), p. 87.
73.
M. Curie, L’isotopie et les éléments isotopes, Presses Universitaires de France, Paris 1924, p. 12.
74.
Ch. G. Darwin, On collision of α particles with light atoms, Philosophical Magazine 27 (1914), p. 499.
75.
E. Marsden, The passage of α particles through hydrogen, ibid., p. 824.
76.
E. Rutherford, Collision of α particles with light atoms, Philosophical Magazine 37 (1919), pp. 537–61. The paper is made of four parts: I. Hydrogen, pp- 537–561; II. Velocity of the hydrogen atom, pp. 562–571; III. Nitrogen and oxygen atoms, pp. 571–580; IV. An anomalous effect in nitrogen, pp. 581–587.
77.
It is interesting to recall what Rutherford wrote in 1921 as a remark about a paper of D. O. Masson, where the term baron was suggested to designate the hydrogen nucleus: ‘At the time of writing this paper in Australia, Professor Orme Masson was not aware that the name “proton” had already been suggested as a suitable name for the unit of mass nearly 1, in terms of oxygen 16, that appears to enter into the nuclear structure of atoms. The question of a suitable name for this unit was discussed at an informal meeting of a number of members of Section A of the British Association at Cardiff this year. The name “baron” suggested by Professor Masson was mentioned, but was considered unsuitable on account of the existing variety of meanings. Finally the name “proton” met with general approval, particularly as it suggests the original term “protyle” given by Prout in his well-known hypothesis that all atoms are built up of hydrogen. The need of a special name for the nuclear unit of mass 1 was drawn attention to by Sir Oliver Lodge at the Sectional meeting, and the writer then suggested the name “proton.” Professor Orme Masson sent the present paper for publication through the writer, and in order to avoid the long delay involved in correspondence, his paper is printed in its original form. If the name “proton” is generally approved, it is merely necessary to change the symbol “b” into “p” in the chemical equations given in the paper. It should be pointed out that a somewhat similar type of nomenclature for the constituents of atoms has been suggested in the interesting paper of Professor W. D. Harkins, entitled The Nuclei of Atoms and the New Periodic System (Physical Review, 15 (1920) p. 73), in D. O. Masson, The constitution of atoms, Philosophical Magazine 41 (1921), p. 281’.
78.
Almost 25 different nuclear models were proposed during those years. The situation has been analyzed in detail in G. Bruzzaniti, op. cit., and R. H. Stuewer, The nuclear electron hypothesis, in W. R. Shea (ed.), Otto Hahn and the Rise of Nuclear Physics, Reidel, Dordrecht 1983.
79.
F. W. Aston, Isotopes, Arnold, London 1922, p. 102.
80.
L. Boltzmann, Weitere Studien über das Wärmegleichgewicht unter Gasmolekülen, Wiener Berichte 66 (1872), pp. 275–370.
81.
A. Pais, Subtle is the Lord, op. cit., p. 60.
82.
E. Fermi, Thermodynamics, Dover, New York 1936, p. 56–57.
83.
E. Schrödinger, Statistical Thermodynamics, Cambridge University Press, Cambridge, U.K. 1946.
84.
This example is taken, with some small changes, from G. Parisi, La statistica di Fermi, in C. Bernardini and L. Bonolis (eds.), Conoscere Fermi, Compositori, Bologna 2001. That is in turn basically taken from an example by Fermi, published in the entry “Meccanica Statistica” of G. Treccani’s Enciclopedia Italiana (all in Italian).
85.
A. Pais, op. cit., p. 423.
86.
Ibid., p. 424.
87.
Ibid.
88.
Ibid., p. 428.
89.
On the quantization of the ideal monoatomic gas. Fermi [30].
90.
P. A. M. Dirac, On the theory of quantum mechanics, Proceedings of the Royal Society A 92 (1926), p. 661.
91.
Fermi [62], CPF I, p. 375.
92.
L. de Broglie, Recherches sur la théorie des quanta, Annales de Physique 3 (1925), p. 22.
93.
E. Schrödinger, Quantisierung als Eigenwertproblem, Annalen der Physik 49 (1926), pp. 361–76.
94.
W. Heisenberg, Über die quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen, Zeitschrift für Physik 33 (1925), p. 879.
95.
M. Born and P. Jordan, Zur Quantenmechanik, Zeitschrift für Physik 34 (1925), p. 858 (English translation B. L. van der Waerden, Sources of Quantum Mechanics, op. cit.); M. Born, W. Heisenberg and P. Jordan, Zur Quantenmechanik II, ibid. (1926), p. 557 (English translation in B. L. van der Waerden, op. cit.).
96.
E. Schrödinger, Über das Verhältnis des Heisenberg-Born-Jordanschen Quantenmechanik zu der meinen, Annalen der Physik 79 (1926), p. 734.
97.
C. Eckart, Operator calculus and the solution of the equations of quantum dynamics, Physical Review 27 (1926), p. 711.
98.
L. de Broglie, La nature ondulatoire de l’électron, Nobel Prize acceptance speech given in Stockholm on 12 December 1929. In Nobel Lectures, Physics 1922–1941, Elsevier Publishing Company, Amsterdam, 1965, p. 247.
99.
Ibid.
100.
In the theory of relativity, momentum is the spatial part of a four-vector, whose time component is energy.
101.
C. J. Davisson and L. H. Germer, Diffraction of electrons by a crystal of nickel, Physical Review 30 (1927), p. 705.
102.
The Compton effect is due to the particle-like interaction between electrons and electromagnetic radiation, and may be thought of as the scattering between an electron at rest and a photon of energy hν and momentum hν∕c. During the scattering the photon is deviated from its original direction, and its frequency changes, due to the loss of energy. As in all scattering processes, momentum is conserved, and the momentum of the incident photon is the same as the sum of the momenta of the electron and the photon after the collision.
103.
W. Pauli, Über das Wasserstoffspektrum vom Standpunkt der neuen Quantenmechanik, Zeitschrift für Physik 36 (1926), p. 336 (English translation in L. van der Waerden, Sources of Quantum Mechanics, op. cit.).
104.
G. Gamow, op. cit., p. 105.
105.
M. Born, Zur Quantenmechanik der Stoßvorgange, Zeitschrift für Physik 37 (1926), p. 863.
106.
W. Heisenberg, Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik, Zeitschrift für Physik 43 (1927), p. 172. English translation The actual content of quantum theoretical kinematics and mechanics, in NASA Technical Memorandum, TM-77379, https://archive.org/details/nasa_techdoc_19840008978.
107.
N. Bohr, The quantum postulate and the recent development of atomic theory, Nature 121 (1928), p. 580.
108.
P. A. M. Dirac, The quantum theory of the emission and absorption of radiation, Proceedings of the Royal Society A 114 (1927), p. 243.
109.
G. Gamow, Zur Quantentheorie des Atomkernes, Zeitschrift für Physik 51 (1928), p. 204; R. W. Gurney and E. Condon, Wave mechanics and radioactive disintegration, Nature 122 (1928), p. 439; Quantum mechanics and radioactive disintegration, Physical Review 33 (1928), p. 127.
110.
R. W. Gurney and E. Condon, Wave mechanics and radioactive disintegration, op. cit.
111.
E. Rutherford, Discussion on the structure of atomic nuclei, Proceedings of the Royal Society A 123 (1929), p. 373.
112.
O. Klein, Die Reflexion von Elektronen an einem Potentialsprung nach der relativistischen Dynamik von Dirac, Zeitschrift für Physik 53 (1929), p. 157.
113.
G. Gamow, Constitution of Atomic Nuclei and Radioactivity, Oxford University Press, Oxford 1931.
114.
A detailed analysis was made in G. Bruzzaniti, op. cit.
115.
E. P. Wigner, ősszetett rendszerek statisztikája az új quantum-mechanika szerint, Matematikai és Természettudománti Értesítő 46 (1929), pp. 576 ff. (German abstract at p. 584). Being written in Hungarian, the paper was unnoticed by most physicists, and indeed in 1931 P. Ehrenfest and J. R. Oppenheimer (Note on the statistics of nuclei, Physical Review 37 (1931) p. 333), starting from different considerations, gave a new and definitive proof.
116.
D. M. Dennison, A note on the specific heat of the hydrogen molecule, Proceedings of the Royal Society A 115 (1927), p. 483.
117.
F. Hund, Zur Deutung der Molekelspektren. II, Zeitschrift für Physik 42 (1927), p. 93.
118.
Kronig was the first to notice an immediate consequence of Uhlenbeck and Goudsmit’s hypothesis about the electron spin (R. Kronig, Spinning electrons and the structure of spectra, Nature 117 (1926), p. 550). Kronig had already thought of relating the electron spin to Pauli’s exclusion principle, but, after a suggestion of Pauli’s, did not publish the idea. According to Kronig, due to its spin, the electron must have an intrinsic magnetic moment, of the order of magnitude of Bohr’s magneton. One should expect the same behavior when an electron is part of the nuclear structure. Then the nucleus should have an intrinsic magnetic moment of the same order of magnitude, unless a very unlikely mechanism takes place, namely, that the magnetic moments of all the electrons cancel each other. If this were true, by the Zeeman effect there would be a splitting of the energy levels, which is not observed. Fermi and Rasetti also entered the discussion, remarking that Kronig’s objection had another consequence; a nuclear magnetic moment should induce a paramagnetic behavior of the atom, which, however, is not observed. Fermi and Rasetti, on the other hand, thought that the magnetic moments of the nuclear electrons could well cancel each other. However, they put forward another important consideration. The electron magnetic moment corresponds to some energy, which, according to the electromagnetic theory of mass, yields an increase of the mass, and therefore of the electron radius. They wrote “This value is about 20 times larger of what the electron radius is usually supposed to be. Actually, there are no direct measures of the electron radius; however, this is a serious drawback, as we know that the nucleus contains a large number of electrons. On the other hand, the linear dimensions of the nuclear structure are known with a fairly good precision […] and they are of about 10⁻¹² cm. The two facts cannot be reconciled, unless one assumes that the nature of the electron changes substantially when it is part of the nuclear structure.” (Fermi [35], p. 227.)
119.
R. Kronig, Der Drehimpuls des Stickstoffkerns, Naturwissenschaften 16(1928), p. 335.
120.
L. S. Ornstein and W. R. van Wijk, Untersuchungen über das negative Stickstoffbandenspektrum, Zeitschrift für Physik 49 (1928), p. 315.
121.
R. Kronig, Der Drehimpuls des Stickstoffkerns, op. cit.
122.
W. Heitler and G. Herzberg, Gehorchen die Stickstoffkerne der Boseschen Statistik?, Naturwissenschaften 17 (1929), p. 673.
123.
F. Rasetti, Raman effect in gases, Nature 123 (1929), p. 205; On the Raman effect in diatomic gases, Proceedings of the National Academy of Sciences 15 (1929), p. 234; Selection rules in the Raman effect, Nature 122 (1929), p. 757; On the Raman effect in diatomic gases II, Proceedings of the National Academy of Sciences 15 (1929), p. 515; Incoherent scattered radiation in diatomic molecules, Physical Review 34 (1929), p. 367; Alternating intensities in the spectrum of nitrogen, Nature 124 (1929), p. 792; Sopra l’effetto Raman nelle molecole biatomiche, Nuovo Cimento 6 (1929), p. 356.
124.
W. Heitler and G. Herzberg, Gehorchen die Stickstoffkerne der Boseschen Statistik?, op. cit.
125.
There is an extensive literature about the history of the β decay. We may cite, among the works of general nature that contain further references: A. Pais, Inward Bound, Oxford University Press, New York 1986; Niels Bohr’s Times, op. cit.; C. S. Wu and S. A. Moszkowski, Beta Decay, Academic Press, New York 1966; G. Bruzzaniti, op. cit..
126.
Very accurate measurements of the γ-rays frequencies allowed Ellis (Ch. D. Ellis, The magnetic spectrum of the β-rays excited by γ-rays, Proceedings of the Royal Society 99 (1921), p. 261; β-rays spectra and their meaning, ibid. 101 (1922), p. 1) to introduce also for nuclei the notion of “stationary state.” In the second paper, Ellis remarkably wrote, about the measurement of the frequency of the γ-rays emitted by radium B: “The information […] about the energies of the stationary states of the radium B nucleus is extra-ordinarily detailed, but, on the other hand, this information is very limited. There is no evidence which indicates whether these levels are occupied by positively charged particles or by electrons.”
127.
L. Meitner, Über die Entstehung der β-Strahl-Spektren radioaktiver Substanzen, Zeitschrift für Physik 9 (1922), p. 131; Über den Zusammenhang zwischen β und γ Strahlen, ibid., p. 145; Über die β-Strahl-Spektra und ihren Zusammenhang mit der γ-Strahlung, ibid. 11 (1922), p. 35.
128.
C. D. Ellis and W. A. Wooster, The average energy of disintegration of radium E, Proceedings of the Royal Society A 117 (1927), p. 109.
129.
Ibid.
130.
N. Bohr, Faraday Lectures: chemistry and the quantum theory of the atoms constitution, Journal of the Chemical Society (1932), p. 349.
131.
For more details see Appendix C.5.
132.
Among the many historical reconstructions of these discoveries, we mention the following: E. Amaldi, From the discovery of the neutron to the discovery of nuclear fission, Physics Reports 11 (1984), p. 1; J. Six, La découverte du neutron, Editions du Centre National de la Recherche Scientifique, Paris 1987; M. De Maria and A. Russo, The discovery of positron, Rivista di Storia della Scienza 2 (1985), p. 237.
133.
H. C. Urey, F. C. Brickwedde and G. M. Murphy, A hydrogen isotope of mass 2, Physical Review 39 (1932), p. 164. The paper by R. Stuewer, The naming of the deuteron, American Journal of Physics 54 (1986), p. 206, is an interesting rendering of the debate that between 1993 and 1935 took place about the naming of the mass 2 isotope of hydrogen.
134.
C. D. Anderson, The positive electron, Physical Review 43 (1933), p. 491.
135.
P. M. S. Blackett and G. P. S. Occhialini, Some photographs of the tracks of penetrating radiation, Proceedings of the Royal Society A 139 (1933), p. 699.
136.
W. Bothe and H. Becker, Kunstliche Erregung von Kern γ–Strahlen, Zeitschrift für Physik 64 (1930), p. 289.
137.
F. Joliot and I. Curie, Emission de protons de grande vitesse par les substances hydrogénées sous l’influence de rayons-γ très pénétrants, Comptes Rendus de l’Académie des Sciences 194 (1932), p. 273; Effet d’absorption des rayons-γ de très haute frequence par projection de noyaux légers, ibid., p. 708.
138.
J. Chadwick, Possible existence of a neutron, Nature 129 (1932), p. 312.
139.
Ibid., pp. 312 ff. A more extended and detailed discussion of the experiment was communicated by Chadwick to the Royal Society on 10 May 1932; cf. J. Chadwick, The existence of a neutron, Proceedings of the Royal Society A 136 (1932), p. 692.
140.
D. Ivanenko, The neutron hypothesis, Nature 129 (1932), p. 798.
141.
Ibid.
142.
Structure et propriétés des noyaux atomiques. Rapports et discussions du Septième Conseil de Physique, Gauthier-Villars, Paris 1934.
143.
J. Chadwick, Diffusion anomale des particules α, ibid., p. 102.
144.
P. A. M. Dirac, Théorie du positron, ibid., p. 203; W. Heisenberg, Considérations théoriques générales sur la structure du noyau, ibid., p. 328.
145.
W. Heisenberg, Über den Bau der Atomkerne, I, Zeitschrift für Physik 77 (1932), p. 1; II, ibid. 78 (1932), p. 156; III, ibid. 80 (1933), p. 587. On this aspect of Heisenberg’s work, see the excellent biography by D. Cassidy, Uncertainty. The Life and Science of Werner Heisenberg, Freeman, New York 1992, and J. Bromberg, The impact of the neutron: Bohr and Heisenberg, Historical Studies in the Physical and Biological Sciences 3 (1971), p. 307; D. M. Brink, Nuclear Forces, Pergamon Press, London 1965. The latter also contains the English translation of some papers of Heisenberg and Majorana’s.
146.
David G. Cassidy, Beyond Uncertainty: Heisenberg, Quantum Physics, and the Bomb. Bellevue Literary Press, New York 2009. p. 203.
147.
See references in note 145.
148.
David G. Cassidy, op. cit., p. 202.
149.
As already noted, according to Heisenberg, the proton-neutron interaction was due to the exchange of an electron, while spin was left unchanged. Majorana, on the contrary, postulated that the interaction involved the exchange of both charge and spin.
150.
Fermi [76, 80a].
151.
The Hamiltonian function is a function which is associated with a physical system and determines its evolution, both in classical and quantum mechanics.
152.
Fermi [80a], CPF I, p. 560.
153.
I owe this remark to G. Bachelard, who characterized the history of science in these terms: “[…] it is a history that starts from the certainties of the present time and discovers in the past the progressive forms of the truth. Thus the history of science appears as the most irreversible of all histories. By discovering the truth, the man of science cancels irrationality. Irrationalism may certainly appear elsewhere, but by now some routes are impossible. The history of science is the history of the defeats of irrationalism.” (G. Bachelard, L’activité rationaliste de la physique contemporaine, PUF, Paris 1965.)
154.
G. Gamow, Constitution of Atomic Nuclei and Radioactivity, Clarendon Press, Oxford 1931. p. 1.
155.
H. A. Bethe, R. F. Bacher, Nuclear Physics, Review of Modern Physics vol. 8 (1936), p. 184. Italics in original.
156.
Ibid., p. 189. Italics in original.

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Giuseppe Bruzzaniti

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Bruzzaniti, G. (2016). 20th century physics: 1900–1933. In: Enrico Fermi. Springer Biographies. Springer, New York, NY. https://doi.org/10.1007/978-1-4939-3533-8_2

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