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William H. Bragg's Corpuscular Theory of X-Rays and γ-Rays

Published online by Cambridge University Press:  05 January 2009

Roger H. Stuewer
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Extract

The modern corpuscular theory of radiation was born in 1905 when Einstein advanced his light quantum hypothesis; and the steps by which Einstein's hypothesis, after years of profound scepticism, was finally and fully vindicated by Arthur Compton's 1922 scattering experiments constitutes one of the most stimulating chapters in the history of recent physics. To begin to appreciate the complexity of this chapter, however, it is only necessary to emphasize an elementary but very significant point, namely, that while Einstein based his arguments for quanta largely on the behaviour of high-frequency black body radiation or ultra-violet light, Compton experimented with X-rays. A modern physicist accustomed to picturing ultra-violet light and X-radiation as simply two adjacent regions in the electromagnetic spectrum might regard this distinction as hair-splitting. But who in 1905 was sure that X-rays and γ-rays are far more closely related to ultra-violet light than to α-particles, for example ? This only became evident after years of painstaking research, so that moving without elaboration from Einstein's hypothesis to Compton's experiments automatically eliminates from consideration an important segment of history—a segment in which a major role was played by William Henry Bragg.

Type
Research Article
Information
The British Journal for the History of Science , Volume 5 , Issue 3 , June 1971 , pp. 258 - 281
Copyright
Copyright © British Society for the History of Science 1971

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References

1 “Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt”, Annalen der Physik, xvii (1905), 132–148Google Scholar; translated in Boorse, H. A. and Motz, L., ed., The World of the Atom (New York, 1966), i, 544–557.Google Scholar

2 “A Quantum Theory of the Scattering of X Rays by Light Elements”, Physical Review, xxi (1923), 483–502.Google Scholar

3 “Photo-electricity”, Proc. Royal Institution, xxv (1928), 341.Google Scholar

4 Ibid., 343. See also Bragg, 's Universe of Light (London, 1933)Google Scholar; reprint by Dover (New York, 1959). 269–270.

5 “A Comparison of Some Forms of Electric Radiation”, Trans. R. Soc. S. Aust., xxxi (1907), 90.Google Scholar

6 For Stokes's 1898 paper, see “On the Nature of the Röntgen Rays”, Mathematical and Physical Papers (Cambridge, 1905), v, 255.Google Scholar A. Schuster and E. Wiechert had also suggested the pulse theory. See Rutherford, E., Radioactive Substances and their Radiations (Cambridge, 1913), 83Google Scholar; W. H. and Bragg, W. L., X Rays and Crystal Structure (4th edn., London, 1924), 2.Google ScholarPubMed

7 The result Thomson published in the first edition of his Conduction of Electricity through Gases (London, 1903)Google Scholar was out by a factor of 2, which he corrected in time for the second edition (London, 1906), 321–325.

8 “Polarized Röntgen Radiation”, Phil. Trans., cciv (1905), 467–479Google Scholar; Proc. R. Soc., lxxiv (1905), 474–475Google Scholar; preliminary announcement in Nature, lix (1904), 463.Google Scholar

9 “Polarization in Secondary Röntgen Radiation”, Proc. R. Soc., lxxvii (1906), 247–255Google Scholar; “Secondary Röntgen radiation”, Proc. Phys. Soc., xx (1906), 200Google Scholar; Phil. Mag., xi (1906), 812–828.Google Scholar

10 For brief accounts of Barkla's and Bragg's life and work, see Allen, H. S., “Charles Glover Barkla”, Obituary Notices of Fellows of the Royal Society, v (1945–1948), 341–366Google Scholar; Andrade, E. N. da C., “William Henry Bragg”Google Scholar, ibid., iv (1942–44), 277–300. See also articles by Forman, Paul in Dictionary of Scientific Biography, ed. by Gillispie, C. C., New York, 1970.Google Scholar

11 Bragg, , op. cit. (1), 79–93Google Scholar; “The Nature of Röntgen Rays”, Trans. R. Soc. S. Aust., xxxi (1907), 94–98Google Scholar; reprinted as “On the Properties and Natures of Various Electric Radiations”, Phil. Mag., xiv (1907), 429–449Google Scholar; Annual Reports of the Smithsonian Institution (1907), 195–214.Google Scholar

12 Andrade, , op. cit. (10), 280Google Scholar, suggests that Bragg's neutral pair was a modified version of P. Lenard's “dynamid”. Not until 1908 did Rutherford and Geiger show that the α-particle is doubly charged. See Rutherford, , op. cit. (6), 136.Google Scholar

13 Bragg, , op. cit. (11), Phil. Mag., 442.Google Scholar

14 Ibid., 445. For Haga and Wind's work see “Die Beugung der Röntgenstrashlen”, Annalen der Physik, x (1903), 305–312Google Scholar; “Über die Polarisation der Röntgenstrahlen und der Sekundärstrahlen”, Annalen der Physik, xxiii (1907), 439–444.Google Scholar

15 “Ueber die lichtelektrische Wirkung”, Annalen der Physik, viii (1902), 149–198, especially 166Google Scholar; Innes, P. D., “On the Velocity of the Cathode Particles emitted by Various Metals under the Influence of Röntgen Rays, and its Bearing on the Theory of Atomic Disintegration”, Proc. R. Soc., cxxix (1907), 442–462.CrossRefGoogle Scholar

16 Marx, E., “Die Geschwindigkeit der Röntgenstrahlen”, Phys. Z., vi (1905), 768–778; 834–835.Google Scholar

17 Bragg, , op. cit. (11), Phil. Mag., 448.Google Scholar

18 “Note on X-Rays and Scattered X-Rays”, Phil. Mag., xv (1908), 288–296Google Scholar; “The Nature of X-rays”, Nature, lxxvi (1907), 661–662.Google Scholar

19 Ibid., 288, 294, 296.

20 “The Nature of γ and X-rays”, Nature, lxxvii (1908), 270–271.Google Scholar

21 Ibid., 270.

22 “The Nature of Röntgen Rays”, Nature, lxxvii (1908), 320.Google Scholar

23 “The Nature of the γ and X-Rays”, Nature, lxxvii (1908), 560.Google Scholar

24 Ibid.

25 “The Nature of the γ and X-Rays”, Nature, lxxvii (1908), 271Google Scholar; “An Experimental Investigation of the Nature of γ Rays—No. 2”, Phil. Mag., xvi (1908), 918–939Google Scholar (with J. P. V. Madsen).

26 Lenard, , op. cit. (15).Google Scholar

27 “Secondary Radiation from a Plate exposed to Rays from Radium”, Phil. Mag., xiv (1907), 176–187, especially 187Google Scholar. Mackenzie also independently observed the forward-backward asymmetry in secondary β-rays excited by γ-rays.

28 Bumstead, H. A., “The Heating Effects produced by Röntgen Rays in Different Metals, and their Relation to the Question of Charge in the Atom”, Phil. Mag., xi (1906), 292–317CrossRefGoogle Scholar; “On the Heating Effects Produced by Röntgen Rays in Lead and Zinc”, Phil. Mag., xv (1908), 432–437Google Scholar; Angerer, E., “Bolometrische Untersuchungen über die Energie der X-Strahlen”, Annalen der Physik, xxi (1906), 87–117CrossRefGoogle Scholar; “Ursprung der Wärmeentwickelung bei Absorption von Röntgenstrahlen”, Annalen der Physik, xxiv (1907), 370–380.Google Scholar

29 Bragg, , op. cit. (25), 935.Google Scholar

30 Ibid., 934; Thomson, J. J., “On the Ionization of Gases by Ultra-Violet Light and on the evidence on the Structure of Light afforded by its Electrical Effects”, Proc. Camb. Phil. Soc., xiv (1906–1908), 421.Google Scholar Also see McCormmach, Russell, “J.J. Thomson and the Structure of Light”, Brit. J. Hist. Sci., iii (1966–1967), 362–387.Google Scholar

31 Bragg, , op. cit. (25), 936.Google Scholar

32 “The Nature of γ and X-Rays”, Nature, lxxvii (1908), 509–510.Google Scholar Bragg did not mention that Cooksey disagreed with his interpretation, believing rather that the electromagnetic momentum of a pulse was responsible for ejecting the β-rays asymmetrically.

33 Bragg, , op. cit. (25), 938.Google Scholar

34 “The Nature of X-Rays”, Nature, lxxviii (1908), 7.Google Scholar

35 “Homogeneous Secondary Röntgen Radiations”, Phil. Mag., xvi (1908), 550–584.Google Scholar

36 Barkla, , op. cit. (34).Google Scholar

37 “The Nature of the y and X-Rays”, Nature, lxxviii (1908), 294.Google Scholar

38 “The Nature of X-Rays”, Nature, lxxviii (1908), 665.Google Scholar

39 Ibid., note added by Bragg.

40 “The Absorption of Röntgen Rays”, Phil. Mag., xvii (1909), 758 (with C. A. Sadler).Google Scholar

41 Barkla, and Sadler, , op. cit. (35), 579.Google Scholar

42 “The Nature of the γ Rays”, Proc. Camb. phil. Soc., xiv (1906–1908), 540.Google Scholar

43 “On the Secondary Radiation caused by the β and γ Rays of Radium”, Phil. Mag., viii (1904), 669–685.Google Scholar More recently Kleeman, R. D., “On the Different Kinds of γ Rays of Radium, and the Secondary γ Rays which they Produce”, Phil. Mag., xv (1908), 638–663CrossRefGoogle Scholar, had found the same thing. Kleeman, a former student of Bragg then studying under Thomson, interpreted this observation in terms of the pulse theory.

44 “On a Want of Symmetry shown by Secondary X-Rays”, Phil. Mag., xvii (1909), 855–864 (with J. L. Glasson).Google Scholar

45 Ibid., 863.

46 Andrade, , op. cit. (10), 282.Google Scholar

47 “Primary and Secondary Gamma Rays”, Phil. Mag., xviii (1909), 275.Google Scholar

48 “Secondary γ Radiation”, Phil. Mag., xvii (1909), 423–448.Google Scholar Madsen, thoroughly convinced of Bragg's corpuscular ideas, described the softening as due to billiard-ball type collisions of the γ-ray particles.

49 “Primary and Secondary γ Rays”, Phil. Mag., xx (1910), 921–938.Google Scholar

50 For specific papers, see Allen, , op. cit. (10).Google Scholar Barkla found evidence for “excess scattering”, an increase in the forward-backward asymmetry with an increase in the primary wavelength. Both Crowther, J. A., “On the Energy and Distribution of Scattered Röntgen Radiation”, Proc. R. Soc., lxxxv (1911), 29–43CrossRefGoogle Scholar, and Owen, E. A., “On the Scattering of Röntgen Radiation”, Proc. Camb. phil. Soc., xvi (1911), 161–166Google Scholar, observed the same phenomenon.

51 “The Röntgen Radiation from Substances of Low Atomic Weight”, Phil. Mag., xxiv (1912), 138–149.Google Scholar

52 For more details on Thomson's work, see McCormmach, , op. cit. (30)Google Scholar, as well as Thomson's papers “On a Theory of the Structure of the Electric Field and its Application to Röntgen Radiation and to Light”, Phil. Mag., xix (1910), 301–313Google Scholar, and “On the Theory of Radiation”, Phil. Mag., xx (1910), 238–247.Google Scholar

53 “Zur experimentellen Entscheidung zwischen Ätherwellen- und Lichtquantenhypothese. I. Röntgenstrahlung”, Phys. Z., x (1909), 902–913Google Scholar; “Zur experimentellen Entscheidung zwischen der Lichtquantenhypothese und der Ätherimpulsetheorie der Röntgenstrahlen”, Phys. Z, xi (1910), 24–31Google Scholar; “Zur experimentellen Entscheidung zwischen Lichtquantenhypothese und Ätherwellentheorie. II. Sichtbares, und Ultraviolettes Spektrum”, Phys. Z., xi (1910), 179–187.Google Scholar The last paper appeared in the 1 March issue, a few weeks after Bragg had written his first letter to Sommerfeld.

54 Bragg, , op. cit. (54), 386.Google Scholar

55 For a discussion of Einstein's Salzburg paper in the context of the development of his thought, see Klein, Martin J., “Einstein and the Wave-Particle Duality”, The Natural Philosopher, iii (1964), 3–49.Google Scholar Also see Hermann, Armin, ed., Die Hypothese der Lichtquanten (Stuttgart, 1965).Google Scholar

56 “Über die Verteilung der Intensität bei der Emission von Röntgenstrahlen”, Phys. Z., x (1909), 969–976; xi (1910), 99–101.Google Scholar

57 The three letters from W. H. Bragg to A. Sommerfeld are deposited in the Archive for History of Quantum Physics (AHQP) at the American Philosophical Society Library (Philadelphia), University of California Library (Berkeley), and the Universitets Institut for Teoretisk Fysik (Copenhagen); the letter from Sommerfeld to Bragg was found by Sir Lawrence Bragg in his father's papers, and a copy of it was kindly sent to me by Sir Lawrence. I should like to express my gratitude to Sir Lawrence and to Dr.-Ing. Ernst Sommerfeld for permission to reprint them all here. The translation of Sommerfeld's letter is my own. For W. Friedrich's Munich Dissertation see “Räumliche Intensitätsverteilung der X-Strahlen, die von einer Platinaantikathode ausgehen”, Annalen der Physik, xxxix (1912), 377–430Google Scholar; E. Bassler's 1909 work on the polarization of X-rays is discussed and referenced on p. 378.

57a Walter and Pohl had cast serious doubt on the validity of Haga and Wind's earlier experiments.

58 “Über die Struktur der γ-Strahlen”, Sbr. bayer. Akad. Wiss. Mathematisch-physikalische Klasse, xxxxi (1911), 1–60.Google Scholar For a modern discussion of the “forward peaking”, see for example Jackson, J. D., Classical Electrodynamics (New York, 1962), 473.Google Scholar

59 For C. T. R. Wilson's original photographs and paper, see “On a Method of Making Visible the Paths of Ionizing Particles through a Gas”, Proc. R. Soc., lxxxv (1911), 285–288.Google Scholar

60 “The Consequences of the Corpuscular Hypothesis of the γ and X Rays, and the Range of β Rays”, Phil. Mag., xx (1910), 415.Google Scholar

61 Ibid., 416.

62 “Energy Transformations of X-Rays”, Proc. R. Soc., lxxxv (1911), 349–365.Google Scholar See also Bragg, W. H., “The Mode of lonization by X-Rays”, Phil. Mag., xxii (1911), 222–223Google Scholar; “On the Direct or Indirect Nature of the lonization by X-rays”, Phil. Mag., xxiii (1912), 647–650.Google Scholar

63 Bragg, , op. cit. (25), Phil. Mag., 938.Google Scholar

64 Bragg, , op. cit. (59), 386.Google Scholar

65 Studies in Radioactivity (London, 1912), 191–192.Google Scholar This is a somewhat different explanation than he gave in “The Secondary Radiation produced by the Beta Rays of Radium”, Physical Review, xxx (1910), 638–640.Google Scholar

66 Bragg, , op. cit. (59), 389.Google Scholar

67 “Radio-activity as a kinetic theory of a fourth state of matter”, Nature, lxxxv (1911), 494.Google Scholar

68 Ibid.

69 “A Difference in the Photoelectric Effect caused by Incident and Divergent Light”, Nature, lxxxiii (1910), 311Google Scholar; Phil. Mag., xx (1910), 331–339.Google Scholar

70 “A Difference in the Photoelectric Effect caused by Incident and Divergent Light”, Nature, lxxxiii (1910), 339Google Scholar; “On the Direction of Motion of an Electron ejected from an Atom by Ultra-Violet Light”, Proc. R. Soc., lxxxiv (1910), 92–99.Google Scholar

71 Bragg, , op. cit. (67).Google Scholar

72 Reports of the British Association for the Advancement of Science (1911), 340–341.Google Scholar

73 Ibid., 341. Whiddington, R., “The Production of Characteristic Röntgen Radiation”, Proc. R. Soc., lxxxv (1911), 323–332CrossRefGoogle Scholar; “Characteristic Röntgen Radiation”, Nature, lxxxviii (1911), 143.Google Scholar

74 Ibid., 341.

75 Nature, lxxxvii (1911), 501.Google Scholar

76 Ibid. This is a curious statement, in view of the radiation pressure experiments of Lebedev and Nichols and Hull at the turn of the century.

77 Ibid.

78 Bragg, , op. cit. (65), vii.Google Scholar

79 Ibid., 191.

80 Ibid., vii.

81 Ibid., 192.

82 Ibid., 192–193.

83 Ibid., 193.

84 Ibid., 188.

85 Ibid., 193.

86 “Radiations Old and New”, Nature, xc (1913), 560Google Scholar; see also 529–532.

87 Ibid., 558.

88 Bragg, , op. cit. (67).Google Scholar

89 See reference (55).

90 Ewald, P. P., “Max von Laue”, Obituary Notices of Fellows of the Royal Society, vi (1960), 139.Google Scholar

91 W. H. and Bragg, W. L., op. cit. (6), 3.Google Scholar

92 “Interferenzerscheinungen bei Röntgenstrahlen”, Sbr. bayer. Akad. Wiss. Mathematische-physikalische Klasse, xlii (1912), 303–322Google Scholar; “Eine quantitative Prüfung der Theorie für die Interferenzerscheinungen bei Röntgenstrahlen”, ibid., xlii (1912), 363–373.

93 Quoted in Compton, Arthur H., X-Rays and Electrons (New York, 1926), 90.Google Scholar

94 “Atomic Theories of Radiation”, Science, xxxvii (1913), 119–133, especially 127, 132–133Google Scholar; also see Allen, , op. cit. (10), 349.Google Scholar

95 “Are Electrons Waves?”, Bell Laboratories Record, iv (1927), 258.Google Scholar

96 “X-rays and Crystals”, Nature, xc (1912), 219.Google Scholar

97 On deposit in the AHQP, reference (69).

98 See identical statement by Bragg in “X-rays and Crystals”, Nature, xc (1912), 360.Google Scholar

99 Ibid.

100 For Nobel Lecture see “The Diffraction of X-Rays by Crystals”, Nobel Lectures: Physics (Amsterdam, 1967), i, 370–382.Google Scholar

101 “The Reflection of X-rays by Crystals”, Proc. R. Soc., lxxxviii (1913), 436.Google Scholar

102 “Aether Waves and Electrons”, Nature, cvii (1921), 374.Google Scholar

103 On deposit in the O. W. Richardson Collection in the Miriam Lutcher Stark Library at the University of Texas. I am indebted to Sir Lawrence Bragg and to the Stark Library for permission to quote from this letter.

104 The exact relationships between Thomson and Compton scattering may be seen from the plots presented by Ann T. Nelms in “Graphs of the Compton Energy-Angle Relationship and the Klein-Nishina Formula”, National Bureau of Standards Circular Number 542 (1953).Google Scholar

105 There is of course a longer wavelength Compton component in scattered X-rays as well as in scattered γ-rays. Since, however, the change in wavelength for X-rays is only a few per cent, while for γ-rays it is of the order of 100 per cent, the longer wavelength γ-ray component is much easier to observe than the longer wavelength X-ray component.

106 For a discussion of Kossel's work see Heilbron, John L., “The Kossel-Sommerfeld Theory and the Ring Atom”, Isis, lviii (1967), 451–485, especially 462–466.Google Scholar

107 Curiously, as I shall show in a future publication, Arthur Compton, while in no way building on Einstein's work, may have received this crucial insight (that a single quantum must interact with a single electron) from Bragg's work. I should also mention that my reason for terming Einstein's hypothesis “long-neglected” in spite of Millikan's 1915 photoelectric effect experiments is that Millikan (in common with virtually every other contemporary physicist except Einstein) did not accept these experiments as proof of Einstein's hypothesis. See my “Non-Einsteinian Interpretations of the Photoelectric Effect” in Stuewer, Roger H., ed., Historical and Philosophical Perspectives of Science (Minneapolis: University of Minnesota Press, 1970).Google Scholar

108 Eddington, Arthur, The Nature of the Physical World; paperback reprint (Ann Arbor, 1958), 194.Google Scholar