In 1920s, a long-lasting controversy on the interpretation of nuclear beta spectrum arose between Lise Meitner and Charles Drummond Ellis. This controversy, and the reactions from the contending parties when it was settled, reflect clearly the difference between the scientific communities in Berlin and Cambridge at that time. The Meitner-Ellis controversy ended in 1929, and it left an anomaly that attracted leading theoretical physicists. A new dispute, this time between Niels Bohr and Wolfgang Pauli, broke out. It concerned the explanation of the continuity of the primary beta particles and dominated the discussions for the next five years. Pauli argued for a new particle, and Bohr for a new theory; both suggestions were radical steps, but they reflected two different ways of doing physics.

1 Prelude: Beta-Spectrum Research in the Pre-Nuclear Years, 1900-1911.- 1.1 Discovery and identification of the beta particle.- 1.2 The first experiments on the velocity distribution of beta particles.- 1.3 Absorption measurements question the inhomogeneity of the beta particles.- 1.4 The Hahn-Meitner vs. Wilson controversy.- 1.5 From unity to complexity: magnetic-deflection experiments, 1910-1911.- 2 The Origin of Beta Rays, and the Growing Complexity of Their Spectrum: The Rutherford Era, 1911-1919.- 2.1 Introduction.- 2.2 Rutherford's 1912 theory, and reactions to it.- 2.3 The beta particle as a nuclear constituent.- 2.4 An extreme complexity of beta line-spectra is brought to light: deflection experiments in the years 1911-1913.- 2.5 Continuity as well as lines: The composite beta spectrum.- 2.6 Rutherford's 1914 theory.- 2.7 The Bohr-Sommerfeld quantum conditions and the beta line-spectrum.- 2.8 Rutherford and the gamma rays.- 3 The Rise of a Controversy: Ellis, Meitner and Smekal Advance Different Beta-Spectrum Theories, 1920-1922.- 3.1 Introduction.- 3.2 Internal conversion, nuclear levels, and Ellis's interpretation of the beta line-spectrum.- 3.3 Analogy between alpha and beta emission, and Meitner's interpretation of the beta line-spectrum.- 3.4 Ellis's response to Meitner's hypothesis, and his interpretation of the continuous beta spectrum.- 3.5 Meitner replies to Ellis, and reveals her view on the continuous beta spectrum.- 3.6 The atom as a unity: Smekal joins the discussion, and is met with a sharp reaction.- 3.7 Two repetitions of the Chadwick experiment lead to contradictory conclusions.- 4 Secondary Effects and Order of Emission: Two Main Questions in the Controversy, 1923-1925.- 4.1 Introduction.- 4.2 Meitner investigates thebeta spectrum of UX1 and takes it as further support for her view.- 4.3 Radiationless transitions: Rosseland suggests an explanation of the emission of primary, and some secondary, beta particles.- 4.4 The nuclear field and the Compton effect: Two possible reasons for the continuous beta spectrum.- 4.5 Ellis and Skinner reinvestigate the beta line-spectra of RaB and C, and serious problems arise.- 4.6 Beta first, gamma second, or is it the other way around?.- 5 The End of the Beginning: The Controversy Enters the Decisive Phase, 1925-1929.- 5.1 Introduction.- 5.2 Ellis adjusts his view on the emission process, but maintains his interpretation of the continuous spectrum.- 5.3 The number of emitted beta particles.- 5.4 Ellis and Wooster's tour de force: A determination of the heating effect of RaE.- 5.5 Continental reactions to Ellis and Wooster's experiment.- 5.6 Some concluding remarks about the controversy.- 6 From Anomaly to Explanation: The Continuous Beta Spectrum, 1929-1934.- 6.1 Introduction.- 6.2 Non-conservation of energy or a new particle? The first phase of the Bohr-Pauli dispute, 1929-1932.- 6.3 Other attempts at explaining the anomalous continuity.- 6.4 The question of upper limits in beta spectra, and the thorium C branching problem.- 6.5 The impact of the miraculous year: The second phase of the Bohr-Pauli dispute, 1932-1933.- 6.6 The two theories of beta decay.- 7 Towards a Theory of Internal Conversion: The Beta Line-Spectrum, 1927-1934.- 7.1 Introduction.- 7.2 Experimental evidence brings about a new view on the origin of gamma rays.- 7.3 The radiation hypothesis proves insufficient to explain internal conversion of gamma rays.- 7.4 A theory of internal conversion is developed.- Summary and Conclusion.- Name Index.