An uninvited guest: The positron in early 1930s physics

Abstract

A few months before its "official" discovery in September 1932 by Anderson at Cal Tech in Pasadena, the positron was almost simultaneously observed by no less than two additional research teams: one at Cavendish Laboratory in Cambridge, England, and one at Institut du Radium in Paris, France. In this paper, we examine this curious case of multiple independent observations by studying the primary literature. This study identifies the motivations that led these researchers to independently design the experiments suitable for the detection of this novel particle and shows that none of these teams were looking for a positive electron.

History of the bubble chamber and related active- and internal-target nuclear tracking detectors

“…[16,17]) and the cloud chamber (with a magnet) for discovery of antimatter (positrons) in cosmic rays (Refs. [11][12][13][14][15]). In addition other strange tracks, associated with so-called V particles that produced forked tracks, also were seen on rare occasion in cosmic rays (Refs.…”

“…[10][11]), together with cloud chambers, the latter often used as an IT large-volume but low-density tracking detector (Refs. [11][12][13][14][15]), were the main instruments used in the late 1920s through the 1950s in cosmic ray research. Both led to important discoveries e.g.…”

Diagnosing disagreements: The authentication of the positron 1931–1934

“…the energy conservation principle). 6 Whilst in 1932 new particles were discovered, these new discoveries did not immediately lead to solutions to the aforementioned problems. 7 Some of the particles were accepted more readily than others, for example the neutron, 8 whilst in other cases, such as the positron's, their discovery marked the beginning of a long process of authentication.…”

“…Despite these spectacular results, Dirac's theory of the electron had also some undesirable consequences. 11 The equa- 6 Bohr's 'attack' of the energy conservation principle is well known and has been discussed in a variety of papers, most recently by [22]and [19]; it will also be the subject of more detailed discussion in what follows. 7 For a review of the 'new particles' in the 1930, see [17], ch.…”

“…However, the discussions during the conference brought out prior disagreements with regard to the nature of the positron. Whilst the historical details of the prediction and discovery of the positron have already been subject to a reasonably complete existing literature [1,2,3,4,5,6], important questions related to the disagreements attending the nature of the positron remain nevertheless puzzling. In particular: Why were Bohr and Pauli so opposed to equating the experimental particle with the Dirac-particle?…”