Hafelekar-Observatory: Disintegration Stars

Introduction Einleitung

In the 1920s and 1930s, Marietta Blau developed the method of detect- In den 1920er und 1930er Jahren entwickelte Marietta Blau die erste ing particles with photographic emulsions, which was the first to record Methode zur Aufzeichnung und Speicherung von Teilchenspuren mit and store particle tracks. She applied the method to measure cosmic photografischen Emulsionen. Ab 1932 wandte sie die Methode zur Mes- rays as of 1932. By courtesy of Viktor F. Hess, Blau and her colleague sung kosmischer Strahlung an. 1937 exponierten Blau und ihre Kollegin Hertha Wambacher exposed photographic plates for several months at Hertha Wambacher mit Erlaubnis von Viktor F. Hess Photoplatten the cosmic-ray observatory at Hafelekar in 1937. The developed plates einige Monate lang am Hafelekar-Observatorium. Auf den entwickelten showed tracks of particles emitted in nuclear reactions of cosmic rays Platten fanden sie Spuren von Teilchen, die in Reaktionen der kosmis- with the emulsion. Due to the starlike shape of those tracks, they were chen Strahlung mit der Emulsion entstanden. Aufgrund der Sternform called Disintegration Stars. dieser Spuren nannten sie diese “Zertr¨ummerungssterne”.

Marietta Blau Marietta Blau - Curriculum Vitae Original Paper

1894 : April 29, born in Vienna. 1919 : PhD graduation with honours: “Uber¨ die Ab- sorption divergenter γ - Strahlung”. 1921 : Physicist in X-ray tube factory in Berlin. 1922 - 1923 : Assistant professor at University of Frankfurt/Main. 1923 - 1938 : Researcher (unpaid!) at the Vienna Radium Institute. 1937 : Discovery of “disintegration stars” at the Hafelekar Observatory. 1938 : Emigration to Mexico. 1939 - 1959 : Professor in Mexico City, Columbia University, Brookhaven National Laboratory and Uni- versity of Miami; three Nobel Prize nominations. 1960 : Return to Vienna.

Photo courtesy Eva Connors. 1970 : January 27, died in Vienna.

For more details, see [2]. Article reproduced from [1].

The discovery of Disintegration Stars Further development

Established in the 1920s, the photographic method of particle detection was the first The study of cosmic rays using the photographic method method to record and store particle tracks. Using this method, glass plates with a was continued in 1938 by Cecil Frank Powell in collab- 70µm emulsion layer (“New Halftone plates” by Ilford) have been exposed to cosmic oration with C´esarLattes, Giuseppe Occhialini, Hugh radiation in the Hafelekar cosmic ray observatory (2290 m above sea level) for five Muirhead and others. Photographic plates have been ex- month. As reference, similar plates have been placed in the Vienna Radium Institute posed to cosmic rays on high mountains and in specially (170 m). designed balloons. In 1947 this work led to the discov- On the plates exposed at higher altitudes, Blau and Wambacher discovered a number ery of the pion, a particle which had been hypothetically of star-shaped structures originating from within the emulsion, which they identified proposed by Hideki Yukawa in 1935. Powell was awarded as disintegration of an argon or bromine atom by a cosmic ray particle. Most of the with the Nobel Prize for Physics in 1950 for the discovery tracks were attributed to protons, either the emitted ones or recoil protons from emit- of the pi-meson. ted neutrons. Track length and grain density pointed to high energy of the incident Later on, the photographic method with nuclear emulsions particle. was extensively used in autoradiography, e.g. in medicine, biological and chemical research.

References

[1 ] M. Blau, H. Wambacher; Disintegration processes by cosmic rays with simultaneous emission of heavy particles; Nature (London) 140 (1937) 585. [2 ] R. Rosner, B. Strohmaier; Marietta Blau - Sterne der Zertrmmerung. Biographie einer Wegbereiterin der modernen Teilchenphysik, Bhlau Verlag, 2003 [3 ] M. Blau, H. Wambacher; II. Mitteilung ¨uber photographische Untersuchungen der schw- eren Teilchen in der kosmischen Strahlung. Einzelbahnen und Zertr¨ummerungssterne; MIR 409 (1937); Sitzungsberi. Akad. Wiss. Wien, Math. NatWi. Kl IIa 146 (1937) 623-641.

Poster by P. Jussel & R. Kissmann photography taken from [3].