In the 1920s and 1930s, Marietta Blau developed the method of detect

Hafelekar-Observatory:
Disintegration Stars
Introduction
Einleitung
In the 1920s and 1930s, Marietta Blau developed the method of detecting particles with photographic emulsions, which was the first to record
and store particle tracks. She applied the method to measure cosmic
rays as of 1932. By courtesy of Viktor F. Hess, Blau and her colleague
Hertha Wambacher exposed photographic plates for several months at
the cosmic-ray observatory at Hafelekar in 1937. The developed plates
showed tracks of particles emitted in nuclear reactions of cosmic rays
with the emulsion. Due to the starlike shape of those tracks, they were
called Disintegration Stars.
In den 1920er und 1930er Jahren entwickelte Marietta Blau die erste
Methode zur Aufzeichnung und Speicherung von Teilchenspuren mit
photografischen Emulsionen. Ab 1932 wandte sie die Methode zur Messung kosmischer Strahlung an. 1937 exponierten Blau und ihre Kollegin
Hertha Wambacher mit Erlaubnis von Viktor F. Hess Photoplatten
einige Monate lang am Hafelekar-Observatorium. Auf den entwickelten
Platten fanden sie Spuren von Teilchen, die in Reaktionen der kosmischen Strahlung mit der Emulsion entstanden. Aufgrund der Sternform
dieser Spuren nannten sie diese “Zertrümmerungssterne”.
Marietta Blau
Photo courtesy Eva Connors.
Original Paper
Marietta Blau - Curriculum Vitae
1894 : April 29, born in Vienna.
1919 : PhD graduation with honours: “Über die Absorption 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 University of Miami; three Nobel Prize nominations.
1960 : Return to Vienna.
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
method to record and store particle tracks. Using this method, glass plates with a
70µm emulsion layer (“New Halftone plates” by Ilford) have been exposed to cosmic
radiation in the Hafelekar cosmic ray observatory (2290 m above sea level) for five
month. As reference, similar plates have been placed in the Vienna Radium Institute
(170 m).
On the plates exposed at higher altitudes, Blau and Wambacher discovered a number
of star-shaped structures originating from within the emulsion, which they identified
as disintegration of an argon or bromine atom by a cosmic ray particle. Most of the
tracks were attributed to protons, either the emitted ones or recoil protons from emitted neutrons. Track length and grain density pointed to high energy of the incident
particle.
The study of cosmic rays using the photographic method
was continued in 1938 by Cecil Frank Powell in collaboration with César Lattes, Giuseppe Occhialini, Hugh
Muirhead and others. Photographic plates have been exposed to cosmic rays on high mountains and in specially
designed balloons. In 1947 this work led to the discovery of the pion, a particle which had been hypothetically
proposed by Hideki Yukawa in 1935. Powell was awarded
with the Nobel Prize for Physics in 1950 for the discovery
of the pi-meson.
Later on, the photographic method with nuclear emulsions
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 über photographische Untersuchungen der schweren Teilchen in der kosmischen Strahlung. Einzelbahnen und Zertrümmerungssterne; 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].

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