LISE MEITNER (1878 – 1968)

  August 10, 2021   Read time 6 min
LISE MEITNER (1878 – 1968)
Collaborating with Otto Frisch, the Austrian-Swedish physicist Lise Meitner provided the first theoretical interpretation of the world-changing experiments by Otto Hahn—namely, that neutron bombardment had caused the uranium nucleus to split (or “fission”) and subsequently release an enormous amount of energy.

Meitner was born on November 7, 1878, in Vienna, Austria, the third child of a financially comfortable Jewish family. After finishing all the public education available to girls at that time in Austria, at the age of 14, she took private lessons in mathematics and physics to prepare for entrance into the university system. Shattering the prevailing social customs, Meitner became a Protestant and never married. She decided to pursue a life dedicated to physics and mathematics—fields dominated almost exclusively by male scientists who had little tolerance for competition by a talented female. Despite these barriers, she enrolled at the University of Vienna in 1901 and studied under the famous theoretical physicist Ludwig Boltzmann (1844–1906). She received her Ph.D. in physics from that institution in 1906.

She moved to Berlin in 1907 to study under Max Planck (1858–1947). Impressed by the work of Marie Curie (1867–1934), she also wanted to investigate radioactivity. Soon after her arrival in Berlin, she met Otto Hahn (1879–1968). Since he was a skilled chemist and she was an excellent physicist and mathematician, they agreed to collaborate and made a variety of pioneering discoveries in radiochemistry for over three decades.

Unfortunately, despite Meitner’s scientific abilities, the director of Hahn’s laboratory (Nobel laureate Emil Fischer; 1852–1919) would not allow Meitner to enter any laboratory or office in which men were working. He assigned her to work in an old carpentry shop. Meitner’s working conditions improved somewhat in 1912, when she and Hahn relocated their research to Berlin’s newly opened Kaiser Wilhelm Institute for Chemistry.

World War I interrupted their collaboration in radiochemistry. While Hahn remained at the institute, Meitner served as an X-ray technician in field hospitals of the Austrian Army. Whenever possible, she would return on leave to Berlin, to maintain an active involvement in their collaborative radiochemistry research program. Her efforts paid off. Soon after the war ended in 1918, Meitner and Hahn formally announced their discovery (made in 1917) of a new radioactive element, protactinium (Pa; atomic number 91). This naturally radioactive element occurs in uranium ores. The longest-lived radioisotope of this element is Pa-231 with a half-life of about 33,000 years.

The discovery made Hahn and Meitner famous within German scientific circles. She became head of a new department of radioactivity physics at the Kaiser Wilhelm Institutes in 1918 and then was appointed the first female professor of physics at the University of Berlin, in 1926. Throughout the 1920s, Meitner maintained a working friendship with Hahn but also began to pursue her own line of research. She focused her research on the physics of beta particles, which she correctly suspected emerged from transitions within the atomic nucleus.

The rise of the Nazi Party in 1933 changed life for Jewish scientists in Germany. Although of Jewish ancestry, Meitner was initially protected by virtue of her Austrian citizenship. So in the mid-1930s, she was tenuously able to collaborate with Hahn as he bombarded uranium with slow neutrons, repeating the neutron irradiation work that Enrico Fermi (1901–1954) had performed in Rome. Their primary goal was to see if they could produce elements beyond uranium through various neutron capture reactions. Fermi had tried but his results were uncertain.

When Germany annexed Austria in 1938, the thin shield of Meitner’s Austrian citizenship vanished. She had to abandon her work with Hahn and flee for her life. Close friends helped her make a daring escape to Sweden through Holland. Once safely in Sweden, she began working at the Nobel Institute of Theoretical Physics in Stockholm. Fermi and his wife, Laura, visited Meitner late in 1938. Fermi was in Stockholm to receive the 1938 Nobel Prize in physics for his neutron irradiation experiments, and Meitner informed him about the similar work she and Hahn had been attempting in Berlin. By fortunate coincidence, one political refugee scientist was able to alert another. Fermi and his family were fleeing to the United States and so he carried a new concern about the latest nuclear physics research in Germany.

After Meitner’s harrowing escape, Hahn continued the neutron bombardment experiments, now assisted by the German chemist Fritz Strassmann (1902–1980). As Hahn and Strassmann continued to bombard uranium with neutrons in late 1938, they unexpectedly encountered small quantities of barium in the target residue. Hahn puzzled over the source of the barium, which behaved chemically like radium but was much lower in atomic mass. He sent a letter to Meitner informing her about the unusual findings. Meitner quickly made the important connection that the uranium nucleus was splitting. During the Christmas holidays in Sweden, she discussed the phenomenon with her nephew, the Austrian-British physicist Otto Frisch (1904–1979). He agreed with her hypothesis and they immediately collaborated on a world-changing short paper entitled “Disintegration of Uranium by Neutrons: A New Type of Nuclear Reaction,” published in the February 11, 1939, issue of Nature. Using the liquid-drop model of the nucleus, Meitner (in collaboration with Frisch) cited the experimental results of Hahn and Strassmann and then boldly proposed that the barium (atomic number 56) was being formed when the uranium nucleus split. They borrowed the term fission from biology and calculated that approximately 200 million electron volts (MeV) of energy was being released in the nuclear fission reaction.

Several days after his visit to Stockholm, Frisch informed Niels Bohr (1885–1962) of what was happening in Nazi Germany and the phenomenon of nuclear fission. Bohr grasped the consequences immediately and carried the news across the Atlantic Ocean, informing many key nuclear physicists in the United States. After Frisch returned to Copenhagen, he performed his own experiments in mid-January 1939 to confirm the process of uranium fission. He then left Denmark and went to England, where he collaborated with the German-British physicist Rudolph Peirls (1907–1955). They calculated the size and explosive power of a possible uranium-235 atomic bomb and eventually joined the British scientific team working on the Manhattan Project at Los Alamos Laboratory in New Mexico.

In 1943, Lise Meitner was invited to join the British team going to Los Alamos, but she refused to use her scientific talents on the military application of nuclear energy. She remained in Sweden after World War II and became a Swedish citizen in 1949. In 1944, the Nobel Prize Committee inexplicably ignored Meitner’s role in the discovery of nuclear fission. They chose to award only Hahn the 1944 Nobel Prize in chemistry, citing “his [emphasis added] discovery of the fission of heavy nuclei.” Equally surprising, after World War II Hahn never publicly acknowledged Meitner’s role in the discovery of nuclear fission—despite three decades of scientific collaboration with her. Hahn’s silence embittered Meitner, and they no longer worked together as pioneers in nuclear chemistry and radioactivity.

Meitner did receive other awards, however, including Germany’s Max Planck Award (1949) and the Enrico Fermi Award from the U.S. Atomic Energy Commission (1966). She was the first female scientist to win the prestigious Fermi Award, sharing the prize that year with Hahn and Strassmann. In 1960, she moved from Stockholm to England to be near her nephew, Frisch, who was then a physics professor at Cambridge University. A few days before her 90th birthday, on October 27, 1968, Meitner died in Cambridge. As a lasting tribute to her numerous contributions to nuclear technology, in 1997 the International Union of Pure and Applied Chemistry approved the name meitnerium for transuranic element 109.