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Commentary
1932: A Year to Remember
T
his is the 70th anniversary of several discoveries and
inventions that played key roles in the development of
nuclear medicine: the discovery of the neutron, the
positron, and deuterium and the invention of the
Cockcroft–Walton accelerator, the cyclotron, and the lapel
microphone––1932 was quite a year!
None of these discoveries and inventions came as a complete surprise. Ernest Rutherford had predicted a third subatomic particle (in addition to the proton and the electron)
that could explain why atomic weight was higher than atomic number (except for hydrogen). In a speech to the Royal
Society in 1920, he predicted (in the same sentence) deuterium and the neutron. The latter he described as “an atom
of mass 1 which has zero nucleus charge” (1). In 1930,
Bothe and Becker found a very penetrating radiation from
beryllium that was bombarded with α particles, and, in
1932, Joliot and Joliot-Curie found that this radiation
knocked protons out of substances containing hydrogen
(2,3). Neither pair of researchers was able to explain these
results. Building on these findings, James Chadwick
(Rutherford’s “lieutenant”) explained it all after 3 weeks of
exhaustive, elegant experiments. α rays from polonium were
easily stopped by a beryllium foil; a counter behind the foil
was silent. When Chadwick placed a slab of paraffin
between the foil and the counter, counts resumed.
Conservation of energy and momentum indicated that the
radiation emanating from the paraffin must be particles with
a mass of 1, and their easy passage through matter gave
them a charge of 0. Chadwick had validated Rutherford’s
prediction, and the neutron was born (4). (The reaction was
stated: 94Be + 42α →126C + 10n.) This caused speculation that
nuclei with the same number of protons might have different numbers of neutrons (bingo: isotopes). After his discovery, Chadwick said, “Now I want to be chloroformed and put
to bed for a fortnight” (5).
The positron was predicted by French physicist P.A.M.
Dirac in 1931, based on his (and Schrödinger’s) quantum
theory of the electron (5). Dirac assumed symmetry existed
within the atom, with positive as well as negative energy
states, and positive as well as negative electrons (and even
protons). Many physicists believed a positron was “out
there” waiting to be found. In 1932, it was––by Carl
Anderson at Cal Tech. In observing cloud chamber tracks
made by cosmic rays passing through lead in a magnetic
field, he found tracks corresponding to particles having the
mass of an electron but curving the opposite way, indicating
they carried a positive charge (6). Physicists had noticed this
before but had always thought the tracks represented negative electrons going the other way.
Deuterium, or 2H, had been
postulated by Rutherford in 1920.
Harold Urey, at Columbia
University, believed it existed. He
reasoned that 2H should have a
slightly higher boiling point than
ordinary hydrogen (1H) and that
they might be separated by distilling liquid hydrogen––no simple
task, because 1H boils at –252.8°C
and 2H at a barely more tepid
–249.5°C. The two isotopes also Dennis D. Patton, MD
SNM Historian
should have slightly different spectra. The distillation was carried out at the Bureau of
Standards in Washington, DC, under Urey’s direction,
because Columbia lacked the required apparatus.
Spectroscopic analysis showed the samples to be enriched in
2H, and Urey published his results in 1932 (7). Urey also
demonstrated chemical and physical differences between the
isotopes that had not been shown for any other isotope pairs.
Deuterium became an indispensable and stable tracer in
countless branches of research. Deuterium and tritium (and
protium, 1H) are the only isotopes with their own names.
The year 1932 also saw the introduction of two
approaches to smashing the atom. The first was initiated by
Rutherford, whose “collision method” of breaking nuclei
depended on naturally occurring α-emitting radionuclides.
He had no control over their energy, the radiation went in all
directions, and intensities were quite low. Rutherford
encouraged British physicists John D. Cockcroft and Ernest
T. S. Walton, both of whom were working at the Cavendish
under Rutherford, to build a particle accelerator that could
achieve the high energies required to penetrate the nucleus.
By a stroke of luck, the group was relocated in 1931 from
their cramped quarters to a room with a very high ceiling,
giving them the idea of building a vertical accelerator consisting of a stack of voltage multipliers. Hydrogen ions (protons), accelerated through 700,000 V, penetrated the nucleus, splitting 7Li nuclei into two α particles (7Li + 1H → 8Be
→ 2α). Rutherford swore them to absolute secrecy so they
could finish their work uninterrupted by visitors (1). By the
time they published their work in 1932, they had created
several new radionuclides, opening the era of particle accelerators (“atom smashers”) and radionuclide production––and big physics (8).
In the same year, Ernest Orlando Lawrence, a physicist
at the University of California, Berkeley, improved on the
Cockcroft–Walton linear accelerator. The British team’s
invention required voltages corresponding to the desired
Newsline
N E WS LI N E
HISTORY CORNER
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N E WS LI N E
In Appreciation
Dennis Patton has served the SNM and the nuclear medicine community well during his 6-year tenure as Historian of the
Society. Under his guidance, the SNM Archives are now housed in a secure, climate-controlled room in the headquarters building in Reston, VA. Many of the items were collected and cataloged by Dr. Patton and are now available to researchers. Separate
collections housed in the Archives contain materials from Marshall Brucer, Robert F. Buntaine, James J. Conway, C. Craig
Harris, Henry Kramer, Michael Ter-Pogossian, and others.
In an effort to preserve the global history of the field, Dr. Patton also began work on gathering material on the history of
nuclear medicine in a number of countries and has recently completed translation of Geschichte der Nuklearmedizin in Europa
[History of Nuclear Medicine in Europe] by M. De Roo and M. Feld (Stuttgart, Germany: Schattauer; 2000). The translated
book will be available at the September 2002 meeting of the European Association of Nuclear Medicine in Vienna, Austria.
“Together with the international database derived from contacts with world leaders, we now have or have access to historical
accounts of the development of nuclear medicine in 43 countries,” said Dr. Patton at the recent SNM Annual Meeting in Los
Angeles. “This by no means fills the need for a unified, comprehensive history of nuclear medicine, and an up-to-date history of the development of nuclear medicine in the United States has yet to be compiled.”
In the last 6 years, Dr. Patton has contributed 14 articles to Newsline on a range of historical topics. These fascinating
pieces have enriched our knowledge of those who came before us in the field and of the progress (and sometimes the wrong
turns) that shaped nuclear medicine as we know it today. These articles are the product of Dr. Patton’s extensive research, wideranging knowledge, unique perspective, and wry humor. Together they constitute a valuable body of work that is being made
available as a group on a new Archives section of the SNM Web site (www.snm.org). This section also will include a description of the SNM Archives, a brief listing of the collections and other materials, a catalog of the library and journals available
at SNM headquarters, the database of information on worldwide history of nuclear medicine, links, and selected reprints of
key articles.
Dr. Patton is to be congratulated for his extraordinary and valuable contributions as SNM Historian. As he leaves this post,
we hope that he will continue to share his insights and the products of his ongoing historical research with Newsline.
––Conrad Nagle, MD
Editor, Newsline
energy of the emerging particles, for example 500 kV to create 500-keV protons. There were many difficulties with such
devices: the path lengths were long, and the high electric
fields were dangerous and unstable. Lawrence saw a way in
which charged particles could be accelerated to high energies by repeated acceleration using relatively low voltages
across two hollow D-shaped metal chambers (“dees”) in a
magnetic field. Protons were accelerated from one dee to the
other by the electric field, bent in a circular path by the magnetic field, then accelerated to the other dee as the electric
field reversed, and so on. His first cyclotron, 11-in in diameter, used a 4000-V field to accelerate protons to 1.22 MeV
(9). (The article by Lawrence and his graduate student M.
Stanley Livingstone appeared back-to-back with that of
Urey on deuterium.)
In a curious twist of fate, the economy-minded
Lawrence always turned off his detectors when he turned off
the cyclotron, thereby missing the discovery of artificially
induced radioactivity (10). He also missed inventing the first
“atom smasher” because he was convinced that 1 MeV
would be needed. Cockcroft and Walton did it first with 0.7
MeV. The cyclotron quickly became a fountain of unprecedented quantities of new radionuclides and a basis for a new
understanding of the nature of the atom. It offered controlled
particle energy, a focused beam, high intensities, and few
high-voltage problems. Lawrence himself stated that he had
the ubiquitous Rutherford and his “collision method” in
mind. He spent the remaining 26 years of his life designing
ever-larger cyclotrons.
Nobel Prizes were awarded to all these pioneers: in
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T HE J OURNAL
OF
physics to Chadwick in 1935, Anderson (and Victor Hess,
who discovered cosmic rays) in 1936, Lawrence in 1939,
and Cockcroft and Walton in 1951; and in chemistry to Urey
in 1934.
All this was dwarfed in the public mind in 1932 by the
invention of the lapel microphone, which for the first time
enabled speakers to gesticulate, pace back and forth, and
retrieve dropped pointers without losing their audience. But
I will leave this story for the next SNM Historian. It has been
a pleasure serving the SNM. The list of people to thank
would occupy many pages, but I am especially indebted to
Dr. Nan Knight, the SNM staff, and the late Marshall Brucer;
and thanks to Prof. E.H. Graul for suggesting the theme of
this History Corner.
—Dennis D. Patton, MD
SNM Historian, 1996–2002
References
1. Oliphant ML. Rutherford. Recollections of the Cambridge Days. Cambridge,
UK: Elsevier; 1972:71–86. Oliphant was a physicist working with Rutherford
at the Cavendish.
2. Bothe H, Becker H. Z Physik. 1930;66:289.
3. Joliot-Curie F, Joliot-Curie I. CR Acad Sci Paris. 1932;194:273.
4. Chadwick J. The existence of a neutron. Proc Royal Soc London A.
1932;136:692.
5. Snow CP. The Physicists. New York, NY; Little, Brown; 1981:85–89.
6. Anderson CD. The positive electron. Phys Rev. 1932;43:491.
7. Urey HC, Brickwedde FG, Murphy GM. A hydrogen isotope of mass 2 and its
concentration. Phys Rev. 1932;40:1.
8. Cockcroft JD, Walton ETS. Experiments with high velocity positive ions. II:
The disintegration of elements by high velocity protons. Proc Royal Soc
London A. 1932;137:229.
9. Lawrence EO. The production of high-speed light ions without the use of high
voltages. Phys Rev. 1932;40:19.
10. Davis NP. Lawrence and Oppenheimer. New York, NY: Simon and Schuster;
1968:60.
N UCLEAR M EDICINE • Vol. 43 • No. 7 • July 2002