Malley M.C. Radioactivity: A History of a Mysterious Science
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A NEW SCIENCE
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Curies had used. Giesel used his technique to produce radium at
Buchler & Company’s chemical factory in Brunswick, Germany,
making his employer the major supplier for European scientists
for several years (Figure 2-5). Giesel was the rst person to apply
a standard chemical test to his new substance. He ignited a small
quantity in the ame of a Bunsen burner. Unlike barium, which
produces a green ame, Giesel’s material colored the ame a beau-
tiful carmine red.
4
e Curies’ ndings caught the a ention of the scienti c world.
e discovery of new elements was always a momentous occa-
sion. But since the Curies had used a totally new method to nd
polonium and radium, an electrical method, their discovery was
especially remarkable—and controversial. Only recently had the
chemical community grudgingly accepted spectroscopy, a method
Figure 2-4. Extraction of radium in the old shed. From Marie Curie, Pierre Curie, trans.
Charlo e and Vernon Kellog (New York: Macmillan, 1923). Image courtesy of History of
Science Collections, University of Oklahoma Libraries.
THE CURIES
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for analyzing light by breaking it into a rainbow of colors, as a legit-
imate tool for chemists. Several decades earlier, when the British
scientists Norman Lockyer and Edward Frankland announced
that sunlight, when passed through a spectroscope, revealed a
new element in the sun—named “helium” a er the Greek word
for sun, helios—an unbelieving chemical community, long used
to relying upon concrete sights and smells for its detective work,
resisted this intrusion of physics with its abstractions into their
eld (Figure 2-6). Now chemists were being asked to accept the
existence of invisible, imponderable elements on the basis of a
physical device which supposedly recorded invisible rays! is was
too much for some to believe.
eir skepticism was understandable, even if not always
well informed. Chemical analysis is fraught with di culties.
Figure 2-5. Friedrich Giesel. Courtesy of Mr. omas W. Buchler, Buchler GmbH.
A NEW SCIENCE
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ere are so many ways that a sample can be compromised dur-
ing the complex and delicate operations required to detect small
quantities of a substance. Wary of mistaking trace impurities of
a known substance for a new element, some chemists suggested
that “radium”was actually barium contaminated by uranium. Or
perhaps its previous exposure to uranium had made the barium
radioactive, in the way that iron can be magnetized by contact
with a magnet.
Some scientists even doubted that Becquerel’s rays existed.
is was not surprising, since the scienti c literature over owed
with work of questionable quality on supposed new radiations.
Giesel wrote to the Curies at the end of 1899 that “Unfortunately
your beautiful discovery was hardly noticed at rst, as people
had become somewhat distrustful because of Le Bon’s work . . . .
even Röntgen did not believe in the existence of the Becquerel
rays . . . ”
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Figure 2-6. Spectroscope. e material to be tested is placed in the ame (D). Light from
the ame then passes through a slit in the tube (B) to a prism (F), and is viewed through the
telescope (C). From Henry E. Roscoe, Spectrum Analysis (London: Macmillan, 1869), 54.
THE CURIES
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e Curies were delighted when the respected spectroscopist
Eugène-Anatole Demarçay photographed radium chloride’s spec-
trum (produced using a high voltage spark generator) and found
a line which did not belong to any known element. is meant
the line came from a new element, rather than from an impurity.
But Marie Curie realized she needed to convince the skeptics on
their own terms. e pa ern produced by passing light through a
prism might satisfy physicists, but many chemists still considered
the spectroscope as a tool for physicists. Rather than using spec-
tral pa erns, chemists traditionally identi ed elements by their
atomic weights. Marie Curie knew that if she could establish an
atomic weight for radium, no reasonable scientist would deny its
existence.
To obtain enough radium for weight measurements, the
Curies would need large quantities of ore. Pitchblende was expen-
sive, but a er uranium was extracted from it, the remainders were
discarded. e Austrian government owned a large pitchblende
mine in the mountains near the village of St. Joachimsthal (mean-
ing “St. Joachim’s valley”) in Bohemia (later Czechoslovakia).
ey were willing to send a generous supply of pitchblende waste
to Paris if the recipients would pay for shipping. e Curies hap-
pily agreed. ey asked Bémont to help them separate radium
from the ore.
e storeroom was too small for such a large operation. e
only facility available at the school was an abandoned shed with no
o o r . e roof leaked and the building provided li le protection
from heat and cold (Figure 2-7). ese facilities shocked Wilhelm
Ostwald, a famous German chemist, who once stopped by for a
visit. He characterized the laboratory as “a cross between a stable
and a potato-cellar, and, if I had not seen the table with the chemi-
cal apparatus, I would have thought it a practical joke.”
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A NEW SCIENCE
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e coveted shipment arrived early in 1899. In order to pre-
vent toxic fumes from concentrating inside the shed, Marie per-
formed most of the work outdoors in the building’s courtyard. She
processed approximately 220 pounds of ore in 45-pound batches,
grinding, dissolving, boiling, stirring, ltering, pouring, and crys-
tallizing, until the entire quantity had been separated into di er-
ent chemical components. Each component was then tested for
radioactivity.
e work would be exhausting even for a muscular man, but
Marie’s petite, pre y appearance belied her inner strength and
determination. It would take nearly four years of heavy labor to
produce enough radium to determine an atomic weight (one tenth
of a gram, in 1902).
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Figure 2-7. e shed where radium was discovered. Source: Musée Curie (coll. ACJC)/
Institut Curie.
THE CURIES
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at feat capped the Curies’ work and crowned Marie’s doc-
toral dissertation, which she presented in 1904. No longer eclipsed
by the x rays, radioactivity was becoming a popular and exciting
eld in its own right. e Nobel Prize commi ee recognized this
by awarding the 1903 physics prize jointly to Becquerel and the
Curies for “‘his discovery of spontaneous radioactivity’” and “‘for
their joint researches on the radiation phenomena discovered by
Professor Henri Becquerel.’”
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3
Rutherford, Soddy, Particles,
and Alchemy?
ere was a spirit of adventure about him coupled with a dogged
determination to reach his quest.
—Frederick Soddy, 1953
If it [atomic energy] could be tapped and controlled what an agent
it would be in shaping the world’s destiny!
—Frederick Soddy, 1904
For an alpha ray
Is a thing to pay
And a Nobel Prize,
One cannot despise,
And Rutherford
Has greatly scored,
As all the world now recognize.
A. A. Robb, c. 1919
RUTHERFORD AND THE RAYS
About the same time that Marie Curie was looking for radio-
active elements, another physicist was investigating the rays.
Ernest Rutherford, a bright and con dent young man fresh from
RUTHERFORD, SODDY, PARTICLES, AND ALCHEMY?
35
New Zealand’s Canterbury College, had le home with a schol-
arship to study with Joseph John (J. J.) omson, director of
Cambridge’s famed Cavendish Laboratory. omson, the English-
speaking world’s leading researcher on electricity, specialized in
ionization (a process that creates electri ed particles) and conduc-
tion in gases.
e son of a farmer and a teacher, Rutherford had became
interested in physics and carried out researches as a student in
New Zealand. His mother provided special encouragement, and
he faithfully corresponded with her throughout his career. In
omson’s laboratory Rutherford continued his work on mag-
netism and high frequency electric waves (later known as radio
waves).
en Wilhelm Conrad Röntgen discovered x rays. e allure
of these mysterious radiations changed Rutherford’s career path
forever. Caught up in the general excitement, Rutherford joined
omson in investigating the electrical conduction which these
rays produced in gases and became quite adept in ionization stud-
ies. Rutherford’s work impressed his mentor and caught the a en-
tion of the wider scienti c community. In 1898 he received an o er
from McGill University in Montreal (Figure 3-1).
ough Rutherford would have preferred to remain in England
at the center of British scienti c activity, he was a racted by
McGill’s state-of-the-art physics laboratory. ese ne facilities
had been donated by Sir William MacDonald, an antismoker
who, ironically, had made a fortune with tobacco. Rutherford
(who happened to be a heavy smoker) accepted McGill’s o er,
and a er he had se led in to his new surroundings, he began tests
with Becquerel rays from uranium. He wanted to nd out whether
Becquerel rays were, as many suspected, a type of x radiation.
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To trace the rays, Rutherford used the electrical methods per-
fected at Cambridge, rather than the older photographic methods
preferred by Henri Becquerel. is choice was crucial, for electri-
cal measuring devices gave quantitative results, while photography
(which involved waiting for an image to form on a photographic
plate) was less precise and relied heavily on the observer’s subjec-
tive interpretation. First, Rutherford repeated Becquerel’s experi-
ments on refraction and polarization of rays from uranium. If
these rays were a form of light, as Becquerel believed, it should be
possible to refract and polarize them. But Rutherford could detect
neither phenomenon.
Figure 3-1. Ernest Rutherford. From the George Grantham Bain Collection, courtesy of
the Library of Congress.
RUTHERFORD, SODDY, PARTICLES, AND ALCHEMY?
37
Rutherford then tested the other possibility, that the Becquerel
rays were a kind of x radiation. From his Cambridge work based on
omson’s electrical theory, Rutherford predicted the ionization
that uranium’s rays would create in air if they were a type of x ray.
His measurements matched the predictions.
e rays were not uniform, as Becquerel and Gerhard Carl
Schmidt had noticed earlier. Rutherford detected two components
in them, one that could be stopped easily (which he called “alpha,”
a er the rst le er in the Greek alphabet, α) and another that could
penetrate many layers of aluminum foil (which he called “beta,”
a er the second le er in the Greek alphabet, β). is behavior
was strikingly similar to a recent discovery by a French physicist.
Georges Sagnac had shown in 1898 that x rays can generate new
x rays when they strike ma er. e secondary radiation, as Sagnac
called it, was more readily absorbed than the original (primary)
radiation. Rutherford believed that the Becquerel rays might be a
mixture of primary and secondary x rays, with the betas being the
primary radiation and the alphas the secondary radiation.
Early in 1899 Becquerel revisited his earlier experiments with
uranium’s rays. A er he could not reproduce some of them and
realized that he had misinterpreted others, Becquerel agreed that
the rays he had discovered were more like x rays than light. So far
as researchers in radioactivity were concerned, Becquerel rays
were a form of x radiation.
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WHERE DID THE ENERGY COME FROM?
Radiation required energy to produce it. Primary x rays received
their energy from the high voltage electric discharge tubes used
to generate them. Secondary x rays received their energy from the