Story of Fission
Unlocking the power of the nucleus
Amit Roy
Variable Energy Cyclotron Centre
How did it all begin?
Henri Becquerel
Discovered Radioactivity in 1896.
Nobel 1903
Pierre and Marie Curie
Discovered Radium and Polonium.
Nobel 1903, 1911(M. Curie)
Ernest Rutherford
Discovered the Nucleus, 1911
Discovered transmutation of elements, 1919
14N + α => p + 17O
Nobel, 1908
The St. Louis Post-Dispatch in 1903 describes atomic
energy...
NEWS ARTICLE: "The most wonderful and
mysterious force in the universe—the atom's power—
will be inconceivable. It could revolutionize the
illumination system of the world. It could make war
impossible. It is even possible that an instrument might
be invented which at the touch of a key would blow up
the whole earth and bring about the end of the world."
The science fiction writer H. G. Wells had written about the
potential of nuclear power in "The World Set Free",
published in 1914.
Rutherford made this opinion public in 1933 at a
scientific meeting, and his remarks were published in
the scientific journal Nature:
NEWS ARTICLE: "These transformations of the atom
are of extraordinary interest to scientists but we cannot
control atomic energy to an extent which would be of
any value commercially, and I believe we are not likely
ever to be able to do so... Our interest in the matter is
purely scientific, and the experiments which are being
carried out will help us to a better understanding of the
structure of matter."
Discovered Artificial Radioactivity
1934, Nature 133: 201 (1934)
27 Al + 4 α → 30 P(2.5 min) + [1 n]
13
2
15
0
I. Curie
F. Joliot-Curie
Discovered neutron in 1932
J. Chadwick
All three awarded Nobel Prize, 1935
Bombarded almost every element
with neutrons, producing artificial
radioactivity in many elements.
1934
Enrico Fermi
Nobel, 1938
Essential part of Raα + Be source
filled with radon gas and Be powder.
Ra source from medical supplies of
Prof. G.C. Trabbachi, Inst of Radium
One of the GM counters used in 1934 by
Fermi's group. The Al wall was between
0.1-0.2 mm thick. Small cylinder was
obtained by cutting bottom of a box of
medical tablets.
Discovery of artificial
radioactivity induced by
slow neutrons.
Proc. R. Soc. Lond. A 1935 149
Years later in 1952, Fermi told Subrahmanyan Chandrasekhar,
"I will tell you how I came to make the discovery which I suppose
is the most important one I have made. We were working very
hard on the neutron induced radioactivity and the results we were
obtaining made no sense. One day, as I came to the laboratory, it
occurred to me that I should examine the effect of placing a piece
of lead before the incident neutrons. And instead of my usual
custom, I took great pains to have the piece of lead precisely
machined. I was clearly dissatisfied with something: I tried every
"excuse" to postpone putting the piece of lead in its place. When
finally, with some reluctance, I was going to put it in its place, I
said to myself: "No! I do not want this piece of lead here; what I
want is a piece of paraffin". It was just like that: with no
advanced warning, no conscious, prior, reasoning. I immediately
took some odd piece of paraffin I could put my hands on and
placed it where the piece of lead was to have been".
The 'Fermi fountain', i.e. the goldfish fountain of the Physics
Institute of Panisperna Street in Rome.,.Water of this fountain
was used for experiments on n- induced radioactivity.
Set-up for n-absorption cross sections
S – n source, P – paraffin block, A – absorber, D - detector
The activation of a silver detector D as a function of the radius r
of the hydrogenated material(water).
Ionization chamber connected to an electrometer
used in the measurements by Fermi’s group in 1935.
Fermi cautiously suggested the possibility of
transuranic elements in n-bombardment of U.
Nature, 133, p. 898-899 (1934)
1934, Ida Noddack (a German chemist who, with
her husband Walter, had discovered the element
rhenium) suggested that "when heavy nuclei are
bombarded by neutrons, it is conceivable that the
nucleus breaks up into several large fragments...”.
She wrote to both Fermi and Hahn.
1935 Otto Hahn, Lise Meitner and Fritz Strassmann
confirmed the uranium experiments of Fermi's group and also
identified the presence of U-239 as a beta emitter with a halflife of 23 minutes.
The Joliot-Curies also confirmed Fermi’s work and, in 1938,
identified a 3.5-hour radioactive isotope that had the chemical
properties of lanthanum. (But they failed to identify it! They
thought it was actinium)
Lise Meitner and Otto Hahn
(Courtesy of the American
Institute of Physics)
Meitner, Hahn and Strassmann’s
laboratory apparatus
Meitner-Hahn beta counter
L. Meitner’s departs from Berlin July,1938 to Holland and
then to Sweden,
Strassmann and Hahn continue experiments.
On examining a 3.5 hr product described by Curie and
Savitch, they find four new substances, all of which they
describe as artificial isotopes of radium.
From the chemical reactions these could only be either
radium or the barium.
Try to separate artificial "radium" from the inactive
barium ballast material by fractional crystallization.
Despite the most varied techniques, Hahn and Strassmann
failed to separate the "radium" from the barium.
E. Wiesner and F. Settle, Jr
J.Chemical Education
Vol78, No7 (2001)p889-893
They add as tracer, natural radium isotopes, (mesothorium and
thorium-X), which separates from artificial “radium”.
-------Hahn wrote to Lise Meitner (19 December, 1938).
“……But we are coming steadily closer to the frightful
conclusion: our Ra isotopes do not act like Ra but like
Ba. ... All other elements, transuranes, U, Th, Ac, Pa,
Pb, Bi, Po are out of the question. I have agreed with
Strassmann that for now we shall tell only you . Perhaps
you can come up with some sort of fantastic explanation.
We know ourselves that it can't actually burst apart into
Ba. Now we want to test whether the Ac-isotopes
derived from the "Ra" behave not like Ac but La.”
Naturwissenschaften, 6. Januar 1939, Volume 27,Issue 1, pp 11-15
Über den Nachweis und das Verhalten der bei der Bestrahlung des
Urans mittels Neutronen entstehenden Erdalkalimetalle
("Concerning the Determination and Relationships of the alkalineearth Isotopes Derived from the Neutron-Irradiation of Uranium,“)
O. Hahn, F. Srassmann
Otto Robert Frisch came to Sweden during X-mas
vacation to his aunt, Meitner.
While taking a stroll, the idea of splitting of a nucleus
came to Meitner considering Bohr's liquid Drop model.
.
Fragment kinetic energy ~200 MeV.
From packing fraction difference, E = mc2
Frisch returned back to Copenhagen and
found Bohr getting ready to leave for America,
“Dear Tanterl, I was able to speak with Bohr only today [3
January] about the splitting of uranium. The conversation
lasted only five minutes as Bohr agreed with us immediately
about everything. He just couldn't imagine why he hadn't
thought of this before, as it is such a direct consequence of
the current concept of nuclear structure. He agreed with us
completely that this splitting of a heavy nucleus into two big
pieces is practically a classical phenomenon, which does not
occur at all below a certain energy, but goes readily above
it..”
Bohr worked on this idea on the six day journey by sea.
In USA he worked with John Wheeler the theory of
fission.
Meanwhile, back in Denmark, Frisch was busy
Following a suggestion of George Placzek:
“I rigged up a pulse amplifier for the special purpose,
and I also built a small ionization chamber; but the
whole thing only took me about two days, and then I
worked most of the night through to do the
measurements because the counting rates were very
low. But by three in the morning I had the evidence of
the big pulses.”
U- lined Ionization chamber ;
Pulse threshold > 5x105 ion pairs (to bias off α from U)
Raα +Be source; paraffin doubled the rate
Thorium also gave large pulses.
Submitted January 16, 1939
Vol 143
L. Meitner and O.R. Frisch
Term "fission" occurs in the paper and was suggested to
Frisch by an American biologist, William A. Arnold, whom he
asked what you call it when a cell divides itself.
Physical Evidence for the Division of Heavy Nuclei under
Neutron Bombardment, O. R. Frisch,
Nature 143, 276 (18 February 1939)
L. Meitner
O. Frisch
Bohr N and Wheeler J A 1939 Phys. Rev. 56 426–50
They also point out that slow neutrons cause fission in 235U and
fast neutrons in 238U.
Experiment : ALFRED O. NIER, E. T. BOOTH, J. R. DUNNING, A. V. GROSSE
Phys Rev 57 (1940) 546
Speculation about the vast stores of energy in the nucleus
prompted a New York Times editorial in February 1939...
NEWS ARTICLE: "The possibility of harnessing the
energy of the atom crops up again. Rutherford...and other
distinguished physicists did their best in late years to
discourage speculations on the subject, because
bombardment was so inefficient that more energy was
expended on the atom than ever came out of it. Now the
picture is changed... Romancers have a legitimate excuse
for returning to Wellsian utopias where whole cities are
illuminated by energy in a little matter."
On August 2nd 1939, encouraged by a group of fellow
physicists, Albert Einstein, writes a historic letter to President
Roosevelt.
“Some recent works by E. Fermi and L. Szilard.which has been
communicated to me in manuscript, leads me to expect that the
element Uranium may be turned into an important source of
energy in the immediate future....... This new discovery would
also lead to construction of bombs......”
The Frisch-Peierls Memorandum
The Frisch–Peierls memorandum was the first technical
exposition of a practical atomic weapon.
The memorandum contained new calculations about the size of
the critical mass needed for an atomic bomb.
The memorandum led to a report by the British MAUD
Committee, the Tube Alloys project and the Manhattan Project.
www.stanford.edu/class/history5n/FPmemo.pdf
Paths taken towards energy
release……
Letters to Editor
Nature 143, 680-680 (22 April 1939)
Number of Neutrons Liberated in the Nuclear Fission of Uranium
H. VON HALBAN , F. JOLIOT & L. KOWARSKI
Neutron source placed in a solution of uranyl nitrate. Small
Dy sheets placed at different locations used to detect neutrons.
Compared by replacing uranyl nitrate by ammoinum nitrate.
More neutrons detected in case of U salt.
Detect fast neutrons (E > 2 MeV) using sulfur to produce 32P
thruogh (n,p) reaction using a photoneutron source.
Instantaneous Emission of Fast Neutrons in the Interaction
of Slow Neutrons with Uranium
LEO SZILARD & WALTER H. ZINN, Phys. Rev. 55, 799 (1939)
A - Radium, B - Be block, C – Paraffin wax, D – Lead block
E – Box filled with Uranium oxide, F - He filled ionization
chamber, G – Cd sheet cap, H - Cd sheet shield
Number of neutrons emitted per fission to be about two.
AUGUST 1, 1939 PHYSICAL REVIEW VOLUM E 56
Neutron Production and Absorption in Uranium*
H. L. ANDERSON, E. FERMI AND LEO SZILARD
Columbia University, NewYork,
(Received July 3, 1939)
Cylindrical tank (90cmdia x 90cm) filled
with 540 liters of 10 percent MnSO4
solution.
A, Photo-neutron source composed of 2.3
grams of radium and 250 grams of
beryllium at the centre.
B, One of 52 cylindrical cans 5 cm in
diameter and 60 cm in height, which are
either empty or filled with uranium oxide.
~ 200 kg of U308 was used
Activity of Mn measured.
1.5 neutrons per thermal neutron absorbed by uranium
1942
Chain Reaction
A nuclear chain reaction could be maintained in a system
in which neutrons are slowed down without much absorption
until they reach thermal energies.
Graphite blocks with 3 inch diameter uranium
cylinders inserted - part of a layer of CP-1,
the first nuclear reactor.
First nuclear reactor, CP-1, in a squash court under the
football stadium. The first sustained chain reaction occurred
on Dec. 2, 1942.
(Fermi with Compton, Szilard, Wigner, Zinn …………)
The first nuclear explosion
occurred at 5:29:45 AM on
July 16, 1945 at Almogordo,
New Mexico.
First mass acquaintance with power of the atom!
Should we fault the Technology?
Controlled Fission
Dhruva & CIRUS reactors
at B.A.R.C., Mumbai
Fast Breeder Test Reactor
at I.G.C.A.R., Kalpakkam
Rajasthan Atomic Power Station
Kalpakkam
Narora
Kaiga
Tarapur, BWR, PWHR
Kakrapara
Kudankulam
Storage Facility
for
radioactive wastes
Use of neutrons from 1
GeV protons for
transmutation of fission
products.
Oklo's Natural Fission Reactors
More than 1.5 billion years ago a nuclear fission reaction took place in
an underground uranium deposit in Oklo, Gabon, Africa. The fission
reaction continued - off and on - for hundreds of thousands of
years. Eventually, the reactor shut down.
Evidence of the Oklo reactor was discovered in 1972 through studies of
the fission products found in the uranium mine.
Depletion of abundance of 235U at Oklo (0.717% instead of 0.7202%).
Isotope ratios of Nd, Ru
Thank You