Big Bang ~
approx.14 Billion years
electron neutrino muon tau baryon meson
3 quarks quark
(larger) (larger) +
First 10th billion of a second-
Lepton + quarks and 4 fundamental forces
•Strong nuclear force
•Weak nuclear force
•Gravity (weak force)
Note: 1 cm3 of lead weighs 11 g. 1 cm3 of pure atomic nuclei
would weigh > 100, 000, 000 metric tons!
•A quark is a fast-moving point of energy. There are several
varieties of quarks.
•Each proton and each neutron contains three quarks.
•Protons and neutrons are composed of two types: up quarks
and down quarks.
• Each up quark has a charge of +2/3. Each down quark has
a charge of -1/3.
• The sum of the charges of quarks that make up a nuclear
particle determines its electrical charge.
• Protons contain two up quarks and one down quark. +2/3
+2/3 -1/3 = +1
• Neutrons contain one up quark and two down quarks
+2/3 -1/3 -1/3 = 0
• The nucleus is held together by the quot;strong nuclear force”.The
strong force counteracts the tendency of the positively charged
protons to repel one another. It also holds together the quarks that
make up the protons and neutrons.
•“Quarks are more like quot;dancing points of energy.quot; -nuclear
18 Quarks. 6 Flavors - up, down, strange, charmed,
top and bottom. (3 colors-red, blue and green.
Antiquarks-complementary colors -cyan, magenta and
Matter accounted for by neutrons &protons~ 10%
Matter unaccounted for -dark matter (missing matter)
~90% (but gravity is felt in universe). 20% of dark
matter may be hot dark matter (neutrinos). 80% of the
dark matter may be cold dark matter-no detectable
radiation (WIMP weakly interacting massive particle)
DISCOVERY OF RADIOCHEMISTRY
Nuclear medicine saves lives.
Nuclear chemistry in labs improve agriculture
Nuclear power provides energy
Timeline of discoveries in nuclear chemistry
Roentgen -1895 discovered X-ray during the
Cathode tube experiment - his gift to medicine.
Becquerel-1895 discovered radioactivity when
photographic ﬁlm was exposed to Uranium.
Thomson -1897 discovered the mass/charge ratio
of electrons during the Cathode ray deﬂection expt
Marie and Pierre Curie discovered radioactive Po
and Ra-1898. ~25 elements have been found to be radioactive.
Einstein 1905- E=mc2 at the age of 26.
Goldstein-1907 discovered the presence and mass
of protons with perforated Cathode tubes.
Milliken-1909 discovered the charge of electrons
during the oil drop experiment
Rutherford -1910 discovered particles during his
famous gold leaf experiment.
Paul Dirac-1928 predicted the existence of
The nuclei of some unstable isotopes undergo a
change by releasing energy and particles
collectively known as radiation
Spontaneous nuclear reactions:
Radioactive Decay (Becquerel).
1) Emission of -particles: 2
238 U 234 Th + 42He
e.g. 92 90
In air, -particles travel several cm.
In Al, -particles travel 10-3mm.
Emission of -particles
2) Emission of -particles: –1e = electrons.
131 I 131 Xe + 0–1e
e.g. 53 54
-particle emission converts a neutron to a proton:
1n 1 + 1–1e
In air, -particles travel 10m.
In Al, -particles travel 0.5mm.
Emission of -rays
3) Emission of -rays: 0
-ray emission changes neither atomic number
In Al, -particles travel 5-10 cm.
Emission of positrons
Emission of positrons ( +-particles):
11 C 11 B + 01e
e.g. 6 5
Positron emission converts a proton to a neutron:
1p 1 + 01e
Positrons have a short lifetime because they
recombine with electrons and annihilate:
0e + 0–1e 2 00
5) Electron Capture: an electron from the
orbitals surrounding the nucleus can be captured:
81 Rb + 0–1e 81
Electron capture converts a proton to a neutron:
1p + 0–1e 10n
Fill in the blanks
239 Pu -> 42He + ?
234 Pr -> 23492U + ?
18 F -> 188O + ?
192 Ir + ? -> 19276Os
Radioactive Decay Rates:
Decay Rate = -dN/dt = kN
where: k is a constant,
N is the number of decaying nuclei.
By rearranging and integrating:
dN'/N' = -kdt'
ln[N(t)/N0] = -kt
where No is the number of decaying nuclei at
N(t) = N0e-kt
Because the rate is proportional to the
number of nuclei, this is called a ﬁrst order
Half-Life: the time required for half of a
radioactive sample to decay.
N(t1/2) = N0/2
ln(N/N0) = -kt
k = 0.693/t1/2; t1/2 = 0.693/k
Isotope t1/2 Decay
238 U 4.5x109 yr
235 U 7.1x108 yr
14 C 5.7x103 yr
Example: Plutonium-240, produced in nuclear reactors
from U-235, has a half-life of 6.58 x 103 years. What
would be the fraction after 100 years?
Plutonium-240, produced in
nuclear reactors from U-235,
has a half-life of 6.58 x 103
years. What would be the
fraction after 100 years?
Libby-1946 developed method of determining age
using 146C. 146C is produced by cosmic radiation.
14 N + 1 n -> 14 C + 1 H 7.5 kg/year
7 0 6 1
14 C -> 14 N + 1 e t 1/2 =5.73 x 103years
6 7 -1
Initially, in live plant C-14 has 14
disintegrations/min/g of C
When the specimen dies, the C-14 is not replaced
and the disintegrations diminish.
•Ex. The dead sea scrolls had 11 dpm/g
(disintegrations/min/g). What is the age of the
1) Up to atomic number 20, n=p
2) Above atomic number 20, n>p is stable.
3) Above atomic number 84, all nuclei are
4) Nuclei with 2, 8, 20, 28, 50, or 82 protons,
or 2, 8, 20, 28, 50, 82, or 126 neutrons are
particularly stable. These are the nuclear
equivalent of closed shell conﬁgurations (and
are called magic numbers).
5) Even numbers of protons and neutrons are
# of Stable Nuclei
Conﬁguration: # Protons # Neutrons
157 Even Even
52 Even Odd
50 Odd Even
5 Odd Odd
An isotope with a high n/p ratio is proton
To convert neutrons to protons, it can undergo
1 1 p + 0–1e
97 Zr 97 Nb + 0–1e
e.g. 40 41
NUCLEAR STABILITY contd.
An isotope with a low n/p ratio is neutron
To convert protons to neutrons, there are
i) Positron emission:
1p 1 n+0 e
1 0 1
20 Na 20 + 01e
ii) Electron capture:
1 p+0 e 1n
1 –1 0
Elements with atomic numbers greater than
84 undergo -decay in order to reduce both
the numbers of neutrons and protons:
235 U 231 Th + 42He
e.g. 92 90
Result of emission,
emission, and electron capture:
2 11p + 2 10n 4
1p mass is 1.00728 amu
0n mass is 1.00867 amu
2He mass is 4.00150 amu
Mass defect = (2)(1.00728 amu)
+ (2)(1.00867 amu) – 4.00150 amu
= 0.03040 amu = 5.047x10-29 kg
Binding energy is the energy required to
decompose the nucleus into nucleons (p and n):
E = mc2
Probably better to write:
E = ( m)c2
E = (5.047x10-29kg) (3x108m/sec)2
E = (5.047x10-29kg) (3x108m/sec)2
= 2.736x1012J/mole 42He
Binding Energy per nucleon for 4He
= (4.54x10-12)/4 = 1.14x10-12J.
Binding energy per nucleon:
4 He: 1.14x10-12J
56 Fe: 1.41x10-12J
238 U: 1.22x10-12J
Nuclei with mass greater than 50-60 amu can
fall apart exothermically – nuclear ﬁssion.
Combining nuclei/particles with total mass less
than 50-60 can be exothermic – nuclear fusion.
The rest masses of proton, neutron,
and He nuclei are 1.007276470
amu, 1.008664904 amu, and
4.031882748 amu respectively.
(a) the Binding energy/nucleon
(b) the Binding energy/mole of
235 U + 10n 137 + 9740Zr + 210n
142 Ba + 91 Kr + 31 n
56 36 0
An average of 2.4 neutrons are produced per 235U.
Small: most neutrons are lost,
Medium: constant rate of ﬁssion,
Large: increasing rate of ﬁssion,
Nuclear reactor fuel is 238U enriched with 3%
This amount of 235U is too small to go
The fuel is in the form of UO2 pellets encased
in Zr or steel rods.
Cadmium or boron are used in control rods
because these elements absorb neutrons.
Moderators are used to slow down the emitted
neutrons so that they can be absorbed by
adjacent fuel rods.
Liquid circulating in the reactor core is heated
and is used to drive turbines. This liquid
needs to be cooled after use, so reactors are
generally near lakes and rivers.
Breeder reactors are a second type of ﬁssion
A breeder reactor produces more ﬁssionable
material than it uses.
239 Pu and 23392U are also ﬁssionable nuclei
and can be used in ﬁssion reactors.
238 U + 10n 239 239 Np + 0–1e
239 Pu + 0–1e
232 Th + 10n 233 Th 233 Pa + 0-1e
90 90 91
233 U + 0-1e
“Chemistry of the stars”
The sun contains 73% H, and 26% He.
1H + 11H 2 + 0+1e
1H + 21H 3
3 He + 32He 4 + 21H
3 He + 11H 4 + 01e
Initiation of these reactions requires
temperatures of 4x107K - not currently
obtainable on a stable basis.
Sources of average annual
exposure to radiation
Discovery of Nuclear Fission
1934-Enrico Fermi discovered 4 particles when U-
238 with neutrons.
1938-Otto- Hahn and Fritz (Sweden) discovered
137Ba to be a product of 238U when repeating
Fermi’s experiment. They wrote to Lisa Meitner
1938-Lisa Meitner who had escaped from Austria to
Swede suggested that neutrons were splitting the
U! Nuclear Fission.
235 U +1 n -> 236 U-> 141 Ba +92 Kr + 3 1 n
92 0 92 56 36 0
Frisch who was Meitner’s nephew was working
with Neils Bohr at the University of Copenhagen
in Denmark. Neils Bohr who was going to US
for a physics conference released the news at the
Enrico Fermi who had just received the Nobel prize
in physics ﬂed from Italy and Mussolini to US
Leo Szilard who discovered that the U-235 ﬁssion
was a chain reaction persuaded Einstein to write
to President Franklin Roosevelt about it in 1939.
• Mainly U-235. Fortunately, U-235 is hard to
• Uranium ore is concentrated and treated with
Fluorine to form UF6. This is low boiling
and can be evaporated at 56 oC.
• 99.3% is non-ﬁssionable U-238. Chemical
reactions don’t help separate isotopes.
• Gaseous diffusion separates the heavier
particles (UF6 with U-235 moves 0.4% faster
• Repeated diffusion over long barriers or
centrifugation concentrates U-235
• Breeder reactors- 238 U + n -> 239 Pu + 2e.
• Under Glenn Seaborg Plutonium bomb was
produced at Hanford, Washington.
• Plutonium can be used for bombs or as a fuel
source. However, small amounts of PuO2
dust in air causes lung cancer. Very toxic.
NUCLEAR BOMBS CONTD
• 1939-(brink of WWII)-Einstein calls attention
the Uranium being a new energy source.
• Manhattan project established by President
Roosevelt builds the A-bomb under Robert
– How to sustain ﬁssion chain reactions, how to enrich
U-235, how to make Pl-239 and how to buil the bomb.
• 1942-Enrico and team who were working under
the bleachers at the Stagg Baseball ﬁeld at the
Chicago University ﬁnd the critical mass of U-
235 (4 kg). 15 kg was obtained.
• 1945- Test detonation of atom bomb assembled
in Los Alamos went off in New Mexico at 5.30
am July 16
• As a response to the Pearl harbor bombing that
killed 2,700 in Hawaii, on Aug 6 and 9 - 1945-
two Bombs were dropped on Japan ( “Big boy”
a U bomb and “Fat man” -which was a
plutonium-239 bomb) under Harry Trumen .
~80,000 died instantly in Hiroshima-100,000
later. Japan surrendered and this was the
beginning of the end of WWII.
Measuring radiation damage-rems
• The radiation energy absorbed is
measured in a unit called rad.
• 1 rad (radiation absorbed dose) is the
absorbtion of 0.01 joule of radiation
energy per kilogram of tissue
• Not all radiation is equally harmful.
particles are 10 time more dangerous
than or or x. So this is factored in,
n=10 for , 5 for low energy neutrons
and n=1 for or or x
• rem (roentgen equivalent man) = n x rad
Chest x-ray is 10 mrem/visit (1
• Radioactive fallout from testing Sr-90,
Cs-137, I-131 causes cancer. Detected
in 1950. Nuclear test ban treaty was
signed in 1963 advocated by Linus
Nuclear Power plants
• Heart of the power plant is the reactor where
fission takes place in the core.
• Nuclear fuel is Uranium oxide enriched with 2-
4% U235 formed into glassy pellets. (bombs
pure U235, Pu239)
• These are housed in steel metal tubes called
cladding and are cooled by water or liquid Na.
Light water reactor -uses water, Heavy water
reactor -uses D2O.
• (Chernobyl 1986-high heat of fusion split H2
and O2 from water and these on recombination
produced an immense explosion)
• Excess neutrons are absorbed (2/3) by Cd rods
and Boron-called control rods to prevent chain
• Water absorbs energy released during fission
and high pressure steam (1000 psi, 285 oC)
drives the turbines to produce electricity.
222 Rn -> 21884Po + 42He
218 Po -> 214 Pb + 42He
• Radon gas is found trapped under soil
• Polonium can get trapped in tissue and
emit alpha particles which could
induce lung cancer.
• A particle range is only 0.7 mm. But
this is greater than the thickness of
epithelial cells in the lungs
• 4pCi/L air is the action level set by
1 Pico curie = 10-12 curies
1 curie = 3.7 x 1010 dps (dps =
disintegrations per second)
Positron emmision topography
Elements that are neutron deﬁcient
and have short half lives can be used
ex C-11, F-18, N-13, O-15 etc.
They are prepared before use
1 P -> 1 n + 0 e +
1 0 1
(Proton -> neutron + positron + neutrino)
0e + 0-1e >2
Positron + electron annihilate to give
The 2 rays are 180 o apart
2 scintillation detectors are placed above
and below. By detecting several million
annihilation rays within a circular slice
around the subject over ~10 min the
region of the tissue containing the
radioisotope can be imaged with
computer signal-averaging techniques
Tremendous amounts of energy are
generated when light nuclei combine to
form heavy nuclei-Sun (plasma ~106 K)
Short range binding energies are able to
overcome the proton-proton repulsion in
211H + 210n -> 42He
E= -2.73 x 1012 J/mol
Binding energy = +2.15 x 108 kJ/mol
Note: (covalent forces are only are fraction H-H
bond E =436 kJ/mol)
The huge energy from 4 g of helium could keep a
100 Watt bulb lit for 900 years
6 1 3 H + 42He
3Li + 0n -> 1
E=-1.7 kJ/mol/ mol tritium
The nucleons combine in a high energy
plasma ( 106 ).
A U-235 or Pu-239 bomb is set off ﬁrst.
A 20-megaton bomb has 300 lbs Li-D
as well as a ﬁssion/atomic bomb.
• The Eberly Family Distinguished
Lecture in Science will be held on
Thursday, April 18, at 4:00 p.m. in
112 Kern Auditorium. The speaker
will be Eric Cornell, a physicist with
the National Institute of Standards
and Technology and the co-winner
of the 2001 Nobel Prize in Physics.
Dr. Cornell will present quot;Stone Cold
Condensation and the Weird World
Within a Millionth of a Degree of