4. Big Bang ~
approx.14 Billion years
subatomic particles
leptons hadron
electron neutrino muon tau baryon meson
3 quarks quark
(larger) (larger) +
antiquark
protons neutrons
First 10th billion of a second-
Lepton + quarks and 4 fundamental forces
•Strong nuclear force
•Weak nuclear force
•Electromagnetism
•Gravity (weak force)
Note: 1 cm3 of lead weighs 11 g. 1 cm3 of pure atomic nuclei
would weigh > 100, 000, 000 metric tons!
5. Quarks
•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
physicists
6. 18 Quarks. 6 Flavors - up, down, strange, charmed,
top and bottom. (3 colors-red, blue and green.
Antiquarks-complementary colors -cyan, magenta and
yellow).
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)
7. 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
positrons
8. RADIOACTIVE DECAY
The nuclei of some unstable isotopes undergo a
change by releasing energy and particles
collectively known as radiation
Spontaneous nuclear reactions:
Radioactive Decay (Becquerel).
4 He
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.
9.
10. Emission of -particles
0
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
1p
0
In air, -particles travel 10m.
In Al, -particles travel 0.5mm.
11. Emission of -rays
0
3) Emission of -rays: 0
-ray emission changes neither atomic number
nor mass.
In Al, -particles travel 5-10 cm.
12. Emission of positrons
Emission of positrons ( +-particles):
4)
0e
1
11 C 11 B + 01e
e.g. 6 5
Positron emission converts a proton to a neutron:
1p 1 + 01e
0n
1
Positrons have a short lifetime because they
recombine with electrons and annihilate:
0e + 0–1e 2 00
1
13. Electron Capture
5) Electron Capture: an electron from the
orbitals surrounding the nucleus can be captured:
81 Rb + 0–1e 81
e.g. 36Kr
37
Electron capture converts a proton to a neutron:
1p + 0–1e 10n
1
______________________________________
14. Fill in the blanks
239 Pu -> 42He + ?
• 94
234 Pr -> 23492U + ?
• 91
18 F -> 188O + ?
• 9
192 Ir + ? -> 19276Os
• 77
15. RADIOACTIVE DECAY
Radioactive Decay Rates:
First Order
Decay Rate = -dN/dt = kN
where: k is a constant,
N is the number of decaying nuclei.
By rearranging and integrating:
N t
dN'/N' = -kdt'
No 0
ln[N(t)/N0] = -kt
where No is the number of decaying nuclei at
t=0.
N(t) = N0e-kt
Because the rate is proportional to the
number of nuclei, this is called a first order
process.
16. Half-Life
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
Examples:
Isotope t1/2 Decay
238 U 4.5x109 yr
92
235 U 7.1x108 yr
92
14 C 5.7x103 yr
6
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?
17. 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?
18. Dating
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
It decays
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
document?
19. NUCLEAR STABILITY
Rules:
1) Up to atomic number 20, n=p
is stable.
2) Above atomic number 20, n>p is stable.
3) Above atomic number 84, all nuclei are
unstable.
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
more stable.
# of Stable Nuclei
With This
Configuration: # Protons # Neutrons
157 Even Even
52 Even Odd
50 Odd Even
5 Odd Odd
21. NUCLEAR STABILITY
An isotope with a high n/p ratio is proton
deficient.
To convert neutrons to protons, it can undergo
-decay:
1 1 p + 0–1e
0n 1
97 Zr 97 Nb + 0–1e
e.g. 40 41
22. NUCLEAR STABILITY contd.
An isotope with a low n/p ratio is neutron
deficient.
To convert protons to neutrons, there are
two possibilities:
i) Positron emission:
1p 1 n+0 e
1 0 1
20 Na 20 + 01e
e.g. 10Ne
11
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
25. NUCLEAR BINDING
ENERGY
2 11p + 2 10n 4
2He
1
1p mass is 1.00728 amu
1
0n mass is 1.00867 amu
4
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
26. NUCLEAR BINDING
ENERGYcontd.
E = (5.047x10-29kg) (3x108m/sec)2
= 4.543x10-12J/42He
= 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
2
56 Fe: 1.41x10-12J
26
238 U: 1.22x10-12J
92
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.
27. The rest masses of proton, neutron,
and He nuclei are 1.007276470
amu, 1.008664904 amu, and
4.031882748 amu respectively.
Calculate
(a) the Binding energy/nucleon
(b) the Binding energy/mole of
Helium.
28. NUCLEAR CHAIN
REACTIONS
Fission
235 U + 10n 137 + 9740Zr + 210n
52Te
92
142 Ba + 91 Kr + 31 n
56 36 0
An average of 2.4 neutrons are produced per 235U.
Chain reactions:
Small: most neutrons are lost,
subcritical mass.
Medium: constant rate of fission,
critical mass,
nuclear reactor.
Large: increasing rate of fission,
supercritical mass,
bomb.
29. NUCLEAR REACTORS
Nuclear reactor fuel is 238U enriched with 3%
235U.
This amount of 235U is too small to go
supercritical.
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.
30. Breeder reactors
Breeder reactors are a second type of fission
nuclear reactor.
A breeder reactor produces more fissionable
material than it uses.
239 Pu and 23392U are also fissionable nuclei
94
and can be used in fission reactors.
238 U + 10n 239 239 Np + 0–1e
92U
92 93
239 Pu + 0–1e
94
232 Th + 10n 233 Th 233 Pa + 0-1e
90 90 91
233 U + 0-1e
92
32. NUCLEAR REACTORS
Fusion
“Chemistry of the stars”
The sun contains 73% H, and 26% He.
1H + 11H 2 + 0+1e
1H
1
1H + 21H 3
2He
1
3 He + 32He 4 + 21H
2He
2
3 He + 11H 4 + 01e
2He
2
Initiation of these reactions requires
temperatures of 4x107K - not currently
obtainable on a stable basis.
34. 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
56 92
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
E=-2x1010kJ/mol
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
conference.
Enrico Fermi who had just received the Nobel prize
in physics fled from Italy and Mussolini to US
1939.
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.
35. Nuclear Bombs
• Mainly U-235. Fortunately, U-235 is hard to
purify
• 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
than U-238)
• 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.
36.
37.
38. 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
Openheimer .
– 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.
39. 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
mrem=10-6rem)
• 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
Pauling.
40.
41. 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
reactions
• Water absorbs energy released during fission
and high pressure steam (1000 psi, 285 oC)
drives the turbines to produce electricity.
42. Radon detectors
222 Rn -> 21884Po + 42He
86
218 Po -> 214 Pb + 42He
84 82
• 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
EPA. (PA~1.5-8)
1 Pico curie = 10-12 curies
•
1 curie = 3.7 x 1010 dps (dps =
•
disintegrations per second)
43. Pet Scans
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
1
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
44. Nuclear fusion
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
the nuclei
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
45. H-bomb
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.
46. • 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
Science: Bose-Einstein
Condensation and the Weird World
Within a Millionth of a Degree of
Absolute Zero.quot;
