Chapter 4 for nuclear engineering DU.pptx

1. Chapter 4
Nuclear Chemistry

2. Content
Nuclear binding energy
Nuclear stability
Radioactivity
Nuclear reaction vs. chemical reaction
Types of nuclear reactions
Transient and Secular Equilibrium
Rates of radioactive decay

3. • A study of the nuclear changes in atoms is termed Nuclear Chemistry
• The disintegration or decay of unstable atoms accompanied by emission of radiation is called
Radioactivity/ Radioactive decay.

4. Nuclear Definitions
• Radiation=Particles and/or electromagnetic “energy” emitted from atomic nuclei
in various nuclear processes. The important nuclear radiations are alpha and beta
particles, positrons, gamma rays, and neutrons.
• Non-Ionizing Radiation= Low frequency radiation in the form of microwaves,
infrared radiation, radio waves, and cell phones.
• Ionizing Radiation = High frequency radiation with enough energy to break
chemical bonds, remove electrons from atoms, break apart atomic nuclei, and
damage DNA.
Ex. Alpha, beta, positron, gamma, UV, and X-rays.

5. Unstable Isotopes
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 439
Excited
nucleus
Stable
nucleus
Energy Particles
+
and
or
Radiation
The original nucleus is called the parent nucleus and the product is called the daughter nucleus

6. Initial Discovery of Radiation
Rutherford (1902)
two oppositely charged plates

7. • Alpha decay: The nucleus releases and alpha particle. This decreases the
mass number by 4 and the atomic number by 2. An alpha particle = He
nucleus. 4
• Beta decay: The nucleus releases a beta particle. This does not decrease the
mass number, but decreases the atomic number by one. (neutron is
converted into a proton and an electron)
• Positron Emission: Similar to beta emission. A proton is converted to a
neutron and a positive particle similar to an electron. Ex. 22Na
• Gamma decay: The nucleus release a gamma ray (high energy photon).
Gamma decay can accompany alpha and beta decay. In gamma decay the
nucleus does not change, it makes a transition to a lower energy state.

8. Absorption of Radiation
Timberlake, Chemistry 7th Edition, page 84

9. When we see a
radioactive decay?
The exact mode of radioactive transformation depends
on the energy available for the transition. The available
energy, in turn, depends on two factors:
• on the particular type of nuclear instability that is,
whether the neutron-to-proton ratio is too high or
too low for the particular nuclide under
consideration-and
• on the mass-energy relationship among the parent
nucleus, daughter nucleus, and emitted particle.

10. Nuclear Stability
• Atomic Numbers 83 and greater are unstable and
radioactive
• Neutron/proton ratio affects stability
• Isotopes with too few or too many neutrons are unstable
• Ex 9C 12C 13C 14C
• Carbon 9 and 14 are radioactive

11. Nuclear Stability
• Why nuclides decay: need a stable ratio of p/n
• Neutron/Proton Ratios: where Z = atomic number (protons)
• When Z<20, the most stable nuclei have n/p ratio of 1:1
• When Z>20, most stable isotopes have n/p ratio approaching 1.5/1
• Unstable atoms with a high n/p ratio (more neutrons) tend to be beta
emitters.
• Unstable atoms with a low n/p ratio (more protons) tend to be positron
emitters.

12. • Particles of equal chargerepel each other in
the nucleus?
• The STRONG FORCE
Proton to Neutron Ratio

13. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

15. Types of Radioactive Decay

16. Alpha and Beta Emission
Alpha Decay
Beta Decay

17. Positron Emission
• Beta Emission
e
Xe
I 0
-1
131
54
131
53 

electron
 Positron Emission
e
Ar
K 0
1
38
18
38
19 


positron
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

18. Fajans-Soddy Group Displacement Law
in an α-emission, the parent element will be displaced to a Group two places to the left and in a β-emission, it
will be displaced to a Group one place to the right.
RADIOACTIVE DISINTEGRATION SERIES
The whole series of elements starting with the parent radioactive
element to the stable end-product is called a Radioactive
Disintegration Series
(1) The Uranium Series (4n+2)
(2) The Thorium Series (4n)
(3) The Actinium Series (4n+3)
(4) The Neptunium Series (4n+1)

22. Nuclear Reaction
Nuclear Fusion is the energy-producing process taking place in the core of the Sun
and stars
The core temperature of the Sun is about 15 million °C. At these temperatures
Hydrogen nuclei fuse to give Helium and Energy. The energy sustains life on Earth
via sunlight

23. Nuclear Reaction
Nuclear reactions deal with interactions between the nuclei of atoms
The focus of this presentation are the processes of nuclear fission and
nuclear fusion
Both fission and fusion processes deal with matter and energy
Matter can be changed into Energy
Einstein’s formula above tells us how the change occurs
In the equation above:
E = Energy
m = Mass
c = Speed of Light (Universal Constant)
Energy Mass Light
Speed

24. Chemical vs. Nuclear Reactions
Chemical Reactions Nuclear Reactions
Occur when bonds are broken Occur when nuclei emit particles and/or rays
Atoms remain unchanged, although they
may be rearranged
Atoms often converted into atoms of another
element
Involve only valence electrons May involve protons, neutrons, and electrons
Associated with small energy changes Associated with large energy changes
Reaction rate influenced by
temperature, particle size,
concentration, etc.
Reaction rate is not influenced by
temperature, particle size, concentration, etc.

25. • Nuclear reactions are different than chemical reactions
Chemical
Reactions
Mass is
conserved
(doesn’t
change)
Small energy
changes
No changes in the
nuclei
Nuclear
Reactions
Small changes
in mass
Huge energy
changes
protons, neutrons,
electrons and gamma
rays can be lost or
gained
Fission = the splitting of nuclei
Fusion = the joining of nuclei (they fuse together)
Both reactions involve extremely large amounts of energy

26. Nuclear Reactions
• Characteristics:
• Isotopes of one element are into
isotopes of another element
• Contents of the change
amounts of are released

27. Induced Nuclear Reactions
• Scientists can also force ( = induce) nuclear reactions by
smashing nuclei with alpha, beta and gamma radiation to
make the nuclei unstable
4 14 17 1
2 7 8 1
+ N O + p
 
4 14 17 1
2 7 8 1
He + N O + H

or

28. Types of Nuclear Reaction
1. Elastic Scattering
2. Inelastic Scattering
3. Photonuclear Reactions
4. Radiative Capture
5. Fission
6. Fusion
Other Types of Nuclear Reactions
1. Special Nuclear Reaction
2. Evaporation
3. Spallation
4. Fragmentation
5. Transfer reaction: Stripping and Pick-up

29. • Nuclear Fission
– As a nuclear reaction occurs, it has the ability to produce a
chain reaction
A chain reaction is a reaction where the products are able
to produce more products in a self-sustaining reaction
series.
– In order to achieve a chain reaction there must be:
• A sufficient mass.
• A large concentration of fissionable nuclei
– The critical mass is when the mass and concentration are
high enough to sustain a chain reaction.
– A sub-critical mass is one that is too small to achieve a chain
reaction.

30. • The fission reaction
occurring when a
neutron is absorbed by a
uranium-235 nucleus.
The deformed nucleus
splits any number of
ways into lighter nuclei,
releasing neutrons in the
process.

31. Induced Nuclear Fission of Uranium-235
• is the origin of nuclear power and nuclear bombs.
• A neutron, , crashes into an atom of stable uranium-
235 to create unstable uranium-236, which then decays.
• After several steps, atoms of Krypton and Barium are
formed, along with the release of 3 neutrons and huge
quantities of energy.
1
0 n

32. • A schematic
representation of a
chain reaction. Each
fissioned nucleus
releases neutrons,
which move out to
fission other nuclei.
The number of
neutrons can increase
quickly with each
series.

33. Chain Reactions
• The neutrons released in the induced reaction can then
trigger more reactions on other uranium-235
atoms…causing a CHAIN REACTION

34. – A chain reaction can quickly get out of control
• materials that absorb some neutrons can help to control the
chain reaction.
– Nuclear reactors have complex systems to ensure the
chain reaction stays at safe levels.
– An uncontrolled chain reaction can result in the
release of excess energy as harmful radiation
• It is on this concept that nuclear bombs are created.
• Nuclear “meltdown” occurs if the chain reactions cannot be
controlled

35. • Nuclear Fusion
– Nuclear fusion is the source of the energy from the Sun
and other stars.
– Fusion is a very desirable energy source as:
• Two isotopes of hydrogen (deuterium and tritium)
undergo fusion at a relatively low temperature.
• The supply of deuterium is unlimited with seawater
being a very large source
• Enormous amounts of energy are released with no
radioactive byproducts.

36. Nuclear Fusion
• joining of two light nuclei
into one heavier nucleus.
– In the core of the Sun, two
hydrogen nuclei join under
tremendous heat and
pressure to form a helium
nucleus.
– When the helium atom is
formed, huge amounts of
energy are released.
The fusion of
hydrogen
nuclei

37. – The problems with utilizing fusion as an energy source are:
• Temperature.
– The amount of energy required to bring two nuclei
together is enormous.
• Density
– The density of the reacting hydrogen nuclei must be
significantly high so that there are enough reactions
occurring in a short period of time.
• time
– These nuclei need to be confined to up to a second or
more at 10 atmospheres of pressure in order for enough
reactions to take place.
Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear
fusion.
“cold fusion” would occur at temperatures and pressures that could be controlled
(but we haven’t figured out how to get it to happen)

38. • A fusion reaction between a tritium nucleus and a deuterium
nucleus requires a certain temperature, density, and time of
containment to take place.

39. – Plasma.
• A very hot gas consisting of atoms that have been
stripped of their electrons and utilized as a confining
mechanism
– Inertial confinement
• An attempt to heat and compress small frozen pellets
of deuterium and tritium with energetic laser beams
or particle beams, producing fusion.

41. 20 g
10 g
5 g
2.5 g
after
1 half-life
Start
after
2 half-lives
after
3 half-lives
Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 757
10 g
5 g
Half-life (t½)
– Time required for the amount of
radioactive atoms to decrease by half.
– Shorter half-life = less stable.

42. 0 1 2 3 4
Number of half-lives
Radioisotope
remaining
(%)
100
50
25
12.5
Half-life
Initial amount
of radioisotope
t1/2
t1/
2 t1/2
After 1 half-life
After 2 half-lives
After 3 half-lives

43. Half-Lives of Some Isotopes of Carbon
Nuclide Half-Life
Carbon-9 0.127 s
Carbon-10 19.3 s
Carbon-11 10.3 m
Carbon-12 Stable
Carbon-13 Stable
Carbon-14 5715 y
Carbon-15 2.45 s
Carbon-16 0.75 s