1. Nuclear Chemistry

2. Some Definitions
Isotope atoms with the same atomic number but different atomic masses
Atoms with an equal number of protons but an unequal number of neutrons
Nucleon a particle found in the nucleus of an atom
A proton or a neutron
Nuclide the nucleus of a specific isotope of an element
Each nuclide has a specific number of both protons and neutrons. Any change in the quantity of either changes the identity of the nuclide.

3. Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Reactions involve the interaction of valence electrons
Regardless of what reaction they undergo, the atomic species NEVER change
Rates of reaction are affected by chemical and physical change
The energy released or absorbed is orders of magnitude less than that of nuclear reactions
Reactions involve the nucleons and inner shell electrons
Regardless of what reaction they undergo, the identities of the nuclides ALWAYS change.
Rates of reaction are almost completely independent of chemical and physical change
The energy released or absorbed is orders of magnitude greater than that of chemical reactions

4. Atomic Notation Atomic Mass Atomic Species
Atomic Mass
Atomic Species
Atomic Number: Number of protons in the nucleus
Atomic Mass: Number of nucleons in the nucleus and their approximate mass.
Atomic Species: Name of the element, dependent on atomic number
Atomic Number

5. Review of the Nucleus The nucleus is made of tightly bound nucleons
Protons carry a positive charge and a mass
≈1.0073amu
Neutrons carry no charge and a mass
≈1.0087amu
Positively charged protons are bound together by the Strong Nuclear Force
Strong nuclear force is very dependent on neutrons

6. Stable Nuclides Belt of Stability
Protons repel each other because of like charges. This is known as the Coulomb force.
The greater the number of protons in the nucleus, the greater the proportional repulsive force
Result: The greater the number of protons, the greater the proportion of neutrons needed becomes
Data points represent stable isotopes with natural abundance greater than 1%

7. Radioactive Nuclides
Nuclides exist which have unstable proton to neutron ratios
These unstable nuclides are called radionuclides
Radionuclides will under go a nuclear reaction or nuclear decay in which they change identity to a more stable nuclide
Many methods exist for a radionuclide to stabilize and each emits a characteristic particle or particles accompanied by massive amounts of energy

8. Gamma Ray Radiation
In a nuclear reaction, the product nuclides can be emitted in a ground state or in one or more excited states
A product nuclide in an excited state will transition to its ground state (or another excited state of lower energy) by emitting gamma rays
Gamma rays are high energy photons represented as

9. U Th He U Th α Alpha Particle Decay + +
A type of radioactivity in which a radionuclide emits a helium nucleus
Most common natural mode of decay for heavy, neutron deficient radionuclides U
238 92
 Th
234 90 He 4 2 + OR U
238 92
 Th
234 90 α 4 2 +

10. Alpha Particle Decay

11. Negatron Beta Particle Decay
A type of radioactivity in which a neutron turns into a proton through the emission of a negatron (an electron) and an anti-neutrino
Most common natural mode of decay for a neutron rich radionuclide I
131 53 Xe 54
 + e −1 OR I
131 53 Xe 54
 +  −1

12. Negatron Beta Particle Decay

13. Positron Beta Particle Decay
A type of radioactivity in which a proton turns into a neutron through the emission of a positron and a neutrino
A positron is an atomic particle with equal mass but opposite charge of an electron C 11 6
 B 5 + e 1 OR  C 11 6
 B 5 + 1

14. Electron Capture
A type of radioactivity in which a proton absorbs one of the inner shell electrons and turns into a neutron
Most common natural mode of decay for light, neutron deficient radionuclides
Has a very similar effect as positron decay, but is more common because it is more energetically advantageous C 11 6
 B 5 + e -1

15. Radioactivity and Matter

16. Ionizing Radiation
Defined as radiation of high enough energy to ionize water (E > 1216 kJ/mol)
Alpha, beta, and gamma rays possess energies greater than 1216 kJ/mol
The ionized water molecules will react with surrounding water molecules
The product OH is a free radical, possessing an unpaired electron.

17. Free Radicals in the Body
Living tissue, in general, is at least 70% water
The rest of the tissue is made up of biomolecules responsible for the structure, proper function and reproduction of cells
Biomolecules carry out these functions through incredibly complex chemical reactions
Living tissue is essentially a bunch of chemical reactions being carried out in solution
Radiation of high enough energy can ionize the water in living tissue, creating the free radical OH
One free radical in solution with other molecules (living tissue) can quickly create more free radicals
Free radicals ionize biomolecules, affecting their ability to function properly

18. Radiation, DNA, and Cancer
Tissue is made of cells
Cells reproduce themselves using the “instructions” embedded in the sequence of nucleotides, or molecular structure, of DNA
The free radicals created by radiation affect DNA like any other molecule, changing its molecular structure
Altered DNA can result in abnormal cell growth or cancer
Tissues made of cells which reproduce more quickly, like those involved in blood cell production, are more susceptible to abnormal cell growth and cancer

19. Radioactivity as a Reaction Rate
Levels of radioactivity are often expressed as the rate at which radionuclides undergo decay
Activity=λN
N is the number of radionuclides available to decay
λ is the decay constant or the probability that a given radionuclide will decay in a given time interval

20. Decay Constant
The decay constant is based on the probability that a given radionuclide will decay in a given way
The decay constant is analogous to the rate constant in chemical kinetics
The decay constant differs in that it is virtually unaffected by changes in physical and chemical properties
Physical and chemical properties of matter are determined by the interaction of valence electrons
No interaction of valence electrons can change the make up of a nucleus
The make up of a nucleus determines the energetic advantage of a particular mode of decay, thus determining the probability that the nuclide will decay in that manner

21. U X α U Th α Calculating Activity + +
Determine level of alpha radioactivity released by 2 moles of uranium (λ= ) U
238 92
 X A Z α 4 2 + U
238 92
 Th
234 90 α 4 2 +
Activity=2( )( )
Activity= disintegrations/year

22. Decay Constants and Half-Lives
When discussing and comparing the radioactivity of nuclides, it is often helpful to use half-lives instead of the decay constant
By integrating time into the rate equation, we obtain
From this equation, we can determine the relationship between the decay constant and the half-life

23. K X  K Ca  Calculating Activity + +
Determine level of negatron beta radioactivity released by 3.75 moles of (half-life= ) K 40 19 X A Z
 +  −1 K 40 19 Ca 20
 +  −1
Activity= 3.75 ( )( )
Activity= disintegrations per year

24. Binding Energy and Mass Defect
Mass defect is the difference in the mass of a nuclide and that of the total mass of its nucleons
An alpha particle is amu lighter than the mass of two neutrons and two protons
Binding energy is the energy required to separate a nucleus into its individual nucleons
Because energy is added, the mass must increase. This is given by the equation

25. Enthalpy in Nuclear Reactions
The enthalpy of a nuclear reaction is determined by the change in nuclear mass from reactants to products
c is the speed of light in a vacuum (c )
If ∆m is given in kilograms and the speed of light is used, ∆E will be in joules
If ∆m is given in atomic mass units and is replaced with the conversion factor MeV/amu, then ∆E will be in MeV.
1MeV=

26. Atomic Mass vs. Nuclear Mass
The nuclear mass of any isotope is equal to its atomic mass minus the total mass of its electrons
Calculate the nuclear mass of given that its atomic mass is amu and the mass of one electron is amu.

27. Calculating Enthalpy Calculate ∆E for the alpha decay of 1 mole
= g/mol
= g/mol
= g/mol

28. Binding Energy and Enthalpy
Fission
Fusion

29. Fission The decay of a larger nucleus into two or more smaller nuclei
Usually initiated by a slow moving neutron
Method of decay for nuclides of mass greater than 100amu
Releases more energy than other decay modes for large nuclei
Can happen spontaneously, but is uncommon
Even though fission is more exothermic than other decay modes, it is less common because of the high energy barrier

30. Calculating Enthalpy - Fission
Calculate the energy released by 1 mole when it fissions via the following reaction
= g/mol
= g/mol
= g/mol
= g/mol

31. Fusion
The nuclear collision and rearrangement of light nuclei into heavier nuclei
Releases more energy than even fission because of the relative difference in mass (binding energy) between its products and reactants
For the reaction
∆m= g/mol which means
Fusion reactions release more energy gram for gram than any other known fuel source
Responsible for the heat produced in the sun, which is a self- sustaining fusion reaction
Has an even higher energy barrier than fission

32. Fission Bomb “Nuclear Weapon”
Chain Reaction – A reaction which is initiated by the products of a previous reaction. Recall Each fission of a U-235 nucleus produces two neutrons which can then fission two more nuclides Critical Mass – The mass of fission material required to maintain a constant rate of fission Supercritical mass – Any mass greater than critical. Causes fission reaction rate to increase exponentially, which can cause an explosion
File:Fission_bomb_assembly_methods.svg

33. Fusion Bomb “Thermonuclear Weapon”
File:Teller-Ulam_device_3D.svg

34. Nuclear Power - Fission
Fission fuel is allowed to react in the core
Control rods are neutron acceptors that keep the reaction at the desired rate
Heat is transferred first to a liquid coolant and then to water which produces high pressure steam
From this point, power generation is the same as with other fuels
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Drawbacks
Possible leakage of radioactive fuel or products
Long half-lives of products cause disposal/storage challenges

35. Nuclear Power - Fusion The Advantages
Light nuclei are available in a virtually inexhaustible supply
Product nuclei in fusion reactions are rarely radioactive
The Limitations
Lack the technology to heat fusion fuel to a high enough temperature (40,000,000 K)
Lack the material technology to contain a fusion reaction
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