1. Nuclear Reactions

2. The Nucleus X Zone of Stability
Nuclide: a unique atom represented by the symbol: A X Z
Zone of Stability

3. Stability
Radioactive Decay: the probability that a nucleus will undergo decomposition to form a different nucleus
Isotopes: Atoms that have identical atomic numbers but different mass number values (neutrons have changed)

4. Important Observations
All nuclides with 84 or more protons are unstable
Light nuclides (P to N ration =1) are stable
For stable heavy nuclides P to N ratio is >1
Special Stability: certain combinations confer special stability (even vs odd)
Magic Numbers: certain combinations confer especially stable nucleus 2,8,20,28,50,82,126 (parallels behavior for stable electrons for chemical stability)

5. Decay
The atomic mass number (A) and atomic number (Z) must remain constant across the reaction!
A: =
Z: =

6. Types of Decay
Alpha Decay () : A very common mode of decay for heavy nuclides. (helium nucleus)

7. Types of Decay
Beta Decay (-) : Most common, The mass number of the decaying remains constant, the net effect is the change of a neutron to a proton!

8. Types of Decay
Positron Production (+) : Occurs for nuclides below the zone of stability, a particle with the same mass as an electron but opposite charge. The net effect is a change of a proton to a neutron.

9. Types of Decay
Gamma ray () : Release of a high energy photon, frequently accompanies other reactions

10. Types of Decay
Electron Capture : process in which one of the inner orbital electrons is captured by the nucleus
Interesting, and why do we not just turn mercury into gold?

11. Types of Decay
Summary of Decay reactions

12. Decay Series
Decay Series: a sequence of nuclear reactions that ultimately result in the formation of a stable isotope.

13. Half-life Half-life (t½)
Time required for half the atoms of a radioactive nuclide to decay.
Shorter half-life = less stable.

14. Half-life
mf: final mass
mi: initial mass
n: # of half-lives

15. Mass Defect
When a system gains or loses energy it also gains or loses a quantity of mass.
E = mc2
m = mass defect
E = change in energy
If E =  (exothermic), mass is lost from the system. 7

16. Nuclear Transformations
Nuclear Transformation: the change of one element to another.

17. F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal

18. F ission Chain reaction - self-propagating reaction
Critical mass - mass required to sustain a chain reaction
Subcritical: When the process dies out
Supercritical: rapid escalation of reaction

19. F ission

20. Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction – requires temp of 40,000,000 K to sustain
1 g of fusion fuel = 20 tons of coal
occurs naturally in stars

21. Fission vs. Fusion 235U is limited danger of meltdown toxic waste
thermal pollution
fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable