1. Nuclear Reactions Chapter 18 Supernova 1999gi in NGC 3184
Credit:Al Kelly (JSCAS/NASA & Arne Henden(Flagstaff/USNO)

2. Alpha radiation particle He - 4 nucleus
Decrease the atomic number by 2
Decreases the mass number by 4

3. Beta radiation particle Electron Increases the atomic number by 1
Leaves the mass number unchanged

4. Gamma radiation emission
High energy photons
Does not effect mass or atomic number
Omitted in equations

5. Positron emission Positive electron Decreases the atomic number by 1
Leaves the mass number unchanged
Usually occur in nuclei that have too many protons to be stable
Protons are converted to neutrons

6. K-capture
An electron in the innermost energy level falls into the nucleus
Decreases the atomic number by 1
Leaves the mass number unchanged
Usually occur in heavy nuclei

7. Write nuclear reactions for:
Alpha emission by Th-230
K-capture of Ar-37
Beta emission by Pb-210

8. Write nuclear reactions for:
Alpha emission by Th-230
K-capture of Ar-37
Beta emission by Pb-210

9. Bombardment reactions
Smack a stable nucleus with a high energy particle
Neutron, alpha particle, positron. . .
The stable nucleus is converted into a radioactive nucleus
Which in turn decays forming stable products

10. Uses
Medicine
Co-60 is used to eliminate malignant cells left after tumor removal
I-131 is used to treat thyroid cancer
Glucose containing C-11, a positron emitter, is given to patients with brain disorders. A PET scanner is then used to see what’s going on
Xe-133 is used for lung imaging

11. Neutron activation analysis
Can be used to find trace amounts of elements
Archaeology
Determine dead thing’s diet
Plants contain more Sr than animals so. . .

12. Smoke detectors
Am-241 ionizes air molecules. If smoke gets in the chamber the flow of ions is impeded, the current drops, and the alarm sounds

13. Irradiated food

14. Rate of radioactive decay (first order)
Rate = kX
k= rate constant
X = amount of radioactive species present at time, t
ln Xo/X = kt
Xo = the amount at t = 0
k =0.693 / t1/2
A = kN
A = activity
Curies (Ci) = 3.700x1010 atoms/s
N= the number of radioactive nuclei present

15. Calculate the activity for 1mg of radium when k = 1.37 x 10-11 s-1

16. The half-life of U-238 is 4. 5x109 yr
The half-life of U-238 is 4.5x109 yr. How long does it take for 60% of a U-238 sample to decay?

17. Age of organic material ( C-14 dating)
Formation of C-14
C-14 is incorporated into CO2. Living plants and animals consume the CO2. When death occurs consumption stops and the C-14 decays.
t1/2 = 5730 y

18. Mass-Energy relations
Photo: Albert Einstein The Hebrew University of Jerusalem

19. Calculate the energy change for the decay of 8
Calculate the energy change for the decay of 8.2g Pu-239 releasing an alpha particle

20. Mass defect
A nucleus weighs less than the individual protons and neutron of which it is composed
Mass defect = (n + p) – (mass of nucleus)

21. Calculate the mass defect for C-12
Mass defect = (6n + 6p) – (C-12)

22. Binding energy
The amount of energy that must be absorbed in order to decompose nuclei
Measures nuclear stability. Maximum values are reached by nuclei with intermediate mass.

23. Calculate the binding energy for C-12

24. Fission Many different isotopes are formed
Nuclei produced have too many neutrons and are very radioactive
Sr-90 is incorporated into the bones of animals where it stays forever
More neutrons are produced than consumed
Chain rxn
Excess neutrons are absorbed by Cd rods

25. Nuclear reactors

26. Why nuclear energy Fossil fuels are quickly being depleted
Produces tons of energy
Can be built anywhere

27. Why not nuclear energy Expensive Accidents
About 4 cents more than fossil fuel
Accidents
Three mile island
Chernobyl
Japan tsunami
Disposal of radioactive waste
Yucca Mountain, Nevada?
Utah?????
Heat pollution

28. Fusion Abundant fuel! Clean Very high activation energy
Needed to overcome the H-2:H-2 electrostatic repulsion
Temp required is about 109 C