1. Radioactivity and Nuclear Energy
Chapter 19

2. All about the nucleus The nucleus is really small.
1/100,000 the radius of an atom
The nucleus is really heavy.
Density of 1.6 x 1014 g/cm3
There is a lot of energy in the nucleus!
A nuclear reaction has more than 1,000,000 times the energy as a chemical reaction

3. How did we find this out? Wilhelm Conrad Roentgen
Took the first X-ray in 1895
Revolutionized the field of physics and chemistry with his discovery
-Once was expelled from school for ridiculing one of his teachers
-Was exploring cathode rays and luminescence when he discovered x-rays
Photo from

4. Henri Becquerel Discovered radioactivity
Put a chunk of uranium ore in a drawer with some photographic plates.
Plates were developed by the uranium
Becquerel determined that the ore must be emitting energy spontaneously
Also determined that these particles were charged.
The radiation was deflected by a magnet

5. Marie and Pierre Curie
Discovered 2 different radioactive elements, radium and polonium.
Painstakingly extracted from pitchblende, a uranium ore.
Pioneers in the field of radioactivity.
Both had rather tragic deaths.

6. Our buddy Rutherford! Discovered the alpha and beta particles.
Did extensive work on the structure of the atom and nuclear transformations

7. What exactly is radioactivity?
Radioactivity is the spontaneous decomposition of a nucleus producing 1 or more particles.
Types of radioactive decay:
Alpha
Beta
Gamma
Positron
Electron capture

8. A few reminders about nuclear equations.
Conservation of Mass applies!
Mass number on Left=Mass number on right.
Atomic Number on left = Atomic number on right
Isotope Notation:
Mass # (A)
Atomic # (Z)

9. Alpha decay () Most common form of radioactive decay
Heavy Radioactive Nuclides.
An alpha particle is a helium nucleus
What would be the symbol for a helium nucleus?

10. Beta decay () (beta-particle production)
 Particle is an electron (symbolism for an electron?)
A neutron has transformed into a proton, the nucleus spits out an electron.
Atomic number Increases by 1
Mass number remains the same

11. Positron Production
A positron is a particle with the same mass as an e-, but with a positive charge.
2211Na --> 01e Ne
The production of a positron appears to change a proton into a neutron.
Mass # stays the same
Atomic # decreases by 1

12. Electron Capture
Electron capture is the process in which an electron is captured by the nucleus.
20180Hg + 0-1e --> 20179Au + 00

13. Gamma Decay Gamma () rays are high energy photons
Gamma emission occurs when the nucleus rearranges
No loss of particles from the nucleus
No change in the composition of the nucleus
Same atomic number and mass number
Generally occurs whenever the nucleus undergoes some other type of decay

14. Practice Problems
Write the nuclear equation for the following radioactive decay processes:
Thorium-232 decays by alpha emission
Radium-228 decays by beta emission
Cobalt-60 decays by beta emission
Americium-241 decays by alpha emission

15. Radioactive Decay Series
Can’t achieve a stable nucleus with just one radioactive particle released.

16. Nuclear Bombardment
Nuclear transformation – change of one element to another
Bombard elements with particles
Use particle accelerators

17. Other Symbols that are useful
Proton: 11p
Neutron: 10n
Positron: 01e
Deuterium: 21d or 21H
Tritium: 31H

18. Sample Problems
Write the nuclear transformation reaction described in the problems below:
Nitrogen-14 plus helium-4 results in the formation of another element and the release of an proton.
Aluminum-27 plus some other particle results in the formation of phosphorus-30 and the release of a neutron.

19. Large Hadron Collider

20. Detecting Radioactivity
Geiger Counter

21. Half-Life
Half-Life is the time required for half of a radioactive sample to decay.
Most active=shortest half-life
Least active=longest half-life
Uranium-238: 4.5 x 109 years
Protactinium-234: 1.2 minutes

23. Sample Problems
Gold-198, which has a half-life of 2.7 days, is used as an implant for cancer therapy. For an implant containing 50 micrograms of Au-198, how much remains after 8.1 days?

24. Using Radioactivity Carbon-14 Dating
compare the amount of C-14 to C-12
C-14 radioactive with half-life = 5730 yrs.
while living, C-14/C-12 fairly constant
CO2 in air ultimate source of all C in body
atmospheric chemistry keeps producing C-14 at the same rate it decays
once dead, C-14/C-12 ratio decreases
limit up to 50,000 years

25. The Shroud of Turin Thought to be the burial cloth of Christ
First documented in 1355.
Carbon dating done in 1988 by three separate laboratories
Shroud date:
Cloth tested was not part of the original
Fire in 1500’s may have altered the carbon content
Authenticity still in question

27. The Real Power, Nuclear Power
Discovered in late 1930’s.
Bombard U-235 with neutrons
Releases 2.1 x 1013 J
26 million times more energy than combustion of methane!
Fission: Splitting heavy nuclei into smaller nuclei

28. Releases 2.1 1013 J/mol uranium-235

29. A Chain Reaction
Talk about Critical Mass

30. How do we harness this energy?

31. The nuclear reactor

32. Nuclear Fusion Process of combining 2 light nuclei
Produces more energy per mole than fission
Powers the stars and sun

33. A few problems with fusion…
Strong nuclear force only effective at short distances
Nuclei are both positively charged
Must overcome electrostatic repulsion
Need temperatures of about 40 million K for fusion to work
Many technical problems still exist
Not clear if technically or economically feasible

34. THE H-BOMB AKA Thermonuclear bomb
Atomic bomb surrounded by fusion materials
Lithium fissions to helium and tritium
Tritium and deuterium fuse
Temps around 400,000,000 degrees C

35. Medical Apps. Of Radioactivity
Radiotracers
Radioactive nuclides that can be introduced into organisms and traced for diagnostic purposes.

37. Positron emission tomography (PET scan)
Designed to find cancer cells
Uses sugar molecules tagged with a radioisotope that emits positrons
Positron + electron = annihilation
Cancer cells grow faster than normal, need more sugar, build-up of radiation at cancer site

38. Problems with radioactivity
Factors Determining Biological Effects of Radiation
Energy of the radiation
Penetrating ability of the radiation
Ionizing ability of the radiation