1. Radioactive Decay
Section 21.2

2. Vocabulary
Radioactive decay: the spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles, electromagnetic radiation, or both
Nuclear radiation: particles or electromagnetic radiation emitted from the nucleus during radioactive decay

3. More Vocabulary
Nuclide: an atom that is identified by the number of protons and neutrons in its nucleus
Radioactive nuclide: an unstable nucleus that undergoes radioactive decay
All nuclides beyond atomic number 83 are unstable and therefore radioactive

4. Types of Radioactive Decay
Alpha decay
Beta decay
Gamma decay
Nuclide emission occurs with all three

5. Alpha Decay
Alpha particle: two protons and two neutrons bound together and is emitted from the nucleus during alpha decay
They are the same as helium nuclei
Have a charge of 2+
Mass is amu

6. More about Alpha Decay Alpha emission occurs with very heavy nuclei
The number of neutrons and the number of protons are reduced in order to increase the stability of the nucleus
Example reaction:
Mass number decreases by 4, atomic number decreases by 2

7. Visual

8. More about Alpha Decay Can only travel a few cm
Low penetrating ability
Can cause damage if ingested or inhaled
Can be shielded with a piece of paper
Helium produced on earth (99%) is the result of the alpha decay of U or Th in underground minerals

9. Beta Decay
Beta particle: an electron emitted from the nucleus during beta decay
A neutron is converted into a proton and an electron
The charge is 1-
Mass is

10. More about Beta Decay
This occurs when the neutron/proton ratio is too large, so the number of neutrons must be decreased
Example reaction:
Atomic number increases by one, the mass number stays the same

12. More about Beta Decay Can travel a few meters in air
Travel at speeds close to the speed of light
Have a penetrating ability about 100 times greater than that of alpha particles
Can be shielded with lead or glass

13. Medical Use of Beta Decay
Iodine-124 experiences beta decay
This isotope of iodine is taken up by the thyroid gland
The beta decay can be measured to see if the thyroid gland is working, while the iodine does not adversely affect the body

14. Gamma Decay
Gamma rays: high-energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground energy state
Usually occurs immediately following other types of decay when the other particles leave the nucleus in an excited state

16. More about Gamma Decay There is no charge and no mass The symbol is γ
Gamma rays are the most penetrating
Require shielding with thick layers of lead or concrete, or both

17. Medical Uses for Gamma Decay
I-131 is used to treat thyroid cancer
Y-90 is used to treat other cancers
Ir-192 disrupts brain and breast cancer

18. Shielding for Radioactive Decay

19. Half-Life
Half-life: (t1/2) is the time required for half the atoms of a radioactive nuclide to decay
No two radioactive isotopes decay at the same rate
It is a random process with the average being reported for a particular nuclide
See page 708 for some examples