1. Part 5: Radioactive Decay
Unit 4: Geophysics
Part 5: Radioactive Decay

2. Nuclear reaction:
A reaction in which the composition of an atom’s nucleus is changed

3. What makes an atom’s nucleus stable?
Strong nuclear force
An attractive force that overcomes the electric repulsion between protons, due to the presence of the neutrons
The neutrons help “glue” the nucleus together

4. How many neutrons do you need to make a nucleus stable?
Elements 1-20: need approximately equal numbers of protons and neutrons
Elements 21-83: need increasingly more neutrons to hold the protons together
Elements 84 and up: no stable combination, all are radioactive

5. How many neutrons do you need to make a nucleus stable?
Too many neutrons can make an atom unstable (emits beta radiation)
Isotopes that are much heavier or much lighter than the most common isotope are usually radioactive

6. Types of Radioactive Decay

7. Alpha decay From the alpha particle (made of 2 protons and 2 neutrons)
Charge of +2
Travels only a few centimeters
Stopped by paper or clothing
Not a particular hazard unless it enters the body

8. Beta decay From the beta particle (a stream of high speed electrons)
A neutron changes into a proton and an electron
The proton stays in the nucleus, the electron is emitted
Charge is -1
Can penetrate solid object a few mm
Can pass through clothing and damage skin
Stopped by heavy clothing

9. Gamma decay
From gamma particle (similar to X-rays, does not consist of particles)
Charge of zero
Accompanies alpha and beta radiation
Penetrates deeply into solid material and human tissue
Must be shielded by lead or concrete

10. Radioactive decay:
When an atom emits alpha, beta, or gamma radiation

11. Nuclear decay problems
Write the nuclear equation for the alpha decay of radium-226

12. Nuclear decay problems
Write the nuclear equation for the beta decay of iodine-131

13. Nuclear decay problems
Write the nuclear equation for the alpha decay of uranium-238

14. Nuclear decay problems
Write the nuclear equation for the beta decay of sodium-24

15. Nuclear decay problems
Write the nuclear equation for the alpha decay of gold-185

16. Other nuclear reactions
Nuclear fusion
The combining of two atoms in one
Uses: occurs in the sun, hydrogen bombs
Nuclear fission
The splitting of one atom into two or more
Uses: atomic bombs, nuclear power plants

17. Mass and energy Remember E=mc2?
In any nuclear reaction, a small amount of matter is turned into a large amount of energy.
Example:
E=mc2?
E=1 g (3.0x108m/s)2
E=9.0x1016 units

18. Four fundamental forces
Strong nuclear force: attractive force that the neutrons provide
Weak nuclear force: occurs in radioactive decay
Gravity: attractive force that exists between all objects, based on mass and distance
Electromagnetic: holds atoms and molecules together