1. Integrated Science Chapter 25 Notes
Radioactivity
Integrated Science
Chapter 25 Notes

2. I. What is Radioactivity?
Radioactivity - Process by which an unstable nucleus emits one or more particles or energy
Nucleus composed of protons and neutrons
Electrons are outside the nucleus

3. I. What is Radioactivity?
A. Nuclear decay
Break down of an atom’s nucleus
Element can become an isotope or a new element
Isotopes –
atoms of the same
element with different numbers of neutrons
Some isotopes are stable and never break down, while some are unstable and break down into a more stable atom.

4. Some reasons that an isotope of an element might be unstable are:
 Too many neutrons in the nucleus
 Too few neutrons in the nucleus
 Nucleus is too big in size (too many
neutrons and protons total)

5. Examples
Carbon-12 (6 protons, 6 neutrons) is stable, but Carbon-14 (6 protons, 8 neutrons) is unstable.
Beryllium-7 (4 protons, 3 neutrons) is unstable, but Beryllium-9 (4 protons, 5 neutrons) is stable.
All elements atomic #93 and higher are unstable due to their large nucleus size.

6. I. What is Radioactivity?
B. When a nucleus decays, it breaks down into a new nucleus, plus ejected nuclear radiation
This is a naturally occurring / spontaneous event when a nucleus is unstable

7. I. What is Radioactivity?
C. There is a “Strong Nuclear Force” present in the nucleus of an atom which holds the protons and neutrons together in the nucleus to remain stable.
 Kind of like nuclear “glue”

8. I. What is Radioactivity?
D. Types of Nuclear Radiation
Nuclear radiation – charged or uncharged particles or energy emitted by unstable nuclei
All radiation can interact with and affect surrounding matter

9. I. What is Radioactivity?
Transmutation – change from one element into a new element plus nuclear radiation

10. I. What is Radioactivity?
4 Types of nuclear radiation
1. Alpha particles (α) –
positively charged, made
of 2 protons and
2 neutrons
Most massive nuclear radiation particle
Slow moving, and quickly loses energy

11. I. What is Radioactivity?
4 Types of nuclear radiation
2. Beta particles (β) – negatively charged,
made of fast moving electrons
- Little mass
- Penetrate matter, but
not deeply

12. I. What is Radioactivity?
Beta Decay example

13. I. What is Radioactivity?
4 Types of nuclear radiation
3. Gamma rays (γ) – high energy, high penetrating power
Not made of matter, no charge
Electromagnetic energy like
light or x-rays, but with more
energy
Stopped by 7 cm of lead
Health hazard due to energy and penetrating ability

14. I. What is Radioactivity?
4 Types of nuclear radiation
4. Neutron emission – a single neutron with no charge
Can penetrate up to 15 cm of lead

15. II. Nuclear Reactions
A. Much energy released into the surroundings during a nuclear reaction
B. In a nuclear reaction, the nucleus changes

16. II. Nuclear Reactions There are two types of nuclear reactions:
1. Nuclear Fission – process where a nucleus splits (or is split) into two or more smaller nuclei and releases energy

17.  Particles can cause chain reactions of
nuclear fission in surrounding atoms
 This is an example of a nuclear explosion

18. Some practical uses of fission reactions are:
Nuclear reactors for a power source
Weapons
Medicine

19. II. Nuclear Reactions There are two types of nuclear reactions:
2. Nuclear Fusion – process where two nuclei combine at very high temperatures to form a larger nucleus and releases energy

20. Where does fusion happen?
This occurs continuously in stars as hydrogen atoms (1 proton, 1 neutron) are joined together to form helium atoms (2 protons, 2 neutrons).
During the process, a large amount of energy is also released.

21. Practical Uses of Nuclear Fusion
We use this energy (solar energy) to warm the earth and homes, and plants use it to make food (photosynthesis), We can capture and convert solar energy into electricity .

22. C. Nuclear reactions, mass, and energy
In both fission and fusion reactions, a small amount of matter is converted into a large amount of energy during the reaction.

23. C. Nuclear reactions, mass, and energy
The Law of Conservation of Mass still applies, as matter (which has mass) is not created or destroyed, but the form is changed.
During the change in form, energy is released as the matter becomes more stable, with less energy

24. III. Dangers and Benefits of Nuclear Radiation
There are both positives and negatives to nuclear radiation and nuclear energy

25. III. Dangers and Benefits of Nuclear Radiation
A. Dangers  can burn skin, can ionize living tissues, can destroy cells, can cause cancer, can cause genetic mutations in DNA, radiation pollution

26. III. Dangers and Benefits of Nuclear Radiation
B. Benefits  can be used to treat diseases, used in smoke detectors, tracers used in medicine, agriculture, research, energy source

27. III. Dangers and Benefits of Nuclear Radiation
Natural sources of radiation

28. Half-life
Some radioisotopes decay to stable atoms in less than a second.
However, the nuclei of certain radioactive isotopes require millions of years to decay.
A measure of the time required by the nuclei of an isotope to decay is called the half-life.

29. Half-life
The half-life of a radioactive isotope is the amount of time it takes for half the nuclei in a sample of the isotope to decay.
The nucleus left after the isotope decays is called the daughter nucleus.

30. Half-life Half-lives vary widely among the radioactive isotopes.
The half-lives of some radioactive elements are listed in the table.
The number of half-lives is the amount of time that has passed since the isotope began to decay.

31. Half-life For example:
If you have 100 atoms of a sample of Carbon-14, and the half-life of that isotope is 5730 years, how many atoms are left after 2 half-lives?
100 atoms  50 atoms  25 atoms
1st half-life 2nd half-life

32. Half-life
If you started with 1000 atoms of a sample of Iodine-131, and you have 8 atoms left, how much time has passed?
Half-life of Iodine-131 = 8.04 days

33. Half-life Step 1: Determine number of half-lives
1000 500 250 125 63 32 16 8
**7 half-lives**
Step 2: What is the half-life of the isotope?
 Half-life of Iodine-131 = 8.04 days

34. Half-life Step 3: Multiply # of half-lives and half-life time
7 half-lives x 8.04 days = days
half-life