1. Physical Science Honors
Nuclear Reactions
Physical Science Honors

2. Strong and Weak Nuclear Force
The nucleus of an atom is held together by the strong nuclear force.
This force holds the protons and neutrons inside the nucleus.
The weak nuclear force is responsible for particles falling apart when the nucleus is unstable.
When this happens the nucleus undergoes radioactive decay and will release nuclear radiation.

3. What is radioactivity?
Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability.
Radioactive materials have unstable nuclei, which emit particles or energy to become more stable.
The released energy and matter from these nuclei are called nuclear radiation.

4. Types of Nuclear Radiation
There are three types of nuclear radiation:
Alpha particles
Beta particles
Neutron emission
Gamma rays
When a radioactive nucleus decays, the nuclear radiation leaves the nucleus.

5. Alpha Particle Emission
Alpha particles are positively charged atoms that are released from the nucleus.
Alpha particles consist of two protons and two neutrons, which is a helium nuclei.
Alpha particles are the weakest radioactive particle and can be stopped by a sheet of paper.

6. Beta Particle Emission
Beta particles are negatively charged electrons that are emitted from the nucleus.
Beta particles are produced when a neutron decays into a proton and electron.
These fast moving electrons have more penetrating energy than alpha particles, but can be stopped by a sheet of aluminum foil or thin plastic.

7. Gamma Ray Emission
Gamma rays are extremely high frequency waves that carry a large amount of energy.
Gamma rays travel as photons – smallest bundle of electromagnetic energy.
Gamma rays have no mass or charge, but rather travel as pure energy.
Gamma rays are the most energetic and destructive nuclear radiation and can only be stopped by lead or thick concrete.

8. Radioactive Decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom emits particles or energy to become more stable.
Radioactive decay takes time.
The time in which half a radioactive substance decays is called its half- life.

9. Nuclear Fission
The process of splitting one, heavier nuclei in to multiple, lighter nuclei is called nuclear fission.
This reaction releases large amounts of energy.
Nuclear fission is used in nuclear power plants and was used to make the atomic bomb.
Fission is a chain reaction – one reaction causes another reaction, leading to many other reactions.

10. Nuclear Fusion
The process in which multiple, light nuclei combine to form one, heavier nuclei is called nuclear fusion.
This reaction releases immense amounts of energy.
Fusion powers our Sun and all the other stars in our universe.

11. Vocabulary review
A subatomic particle found in the nucleus of an atom.
A version of the same atom with different masses due to different number of neutrons
Force of attraction between two bodies due to their masses.
Combined electrical and magnetic force.
(to be discussed in more detail later

12. Force of attraction between protons and neutrons which holds the nucleus together
Force associated with the nuclear decay of atoms.
Nucleus “spits out” a particle that has 2 neutrons and 2 protons
Nucleus “spits out” a high speed electron

13. Nucleus “spits out” a packet of EM radiation.
No change in atomic mass or number.
An atom with an “unstable” nucleus that will emit particles to achieve stability.
Nuclei combining to form nuclei with greater mass and releasing TONS of Energy!

14. Breaking apart nuclei into smaller nuclei and releasing a large amount of energy
Process (fission, fusion, decay) in which the structure of an atomic nucleus is altered through release of energy or mass or by being broken apart.
The amount of time it takes for half of any quantity of a given radioactive isotope to decay.

15. 100% of the U-235 Nuclei are fissioned due to the chain reaction.

16. It acts like a domino effect as each reaction provides neutron products to start another reaction.
U-238 does not have any neutron products to start a chain reaction. The lone neutron is absorbed into U-238 to form U-239.
U-239 is a more stable isotope of Uranium. U-239 has one more neutron than U-238

17. 100% 1
92% 10
82% 20
10%
several 0%
As U-238 nuclei increase the reaction slows down quite a bit because the number of released neutrons for the chain reaction decreases.

18. Chain reaction continues
Chain reaction stops
Chain reaction lasts longer when the control rods are pulled mostly out of the reactor.
You don’t want to lose control of the chain reaction and cause a meltdown or other disaster.
Power has a time component. (Joules / second)