The nucleus and nuclear reactions Flashcards
The nucleus
- The nucleus is a very dense particle at the center of each atom that is made up of all the protons and neutrons in that atom.
- The nucleus makes up most of the atoms mass
- The nucleus is very small compared with the diameter of the atom.
Atomic number
The atomic number is equal to the number of protons in the nucleus.
Atomic mass
The atomic mass is the total number of protons and neutrons in the nucleus.
How to find the number of neutrons
Subtract the number of protons from the atomic mass.
Isotopes and elements
- Two atoms with the same number of protons are the same element.
- Two atoms with the same number of protons and neutrons are the same isotope.
Nuclear reactions
- Nuclear reactions involve changes to the composition of the nucleus.
- When a nuclear reaction occurs the number of protons or neutrons changes and/or the arrangement of the protons and neutrons change
Types of nuclear reactions
The two major types of nuclear reaction are fission and fusion.
Nuclear fission
In nuclear fission, the nucleus splits apart.
Nuclear fusion
In nuclear fusion, two nuclei join together.
Steps in nuclear fission
- A fast neutron is shot into a large nucleus
- The neutron joins with the nucleus, creating a new isotope.
- To reach a more stable state, the unstable nucleus splits apart into two nuclei and some extra neutrons.
- The extra neutrons that are given off fly off with great speed and hit other nuclei, starting nuclear chain reactions.
Energy released by nuclear fission
When fission occurs, the nuclear potential energy drops, so kinetic energy is released.
Composition changes in nuclear fission
In fission, the protons and neutrons rearrange from one nucleus to two nuclei, but the total number of each doesn’t change.
Steps in nuclear fusion
- Two nuclei hit each other at a high speed (original substances must have a very high temperature)
- The two nuclei join together, forming a larger nucleus.
- The energy released adds heat, speeding up other nuclei and continuing the reaction in a nuclear chain reaction.
Energy released by nuclear fusion
If two nuclei have low atomic numbers, the new nucleus has lower nuclear energy than the original, and energy is released.
Composition changes in nuclear fusion
In fusion, the protons and neutrons rearrange from two nuclei to one nucleus, but the total number of each does not change.
Nuclear radiation
- some isotopes have unstable nuclei
- Unstable nuclei can reach a more stable state by emitting particles, called nuclear radiation
- The particles have a lot of kinetic energy, so they are ionizing radiation.
Radioactivity
- A substance is considered radioactive if it emits nuclear radiation.
- A radioactive decay occurs each time unstable nuclei become more stable by emitting a particle
- In each radioactive decay, changes occur to the nucleus’ composition and energy.
Types of nuclear radiation
- Alpha
- Beta
- Gamma
Alpha radiation
A nucleus emits an alpha particle with two protons and two neutrons.
- most energy
- most deadly
- easiest to stop (piece of paper)
Beta radiation
One of the neutrons turns into a proton, and the nucleus emits an electron.
- less energy
- less deadly
- harder to stop (metal sheet)
Gamma Radiation
The protons and neutrons rearrange in the nucleus to reach a more stable state and the nucleus emits a photon.
- least amount of energy
- least deadly
- hardest to stop (thick walls of concrete)