Introduction
The nucleus is the center of an atom. It is made up of nucleons - protons and neutrons - and is surrounded by the electron cloud. The size of the nucleus is between 1.6 fm to about 15 fm . These sizes are much smaller than the size of the atom itself. The nucleus has most of the mass of an atom, though it is only a very small part of it. Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus with a very small contribution from the orbiting electrons.
Because the nucleus is only made up of protons and neutrons it is positively charged. The nucleus is held together by the strong nuclear force.
If a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time. This is called radioactive decay and radioactivity.
Task
- Which particles make the nucleus of an atom?
- What does the atomic number symbolize?
- What are isotopes and how do they differ?
- What are nuclides?
- Which force makes the protons and neutrons stay together?
- Who discovered radioactivity?
- What is radioactivity?
- What kinds of decay there are?
- How do they differ?
- What is the half-life period?
- What is ionizing radiation?
- How can radioactive isotopes be used?
- What are nuclear reactions?
- What is nuclear fusion and where can it be observed?
Process
Answers
- The nucleus of an atom is made by protons and neutrons.
- The atomic number symbolizes the amount of protons in the nucleus.
- Isotopes are variants of a particular chemical element which differ in neutron number. All isotopes of a given element have the same number of protons and electrons in each atom.
- A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state.
- The protons and neutrons are kept together by the nuclear force, which only works inside of the nucleus.
- Radioactivity was discovered primarily by Henri Becquere in 1896, but the term 'radioactivity' was coined by Marie Curie and her husband Pierre.
- Radioactivity is the process by which an unstable atomic nucleus loses energy by emitting radiation.
- There are alfa, beta and gamma decays.
- - In alpha decay an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two. - In beta decay a beta ray (fast energetic electron or positron), and a neutrino are emitted from an atomic nucleus. - In gamma decay an excited nucleus loses its energy by emitting a gamma ray.
- Half-life is the time required for a quantity of matter to reduce to half its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo, or how long stable atoms survive, radioactive decay.
- Ionizing radiation is radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Ionizing radiation is made up of energetic subatomic particles, ions or atoms moving at high speeds, and electromagnetic waves on the high-energy end of the electromagnetic spectrum.
- Radioactive isotopes can be used in radiocarbon dating, radiometric dating, radiotherapy, technical diagnostics.
- Nuclear reactions are reactions in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce one or more nuclides that are different from the nuclide(s) that began the process.
- Nuclear fusion is a reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei and subatomic particles. This reaction can be observed in the center of stars, where hydrogen atoms are fused together to form heavier elements.
Evaluation
If the questions presented before can be answered, then the task has been completed.
Credits
Edvīns Šilters, Vilnis Reguts, Austris Cābelis, Ilgonis Vilks: Fizika 12.klasei; Lielvārds 2008. gads